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JANUARY 1973 www.americanradiohistory.com

1. Q PRESET RESISTORS stage gain will be cut to about 10 multiplying the grid to cathode circuit resistance by about 10 to get the ef fective input impedance of the ampli fier A 12AX7 tube could provide a much higher gain and input impedance than that However it may be that values are kept low here to maintain gain up into the megacycle region in those days no English speaking de signer had heard of megahertz What the 3 5 k preset was for is not exactly obvious but it could have been a calibrate control so the 10 k pot indi cates some definite scale in volts cm on the scope face Now we come to the reader s ques tion The 12AU7 triode as anyone who has designed circuits to use it will know is quite non linear although it Figure 2 One way of biasing a 12AX7 input cathode follower New from Dolby The M16 a compact sixteen track noise reduction unit New monitoring facilities in record play and recorder rest modes All solid state control logic and Signal switching Simple remote operation of all functions from console and recorder Standard Dolby A type noise reduction characteristics The Dolby system has become an integral part of modern multi track professional recording practice A new unit the M16 has been developed for these applications and iS now in production OO Doiby Laboratories Inc 1133 Avenue of the Americas New York NY 10036 Telephon
2. Company SSS es Zip CHICAGO LOS ANGELES TORONTO Dist in MILAN HAMBURG PARIS LONDON e BEIRUT SE Circle 17 on Reader Service Card www americanradiohistorv com 26L Aienuef qp ce db January 1973 34 20 The Audio Cyclopedia 2nd ed Dr Howard M Tremaine New and updated here is the complete audio reference li brary in a single volume It provides the most comprehensive information on every aspect of the audio art This new edition includes the latest audio developments in cluding the most recent solid state systems and integrated circuits It covers all sub jects in the fields of acoustics recording and reproduction with more than 3400 re lated topics Each topic can be instantly located by a unique index and reference system More than 1600 illustrations and schematics help make complicated topics masterpieces of clarity 1760 pages 6 x 9 hardbound 29 95 1 The Technique of the Sound Studio Alec Nisbett This is a handbook on radio and recording techniques but the princi ples described are equally applicable to film and television sound 264 pages 60 diagrams glossary indexed 5 x 8 clothbound 14 50 7 Acoustical Tests and Measurements Don Davis Provides solid understanding of the entire subject of acoustical measure ments based on actual field test work using commercial equipment 192 pages 5 x 8 hardbound 6 95 8 Handbook of Electronic Tables a
3. U ai it a eT e SE TT N n J W W jem A f m z ik F i n Bas d i p w A F i P r i a 4 2 T THE SOUND ENGINEERING MAGAZINE JANUARY 1973 1 00 WWW americanradiohistorv com Built better Performs longer Costs less Wire windings are OUT conductive plastic is IN for high performance audio controls With its new Series 300 SLIDELINE Duncan Electronics replaces noisy rough and grainy wire elements with smooth noise freee RESOLON conductive plastic which actually improves with use RESOLON elements and precious m3ial wipers used in all Series 300 controls bring consistent low noise operation and superior performance to linear motion faders for broadcast and recording And the cost is less than many high grade wirewcund controls of the past Series 300 is offered in 6 different stroke lengths and features longer life of 10 million traverses minimum infinite resolution and linear audio and constant im pedance outputs for every audio need Dual channels can be contained in a standard single housing only 134g wide the most compact dual at tenuator available to the industry Two dual units can be coupled and driven by a common knob to create 4 channels for master controls or quadrasonics For complete specifications call or write for our FREE brochure Duncan Series 500 N tame tod load ime TR gre 92626 wi
4. If you have an occasion to work with electronic music but do not really understand composers or how they think read this It will help in communicating with the composer the next time electronic music must be devised to fit a commercial track much new and unique apparatus has been devised for special purposes SS SSS A ROADLY SPEAKING electronic music is any music involving electronics in its composition perform ance or reproducton Dedicated composers how ever mean anything but this general description by the term They mean specifically that particular type of creative composition which they practice and which sounds idiomatically different from any music generated by non electronic processes Electronic music is therefore the modern example of a musical idiom resulting from technological progress THE ELECTRONIC IDIOM In music theory we speak of certain periods in musical history as being primarily contrapuntal e g the sixteenth century and the late Baroque periods while others are homophonic or primarily chordally oriented the Classical era and the Impressionistic periods Some eras in musical history are characterized as modal the Renaissance and the early twentieth century while others are of a major minor type in that they use the major and minor scales as the basis for musical composition the Classical and Romantic periods are of this type The music of some nations and ethnic groups is pentat
5. cording audio business have realized that the current crop of students could well be the future studio musicians producers and engineers as well as studio owners Thus for the first sem inar we were able to get brochures catalogues reprints and AV materials such as tapes records slide sets films and even guest lectures from such as Ampex Gotham Audio Audio Dis tributors JBL and ELPA Marketing Our current class has 30 students Thus I will ask you to look around your office and see if you could spare 30 sets of anything that will be passed on to some bright young folks who are seriously interested in the workings of a recording studio the equipment and the people who operate it Can you think of a better way to get your mes Sage across to your future Customers Jack W Gilfoy Owner Mer Gilfoy Sound Studios 300 Gilbert Ave Bloomington Ind 47401 The dbx 202 voltage controlled amplifier provides a dbx has a VCA linear voltage per decibel gain range from 100 dB m h to 30 dB with excellent linearity and unit to unit wit supenor tracking Input noise is 6 mV yet peak input may be gain ran ge as high as 100 volts Unit demonstrates excelient noise frequency response and low distortion Size is 1 x2xY2 inch It s available now for 47 00 distortion Mode 203 with relaxed specifications is also head room availabie for 39 00 dbx Incorporated 296 Newton Street tracking Waitham Massachusetts
6. l Please send me copies of E the db Magazine binder My check for ________is enclosed sorry no C o d Name Address number and sirect city Stale zip New York State residents please add 7 sales tax Mail to db the Sound Engineer ing Magazine 980 Old Country Road Plainview N Y 11803 4 Ate Ape K i oF ff RECORDLEVEL A T a z RECORD a Fa z oe ee ponr at ie a nl BE DH Were a new mastering tape d P enian so the PU g of older tapes Wh dont apply to us Initially a AA our extra quality needs some getting used to To upgrade your original eld 4 j recordings you ll have to adjust your equaliza tion and bias controls to our specifications Thats not much work but it s necessary And its worth it When you play back your first reel of Maxell mastering tape you ll notice how clean it works Our tape doesn t use a carbon backing sotheresno messy carbon shedding Sheddings cause noise thumping and interference On the reel carbon can also transfer to the recording surface and cause dropouts Because of the care we take in the manu facturing process you won t find any pinholes in our oxide coating No pinholes and no shedding mean Maxell mastering tape is virtu ally 100 free from dropouts And you get Maxell s low noise level wide range and freedom from distortion with We offer you better quality masters work for them _ EQUALIZ MGH
7. describe situations in life as well as in music Electronic music is able to simulate human emotions in some new ways as well as those common to conventional music The musical collage is one result of a new way of dupli cating human emotion Here scraps and snippets of the most diverse aural materials are presented in juxtaposition in such a way as to make the listener aware of large scale relationships The materials for such a work may be gathered by tape recorder and assembled through editing and splicing methods In musical or non musical mate rial recorded live and then altered often referred to as music concrete the composer tries to show his virtuosity in manipulation and in the novel ways in which he ar ranges his material It is important to note that the com poser may seek and achieve negative usually for the sake of social protest effects A listener not in sympathy with such a protest may object and question the validity of such work In summary if the primary stylistic idiom of electronic music is the exploitation of new timbres and rhythmic patterns the primary modes of expression derive either from continuously varying textures with occasional abrupt changes or from continuous change of the pointillistic type with interspersed moments of respite THE APPARATUS Much of the apparatus used for electronic music is famil iar audio equipment such as amplifiers tape recorders oscillators speakers and so forth O
8. A EU every reel in every size in every batch without fail Thats a statement about quality perfor mance you wont find other manufacturers making anymore We re eager to draw your atten tion to the edge to edge end to end quality youll find in Maxell mastering tape Send in the coupon for documented evi dence about Maxell tape performance Then think about the repeat sessions Maxell quality will eliminate Thats a lot of work you won t have to do Send to Maxell Corporation of America 501 Fifth Avenue Dept 1DM New York New York 10017 Gentlemen Send me technical information and tell me how I can get Maxell mastering tape name title company address CI en i maxell L The answer to all your tape needs js A a dy S S y C ZZ a EE eee a e o o ere M Circle 22 on Reader Service Card www americanradiohistorv com 46L Menuer qp db January 1973 6 George Alexandrovich THE AUDIO ENGINEER S HANDBOOK Signal distribution methods The output of almost every audio system be it a mixing console tape machine cart machine turntable or telephone line inevitably winds up being fed into more than one chan nel Console output usually feeds a program line monitor circuit patch bay sometimes transmitter or tele phone lines house a p a system and so on Tape machines are quite often Figure 1 Signal distribution using the unbalanced Output of a conventional
9. and foam filled earcushions to screen out ambient noise It ts adaptable to any appli cation or equipment by means of non terminating cordage and features exclusive Telex audiometric type driver elements And both headphone and microphone are designed to stand up even if the sportscaster has to work in all types of weather extremes and can t avoid some hard bumps In fact if the broadcaster doesn t hold up as well as the CS 90 there is a push to cough switch that mutes the mike when necessary Constructed of high impact ABS plastic and stainless steel Styled in non reflective black and grey to eliminate glare on camera Write for further information PRODUCTS OF SOUNO RESEARCH COMMUNICATIONS DIVISION 9600 ALDRICH AVENUE SOUTH MINNEAPOLIS MINN 55420 CANADA DOUBLE DIAMOND ELECTRONICS LTO Scarborough 4 Ontane EUROPE ROYAL SOUND COMPANY INC 409 North Main Street Freeport NY 11820 USA INTERNATIONAL TELEX EXPORT DEPT 9600 Aldrich ave So Minneapots Minn 420 U SA Circle 30 on Reader Service Card www americanradiohistorv com 26L Avenue qp db January 1973 10 Mr Webster enters a new word Nww americanradiohisto om C tec b6 tek n a new word meaning Electrodyne Langevin and Gauss 1 a manutacturing facility where Electrodyne and Langevin audio control equipment and Gauss tape duplicators are designed and built 2 a company which sells these products 3 an organization determi
10. change is abrupt and frequent This is a style derived and extended from the serialists and the pointill ists If any sound should have any length or continuity to it the effect is a contract to the normally short frag mented texture This technique is also characteristic of electronic music particularly because of the ease with which it may be assembled through tape splicing and edit ing techniques Electronic composers often seem to treat their material as if it were solid having texture and substance There is a definite relationship between electronic music and the various graphic arts which concern themselves with tex ture shape intensity design pattern etc as the primary elements as is particularly true of abstract painting and decorative sculpture and design In each case the object presented for contemplation is not an easily recognizable object but a pattern of materials in which the relationship is all important Electronic music of course has that same characteristic of all music the temporal distribution of its elements Music develops in time just as do all human experiences this is perhaps one reason why it is capable of carrying such emotional power The patterns of music are able to mock the patterns of human emotion Such eee electronic instruments have been designed which can violate acoustical laws musical terms as crescendo diminuendo recapitulation development sotto voce pesante etc
11. class AB line amplitier Did you ever wish that you had a photographic memory and a hundred pair of hands to help with your mixdowns That s what you get with our Automated Mixdown System instant replay of what you did and how you did it YOU make the decisions and IT does the work A vital part of this system is the Model 940 Automated Fader an infinite resolution self contained level control module capable of either manually or automatically setting audio levels It con tains all the electronics front panel controls and metering necessary to record play back and update channel fader set tings In addition it may be used as an automated master fader or may be externally controlled for gate or mute functions An Auto Manual switch is provided which allows the module to operate as a normal audio fader by passing the automation electronics entirely The module incorporates the Automated Processes Model 2550 VCA and a conductive plastic slide attenuator of the same quality and reliability that has made our Model 440 and 475 faders so popular feeding or connected to several cir cuits at once for example a cross bar switcher The same goes for car tridge machines and turntables Tele phone lines have to be treated some what differently because they are not simply loads for the signal source but signal can also be fed back through the same line in this case the line is acting as a si
12. configuration is used and good high frequency response is necessary the feed forward technique is an excellent choice as it makes maxi Figure 4 Large signal response of a 301A with feed forward compensation as in Reference 2 C2 27rfo R2 where fo 3 MHz Typical values R2 R1 30 k C2 3 pF OUTPUT VOLTS A H N COO SEE To CCP SS cOK OOK IM IOM FREQUENCY IN HERTZ mum use of available amplifier bandwidth with only one additional component beyond the standard compensation hookup It was mentioned that slew rate may also be extended by increasing the current available to charge and discharge the compensation capacitor This is perhaps the most direct approach to the problem and when properly exe cuted allows the large signal bandwidth to approach the small signal bandwidth There was a drawback to the approach however as it required a redesign of the basic op amp as the bias current in both the 741 and 301A op amps is fixed by design The i c which solved the slew rate problem by virtue of a new class B input stage is the Signetics 53134 a fast slewing general purpose op amp with small signal and d c characteristic similar to the 741 It also features the same pin arrangement and similar d c Operating characteristics thus making it an equivalent substitute in other senses The 531 is capable of slew rates of 30 ysec in the worst case unity gain fol lower condition and even faster response at higher gain
13. counter in the build out resistors And as a last bonus we increase the reliability of the system because even in the event of single amplifier failure the other can continue provid ing signal feed although with 6 dB lower level It is suggested that amplifiers for such a distribution system should be small power amplifiers capable of sus taining loads of several ohms without losing output voltage This sort of safety is nice to have to be able to supply many lines total load of 8 L400 watts and 10O watts is more than JO O watts This is the New Math suggested by the Phase Linear 400 watt RMS Direct Coupled Stereo Power Amplifier The difference is dramatic and it s in the listening You might be startled to hear your stereo deliver the life size sound of a musical instrument for instance free from clipping and distortion In this regard Julian Hirsch said in Stereo Review The Phase Linear was in a class by itself Hear the 400 at your dealers now it makes a powerful difference Price 499 00 Phase Lineair CORPORATION 405 Howell Way Edmonds Washington 98020 206 774 3571 Circle 13 on Reader Service Card www americanradiohistorv com ohms is equivalent to 150 six hundred ohm lines and as a safety feature Sometimes in a large crossbar a switcher short may occur flipping all relays closed or wrong patching can produce shorting of many lines The last consideration in the cir cuits o
14. dimension to the complex tone so far generally overlooked This is its continuous variability The electronically gen erated complex tone is an array of mathematically related frequencies in which certain sets of frequencies may be varied at will Thus chameleon like the complex tone may be made to shift its structure gradually This yields the possibility of a continuous music without breaks or notes but simply a continually changing structure CONTROLS Along with a discussion of the complex tone must go a dis cussion of the method available for controlling a musical instrument Basically there are four types of controls the linear access switching array the random access switching array linear access linear controllers and random access linear controllers Of the familiar instruments the piano has a random access switching array the keyboard for frequency con trol the trombone on the other hand is linear access linear controlled Most woodwind instruments are random access switched and in fact this has been the most popular method for controlling a musical instrument s pitch or fre quency with the linear control approach popular in string instruments Linear access controls are those which must be operated in an incremental fashion that is the operator must pass through ali intervening points when passing from one point to another In a random access controller the operator may move directly to any desired point with out
15. for the full story on Son of 36 Grand auditronics inc P O Box 12637 Memphis Tenn 38112 901 276 6338 Circle 16 on Reader Service Card www americanradiohistorv com 6L Alenuef qp Se db January 1973 26 WALTER JUNG Optimizing Op Amp Speed NE OF THE BIGGEST PROBLEMS associated with popular general purpose integrated circuit op amps such as the 709 741 and the 301A has been their speed or lack thereof This may not be so obvious the first time you look over a data sheet but will quickly hit you right in the face the first time you try to get a 20 dBm signal at 20 kHz through a 741 There are of course readily measurable parameters which determine an op amp s high frequency behaviour in some cases these are under our control in others they are not But a sound understanding of the whys behind all of this is a prerequisite to achieving good high fre quency performance from the attractively priced i c op amps It can be done so let s look into how we go about It There are two key parameters which directly affect the usable high frequency response of an operational ampli fier They are its slew rate and gain bandwidth product Slew rate is the maximum rate of change of the output voltage under large signal conditions Here large signal means a voltage swing at or near the i c s specified maxi mum generally 20 V p p or more It is commonly specified in volts per micr
16. needs Reduces chances of costly errors Ideal reference book it is an excellent source for the be ginner technician the non electrical en gineering man or general non engineering scientific and technical personnel 800 pages Hardbound 28 50 25 Operational Amplifiers Design and Applications Burr Brown Research Corp A comprehensive new work devoted en tirely to every aspect of selection use and design of op amps from basic theory to specific applications Circuit design tech niques including i c Op amps Applica tions cover linear and non linear circuits A D conversion techniques active filters signal generation modulation and de modulation Complete test circuits and methods 474 pages 15 00 26 The Design of Digital Systems John B Peatman Textbook for students desiring to develop a creative approach design capa bility through digital systems approach Answers these question Under what cir cumstances it is desirable to implement a system digitally What are some of the components available for implementing the system How do we go about design ing it 448 pages 15 50 31 Solid State Electronics Hibberd A Basic Course for Engineers and Techni cians An extremely practical reference book for anyone who wants to acquire a good but general understanding of semi conductor principles Features questions and answers problems to solve 1968 169 pp 10 25 32 Circuit Design for Audio AM FM and
17. new art of sound still called music for want of a better term The significance of this remark is to emphasize the difference in all respects excect the use of sound between conventional and electronic music Electronic music is not just a new technique but a new style and even a new music Today electronic music has become a satisfying mode of exploration and expression Its effects are widespread in the educational institutions and many newcomers are added to its ranks each year for the reasons given previ ously Although the popularity of electronic music as a listening entertainment is still low this is compensated for by the large number of practitioners who are able to get a creative satisfaction from manipulation of both com mercial and hand made equipment In addition the re search into the physics and psychology of music being done makes it a valuable addition to the realm of knowl edge Being only about as old as the tape recorder it ts already proving its significance and we can expect much in the future as greater skill is gained in its use IE If you can afford One of the others you can afford two of ours Ion of 36 Grand Son of 36 Grand is a complete recording remixing console expandable to 26 in 16 24 out Full quad capability and flexible pushbutton monitoring of any mode FET logic record play mode switching Built in patch bay Prices start at less than 18 000 for 16 in 16 24 out Write or call
18. originates in the composer s imagi nation undergoes interpretation as he attempts to generate it with his equipment The power of his music depends both on the power of his imagination and his skill in gen erating what he wants from his equipment This is not to say that he will not be open to suggestion from random or accidentally generated sounds but if he is honest with himself he will insist on digesting all such sounds men tally before designing the situation in which they might be used The electronic music composer is confronted with a situation where he may control his music to a greater degree than any previous music In the matter of expression each composer finds his own aesthetics and techniques However because of the idiom natural to electronic music certain types of expres sion are common In the first place there are no necessar ily discrete instruments in electronic music Sounds of one color may gradually and continuously be transformed into any others with no audible breaks between them As a result expression in electronic music often is a result of a series of continuous overlapping changes and the music resembles a mobile which rotates and changes gradually but which makes no sudden disruptions of its basic nature With such a context a sudden and abrupt halt or shift is a strong dramatic device usable occasionally as an element of surprise A second approach is just the opposite to that described above Here
19. passing through other points In the other aspect of the controller type definitions linear controllers have infinite resolution analog while switching arrays have prede termined steps digital Although frequency is well controlled in conventional musical instruments most of the other parameters of a musical tone are nearly uncontrollable Here electronic music shines for it has controls for every known param eter of a musical tone These controls may be any of the above four types but by far the most popular is the linear access linear controller better known as the potentiometer or pot We have pots which vary attack time decay time all aspects of tone color modulation levels reverberation and even frequency This is a very important part of the current electronic music style simply because this very plentitude of pots for so many functions determines its basic characteristics And so the new electronic music composer must learn that he can vary many parameters he must listen to the effects of such variation and decide what he can do with these new techniques If he is left unaware of this area he will miss an important aspect of electronic music and he won t gain this knowledge except from electronic music composers in the laboratory This is one of the electronic ree Electronic composers often seem to treat their material as if it were solid music composition teacher s responsibilities It is quite possib
20. sent to above address WWW americanradiohistorv com 46L Asenuer qp db January 1973 2 M These are witzerlani s finest quality stop watches manufactured by Hever Leonidas S A Hewer has been the leading manufacturer af quality stopwatches for over 100 years Their reliability and design leadership are well known throughout the world 1 5 second recorder central 0 60 minute register 2 Crown functions with time out and locked return 7 jewels shock pro tected 58 00 FILM MASTER 60 second recorder cen tral 0 60 minute reg ister Records on out side scale consumed 35 mm film from 1 90 feet on intermediate scale consumed 16 mm film from 1 36 feet Framespeed 24 pic tures second 2 crown functions with time out and fly back return 7 jewels shockprotected 61 00 All are fully guaranteed for one year with service available m 90 countries Isn t it time you had one of these new models if yea are seeking a stopwatch for a special appli cation please let us know Hemer stopwatches are available for sports aircraft automotive mdustrial scientie and many other esas 1 5 second recorder central 0 60 minute register 1 crown function with side Slide 7 jewels shock protected 50 00 WRIST TIMER for pro gram directors in radio TY and film 1 5 second recorder cen tral O 60 minute reg ister Dial reading iN dicates elapsed time remaining time can b
21. t be truly convinced until you hear the SENTRY IV That s why W we re scheduling studio demonstrations now all across the country You can arrange an audition through your E V sound specialist Or write us today But be prepared to accept a new standard in sound The Electro Voice SENTRY IV monitor speaker system Sentry IV Professional Monitor and Sound Reinforcement Loud Speaker Response 50 18 000 Hz Dispersion 60 x 120 from 600 to 15 000 Hz Sound Pressure Level 117 dB at 4 on axis with 50 watt input Dimensions 27 3 47 w x 20 5 8 d 50 3 4 h as shown Weight 148 Ibs 501 00 suggested professional retail net ELECTRO VOICE INC Dept 131BD 686 Cecil Street Buchanan Michigan 49107 locke OTCE a Guiton In Canada EV of Canada Ltd 345 Herbert Street Gananoque Ontario COMPANY In Europe Electro Voice S A R merstrasse 49 2560 Nidau Switzerland Circle 12 on Reader Service Card www amearicanradiohistorv com
22. this area that so much new territory exists Conventional acoustical music is performed on instruments obeying natural acoustical laws These laws having never been broken are the foundation of conventional music Now electronic instru ments have been designed which can violate acoustical laws and generate sounds never heard in nature These sounds are usually unique in their timbre or overtone structure it is probably for this reason that composers seeking the new as they are inclined to do have made electronic music an idiom of new timbres A second aspect of electronic music is its control of time This music may be constructed in such a way that it does not depend on a performer s sense of time For this reason extremely com www _americanradiohistorv com Serious composers have never failed to experiment with any new idioms coming to their notice a plex temporal patterns and rhythms may be generated electronically To sum up the idiom of electronic music as it is cur rently being practiced is the exploitation of a wide variety of new timbres in an extremely elaborate time sequencing arrangement On the other hand there is little harmony and melody and not a great deal of counterpoint as one usually defines the term in the majority of examples EXPRESSION AND INTERPRETATION As there is normally no interpreter of an electronic com poser s music this task falls on the composer himself In fact the music which
23. tion Pump Price on request 2 Mag nasync Mark IX 35MM Mono Film Re corder in 7 Rack 950 00 3 Fairchild Mono Limiter 250 00 4 Altec 9473A Dual Limiter 350 00 5 Capps Con denser Mike with Power Supply 50 00 6 Altec Condenser Mike with Power Supply 50 00 7 4 Melcor CL 20 Lim iter Compressors at 100 00 EACH 8 Universal Equalizer VE100 Klein amp Hum mel Price on Request 9 Ampex Mono and 2 Track Stereo Tape Machines in good condition Prices on Request 10 Ampex Tape Machine Electronics 300 350 351 and 352 Prices on Request 11 Scully 8 Track Recorder in Scully Cabinet Price on Request 12 4 Spring type Echo Chambers 600 ohms in and out on Cannon Connectors in 30 Rack on Wheels Price on Request Contact Irv Joel A amp R RECORDING INC 322 W 48th St NY 10036 Tele phone 212 582 1070 SCULLY TAPE RECORDERS one to twenty four track and model 270 auto players many models in stock for im mediate delivery SCULLY LATHES Previously owned and rebuilt Variable or automatic pitch Complete cutting systems with Westrex heads MIXING CONSOLES Custom designed using Weigand Audio Lab modules From 7 000 00 Weigand Audio Laboratories R D 3 Middleburg Pa 17842 Phone 717 837 1444 AMPEX PARTS head stacks and head assemblies complete inventory Write for price quotation Accurate Sound Corporation P O Box 2159 Garland Texas 75041 Telephone 214 278 0553 www americ
24. to db inset Although a complete discussion of frequency com pensation techniques and stability criteria are beyond the aim of this article the basic facts should be pointed out In a feedback amplifier configuration a prerequisite for closed loop stability is the rate of rolloff of the response curve where it crosses the closed loop gain level For a 20 dB per decade 6 dB per octave rolloff as shown the phase shift associated with this response is 90 degrees which cannot result in oscillation even under the worst case condition of unity gain This necessary ingredient for closed loop stability in operational amplifier circuitry is what led to the general purpose internally compensated i c op amps such as the 741 In a similar manner the 301A with a 30 pF compensation capacitor will yield identical results as will the ubiquitous 709 with its three compensation components Now the above states what is necessary for stability under unity gain closed loop conditions Does everyone operate 74l s at unity gain Hardly and look what a penalty you pay in bandwidth and slew rate when you use a 741 or other op amp compensated for unity gain at higher gains This curve we have been discussing is of course the small signal response of the amplifier At any closed loop gain you will get no more bandwidth than there is avail able from the device at the point where the closed loop gain intersects the open loop curve Check a few examples from
25. 02154 USA send for one Circle 21 on Reader Service Card www americanradiohistorv com Help college help you Businesses like yours gave over 340 000 000 to higher education last year It was good business to do so Half of all college graduates who seek work go into business The more graduates there are and the better edueated they are the more college serves the business community Your money was vital to colleges It relieved financial pressures made planning more flexible and contributed to the kind of basie and applied research that puts new knowledge and technology at the service of industry So that colleges can continue to help you give to the college of your choice now For information on ways to do it please write on your letterhead to Council for Financial Aid to Education Ine 6 East 45th Street New York N Y 10017 Ask for the free booklet How Corporations Can Aid Colleges and Universities FRE Council for Financial Aid to Education Inc Advertising contributed for the public good ey Sune db binders only 4 95 postpaid Heavy weight binders are now available to hold the thirteen issues of Volumes and 2 Rich brown leather grained virgin vinyl with our name printed in black on the spine and front Cover is electroni cally sealed over rigid board to give your volumes of db lasting protec tion Keep your Copies preserved in perfect condition protected from dust and damage
26. 0A has inherited some characteristics from its predecessor PRICE 685 the same as the 1968 introductory price incredibly As two amps in one it will probably give you or your customers a welcome cost break when you design your next multiple amp system WARRANTY three years covering all costs of parts labor and round trip shipping COOLING excellent heat dissipation provided by massive cooling fins and the entire chassis itself DEPENDABILITY stringent pre and post inspection and testing proves every electronic component every Circuit module and every finished unit to bring you one step closer to install and forget field dependability PEOPLE the same innovative design team and care ful craftsmen who made the DC300 such a sound success And the same knowledgeable customer service men ready to discuss your special application and send you detailed technical data Phone 219 294 5571 or write Crown International Box 1000 Elkhart Indiana 46514 crown MADE ONLY IN AMERICA Circle 26 on Reader Service Card www americanradiohistorv com 26L Menuer qp Gd nv IOO pf 3 1 2 4 3 RESOURCE 3000 R e PIN N aSk R2 av IOK E AL r o 600n Ri n IOK R3 20K 1 2 RE SOURCE ISV 47pf 3000 a 2 8 6 3 IOK gt 5V Figure 5 A single ended to double ended line driver dBm level but at O or 4 levels the distortion is less than 0 05 per cent at any audio frequency If higher power op amps are used the circ
27. 65 this excellent English trans lation covers wide gauge films panoramic films circular panoramic cinematography technical fundamentals of stero sound re cording for film as well as details of the Soviet systems now in use 284 pages 15 00 33 Noise Reduction Beranek Designed for the engineer with no special training in acoustics this practical text on noise control treats the nature of sound and its measurement fundamentals of noise con trol criteria and case histories Covers advanced topics in the field 1960 752 pp 19 50 27 Noise amp Vibration Control Edit by Leo L Beranek Practical design and reg ulatory information formulas choice of materials and structures city codes and hearing protection indispensable for de sign engineers public offictals who prepare regulations for noise control safety and environmental engineers involved in noise and vibration controls Covers data analysis transmission of sound psychophysiological design criteria hearing damage risk etc Wealth of detail comprehensive index and concise appendices 650 pages 29 50 28 Environmental Acoustics Leslie L Doelle Applied acoustics for those in envi ronmental noise control who lack spe cialized acoustical training Basic informa tion in comprehensible and practical form for solving straightforward problems Ex plains fundamental concepts pure theory minimized Practical applications stressed acoustical prop
28. 90 80 40 eG a a a 4 e e LJ s j 3 a t G U 1 t t i z t g u t i ECO 1t Ico U ECHO 3 ECHO 4 ECmMO 8 EmO S a ASTURAS u REVERB unit 179 7 325 RED 6 individual send controls 2 quality reverb springs sach input assignable to either or both outputs ROPY 4 w PROKIT DIVISION GATELY ELECTRONICS 57 WEST HILLCREST AVE HAVERTOWN PA 19083 215 446 1415 Circle 18 on Reader Service Card www amaricanradiohistorv com 46L Avenuer qp 61 db January 1973 20 TIMEKEEPER TAPE TIMERS The Standard Model is calibrated for 7 5 and 3 75 ips and can also be used at 15 ips Dimensions are 1 x 3 It is priced at only 49 95 The Professional High Speed Model is calibrated for 7 5 and 15 ips it measures 2 2 x 3 and is Priced at 99 95 TIMEKEEPER P O BOX 835 GREAT NECK N Y 11021 Name Address City State 0 0000000000000000000000000000000000000000000000000000000000000000000 The well known TIMEKEEPER TAPE TIMERS are now available for immediate delivery Our latest shipment has arrived and we are ready to fill your order TIMEKEEPER TAPE TIMERS are easily mounted on any Y4 inch recorder They are fully guaranteed to meet with your complete satisfaction or your money will be promptly refunded At these iow prices you can no longer afford to be without a tape timer Difference from the Stop Watch Since the stop watch measures time indepen
29. HEHE HEHE W W W ee EW ae WWwWWw americanradiohistorv com Using a Bruel amp Kjaer Type 3347 Real Time 1 3 octave Analyzer we plotted room response in some of the busiest recording studios in the country Then we repeated the response measurements R substituting a new Electro Voice eal proof in real time c the existing studio monitor a new order of quality sw ably flatter Measurably wider range Even where broad band IS here equalization had been attempted and was in use versus the SENTRY IV unequalized But perhaps most impressive the working studio engineers judged the SENTRY IV subjectively better sounding than the speaker systems they had been using for years In every single studio In every case the There are a host of good reasons why including lower distortion and outstandingly uniform dispersion from the first new sectoral horn design in 25 years With response at 60 off axis that is identical to on axis performance Plus three new drivers full range horn loading and a computer aided design that led to more efficiency and higher power handling than any of the standard monitors You can read about SENTRY IV design in an AES convention preprint we ll send you It was written by our Ray Newman left the man behind the SENTRY IV We can also show you curves and specs that make impressive reading And even better listening pre aha But we know you won
30. ING AMPLIFIER Where the previous cir cuit converted double ended signals to single ended ones this circuit performs the exact opposite converting single ended signals to double ended ones The circuit shown provides a moderate amount of power 14 dBm with low distortion in the audio band Up at 20 kHz the t h d rises to 0 2 per cent at the 14 REFERENCES 1 R Dobkin Fast Compensation Extends Power Bandwidth Na tional Semiconductor Application Note LB 4 April 1969 2 R Dobkin Feedforward Compensation Speeds Op Amp Na tional Semiconductor Application Note LB 2 April 1969 3 W E Hearn Fast Slewing Monolithic Operational Amplifier IEEE Journal of Solid State Circuits Volume SC 6 no 1 pp 20 24 February 1971 4 W E Hearn Application of the SE NE531 Fast Slewing Op erational Amplifier Signetics Corporation Application Memo 116 February 1971 5 W G Jung A Differential Bridging Amplifier db pp 21 27 July 1971 6 W G Jung The Pitfalls of the General Purpose IC Opera tional Amplifier as Applied to Audio Signal Processing presented to the 43rd AES Convention in September 1972 AES preprint 893 contains a bibliography of twenty nine references pertinent to ic s in audio applications www amaearicanradiohistory com Say farewell to the grand old DC300 and welcome to THE PROBLEM SOLVER the amp that is going to make your job easier and your customers happier The original model DC300 was a
31. LECTRONIC MUSIC Robert C Ehle OPTIMIZING OPAMP SPEED Walter Jung COLLECTING OLD RADIOS FOR FUN AND PROFIT Robert C Ehle LETTERS THE AUDIO ENGINEERS HANDBOOK George Alexandrovich THE SYNC TRACK John Woram THEORY AND PRACTICE Norman H Crowhurst NEW PRODUCTS AND SERVICES BOOKCASE CLASSIFIED PEOPLE PLACES HAPPENINGS db is listed in Current Contents Engineering and Technology Robert Bach Larry Zide PUBLISHER EDITOR Bob Laurie John Woram ART DIRECTOR ASSOCIATE EDITOR A F Gordon Marilyn Gold CIRCULATION MANAGER COPY EDITOR Richard L Lerner ASSISTANT EDITOR GRAPHICS Crescent Art Service Eloise Beach db the Sound Engineering Magazine is published monthly by Sagamore Publishing Company Inc Eo contents copyright 11803 Telephone 516 433 6 1973 by paramore Publishing Co Inc 980 Otd Country Road Plainview L I 530 db is published for those individuals and firms in professional audio recording broadcast audio visual sound reinforcement consultants video recording film sound etc Appli cation should be made on the subscription form in the rear of cach issue Subscriptions are 6 00 per year 7 00 per year outside U Possessions Canada and Mexico in U S funds Single copies are 1 00 each Controlled Circulation postage paid at Harrisburg Pa 17105 Editorial Publishing and Sales Offices 980 Old Country Road Plainview New York 11803 Postmaster Form 3579 should be
32. NIC MUSIC Music in general may be thought of as a type of interac tion between musicians musical instruments and listeners As such each of these elements will affect the style of the resulting music So far we have discussed the effects on style resulting from the first two of these Finally the effect on the style of electronic music due to the listener must be taken into account This means a discussion of the effects on style due to intended applications of music Part of the transition from conventional to electronic music has been for many composers the utilization of one or more compromises involving mixtures of techniques as previously described On the other hand pure and abso lute music composed electronically undeniably is no com promise It is as we have discussed unfettered by necessi ties common in conventional music although it may introduce new necessities peculiar to itself Thus due to its nature it is more useful and acceptable in some forms than others It seems to be most usable in those forms involving electronic distribution radio television phono graph records and motion pictures It is also at home where no visible performer is required to occupy the vis ual attention of the listeners as is the case in ballet and theatrical productions Eventually we might have fully developed electronic concert instruments which overcome the many present limitations thus allowing electronic con cert music to b
33. NICS HIGH SPEED in cassette tape duplicator Special model accepts 712 or 15 inch standard two track stereo master tape Duplicates four cassettes simultaneously Ideal for recording stu dio use to make reference cassettes from 15 inch stereo or mono masters One year old in perfect condition 2900 00 Call 305 947 5611 Criteria Recording Studios 1755 NE 149 Street Miami Florida 33161 RECORDING CONSOLE LIGHTED PUSH BUTTONS Switchcraft PL series 319 buttons 306 push lock push release 13 momentary colors R B Y G and W Brand new have excess supply Retail 9 per button selling for 2 50 per but ton Also have 20 SMX 11 Langevin slide attenuators 20 per slide Interstella Electronic R amp D Corp P O Box 1635 Annex Station Prov R I 02901 Call 401 353 2551 CASSETTE DUPLICATOR C E E model DC 1542 high speed two track and model 2CTS cassette master adapter Latest design brand new Sells for 3125 only 2100 R Blumenstein Box 101 Bala Cynwyd Pa 19004 ELECTRODYNE 1204E CONSOLE Twelve wired fifteen inputs four outputs four echo send return two limiters two pan pots Excellent condition Xanadu Pro ductions P O Box 130 Maynard Mass 01754 617 897 8576 DISC CUTTING LATHES AND SYSTEMS As a result of recent trade in offerings we are able to supply previously owned Neumann AM 32b Disk Cutting Lathes most with automatic pitch depth control as well as SX 68 Cutting systems
34. TV Texas Instruments Texas Instruments Electronics Series Discusses the latest ad vances in design and application which represent the results of several years re search and development by Tl communica tions applications engineers Emphasizes time and cost saving procedures 1967 352 pp 15 00 35 An Alphabetical Guide to Motion Picture Television and Videotape Produc tions Levitan This all inclusive authorita tive and profusely illustrated encyclopedia is a practical source of information about techniques of all kinds used for making and processing film and TV presentations Gives full technical information on mate rials and equipment processes and tech niques lighting color balance special effects animation procedures lenses and filters high speed photography etc 1970 480 pp 24 50 www americanradiohistorv com if more than one copy of a title is wanted Full payment must accompany your order We cannot ship c o d Checks or money orders shouid be made payabie to Sagamore Pubilshing Company inc Because of the time required to process pe e atlow several weeks for the receipt of ooks 40 Radio Transmitters Gray and Graham Provides in a logical easy to understand manner a working knowledge of radio transmitters for quick solution of problems in Operation and maintenance 1961 462 PP 16 00 23 Wide Screen Cinema amp Stereophonic Sound M Z Wystozky First published in USSR in 19
35. a A sound ide i Series 220 Slideline 547 i i TAL Circle 10 on Reader Service Card www americanradiohistorv com COMING NEXT MONTH Part one of special issues devoted to the problems of tape recording ma chines tapes and the interfacing be tween these two components is next month Norman H Crowhurst has prepared a look at where tape recording is to day from a manufacturer s view He takes you quickly through the begin nings to the present and peeks at the future Marvin Soloff of Maxell tape has come up with an interesting useful and sophisticated way to set up a pro fessional machine so that it gets the best out of the modern tapes any body s now in use And Steven Temmer has translated an article from the German originally published in that country that de scribes in detail the original thinking and execution that has gone into the A 80 multi track Studers There are lots of good closeup pictures And there will be our regular col umnists George Alexandrovich Nor man H Crowhurst Martin Dickstein and John Woram Coming in db the Sound Engineering Magazine ABOUT THE COVER e What could be more appropriate to Robert C Ehle s ELECTRONIC Music article beginning on page 22 It s a Moog 2 26 52 omitted this month PZ ASST CIRCULATION MGR THE SOUND ENGINEERING MAGAZINE JANUARY 1973 VOLUME 7 NUMBER 1 WHAT TO LISTEN FOR IN E
36. ain as the 12AU7 has you ll find out Achieving stability wide range frequency response with enough feedback to produce satisfactory line arity 1s almost impossible So this designer evidently settled for using the gain of one half of the 12AU7 without feedback and using the other half to correct the non line arity of the first half From my own design experience I would imagine he could do better that way and cer tainly without the stability problems Reverting to FIGURE l to explain how it works the 12AU7 triode ampli fies much more on positive going grid signal than on negative going The lin earizing part works by feeding back out of phase signal from its plate pin 6 to its grid pin 7 This has the ef fect of modifying the apparent value of the portion of the 500 k variable used as a load at the grid pin 2 of the amplifying stage This loading modifies signal amplitude by virtue of the source impedance at the plate pin l of the 12AX7 The loading is also modified during the grid swing at pin 2 of the 12AU7 Figure 4 A more obvious way of getting linearity using two stages to get more gain then applying negative feedback B because of the similar swing delivered to pin 7 through the portion of the 500 k When swing is positive gain of the 6 7 8 portion increases reducing the effective resistance value presented by the 500 k to pin 2 thus loading the signal more when the gain increases Whe
37. anradiohistorv com CATV MATV PRODUCTS WALLPLATES AMPLIFIERS o a AVA ELECTRONICS CORP 414 LONG LANE UPPER DARBY PA 1908 tif ma 6 inn CONNECTORS SPLITTERS EXCLUSIVELY IN USA Satin moving coil Cartridges Impedance matches mag netic input M14LE elliptical 99 95 M14LX Shibata 129 95 Send check to Michael Scott Enterprises Room 24 6056 West Broadway Minneapolis Minn 55422 ONE STOP FOR ALL your professional audio requirements Bottom line ori ented F T C Brewer Company P O Box 8057 Pensacola Florida 32505 PRESTO 8N DISC RECORDER Equipped with Grampian recording head and Gotham Power amplifier Best offer or trade for Ampex 350 351 Northwestern Incorporated 011 S W Hooker St Portland Oregon 97201 WANTEO OLD MICROPHONES 1920 to 1940 All makes and models Also literature Write Bob Paquette 443 N 31st Street Mil waukee Wis 53208 DO YOU SEEK REPRESENTATION in New England States Experienced audio representatives with wide contacts seeks additional audio lines Highest referen ces Write or call Frank Barmakian Sales 100 Hatherly Road Waltham Mass 02154 617 894 4849 WANTED two Marantz Model 9 power amplifiers in good condition Send par ticulars to Box 835 Great Neck N Y 11021 EMPLOYMENT MAINTENANCE ENGINEER Large three Studio operation 24 track with high speed duplication facilities Full knowl edge of Scully and Ampex r
38. are strength ened to withstand rough handling Over all dimensions are 4 25 by 1 15 inches Mfr Duncan Electronics Circle 52 on Reader Service Card you write it Many readers do not realize that they can also be writers for db We are al ways seeking good meaningful articles of any length The subject matter can cover almost anything of interest and value to audio professionals Are you doing something original Or unusual in your work Your fellow audio pros might want to know about it You don t have to be an experi enced writer to be published But you do need the ability to express your idea fully with adequate detail and information Our editors will polish the story for you We suggest you first subinit an outline so that we can work with you in the development of the article You also don t have to be an artist we ll re do all drawings This means we do need sufficient detail in your rough drawing or schematic so that our artists will understand what you want It can be prestigious to be published and it can be profitable too All arti cles accepted for publication are pur chased You won t retire on our scale but it can make a nice extra sum for that special occasion Display illustrated is the We frequency response characteristic of a 20 Hz to 20 KHz filter from 10 Hz to 50 KHz over a 60 dB dynamic range Waveform at right shows the resonance of the same filter with sensi tivity increase
39. ck 2 or 4 channel po a uz uz ee eS See ee ee aS z 1 TELEX COMMUNICATIONS DIVISION i g 9500 ALDRICH AVE SO e MINNEAPOLIS MINN 55420 g DBS PLEASE SEND INFORMATION ON DUPLICATOR U u i PRODUCTS OF SOUND RESEARCH NAME oO m i TITLE NN INSTITUTION i z q RBDRESS g COMMUNICATIONS DIVISION i f 9600 ALDRICH AVE SO MINNEAPOLIS MINN 55420 B CITY STATE ZIP i CANADA DOUBLE DIAMONO ELECTRONICS LID Scarborough 4 Onterio Lmzoozowzzzozwowzozzowzwazww i I NON TOLER ERPORTOEST S600 Aceon ace So MionsznOE Mia AJOU SA Circle I on Reader Service Card WWW amaricanradiohistorv com NEW PRODUCTS AND SERVICES ELECTROSTATIC SPEAKERS Four models of this electrostatic system and dynamic bass woofer are now available that use thinner mem branes to deliver greater acoustic out put for realistic studio sound pressure levels Sturdy elements permit studio levels without destruction Dispersion is broadened by placing multi element arrays at precise elements In the ES 224 model pictured two 10 inch long throw woofers are used along with a total of 24 electrostatic elements which are crossed into at 350 Hz An ampli fier power of 150 watts is suggested for rooms up to 6000 cubic feet Mfr Crown International Circle 57 on Reader Service Card METAL REELS Seven inch metal reels are available encased in a storage case The reels with standard slotted hub are made of a
40. co California 94105 415 397 5377 If you re seriously into music Nou Q for up to four additional input modules sound reinforcement you want more and other optional accessories than hi fi products can give including talkback remote you But full professional stu what ou need transport control quad pan dio gear costs an arm and a leg and you pay for a lot of things you may not really need That s why there s a TASCAM Model 10 It s an 8 in 4 out mixing console and it s just 1890 With the Model 10 you get what you have to have Without sacrificing a single necessary function Each input module gives you mic and line atten uation three bands of peak and dip equalization two with frequency selection pre and post echo send and receive circuitry pan function and a unique Straight line fader Each of the four submasters has a meter control switch line echo independent monitor level control echo receive level control and a straight line fader You also get a master gain module and 4 VU meters with LED peak indicators Plus pre wired facilities for ner and Feadphone monitor That s what you need and that s what you pay for Some things hcwever you may or may not need and we leave that choice up to you For instance the basic Model 10 is high impedance in and out but studio line impedances are available optionally You ll probably want low impedance mic inputs but you may not need all low impedance lin
41. curve 1 of FIGURE 2 to appreciate this At 20 dB gain bandwidth is 100 kHz fine But look at the 40 dB gain situation Here you have only 10 kHz of bandwidth harly hi fidelity response and above 5 kHz you have very little feedback to lower distortion and output impedance You will be operating essentially open loop at these fre quencies and in essence do not even have a feedback amplifier at all But back up a moment and consider what was said about the compensation necessary for a particular gain level For stability the open loop rolloff should be 6 dB per octave where it crosses the closed loop gain level It does not matter if it undergoes another phase shift beyond this point because the additional phase shift cannot cause an oscillation because of insufficient gain around the loop at this frequency What does this mean It means we can lighten up the compensation for the higher closed loop gains and still have adequate stability And the biggest thing it buys for us is additional bandwidth and an im proved slew rate The bandwidth you may appreciate by regarding curve 2 of FIGURE 2 This is the open loop response of a 301A or 709 compensated as shown in the corresponding inset Now look at the 40 dB gain curve and where it intersects the open loop response at 100 kHz rather than 10 kHz a full decade more of frequency response and a 10 times improvement in distortion reduction from 100 Hz to 10 kHz The point we are making here
42. d 40 dB vou nt quite hear Harmonics noise and hum don t mask peaks and nulls in audio frequency response measurement when you use the Systron Donner 711 801B Spectrum Analyzer The coherence of the tracking oscillator output and the analyzer scanning signals assure it The variable persistence CRT display of the 711 801B lets you store signals up to six hours You can study audio frequency signals that need slow scan rates for high resolution Or you can retain intermittent or varying signals for later visual analysis or photography You can choose logarithmic or linear frequency scan from 10 Hz to 50 KHz with the 711 801B Frequencies may be measured within 1 throughout the linear frequency range At 4 995 there s no more useful instrument for many audio measurements in the lab or on the production line Ask your nearest Scientific Devices Office for a demonstration or contact Microwave Division 14844 Oxnard Street Van Nuys California 91409 Phone 213 786 1760 In Europe Systron Donner GmbH Munich W Germany Systron Donner Ltd Leamington Spa U K MICROWAVE DIVISION SYS TRON DONNER The Systron Donner Instruments Group Computer Systems O Concord Instruments O Datapulse O Kruse Electronics O Microwave O Trygon Electronics Circle 25 on Reader Service Card WWW amaricanradiohistorv com 464 Menuer qp Lg db January 1973 22 ROBERT C EHLE What To Listen For in Electronic Music
43. dently of the travel of the tape its measurement inevitably varies with the elongation or contraction of the tape and with the rotating speed of the tape recorder subject to Change by voltage and other factors The stop watch can be stopped during the travel of the tape but it can not rewind together with the tape back to the desired position With the Tape Timer moving in unity with the tape recorder fast forwarding of the tape involves the quick advance of the pointer while rewinding of the tape moves the pointer backward by the corresponding time Correct time keeping of the Tape Timer is never de ranged by continuous repetition of such actions during the travel of the tape as stop rewinding and fast for warding Unlike the stop watch the Tape Timer is not affected by various factors of the tape recorder and so the editing reproduction and revision of your recorded tape can be done at will Features e The recorded portion of the magnetic tape can be read at a glance by a scale division of second as accurately as a clock e The performance of the Tape Timer synchronized with the tape prevents such errors as caused by the elonga tion or contraction of the tape and by the variation of speed in the rotation of the machine Fast forwarding of the tape involves the proportional increase of the advance on the Tape Timer When you rewind the tape the pointer will be automatically moved back by the space of time exactly corre
44. e 212 489 6652 346 Clapham Road London SW9 Telephone 01 720 1111 Tiger Building 30 7 4 Chome Kuramae Taito Ku Tokyo Telephone 03 861 5371 Circle 24 on Reader Service Card www americanradiohistory com New simplified line up procedure Complete self contained power supply and interface circuitry Add on A8X provides simple expansion to 24 track operation Only 8 000 for full sixteen track capability In addition to the obvious economy of space installation time and maintenance which the M16 offers its cost per channel is substantially lower than that of other Dolby noise reduction units Full information about the M16 including accessories auxiliary and independent eight track units and prices available upon request Dolby and the double D symbol are trade marks of Dolby Laboratories Inc e261 Menuer qp cl db January 1973 14 Figure 3 An alternative way of biasing the cathode follower handles the widest swing of any of that group of tubes Better tubes came out later but we will assume the de signer was making best use of what was then available Here he is faced with a linearity problem Of course feedback as a means of improving linearity had been known long before the 12AU7 tube was even designed So why not use the two halves of the tube in cascade and use lashings of feedback e g FIGURE 4 If you struggle with de sign details using a tube with as little stage g
45. e read on 60 minute turning bezel 2 crown functions with time out and locked return button with safety bolt 7 jewels shockpro tected 74 00 GUARANTEE 100 absolute satisfaction or your money returned j within 10 days without question To order send check directly to TIMEKEEPEF P O Box 635 Great Weck N Y 11021 M T Slate residents aid 7 sales tan letters The Editor We are excited about what is going on in Indiana and we want everyone to know about it In fact there are three Ist class 16 track studios cur rently operating within a 50 mile radi us and one of them even has a com plete system of DBX Dolby noise re duction as well as quadraphonic mix down facilities In short for those of you who might have overlooked this territory in the past the pro audio recording scene is definitely on the move Yet there is another reason that prompts me to write this letter For years I have had individuals call me and knock on the studio door wanting to know how they can become record ing engineers or how to start a studio For reasons that are related to the fan tastic growth of the record business communications industry the current generation is really turned on to the recording studio scene Finally we offered a course last September in Re cording Studio Techniques Four days after I announced the plan we had a full house all of whom were either students or instructors at Indiana Uni ve
46. e Microphone Award on behalf of Ray Dolby for the latter s development of the noise reduction system for magnetic record ing that bears his name Making the award is Oliver Berliner grandson of Emile Berliner inventor of the micro phone and the disc record opuloc A New Accurate Digital Timing Instrument for Recording Studios Broadcasters and Other Demanding Applications Timekeeper is proud to introduce a new inexpensive Electronic StopClock a compact instrument featuring an easily read visual display Only 5 wide x 3 high x 5 deep it uses modern digital circuitry to provide accuracy of a very high order with exceptional long term stability The large 8 high seven segment numerals can easily be read from a dis tance of more than 15 feet Maximum count is one hour 59 59 9 Three remote mounted push buttons are used for man ual control START STOP and RESET These buttons may be placed in a console operating desk or any con venient location The clock may be remotely located in the equipment or on a desk or table A mounting flange is provided Operation is similar to any conventional stopwatch The green button starts the clock the red button stops it The black button resets it to zero These may be de pressed in any order or all at once without damage to the clock If it is desired to start the clock by releasing a button rather than depressing one the green and black button are pr
47. e a limited number of regular back issues available You may order these copies at 1 00 each from Circulation Department db The Sound Engineering Magazine 980 Old Country Road Plainview New York 11803 ALL IN ONE BPORTSGASTER HEADSET Beautiful schooner Exciting li West Indies Isles And you If you re congenial and would like to sail with a small intimate group we re for you and you re for us Now forming to sail Your Share from 245 10 great days Hurry Write today for information Windjammer Cruises Name Address mea p City CS tate Zia Phone awa P D Box 120 Dept 970D Miami Beach Florida 33139 This sportscaster can roam about a football field rubberneck at a basketball game or quickly position himself for an important golf shot All with just one piece of equip ment The new Telex CS 90 Sportscaster headset lets him broadcast live fixed station or mobile listen to production cues and monitor his Own transmission all with hands free convenience He can do all this because Telex has now combined the finest professional microphone available one of proven broadcast quality with an equally high performance headphone This wide range dynamic boom microphone has a low frequency response to transmit his voice clearly and crisply and an omni directional design to pick up colorful crowd noise The two channel headphone fits comfortably with a padded headband
48. e inputs So we don t make you pay for them You can order any combination of high and low input output impedances according to your application Details and specs on the Model 10 are available for the asking At the same time we ll tell you about our new Series 70 Recorder reproducers We ve got what you need _ MBE TASGAMA CORPORATION 5440 McConnell Avenue Los Angeles California 90066 Circle 20 on Reader Service Card www americanradiohistorv com 26L Menuer qp db January 1973 4 PRODUCER S ARRANGER S STUDIO WORKSHOP A four day workshop from March 29 to April 1 An intense forum seminar to be conducted at Vanguard Studios and the Institute of Audio Research facilities The Workshop will focus on ex tending the producer s creative and artistic skills through more efficient and expanded use of studio facili ties John Woram heads the Workshop which will include a number of special guests as well A printed Workshop program amp additional details may be obtained by writing to the address below or by phoning 212 677 7580 institute of audio research inc 64 University Place New York N Y 10003 Gilfoy Sound is currently undertak ing a 2nd seminar The Studio Track column in the September 13 1973 issue of Billboard was very kind in giving us an accurate spread Billboard pointed out that we had gotten con siderable help and interest within the industry Many individuals in the re
49. eader Service Card www amaearicanradiohistory com Why pay an answering service when you can own your own Dictaphone has a machine that makes sure that you never lose another cent through a missed phone call or a garbled message In fact we have a whole line of them They re called ANSAFONES They answer the call and give out a message in your own voice and then record the incoming caller s message There s even a model which will allow you to cali in from any phone in the world and get your telephone messages played back to you automatically ANSAFONE telephone answering machines are not toys They re sophisticated high quality business machines designed to work for you 24 hours a day 7 days a week They help big companies cover their switchboards at night during off hours distributors take orders 24 hours a day and small businesses keep the phone covered and stay open for business around the clock You can buy one outright or possibly lease it for less than you would pay an answering service If your business depends upon the phone for orders or incoming information ANSAFONE can help you For a free brochure describing how much ANSAFONE can help you in your business mail this coupon today Dictaphone and Ansafone are registered trademarks of Dictaphone Corp Rye New York E B Dictaphone 6338 Lindmar Drive Goleta Calif 93017 Please send me complete information on Dictaphone s line of
50. eal antiques in the radio world some of the sets built in the nineteen thirties must certainly be classic units by any standards In this era eminence must be decided on the basis of extras refinements and a certain over design Here such features as noise limiter circuits motor driven tuning many bands many tubes tuning meters or eyes afc sig nal seeking tuning and so forth can be considered as outstanding qualities What we are seeking is the radio equivalent of the Dusenberg or the Rolls Royce of the same era There was an extraordinary extravagence in some of the sets marketed during the twenties and thirties and some daring engineering as well Such factors should make certain models greatly sought after The folklore of the old radios is certainly apropos The story has been told of one manufacturer suspecting that people bought those sets with the most tubes who installed several unnecessary tubes in each set and connected only the filaments so they would light up Old timers also like to tell about the early days of radio broadcasting when there were no FCC limitations on power and when www americanradiohistorv com the band was not crowded In these days reception up to half a continent away was a common occurrence on the a m band Distance reception seems to have been a favor ite pastime Many fancy long wire dipoles were manufac tured with matching transformers in large tin cans that could be strung up between po
51. ecome a reality Today however electronic music is a very abstract art this is due to two facts first the general absence of a visible performer and second the newness and unfamiliar nature of much of it Thus electronic compositions are art objects comprehensible either in themselves or through the words written about them but lacking much of the social conventions of traditional music In this respect it has much in common with art and in particular the ab stract art of the twentieth century I think that composers sense this similarity and respond with a style of composi tion noticeably more abstract and complete in itself than they would employ for traditional music This means that electronic music abstract as it is must be more complete in itself than conventional music It must be able to explain itself and complete itself It can www americanradiohistorv com the piano has a random access switching array the trombone is linear access linear controlled not depend on successive interpretations or bravura per formances to compensate for intrinsic deficiencies For this reason Composers must pay more attention to form and structure and many are doing so As a result it may be more complex remember repeated hearings of the works intended and simple by electronic means this has not always been the case Also electronic music should be expected to yield more on repeated hearings and to hold interest for a very l
52. ecorders console systems and audio electronics required Good pay Great people Send complete resume including personal in formation to W Craig Kenney Flite Three Recordings Inc 1130 East Cold spring Lane Baltimore Md 21239 301 532 7500 EXPERIENCED DISC MASTERING EN GINEER for well known cutting room in New York City Top Salary and benefits Write to Box 2 A db Magazine 980 Oid Country Road Plainview N Y 11803 26L Kienuep qp GE db January 1973 36 CLASSIFIED FOR SALE AMPEX ONE INCH VIDEOTAPE RE CORDER model 7500 excellent condi tion 12 reels tape service manual 950 00 Ophthalmological Electronics Laboratory Southhampton Hospital Southhampton N Y 11968 516 283 5835 SOLID STATE AUDIO MODULES Con sole kits power amplifier kits power supplies Octal plug ins mic eq line disc tape play tape record amplifiers Audio and tape bias oscillators Over 50 audio products send for free catalog and applications Opamp Labs Inc 172 So Alta Vista Blvd Los Angeles Ca 90036 213 934 3566 HAECO announces complete repair ser vice and overhaul for ali Westrex cut terheads Conversions of 3D ll and old er models to higher performance stand ards and reliability Helium cooling systems and hi temp coils can protect your investment Repair insurance pro gram available Rapid service Lower cost HAECO 14110 Aetna Van Nuys California 91401 AUDIO EQUIPMENT
53. en a 500 or 600 ohm load is connected does the stage distort seriously and more the lower the load resistance value The apparent impedance at the grid of the stage shown in FIGURE 5 is the impedance from grid to cathode multiplied by the working gain of the stage This means that when the gain is high because no matching load is connected the impedance of both the resistor from grid to cathode and of the diode and resistor shunting it is multiplied by a large number and the shunting effect on the input source re sistance shown as a resistor in FIG URE 5 but the plate resistance of a previous stage in a practical circuit is slight Virtually no offsetting distortion OCCUTS As the output is connected to a pro gressively lower load value the work www amaricanradiohistorv com SOURCE RESISTANCE Figure 5 A revised form of cathode follower output stages subject of an earlier patent by the author This can keep distortion low over a wide range of output loading ing gain of the stage drops so that the grid circuit values as loads across the input source resistance also drop Thus the diode and its associated re sistance produce more offsetting dis tortion as the loading is changed so that more distortion occurs to be off set By proper choice of values dis tortion can be kept low over a wide range of load values Digging out that patent file brought back memories as I thumbed through a whole bunch o
54. ern University in Evanston Illinois Loudspeaker experts will square off for what is expected to be a battle royal Presenting various subjective evaluation techniques are C G McProud and Julian D Hirsch and presenting opposite but differing views on objective measurement are such advocates as Dan Queen and Paul Klipsch To balance the technical presentations academic viewpoints will be presented by prominent faculty members from two universities includ ing a session on psychoacoustics by Dr Carhart of Northwestern Univer sity A panel of these experts will dis cuss how subjective and objective mea surements can be correlated There will also be a meet the experts noon time session Advance registration fee is 3 00 Write Midwest Acoustics Con ference c o D Burkhard Industrial Research Products Inc 321 Bond Street Elk Grove Village Ill 60007 Phone 312 439 3600 Bubbers Acoustic Research president Victor Amador has announced the appoint ment of John J Bubbers to the posi tion of director of engineering He re places Roy Allison who is leaving to continue his research work in the field of room acoustics John Bubbers prev iously had a long association with Stanton Magnetics Inc where he was vice president of field engineering and professional products manager Prior experience includes ownership of B amp C Recording where he was instrumental in the introduction of stereo recording and the manufac
55. erties of materials and con struction listed actual installations with photos and drawings Appendixes illustrate details of 53 wall types and 32 floor plans and other useful data 246 pgs 18 50 21 Acoustics Room Design and Noise Control Michael RAettinger 1968 The enormous problems and hazards presented by noise are dealt within an orderly and practical manner With many charts graphs and practical examples the text covers the physics of sound room acous tics and design noise and noise reduc tion 392 pages 17 50 22 Acoustics of Studios and Auditoria V S Mankovsky Basic theory plus a mass of design data covers the field with special reference to studios and places of public performance For acoustical designers and specialists in sound transmission in cinema and broadcasting Features exhaustive treatment of studio acoustics by the sta tistical geometric and wave methods in parallel 416 pgs 15 00 CLASSIFIED FOR SALE NEW YORK S LEADING supplier of pro fessional audio video equipment and hi fi stereo Components All major brands in stock Call for quote sales service leasing trade ins Martin Audio 320 West 46th Street 10036 Telephone 212 265 6470 STUDIO TAPE ELECTRONICS Advanced design incorporates all the desired fea tures for updating or expanding out dated recorders or building new sys tems Prompt delivery Inovonics Ine 1630 Dell Avenue Campbell Ca 95008 INFO
56. essed simultaneously When the black but ton is released the clock will start automatically The accessory plug on the rear panel may be used for all remote operations All BCD information is available at this plug for accessory units such as digital printers Model T 1 slave units etc s The Model T 1 is supplied for 120 volt 60 Hz operation Electronic StopClock in an attractive simulated walnut grained enclosure with 1 85 a red lucite face However 120 volt 50 Hz operation is available at no extra charge if so specified at the time you place your order The Model T 1 is priced at 185 00 As with all Time r keeper products it is fully guaranteed to meet with your complete satisfaction or your money will be promptly refunded It is guaranteed for one year against any defects in manufacturing The Timekeeper Electronic StopClock is a must More than a high quality timer it provides the added con venience of full visual display high accuracy and sta bility plus operational flexibility Order one soon You will be delighted with it TIMEKEEPER Name P O Box 835 Great Neck N Y 11021 Address ZER Please send me _____ Model T 1 Timekeeper Electronic StopClock s City__ 8 m at 185 00 N Y S residents add 7 sales tax Add 1 00 shipping per order enclose Se State ee ee ees eee KW ee iii iin Lam eee EE EE EB SOE EE EB BSB BSB BSE BSS SBE BSB SBS ESE SBE EE eee NM WM ee 8 mm MMe Eee a Ee HE
57. f FIGURE 1 and 2 is use of transformers in addition to the build out resistors Sometimes in order to provide d c isolation or change the output voltage a transformer may be connected after the 600 ohms resistor But the combined impedance of the windings and transformer losses may make it necessary to change the value of the build out resistor until you read the impedance we were after across the secondary of the isolation trans former The circuits described offer several important advantages distortion can be made extremely low because no large power transformers are used frequency response can be made ex tremely flat for the same reason and the noise caused by magnetic fields is also minimized One of the most important things almost was forgotten the whole dis tribution system can be packaged into space smaller than a pack of cigar ettes And most of the space will be occupied by capacitors resistors con nectors power supply switches con trols and not the amplifiers m Copies of db on Microfilm Copies of all issues of db The Sound Engineering Magazine start ing with the November 1967 issue are now available on 35 mm micro film For further information or to place your order please write di rectly to University Microfilm Inc 300 North Zeeb Road Ann Arbor Michigan 48106 A subsidiary of Xerox Corporation In addition to Microfilm Copies available through University Micro film we hav
58. f documents till I found the one I somewhat vague y re membered Each had its own little memory of solving a circuit problem I had not realized there had been so many because that part of the file had become a closed phase in my life We left tubes behind when we moved into solid state And now we are moving quite a way from the early transistor circuits as computer designed integrated cir cuits take over more and more of the work Its a changing world indeed The other side of my present activity combines with these memories to raise even larger problems In those days we solved problems by applying our ingenuity directly to the physical phenomena and the math ematics that described them Today computers do all that and more Yet education far from moving into step with these changed requirements has the people who design math programs getting even further from reality than they were when I went through school They seem to have a math world of their own completely un connected with the real world They are inventing all kinds of un realistic things for kids to learn that will never be of any use to them And because those with practical minds that could become the engineers and inventors of tomorrow naturally shy away from these meaningless bits of garbage they drop out before ever they get far enough to think about meeting college entrance requirements Where s it all going to end E etabitmore A72 F
59. figuration or combination And has full track select capabilities on all 2 channel cassette slave modules FAST It s twice as fast as our model 235 on reel to cassette Meets pro fessional high volume needs with 8 1 duplicating capabilities on cassettes And it handles up to 10 slaves at once with no additional electronics EASY TO OPERATE Even for the inexperienced operator Telex 300 operates easily and correctly Fail safe controls prevent master erasure New electronics package offers re fined electronic settings And mo mentary push button controls and time delay circuits provide smooth positive tape handling ENGINEERED TO PROFES SIONAL STANDARDS The Telex 300 is reliable Built for professional use and designed to last for years with minimal service Hysteresis synchronous motors maintain true tape speed from start to finish Select grade duplicator heads pro vide long life with excellent frequency re sponse And the Telex 300 has Commercial Underwriters Laboratories listing Competively priced the Telex 300 lets you build the system joli state elaswenies Bias 1 oscillator module and two you need today And add to this system for tomorrow s Or four channel amplifiers Standard table top console requirements Made in the U S A Open reel master 15 30 IPS Full track Half track or 2 Cassette master 7 5 15 IPS channel Quarter track 2 or 4 Half track 2 channel Quarter channel tra
60. first 60 dB e Fast scan rate of 800 micro seconds per variable function scans 128 variable functions 10 times per second e Long term accuracy and system to system compatibility with 1 dB e Operates on any audio recording medium with 5 KHz bandwidth and a 35 dB signal to noise ratio Data recording level non critical Thoroughly protected against long or short term dropouts The programmer is only the begin ning Contact us for details on the Model 256 E D and other automa tion components and systems AUTOMATED PROCESSES INC gt OO MARCUS DRIVE MEDALE AEW FORA TSG SI6 694 8212 Circle 27 on Reader Service Card www americanradiohistory com 26L Menuer qp db January 1973 8 about the drawback of using a single amplifier and about the excessive crosstalk that one would get if the Output impedance of the amplifier was anything but almost zero In Fic URE 1 I am demonstrating the atten uation of the signal to be rejected in order to prevent the crosstalk By combining two amplifiers a few things happen First we get balanced output By adjusting the gains of each amplifier accurately we can achieve perfect a c balance Secondly output voltages of each amplifier add up producing 6 dB higher output This way amplifiers which individually produce about 20 The difference between dBm into 600 ohms when combined add up to 26 dBm This very nicely compensates for the 6 dB loss we en
61. g the intensity of the bulb corresponded to the intensity of the signal or for settings of various controls intensity of a bulb indicated the setting of the volume control or of a tone control This is only a brief listing of the features and peculiari ties to be found in certain of the older sets The collector is certain to discover many more novelties for himself as cach set has some These things were the edge one manu facturer had over his competitor and each one tried to capture the public imagination by engineering gimmicks as well as number of tubes and sensitivity Today when the vacuum tube itself is a dying thing old radios have a particular attractiveness as representa tives of the past of electronics an earlier era of our business hobby m U S amp FOREIGN PATS m Y MS 200 MAGNETIC TAPE HEAD saves your heads prolongs tape life Non flammable non conductive odorless and non toxic And it comes with a get right down there extension nozzle For all types of recorders and EDP installations spray away magnetic tape head problems with MS 200 Manufacturers recommend it For FREE sample of MS 200 write on company letterhead please or use coupon for data and prices O Please send me data and prices on MS 200 intend to use MS 200 on SEE Name Address City State iller stephenson chemical co inc Danbury Connecticut 06810 203 743 4447 Title Dept
62. get some old radios and build a p a system from the parts We went door to door for several blocks and collected no less than two dozen sets from peoples attics which they didnt want Many of them did not work Among the sets we collected was an Atwater Kent with the familiar domed top There was a set with inductive tuning I can t recall the brand There were many other very old types with the nonoctal tubes and with special unmarked parts designed by the manufacturer no stand ard resistors or capacitors I had already seen some very old sets I had inherited an RCA Radiola 26 which ran from a large battery pack I never got it to work I had a friend with a somewhat newer RCA set with large blue tubes that looked like lightbulbs and it did work At any rate I was impressed by the variety and by the elaborateness of some of these old sets They have very pretty coil work in the r f section and those with many bands can have some elaborate turret type band switches and I never could get over the fact that they could be obtained very cheaply and sometimes free Like old auto mobiles all this impressive machinery was devised for a purpose better served by newer models and most units were apparently worthless However like old cars I sus pected that there might be a movement to collect some of the rarer or more impressive specimens So far this collectors hobby has not gone very far But the time seems to be ripe for it to get go
63. gnal source Interaction 600 INSTANT REPLAY The WRITE record READ playback and UP DATE modes may be set by switches on each individual fader or by one master PRE SET switch which sets each fader to a previously se lected and stored operation mode Master override switches set all faders to the record or playback mode When used in conjunction with the Model 256 Pro grammer electrical perform ance characteristics are compatible with state of d the art professional studio consoles and components The Model 940 Automated Fader fits in the space normally occupied by a conventional fader so that no addi tional console panel area is re quired in retro fit applications Mounting dimensions are 7 high x 1 2 wide x 4 deep over mating connector You can automate your studio NOW with the Model 256 Programmer the Model 940 Fader Modules and our other automation controls or with a pre wired ready to use 16 or 24 channel automation consolette and there s more to come AUTOMATED PROCESSES INC p gt BO MARCUS ORIVE MELVILLE NEW FORK 1186 508 694 9272 Circle 27 on Reader Service Card www americanradiohistorv com of the signal distributed and the sig nal coming back from the telephone line is an important point in a dis cussion about sound distribution There are many ways distribution of signal can be accomplished The most simple and straightforward method using several se
64. great amp the first super power low distortion amp in the world when Crown introduced it five years ago Meanwhile top sound systems design ers have used it successfully in hundreds of demanding situations and made some excellent recommendations for improvements The response of the Crown design team was not an updated DC300 but a totally new and different amplifier the DCSOOA It is the only high power low distortion amp specifically designed for com mercial sound applications CAUTION There are some large consumer type amps attempting to sell in the com mercial sound field without providing adequate continuous power for all load impedances Power You Can Count On One of the DC300A s most outstanding features is that it has double the number of output transistors This means effectively twice the muscle of the old DC300 at the same price Each channel has eight 150 watt devices for 7200 watts of power dissipation per channel The DC300A is rated at 150 watts per channe continuous into 8 ohms with both channels driven 300 w ch into 4 ohms or 500 w ch into 2 5 ohms Two Amplifiers in One As a dual channe amplifier with separate level con trols and circuitry for each channel the DC300A is almost two amplifiers in one This gives you additional flexibility in controlling your speaker load as when driv ing separate front and back speaker systems in a large auditorium or when bi amping a system For 600 watts continuous
65. great extent These tubes were usually manufactured by a particular company for use in its own products and were not interchangeable with another manufacturer s product A distinguishing feature of tubes from this era pre nineteen twenties is the light bulb shape of the glass envelope and often a blue colored glass This is probably the earliest type one is likely to en counter and a working set with such tubes is a rarity The real enthusiast might want to rework tubes which no longer work in order to restore such a set Very often old sets were not built to work from 110 volt power sources These often did not exist and there was less standardization as to voltage frequency or even a c or d c Commonly battery packs were used These were chests which had to hold three sets of batteries the A B and C voltages The A voltage was a bias supply the B voltage has become our familiar B while the C supply was for the filaments Batteries used in these battery packs resembled those in our automobiles more than any thing else Size and weight were impressive as the battery pack was usually larger than the radio which also was large The collector who is able to find one of the old battery powered sets such as the RCA Radiola 26 should be able to build a modern power supply for it to replace the battery pack The radio receiver itself could be restored in exact Original condition If the very old sets we have been discussing are the r
66. he If you are thinking about mixdown automation and you probably should be here s something to consider The programmer is the heart of any mixdown memory system and we have one that works It s called the Allison Re search Automated Processes Pro grammer Model 256 E D with provision for up to 256 variable dynamic functions This assures capacity to provide total automa tion of the entire console not just level control but automatic mem ory of the control functions of panning equalization echo sends submasters masters switching echo returns the works THAT S TOTAL RECALL What Else e Capacity for literally thousands of switching functions gearworks This can be the resistance of the output wire and the ohmic re sistance of the contact in the case of a plug in p c board We may adjust the amplifier impedance to be zero while the contact resistance may be 0 1 ohm In order to achieve 70 dB of isolation the common point re sistance should be less than 0 2 ohms FIGURE 1 and 2 show how a con ventional amplifier and a combination of two such amplifiers can be ar ranged in a push pull circuit produc ing balanced output without the use of transformers In the beginning we were talking 300 OUTPUT OUTPUT 2 OUTPUT 3 _ TOTAL REGAL e Infinitely variable stepless con trol of mixing parameters accurate to within 0 2dB over the first 40 dB of working range 2 dB over the
67. in particular institutional equipment such as classroom phonographs Some of the more claborate yo in here there s magnetic tape u usuall d this because MS 200 Magnetic Tape Head Cleaner is faster more convenient and more efficient that cotton swabs You can apply MS 200 with complete safety while tape is running It quickly removes dirt dust and oxide build up console radios of the thirties had large transformers and high power amplifiers Some even used special noise lim iters and so forth One of the more daring moves must have been to put a solid wooden back on the traditionally open backed cabinet and perhaps install a bass reflex vent or some other sort of resonator plumbing A few manufacturers actually did such things but they were definitely in the minority So there is a large umount of novelty in the old radios There is also a certain peculiarity The aesthetics of the de sign of the cases and of the dials is definitely quite differ ent from that of modern sets After all the really old sets are actually Victorian furniture with all the orna mental frillwork of the period Peculiarities in the use of lights is also fascinating Often sets would have as many as a half dozen bulbs each with a different colored filter The bulbs would be switched by the bandswitch so that a color would correspond to a particular band Other manufacturers used bulbs to indi cate various things such as tunin
68. ing There is one primary reason why the collecting of old radios is not as big as the collecting of old automobiles radios did not suffer the nearly complete destruction dur ing the war that automobiles suffered Thus they are still plentiful and any visit to an antique store will turn up one or two Perhaps old radio collecting is a hobby which will catch on at some future time If so now is the time to get started before the prices on prime units skyrocket This article is a suggestion to the audio fan and elec tronics experimenter that he ought to think about the pos Collecting Old Radios sibility of some of these old sets becoming collectors items and to consider obtaining a few for his own personal col lection I would like to offer some suggestions as to what might constitute a valauble find or a real rarity In the first place age is a real factor in the value of a set Any set with octal tubes is almost modern after all octal tubes are still being manufactured A set with non octal tubes that works can be considered to have some significance The type of tube in use immediately before the octal tube was a set of tubes having as many pins as the tube had elements These pins were sized so as to per mit orientation The number of pins was from four to seven on top A receiver with this type of tube dates from the nineteen thirties or earlier Tubes used in sets before the type mentioned above were not standardized to any
69. ing up input impedance and ensuring that the input can handle wide swings before the control stage is reached But let s take a closer look Did I say the cathode follower would raise the input impedance As shown that is fixed at 220 k And as a 12AX7 has a grid base of about 3 volts or so returning the 220 k to ground will strangle the tube so it operates near cut off There were two good ways to Operate the bias of a 12AX7 One Figure 1 The schematic sent to me by a reader of a scope amplifier age pami es u th ae Se 5 6 155 Michael Drive Syosset New York 11791 Circle 23 on Reader Service Card WWW amaricanradiohistorv com would use a resistor of 5 to 10 meg from grid to cathode FIGURE 2 rely ing on grid current biasing The other would use a cathode bias resistor FIGURE 3 With either of the latter circuits the cathode follower would provide a very high input impedance and big swing handling capabilty But assum ing the same cathode oad and follow ing gain control circuit of FIGURE were used just changing the bias ar rangement what is the working gain of the cathode follower by which in put impedance gets multiplied The plate load connected in the cathode will be 22 k in parallel with 13 5 k which figures to about 9 k Taking 80 k as an appropriate value of plate resistance with an amplifica tion factor of 100 this means the
70. is that to take full advantage of an op amp s capabilities you should com pensate it to suit the particular application Compensation also directly affects slew rate as you www amaearicanradiohistory com may have already guessed The slew rate limiting is actu ally caused by the op amp circuits inability to charge and discharge the compensation capacitance at high frequen cies and high voltage swings This leads to a triangulation effect where a sine wave Output gradually turns into tri angular waveform as the amplifier crosses into its slew rate limited region The solution to this problem is to either reduce the compensation capacitance or increase the current s available to charge and discharge it or alternately use some means to bypass the capacitance charging problem All of these techniques work and sev eral practical circuits exploiting then will now be ex plored OUTPUT VOLTS PEAK eer ABFAREM AMEA FREQUENCY IN HERTZ for 741 and 301A compensated for unity gain Curve 2 is typical for 301A compensated for 20 dB gain as in Figure 2 box B Figure 1 Large signal response of general purpose op amps with various compen sation conditions Curve 1 is typical FOR 301A Fis R R WHERE Cs 30pf Eo First consider the case of general purpose amps the 709 741 and the 301A The 741 is inflexible as far as extending its h f performance goes and cannot be con sidered f
71. le to compose a piece of music with no abrupt breaks of any sort but only linearly varied param eters of the sort controllable with the potentiometer Here is a style derived directly from the unique capabilities of electronic techniques SCALES AND INTONATION Ever since the dark ages our western music has made use of portions of the twelve note chromatic scale or varia tions of it with regard to tuning procedures It has served us well for we have had ten plus centuries of music from it However is it really the only usable scale Composers have often asked this question and some have gone to the extremes of building new instruments for experiments with other scales Now with electronic music every music stu dent may try the experiments for himself Every serious contemporary composer should have the experience of sit ting down at an instrument tuned in nineteen or thirty one tone equal temperament or perhaps a forty three tone non tempered scale An hour of improvising at such an instrument may open his ears so to speak and so change the course of music The interested theorist may want to refer to Joseph Yasser s Theory of Evolving Tonality or Harry Partch s Genesis of a Music for work involving new scales There are many untried possibilities New scales and no scale both are characteristics of the emerging electronic music style Both need to be studied listened to practiced and taught AESTHETIC ORIENTATION OF ELECTRO
72. les or trees After the a m band reached its state of saturation interest in distance reception switched to the short wave bands It seems that this mode of entertainment was not restricted to the hams of the era but that at one time most radio listeners en joyed listening to long distance reception on the short wave bands Anyone interested in the technology of electronic equip ment will find it interesting to explore the circuits used in some of these old sets Today there are certain tech niques which have become so common that they are con sidered standard In the days the old sets were manufac tured these standards did not exist and engincers tried any possible method to achieve results I ve already mentioned inductive tuning which became common in automobile radios and some military sets but which eventually was re placed by capacitance tuning in console radios One who explores these old sets will discover all sorts of novelties such as peculiar tuning indicators unusual tubes and appli cations different types of bias ctc If some of these cir cuits do not work the modern technician can be quite confused trying to figure out what they were supposed to do not to mention how they work Another item of interest is the early attempts to im prove sound quality The term high fidelity is not as new as some of us might think Some manufacturers RCA in particular were using the term to describe their products in the thirties
73. ls or mechanical shock This means you Headquarters 2 West 46th Street STELLAVOX mai ep New York NY 10036 Tel 212 265 4111 tape recorders can install it in studio or gontrol room or take it m za 1 ak Mon ini NEUMANN i est Coast Sales Office 1710 N La Brea Ave disk cutting systems with you on location The remote reverb time Hollywood CA 90046 Tel 213 874 4444 K control is standard equipment And the 240 i aa Ja equallror deli 4 ia ianed ld like a no obligation introduction to the EMT elivered to you sealed pre alignad pre ten EMT 140 s little brother EMT 240 Please polarity testers sioned ready to go to work send me literature and price information area is The coupon will bring you more information M W Mail it today pna light beam meters TITLES se D Gl a PA EG WF c SUR GOR ice sal www americanradiohistory com 26L Alenuef qp al db January 1973 18 Wanted 700 000 busy executives If you can spend some time who can even a few hours with someone who needs a hand not a handout call your local Voluntary Action Center Or write to Volunteer Washington D C 20013 We need you O otis ra lt The National Center for aunt Voluntary Action advertising contributed for the public good POWER AMPLIFIER gt WWW americanradiohistorv com The Stereo 400 is capable of deliv ering 200
74. mp Formulas 3rd edition A one stop source for all charts tables formulas laws sym bols and standards used in electronics In cludes an 8 page full color fold out chart showing latest FCC allocations for the en tire frequency spectrum 232 pages 5 x 8 hardbound 5 50 Sagamore Publishing Company Inc 980 Old Country Road Plainview N Y 11803 Please send me the books have circled below My full remittance in the amount of _ is enclosed N Y State resi dents add 7 sales tax 12 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Name Address City__ State FA o E Special Instructions Canada and foreign Add 1 00 per book oo pe ee cm gum zm ew WW SD TP ZY OF ee eee eee a ee ee ua m gm pm ee an an an z A PA A A ORA A ee aed As a service to our readers we are pleased to offer books from prominent technical publishers All prices listed are the publishers net Shipping charges are included To order use the coupon at the bottom of the page Indicate quantity on the speciai instructions line 24 Basic Electronic Instrument Handbook Edited by Clyde F Coombs Jr Hewlett Packard Co A basic reference background for all instruments Offers saving in time and effort by having complete information in one volume on how to get the most bene fit from available devices how to buy the best instrument for specific
75. n the other hand much new and unique apparatus has been devised for special purposes One interesting observation is that nearly any electronic technique applied to the generation of audio signals may have strikingly fresh qualities For ex ample electronic music has employed both frequency and amplitude modulation waveform clipping single sideband suppressed carrier techniques resonant and non resonant filtering pulse width modulation and a host of others not so easily described Some special audio equipment used includes variable speed tape recorders multi channel am plifiers and speakers and a great multitude of filters includ ing very narrow band types and tracking filters The well known but little used theremin employs the principal of the beat frequency oscillator commonly found in com munications receivers Reverberation devices are much used and many techniques have been devised including the sheet metal reverberator the spring unit and the new electrostatic reverberation unit Multi channel tape re corders developed for telemetry applications have found use in systems of up to fourteen channels THE COMPLEX TONE The concept of the complex tone is an interesting one and is truly a part of the electronic style It must be under stood to be distinctly different from the simple tones such as the sine square and triangular It is also different in nature from the harmonic tones produced by conventional instruments and fr
76. n the swing is negative the re verse happens By adjusting the setting of the 500 k preset quite good linearity can prob ably be obtained better than likely by sacrificing an equivalent amount of gain in linear feedback Going over this turned my mind back to some work I did almost twenty years ago but my memory of it was a bit vague so I had to turn up the wording on that particular patent to remember just how it worked The circuit shown at FIGURE 5 was de signed to be used as the output stage for a preamp In those days there were two camps those who used matching transformers to match line impedance usually 500 or 600 ohms up to the plate load value required by the tube and those who used cathode follower outputs Neither was altogether ideal The transformer output had frequency re sponse limited by the transformer which could also change with loading if the line impedance was not precisely 500 or 600 ohms as specified And the cathode follower loaded with 500 or 600 ohms which it matched produced distortion The function of the circuit in Fic URE 5 was to offset the distortion pro duced by the cathode follower The diode and resistor in series shunting the grid to cathode resistor did the same thing as the other triode pins 6 7 8 of the 12AU7 in FIGURE l But it has a somewhat more compli cated function If no matching load is connected the cathode follower produces little distortion Only wh
77. ned to maintain the traditional quality and technical excellence of these products If you really want to find out all about us don t look in the dictionary Just call Don McLaughlin Bart Bingaman or Phil Hanson at 213 875 1900 etec Saticoy No rth Hollywood California 91605 of Computer Equipment Corp Circle 19 on Reader Service Card www americanradiohistory com 464 AKienuer qp db January 1973 12 Norman H Crowhurst THEORY AND PRACTICE e Technologically we live in a rap idly changing world This gets brought home to me when I get the periodic letter metaphorically out of the past from someone who wants something explained about a piece of equipment made a few years ago One such letter was from a man having problems with a tube operated scope amplifier the schematic for which is reproduced at FIGURE 1 He wondered what function the tri ode using pins 6 7 8 of the 12AU7 served in the circuit Fairly obviously the 6 7 8 pins of the 12AX7 serve as For less than the price of a small console you can own the whole studio mi ni studio To find out more about our remarkable MiniStudio and the name of your nearest participating dealer call toll free 800 645 2075 In New York call collect 516 364 1750 Or write us directly LAMBLAORATORIES a cathode follower I almost wrote emitter follower from force of habit which serves the dual purpose of step p
78. new and used Custom consoles built to your specifica tions using the components of your choice Whether you re building a new studio or remodeling your present one check us first for a package price Am boy Audio Associates 236 Walnut Street South Amboy N J 08879 201 721 5121 FOR SALE Bulk quantities of used 4 v2 and 1 inch tape Vanguard Records 71 West 23rd Street N Y 10010 212 255 7732 AUDIOTECHNIQUES INC WANTS TO BUY your used Scully Model 280 series tape recorders any width from quarter inch to two inch Write or phone Bob Berliner or Ham Brosious giving condi tion serial number and configuration Audiotechniques Inc 142 Hamilton Avenue Stamford Conn 06902 203 359 2312 SAVE ON YOUR STYLUS COSTS World s finest recording styli for all Westrex 3D models and HAECO SC 2 12 80 unwired 13 80 wired Quantity purchases at additional savings Satis faction guaranteed Send check or money order with your order to HAECO 14100 Aetna St Van Nuys Ca 91401 LARGE RECORDING STUDIO FOR SALE Fabulous location and great sounding studio Boston area 7000 square feet Air conditioned and con taining many pieces of good recording equipment and instruments included Price reasonable Write P O Box 8 Newtonville Mass 02160 or call 617 969 8295 or 482 858 PEOPLE PLACES HAPPENINGS The seventh annual Midwest Acous tics Conference is scheduled for April 7th at Northwest
79. nodized aluminum with a smooth satin finish Precise warp proof con struction assures accurate alignment and tape tracking The reel comes in a library shelf plastic container with a hinged cover containing a self locking latch Designated the LR 7M it is fur nished complete with blank self stick labels Mfr TDK Price 7 50 Circle 56 on Reader Service Card Gotham distributes more than 500 products including STUDER studio consoles NEUMANN quad microprones STELLAVOX mixers WOELKE wave analyzers in reverberation in reverberation The Reverb Foil EMT 240 It s bound to be a resounding success because it s only 1 5 the size of its big brother But small as it is the EMT 24C represents a big advance An electrolytically produced foil of almost pure gold 12 inches square and 0 7 mils thick replaces K H ioudspeakers LYREC tape timers EMT Reverb units l GOTHAM digital delay systems EMT compressors DANNER linear attenuators EMT turntables Now meet the smallest name The EMT 140 is the biggest name h di i matic ie mata ie a NEUMANN the steel plate used in the 140 Which assures Staple this coupon to your company letterhead edie less coloration as a result of significantly in and mail to our New York office 2 i G rotary attenuators creased resonance density 4 WOELKE The EMT 240 is not affected by high ambient KUDIG CORPOR ATDA u meters F noise leve
80. o design into our systems tran sistorized amplifiers some of them i c type operational amplifiers which have an output impedance of several ohms and in some cases fraction of an ohm I have run into some engi neers who were somewhat confused by this fact having worked all their lives with 600 or 150 ohm source impedances The first thing that comes to their mind is how do I feed a 600 0hm line from the zero impe dance source In most cases you just connect it and forget about it In some cases you have to think before you connect it If the line can be fed from any source impedance an amp lifier potentiometer fader or trans former then interconnection is direct If the load is a passive equalizer de signed to work in a 600 ohm circuit then you have to provide impedance matching This can be done simply by connecting a 600 ohm resistor between the amplifier and the equalizer If you feed a telephone line which is about 600 ohms then a build out resistor of 600 ohms is needed and in the case Of a dial line d c decoupling Figure 2 A balanced output without transform ers because of voltage on the line Before we proceed let us define re quired properties of the circuit to be used for signal distribution First of all there should be adequate level at each output with enough headroom for peaks Secondly isolation between the lines must be such that if one line or several or even all but one are shor
81. om combinations of harmonic tones chords The sine square sawtooth and other funda mental tones have a fundamental and in all cases except the sine regular overtone structures harmonic tones from conventional instruments have individual harmonic ar rangements or nearly harmonic as in the case of the piano The nearest thing to the complex tone in conven tional music is the type of semi pitched percussive tone produced by chimes tympani etc These instruments however normally have attacks and short envelopes in standard practice Electronically produced complex tone may be made to have any envelope Basically the complex tone is a modulation product of two or more simple or harmonic tones Therefore it con www americanradiohistorv com 46L Alenuer qp Ec db January 1973 24 there is little harmony and melody and not a great deal of counterpoint p b an tains them both and or sums and differences of both The variety of complex tones is extremely wide No one has even begun to categorize the various types and the surface has only been scratched in their application in electronic music Certain basic categories may be made according to the type of modulator employed in the generation process unbalanced balanced ring frequency amplitude phase etc Other categories may depend on the number of input tones and their individual complexities Although already used on occasion there is however a
82. ong time as a result To sum up electronic music is generally abstract and serious in style It is probably intended more for individu als than for the masses and lends itself easily to economi cal distribution to interested individuals on a widespread basis SUMMARY The style of electronic music is influenced by three fac tors The capabilities of available instruments the knowl edge skill and intentions of the composers and the intended audience or application and the method of dis tribution Electronic music instruments are capable of a wide range of new tone colors new scales and rhythms They are also capable of many new types of control over con ventional instruments Electronic music composers are learning of the new freedoms as well as the new disciplines required of them by the medium they are beginning to be aware of ways to teach these things to their students Much remains to be done here Electronic music audiences are small but dedicated They expect serious work and thanks to the relative eco nomics of electronic recording and broadcasting tech niques are able to get what they want Probably ninety nine per cent of the contact between listeners and elec tronic music ts through phonograph records Electronic music is abstract and relatively pure as an art form A comment by the noted conductor Antal Dorati on the subject is significant Mr Dorati suggested that electronic music may be part of a
83. onic that is based upon the five note scale equivalent to the black notes in one octave on the piano while other nationalities employ six eight or ten or more notes in their scales All of these characteristics pertain to the idiom of a particular type of music Robert C Ehle PhD is with the School of Music Uni versity of Northern Colorado Greeley Colorado Serious composers have never failed to experiment with any new idioms coming to their notice and so all the idioms originating in folk music have been explored in serious musical composition A peculiar result of all this is that composers tend to develop trademarks Scriabin had his mystic chord Liszt liked augmented chords Tchai kovsky used sequences Bela Bartok developed the Hun garian folk idiom in his music while many American composers use jazz styles in their music Each country has its own folk idiom composers and there are peculiar and distinctive characteristics in each national style Through out the history of music composers have had their favorite chords progressions or tricks which they made sufficiently famous so that anyone using them would be accused of plagiarism Today composers seeking new idioms will try anything to avoid this accusation Thus we come to the style of electronic music So far the idiom of electronic music seems to be going in the direction of new timbre generation and control This is perhaps to be expected since it is in
84. or the applications we have been discussing The situation is quite different with the 709 and 301A how ever and they can be quite useful in a variety of high speed hookups For instance in closed loop gain configu rations of 20 dB or more both the 709 and 301A have slew rates approaching 3 5 volts per microsecond when compensated as per curve 2 of FIGURE 2 And at higher gains slewing rate will improve proportionally as long as the minimum compensation necessary to stabilize the loop Is used 80 60 AVERAGE IN dB 40 CORNER FREQUENCY FOR 40dB AMP USING UNITY GAIN COMPENSATION 20 CORNER FREQUENCY FOR 40dB AMP USING LIGHTER COMPENSATION 10 100 IK IOK FREQUENCY IN HERTZ 1OOK IM Figure 2 Unity gain frequency Box A Standard unity gain compensation for general purpose op amps which results in open loop response as shown in curve number 1 Box B Externally compensated op amps Compenated to produce the open loop response of curve number 2 Ro 3014 COMPENSATED FOR 20dB MINIMUM GAIN _ 30pf _ Cy TO Spf EIN Eo E Ro 709 COMPENSATEC FOR 20 dB MINIMUM GAIN Eo wwyw amearicanradiohistory com 26 Menuer qp e db January 1973 28 OUTPUT VOLTS PEAK FREQUENCY IN HERTZ Figure 3 Large signal response of a 301A with fast compensation See reference 1 CI AR1 Cs Cs 30 pF R1 R2 C2 10 C1 Typical values C1 30
85. osecond Slew rate is directly related to the full power bandwidth according to the relationship Sr 2rEo Fp Sr Slew rate where Eo Maximum output before slew rate limiting peak Fp Full power bandwidth Graphically this may be understood by referring to FIGURE 1 which is a plot of large signal response versus frequency Note that curve number 1 which is typical for a 741 amplifier begins to slew rate limit at 10 kHz and at 20 kHz available output is reduced to half of the full power available at low frequencies To deliver a 10 volt peak signal at 20 kHz we can compute the slew rate required as Sr 6 28 10 2x10 1 256x10 volt hertz or 1 256x10 v s 1 256 V ys This 1 256 volts per microsecond slew rate is a mini mum requirement In practice the circuit should have a working slew rate in excess of this figure to prevent rise of distortion at the onset of the rate limiting The second key parameter is the circuit s gain band width products this is also called the unity gain frequency This is the frequency at which the circuits natural open loop gain has fallen to 1 or O dB For general purpose i c op amps such as the 709 741 and 301A compen sated for unity gain this figure is approximately 1 MHz The plot depicting this gain is shown by curve of Fic URE 2 The corresponding amplifier connections which will display this response characteristic are shown in the Walter Jung is a frequent contributor
86. output at 8 ohms the DC300A converts to a mono amp with two plug in parts This makes it possible to drive a 70 volt line directly without a matching transformer Superior Output Protection The DC300A output protection circuitry is a rad ically new design which completely eliminates DC fuses and mode switches and further reduces service problems to the negligible level It is superior in every way to the old Vi limiting circuit pioneered by Crown and now used by most other high power amplifiers since it intro duces no flyback pulses spikes or thumps into the output signal whether operating as a single or dual channel amp PROBLEM SOLVER Gone too is the need to baby the amp by carefuily juggling load configurations The Problem Solver can drive any speaker load resistive or even totally reactive with no protection spikes Parallel speakers with no deterioration of sound quality since changing the load impedance only affects the maximum power available not the ability of the amp to keep on producing clean sound Lowest Distortion and Noise Also new is the DC300A s IC front end which sets new world s records for low distortion and noise At the 8 ohm rated output IM and harmonic distortion is less than 0 05 full spectrum hum and noise is 110db below Servicing if ever necessary is a snap since removing the front panel accesses the entire circuitry Although it is a completely redesigned model the DC30
87. pF C2 300 pF There are other approaches to slew rate improvement perhaps more sophisticated in concept but no more complicated in practice The first trick is a two pole compensation method used with the 301A to extend its power bandwidth by a factor of two or more This circuit is shown in FIGURE 3 with the resultant power bandwidth It should be noted that this is a general purpose circuit which can be used either differentially as an inverter or as a follower It offers advantages at lower closed loop gains between 1 and 10 where the additional compensation necessary nor mally limits slew rate At gains beyond 10 the minimum standard compensation technique is both faster and more simple A big leap forward in slewing rate may be accom plished with the 301A by applying feed forward com pensation This technique shown in FIGURE 4 with the resultant full power response is the fastest of all the techniques applicable to the general purpose op amps It extends the unity gain bandwidth to 10 mHz and raises slew rate to 10V us Its chief disadvantage is that it is limited to the inverting configuration as shown As may be noted from the open loop gain curve number 3 of FIGURE 2 the circuits prime advantage is a dramatic in crease in available high frequency gain Curve 3 the feed forward response provides a bandwidth equivalent to the 20 dB compensation of curve 2 even though operating at unity gain So where an inverting
88. parate ampli fiers fed from the same source This method offers excellent crosstalk iso lation between the output channels and maximum reliability but also is the most expensive The next simplest is the use of multiple taps of the single amplifier s output transformer for connecting several loads Failure of the amplifier or a short circuit of a single line re sults in a shut down of the entire distribution circuit In addition isola Ra 600 WWO SIGNAL 2 Rs CROSSTALK 70 dB Ra 600 3000 e 0 2 A tion between the lines is inadequate This means that if impededance of one line changes for some reason for instance accidental double loading then the output of the remaining lines will change too In some cases where only one 600 ohm line is being fed and the rest of the lines are bridging 10 k or higher the effect of inter action between the lines is not so pronounced but still exists If the amplifier has no output transformer but is connected to the load through a decoupling capacitor several loads can be connected across the output providing the total load does not ex ceed the maximum permissible load for the amplifier Additional isolation and safety can be achieved by pro viding isolation resistors in series with each feed However this produces side effects such as loss of level change in line impedance and pos sible loss of high frequencies However lately we have become able t
89. perfected thoroughly tested Sound Mixing Console like the one shown in your studio in ess than a day So you can start using it immedi ately Instead of waiting indefinitely Reason All modular components are built precisely to specs Design ed for ultra fast installation Another Surprise no bother with in studio modifications later on Neve Console craftsmanship is unmatched For ex ample fantastically low distortion never above 0 075 at 1 kHz On time delivery It s always a mat ter of policy with Neve And a matter of honor as well We ll custom design a console for your particular needs We also offer a wide choice of stock audio control consoles Neve Con soles are used in major studios for music recording broadcasting ad commercial and motion picture pro duction in 24 countries The sound of Neve is world wide Write for more facts Now You ll never be disappointed with Neve Neve Write for Bulletin DB 1 Neve installs consoles in hours 4 ve X I vs ai Lena Neve Console in Andr Perry s Studio A Montreal Canada Rupert Neve Inc Berkshire Industrial Park Bethel Conn 06801 203 744 6230 Hollywood Suite 616 1800 N Highland Ave Hollywood Ca 90028 213 465 4822 Rupert Neve amp Co Ltd Cambridge House Melbourn Royston Herts England Rupert Neve of Canada Ltd 7528 Bath Rd Malton Toronto Ontario Canada 416 677 6611 Circle 29 on R
90. rsity Outsiders didn t even have a chance to enroll in the first seminar Still the phone calls and letters have continued to come from many miles advertisers index Audiotronics 25 Automated Processing 6 7 Beyer Facing Cover 2 Cetec Inc 0 0 10 11 Crown nt Gace ee eee eee DE eee eee ee Dolby abs 030 4 000002 5 Duncan Cover 2 Electro Voice Cover 4 Gately ZZA Inst of Audio Research NZS Lamb Labs 12 Maxell ee ee a I Miller Stephenson TENZI gt Neve E eee oO Phase Linear 8 Quad Eight 15 Systron Donner 2l Tascam DEJA 3 Telex OD AG Timekeeper 20 Cover 3 Windjammer 18 www americanradiohistorv com THE SOUND ENGINEERING MAGAZINE SALES OFFICES New York 980 Old Country Road Plainview N Y 11803 16 433 6530 Dallas Roy McDonald Associates Inc Semmons Tower West Suite 714 Dallas Texas 75207 214 637 2444 Denver Roy McDonald Associates Inc 846 Lincoln Street Denver Colorado 80203 303 825 3325 Houston Roy McDonald Associates Inc 3130 Southwest Freeway Houston Texas 77006 713 529 6711 Los Angeles Roy McDonald Associates Inc 500 S Virgil Suite 360 Los Angeles California 90020 213 483 1304 Portland Roy McDonald Associates Inc 2305 S W 58th Avenue Portland Oregon 97221 503 292 8521 San Francisco Roy McDonald Associates Inc 625 Market Street San Francis
91. s with appropriately smaller compensation An additional factor of importance in audio use is the improved output stage used which posses a minimum of distortion and a wide bandwidth thus allowing lower distortion at the upper end of the audio band where crossover distortion often creeps up in earlier op amp designs when they are loaded heavily An example of a circuit exploiting the 531 s capability is the single ended to push pull convertor of FIGURE 5 Here two 531 s are cross connected as a self balancing combination gain stage and phase splitter Al is a high input impedance follower with gain suitable for bridging purposes With the values shown it operates at a gain of 6 dB by virtue of the 2 to 1 ratio of RI R2 RI which R1 would normally be directly grounded in a stage such as this feeds the summing junction of A2 The virtual ground at A2 pin 2 serves the same purpose as a direct ground on R1 as far as Al is concerned and at the same time also drives A2 as an inverting stage via the current flow in R1I R2 By making R3 R1 R2 the gain of A2 is fixed at 1 thus creating a mirror image of Al s signal at A2 within the tolerance of the resistances of course The gain at both outputs may be adjusted simultaneously by varying the tap on R1 and R2 if desired or by making R1 and R2 a pot equal to R3 This circuit configuration can be a very useful one as it is a handy complement to the past db article A DIF FERENTIAL BRIDG
92. sponding to the rewound length You are free to stop rewind fast forward or forward the tape even continuously and repeatedly without deranging the timing on the machine thus prohibiting errors These excellent characteristics will enable you to simplify the most complex procedure of editing revising and other wise processing your tape recording e Every fast rotating part is provided with a precise ball bearing so that the Tape Timer can be employed at high speed with no need of lubrication e This trouble free high precision Tape Timer within an error of 2 1000 can be simply fltted to any recording or editing machine Please send_______ Professional Tape Timers at 99 95 each Please send Standard Tape Timers at 49 95 each Total for Tape Timers ___ N Y State Residents add 7 Sales Tax _ Add 1 00 shipping per order _____ Enclosed is check for _ LD www americanradiohistorv com SLIDER POT gt A new conductive plastic linear motion attenuator has been designated the Series 220 Slideline It has a 23 inch stroke is completely interchange able with earlier 200 series units and most other attenuators of similar size The conductive plastic element called Resolon is stated to be the same used in military precision pots and provides extended low noise life It is offered in both single and dual channels hav ing either linear or audio outputs Housings and terminals
93. ted the remaning line will continue functioning without affecting the level or the quality of the signal Also if signal is applied to any one of the lines it should not be detected in the remaining lines With noise levels today being 70 or more dB below program level it is desirable that crosstalk between the channels be as low as the noise level Addi tional requirements are that all distri bution channels have constant source impedance If someone is still thinking in terms of electron tubes this is a tall order but if you are with it in transistors and operational amplifiers the outlined requirements are fairly simple to ful fill Most of the class AB amplifier circuits with large amounts of nega tive feedback have output impedances of less than 1 ohm This means that by using a build out resistor of 600 ohms we are assured of at least 50 dB of isolation between channels If source impedance is zero then isola tion will be infinite In experimenting with the printed circuit layouts I was able to produce not only zero source impedance but also negative impe dance so that by connecting the load the output of the amplifier went up Grounding of the different parts of the circuit produced this effect By allowing different parts of the circuit to be grounded at different locations Or moving the grounding point we can produce a practical zero source im dance But then a few other things may throw a monkey wrench into t
94. telephone answering systems Name_ Address City State ZB Telephone No MN1172 1 563 10 2 4 4 310 www americanradiohistorv com Lone SEE MA ier A A A M 0 26L Menuer qp LE db January 1973 32 ROBERT C EHLE NYONE OVER THIRTY can certainly remember the pre t v days and the family gathered around a big console a m radio in the living room listen ing to the old radio shows The a m console radio in those days was a truly impressive piece of equip ment it had a minimum of three bands and often as many as eight or nine The range covered was often from 150 kHz to 16 MHz or higher Fancy dials had planetary drive for different tuning speeds and some radios had motor driven tuning What happened to all of these old instruments Some were retired to attics while others were traded in on the early t v sets As a youngster I used to collect these radios usually to dismantle for parts but the most impressive specimens were reserved for use and experimentation In my youth I had at one time or other two Grunow All Wave sets one Silvertone with motor drive tuning one GE also with motor drive tuning and two Zenith sets with 6L6 output tubes high power for their time I also had an assortment of less impressive sets including several early record players and changers These usually became parts rather quickly One day a neighborhood friend we were about twelve years old suggested that we
95. tely 2 to 8 kHz A 3 kHz oscillator is built in There are no level or discriminator controls fil ters are switchable and there is built in meter overload protection Mfr Manko Instruments Pricer Mace Circle 50 on Reader Service Card D zm rng je is B 8 6 a em Zab g 3 0 o NOISE GATE Re esens H Lie p RISE 4 AK ES Model NS 120 is a variable noise gate suppressor designed for maxi mum fiexibility in applications ranging from multi track mixdown noise gat ing to noise suppression for film dub bing and real time background noise attenuation A fast acting all electronic device uses no 1 d r units to achieve an attack time of less than 25 sec Re lease time is adjustable from 0 03 to 5 seconds and an attenuation range control permits a normal 0 dB to 50 range A 28 V d c bipolar power supply is recommended for maximum output of 24 dBm into 600 ohms Sixteen channels can be mounted in one 3 2 by 19 inch rack Mfr Quad Eight Price 98 00 Circle 60 on Reader Service Card AUDIO VIDEO SYNCRONIZER ENAMI DISMAY ECO SYNCHRONIZER Designed to syncronize an audio tape recorder to a quad or slant track video tape recorder or to another audio tape recorder the BE 450 keeps two mag tapes in frame to frame lock regardless of normal tape stretch or slippage The unit compares identical SMPTE edit codes recorded on any two mag tapes Providing the tapes are wi
96. thin 30 seconds of sync the unit automatically adjusts control voltage to one of the recorders until tapes are in perfect sync It then keeps the tapes in sync Or manually adjusted offset in a frame to frame lock Mfr EECO Circle 53 on Reader Service Card PROKIT THE FLEXIBLE MIXER SYSTEM with RAVE REVIEWS LARRY ZIDE in No kit have ever built has had the quality of componentry that esouroenamecame urcazme exists in this unit This unit is fully professional in every way nothing about it is consumer Well worth the asking price of 299 00 kit ED DELL in he fo one of the finest pieces of MS 0 A iy f q WJ 8 audio equipment available to the ja NI U home user In use the SM 6A 4 is the equal of any piece of audio equipment it has ever been our pleasure to use Intermodulation distortion 60 8 6 000 Hz 4 1 on the microphone inputs was 0 008 0 6V out In use the SM GA is a solid smooth well built unit m a w dow ice Gd 4 CIOs P a 4 i I OS am 1 D s i I i ti bi as t or er t J D i y 7 wine wi m L ag aux a mike MIx R man _ A mauran U 4 X0387 MIXER 29957 499mneo 6 mic 6 line and 2 mag phono inputs low noise IC circuitry VU meters RUOWLY M DK eure BOUALIEER PAGE so individual high and low frequency equalization for each SM 6 input me 92
97. ture of stereo records He also is presently executive vice president of the AES and holds a Fel lowship in that organization www americanradiohistorv com Cetec Inc a recently formed sub sidiary of Computer Equipment Corp El Monte California is now produc ing the Electrodyne Gauss and Lange vin lines of professional audio consoles tape duplicating equipment and instru ment loudspeakers at its plant in North Hollywood The lines were ac quired by Cetec from MCA Technol ogy Inc under a purchase agreement conclued October 1 1972 Phillip L Gundy executive vice president of Computer Equipment Corp has been elected to serve also as president of Cetec Inc M Ned Padwa is vice president and general manager Keith O Johnson and Don McLaughlin founders of the original Gauss and Electrodyne Corporations have joined Cetec Inc as vice presidents of ad vanced development and product plan ning respectively Recording Engineers Institute an nounced its March classes beginning Monday March 19th A 10 week course in all facets of recording engi neering ranging from the operation of studio consoles to the use of auto mated mixdown computors is offered The classes are being held in Echo Sound Studios 2686 Hempstead Turn pike Levittown L I New York el Berliner and Kahn Labeiled a Bundle for Britain we see Dolby Labs USA manager Mor ley Kahn on the right accepting the 1972 Maker of th
98. uit can of course deliver pro portionally more power What we have tried to accomplish in this article is to illustrate the basic problems which limit high frequency performance in popular i c op amps To a large degree these problems can be circumvented by careful considera tion of the reasons that cause them and selection of Corrections to Walter Jung s previous Automating the Audio Control Function series Part 3 August September Errors exist on schematic of Figure 5 B on page 50 Pins 2 and 3 of A4 should be interchanged R26 and C3 should be connected Unmarked connection from the DPS to 15V is pin 9 R18 should be 470 ohms not 470 k In Figure 2 on page 47 C6 connects between pins 2 and 1 of op amp 301A In part 4 as it appeared in November the fol lowing errors or omissions occurred In Figure 2 the 10 k and 0 source resistances Curves are interchanged The curves were not reproduced accurately We can supply an accu rate curve to any one requesting it Table 2 at 2 input bias current should be 50 nanoamps not milliamps In the caption for this table HA 240S should be correctly HA 2405 And finally in Figure 6 the truth table is wrong Gains should be 0 6 12 18 not 0 6 12 18 We regret any difficulties these may have caused db January 1973 30 optimum components for the particular application EJ Can t believe it We ll prove it Neve can install a sophisticated
99. unctions Gain switch and position control 100 Millisecond scan rate Bi phase digital encoding with SMPTE time coding compatibility Exclusive Leveloc updating facility VCA resolution 1 dB O 45dB Dropout and splice immunity Buffer memory Expandable and fully compatible function encoding Tape machine speed variation tolerance 15 Compumix mixdown system ecc Cie sce Lie cc Cie ec CEH ecc ERW e DY ea oDe sa De sq errs p M a 8 aspe i l quad eiaGahi electronics 11929 Vose Street North Hollywood Callfornia 91605 213 764 1516 Circle 28 on Reader Service Card www amaearicanradiohistory com 16 Menuer qp S db January 1973 16 Today s TAPE DUPLICATOR built for tomorrow s needs The new Telex 300 system tape duplicator lets you build Open reel slave 7 5 15 IPS Cassette slave 7 5 15 IPS your own system with individual components to meet your iaei ida me al o a eee gt Ne c r ps annel exact duplicating needs All components are totally com satyna patible and with complete add on capabilities the Telex 300 is all you ll ever need in a tape duplicator FLEXIBLE Duplicates reel to reel cassette to cassette reel to cassette and cassette to reel Buy only those com ponents you need now add others as your needs change All modules fit into standard table top consoles Telex 300 duplicates any track con
100. watts continuous power per channel into an 8 ohm load 300 watts per channel into 4 ohms and 100 watts into 16 ohms It can also be switched to provide a mono 600 watt output into 8 ohms which can also directly drive a 70 7 volt distribution system Safety circuits are built in with adjustable clamping of sustained over loads There are switchable linear phase filters at 10 Hz and 15 kHz a thermal cutout indicator lamp individual input gain controls heavy duty power switch and individual load protection Mfr Dynaco Price 400 kit approximate Circle 59 on Reader Service Card MATRIX DECODER Full side to side and front to back logic is employed in the SQD 2000 matrix decoder designed for SQ mat rixed material Complete audio control is offered including movement of the quad field 180 degrees or front chan nel or rear channel reverse Four meters indicate the audio level being monitored Separate volume controls are provided for each channel as well as a master volume Inputs and out puts are high level unbalanced suit able for monitoring rooms or audition ing SQ quad encodings Mfr Sony Corporation Price 299 50 Circle 54 on Reader Service Card FLUTTER METER Announced as the first fully auto matic portable flutter meter the Model M 1 is also a sensitive audio voltmeter A percentage demodulator permits extremely accurate measurements of flutter from carriers at any frequency between approxima
101. with tube electronics packages Ali equip ment serviced by us as the original im porter Gotham Audio Corp 2 West 46th Street New York N Y 10036 212 265 4111 MUST SELL One Gates stereo States man five Channel mixer two Gates Stereo Cartridge players All in mint condition hardly used Original cost 5400 sell for 2200 Steve Golub 1420 Ocean Parkway Brooklyn N Y 11230 New York N Y USED EQUIPMENT IN EXCELLENT CONDITION For sale One Shure model 300 ribbon mic 60 one E V model 666 mic 30 seven E V model 655C mics at 35 each and nine E V model 502B transformers at 4 50 each Send check to Timekeeper P O Box 835 Great Neck N Y 11021 FAIRCHILD 663 limiters five available at 100 each Fairchild model 675 Dy namic De esser one available at 100 Accurate Sound Corporation P O Box 2159 Garland Texas 75041 Telephone 214 278 0553 AMERICA S LARGEST SELECTION of new and used broadcast and recording equipment Latest bulletins available The Maze Corporation P O Box 6636 Birmingham Ala 35210 WHATEVER YOUR EQUIPMENT NEEDS new or used check us first Trade your used equipment for new Write for our complete listings Broadcast Equip ment amp Supply Co Box 3141 Bristol Tenn 37620 USED EQUIPMENT SALE 1 Neumann Mono Cutting System complete with He lium Cooled ES 59 Cutterhead Spencer Microscope Neumann Cutting Amp in rack wired for stereo and Gast Suc

JANUARY 1973 www.americanradiohistory.com

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