McIntosh MC-752 User's Manual
Contents
1. 652 08 VARIOUS REGULATORY AGENCIES REQUIRE THAT WE BRING THE FOLLOWING INFORMATION YOUR ATTENTION PLEASE READ IT CAREFULLY WARNING TO PREVENT FIRE OR SHOCK HAZARD DO NOT EXPOSE THIS UNIT TO RAIN OR MOISTURE CAUTION TO PREVENT ELECTRIC SHOCK DO NOT USE THE POLARIZED PLUG ON THIS UNIT WITH AN EXTENSION CORD RECEPTACLE OR OTHER OUTLET UNLESS THE BLADES CAN BE FULLY INSERTED TO PREVENT BLADE EXPOSURE The serial number purchase date and McIntosh Laboratory Service Contract number are important to you for possible insurance claim or future service Record this information here Serial Number Purchase date Service Contract Number Upon application McIntosh Laboratory provides a Service Contract to the original purchaser Your McIntosh Authorized Service Agency can expedite repairs when you provide the Service Contract with the instrument for repair MC 752 POWER AMPLIFIER 039475 Your MC 752 Stereo Power Amplifier will give you many years of pleasant and satisfactory performance If you have any questions please contact CUSTOMER SERVICE Mcintosh Laboratory Inc 2 Chambers Street Binghamton New York 13903 Phone 607 723 3512 Take Advantage of 3 years of Contract Service Fill in the Application NOW 1 McINTOSH THREE YEAR SERVICE CONTRACT An application for A THREE YEAR SERVICE CONTRACT is included with this manual2. 40 RL 4 OHMS 30 RL 8 OHMS FREQUENCY IN Hz OUTPUT SIGNAL WAVEFORM SHOWING ACTION OF POWERGUARD TO ELIMINATE OUTPUT SIGNAL CLIPPING AMPLIFIER INPUT IS OVERDRIVEN BY 20 dB FOR BOTH OSCILLOGRAM TRACES Las TT LN LT UN TA p x TIME La UL L il L LU Li LU i 100K Welntosh McINTOSH LABORATORY INC 2 CHAMBERS ST BINGHAMTON N Y 13903 2699 607 723 3512 The continuous improvement of its products is the policy of McIntosh Laboratory Incorporated who reserve the right to improve design without notice Printed in U S A 039475
3. or signal source to the power amplifier inputs To minimize the possiblity of hum the shielded cables should be run parallel to each other or loosely twisted together Locate the cables away from speaker leads and AC power cords Connect the left output of the preamplifier to the Left input jack of the power amplifier Connect the right output of the preamplifier to the Right input jack of the power amplifier OUTPUT Selection of the proper gauge wire to connect the loudspeakers preserves the quality of sound repro duction for which the loudspeakers have been de signed If undersize wire is used resistance is added to the amplifier loudspeaker combination which adversely affects the performance Added resis tance causes reduction of damping characteristics modification of freguency response and reduction in power output Use ample size wire to connect the speakers to the amplifier In all cases the leads to and from the speaker should be twin conductor or twisted together When using 8 ohm speakers and for the normally short distances of under 30 feet between the amplifier and speaker No 18 wire or larger can be used For distances over 30 feet use larger diameter wire Select the correct size wire for the distance from the chart MAXIMUM WIRE LENGTHS AMPLIFIER TO SPEAKER Wire For 4 Ohm Load For 8 Ohm Load Gauge Feet Meters Feet Meters 18 15 4 6 30 91 16 25 7 6 50 15 2 14 40 12 2 80 24 4 12 60 18 3 120 36 6 10 100 30
4. 15 Alddns HA2AHOA4SNVHL SAHOLIMS NOLLI310Hd asna 191110 qgalvindad YAMOd NIVW H3MOd DV OV AlddNS HALINI LNIHH9 1 5 JAI LVDAN AAILVDAN LAdLNO AAILISOd AAILISOd ANY 1 YOLVNNALLY OSINOYWLOA 1S TOHLNOO 13A 1H A TT LN2HHNO WOvedsss AAILVDAN YAMOd SAILVDAN AOVLIOA AAILVDAN 1NdLNO JAILY93N 1 JAILISOd 1439494 2 HOLINOW AHLNIS HOLVNNILLV SINOYLOAT14S 10H LNOD 13437 1437 HJAIHO JAI LISOd wedged 490 9 Performance Charts HARMONIC DISTORTION IN PERCENT 0 14 0 13 0 12 0 11 0 1 09 08 07 06 05 04 03 02 01 INTERMODULATION DISTORTION IN PERCENT HARMONIC DISTORTION VS POWER OUTPUT RL 8 OHMS BOTH CHANNELS OPERATING UN CUI EME LL LTL 4 1 10 10 POWER OUTPUT WATTS RMS INTERMODULATION DISTORTION vs POWER OUTPUT 8 OHM OUTPUT INPUT FREQUENCIES 60 Hz AND 7 kHz INPUT RATIO 4 1 0 3 0 2 0 1 1 10 100 POWER OUTPUT IN EQUIVALENT AVERAGE WATTS 10 POWER OUTPUT IN WATTS RMS OUTPUT SIGNAL AMPLITUDE 0 02 THD POWER BANDWIDTH BOTH CHANNELS OPERATING 140 130 120 i 100 90 LL L 80 70 60 50
5. 5 200 61 0 Wire lengths above represent the wire resistance equal to 5 of the speaker impedance For multiple speaker operation run separate leads from the amplifier to each speaker CONNECTING LOUDSPEAKERS Connect the leads from the left loudspeakers to the left L and common C terminals Connect the leads from the right loudspeakers to the right R and common C terminals AC POWER Plug the amplifier AC power cord into a 120 volt 50 60 Hz switched outlet on the preamplifier FUSE A 4 amp fuse protects the MC 752 circuits The fuse does not protect additional equipment con nected to the rear panel AC power outlet Gp ey easy Sega 205 Installation and Operation INSTALLATION The compact design of the McIntosh MC 752 allows it to be easily placed a variety of ways The typical installation is to simply place it directly on a shelf or cabinet The bottom feet must be left in place since they raise the amplifier above the mounting shelf to allow the circulation of air through the bottom panel and up through the heat sinks The mounting space must be left sufficiently open at the back or top to allow what heat that may be generated to easily ventilate CONTROLS AND PANEL INFORMATION INPUT LEVEL The maximum input sensitivity of the MC 752 is 1 4 volts with the input level controls at maximum turned fully clockwise With 1 4 volts fed in the MC 752 will produce its rated output power All McIn
6. The terms of the contract are McIntosh will provide all parts materials and labor needed to return the measured perfor mance of the instrument to the original perfor mance limits The SERVICE CONTRACT does not cover any shipping costs to and from the authorized service agency or the factory Any Mcintosh authorized service agency will repair McIntosh instruments at normal service rates To receive service under the terms of the SERVICE CONTRACT the SERVICE CON TRACT CERTIFICATE must be presented when the instrument is taken to the service agency Always have service done by a Mcintosh authorized service agency If the instrument is modified or damaged as a result of unauthoriz ed repair the SERVICE CONTRACT will be cancelled Damage by improper use or mishandling is not covered by the SERVICE CONTRACT The SERVICE CONTRACT is issued to you as the original purchaser To protect you from misrepresentation this contract cannot be transferred to a second owner Copyright 1985 by Mcintosh Laboratory Inc 5 To receive the SERVICE CONTRACT your pur chase must be made from a Mcintosh franchis ed dealer Your completely filled in application for the SERVICE CONTRACT must be postmarked within 30 days of the date of purchase of the in strument 7 To receive the SERVICE CONTRACT all infor mation on the application must be filled in The SERVICE CONTRACT will be issued when the completely filled
7. de Commission Regulation con cerning power output claims for amplifiers used in home entertainment products POWER OUTPUT 100 watts minimum sine wave continuous average power output per channel both channels operating across 4 ohms from 20 to 20 000Hz 75 watts minimum sine wave continuous average power output per channel both channels operating across 8 ohms from 20 to 20 000Hz OUTPUT LOAD IMPEDANCE 4 ohms to 8 ohms POWER BANDWIDTH 20 to 20 000Hz TOTAL HARMONIC DISTORTION 0 02 maximum at any power level from 250 milliwatts to rated power per channel 20 to 20 000Hz both channels operating INTERMODULATION DISTORTION 0 02 maximum at any power level from 250 milliwatts to rated power per channel any com bination of frequencies from 20 to 20 000Hz with both channels operating FREQUENCY RESPONSE 0 0 25dB from 20 to 20 000Hz at rated power SIGNAL TO NOISE RATIO A WEIGHTED 110dB below rated output 91dB IHFA Ratings IHF DYNAMIC HEADROOM 1 4 dB at 8 ohm load 105 watt music peaks 2 6 dB at 4 ohm load 182 watt music peaks DAMPING FACTOR Greater than 40 INPUT SENSITIVITY 1 4 volts Level control provides for higher input voitages 2 5 volt position indicated INPUT IMPEDANCE 22k ohms General Information SEMICONDUCTOR COMPLEMENT 27 Silicon Diodes 43 Bipolar Transistors 2 Integrated Circuits POWER REQUIREMENTS 120 volts 50 60Hz 0 3 4 amps Mechanical Information SIZE 13 1 8 33 3 c
8. ed heat Under normal conditions the output transistors oper ate well below their safe temperature limits If ventila tion is restricted by improper mounting or if amplifier efficiency is destroyed by operating it into a short cir cuit or a very low impedance extra heat will be pro duced If this abnormal condition occurs thermal switches on either channel heat sinks will turn off the AC power to the amplifier This prevents the output transistors from producing life reducing heat Look for restricted ventilation a short across the amplifier output terminals or improperly matched outputs The thermal switches will automatically turn the power back on when the problem is corrected and the heat sink temperatures return to normal This additional protection assures you of reliability even under the most extreme operating conditions All power transistors have limits for the maximum amount of electrical current they can handle The MC 752 output transistors and power supply have been designed to allow very high current flow into properly matched load impedances If however a short circuit or very low value of load impedance is applied to the output of the MC 752 destructive cur rents could be reached if they were not controlled by the SENTRY MONITOR circuit This circuit senses the dynamic operating conditions of the amplifier output stages and controls the current flow confin ing it to safe limits The SENTRY MONITOR circuit does not
9. hese are the extra values that you receive when you invest in McIntosh equipment It is precisely for this reason that it takes longer to complete a Mcintosh engineering design task But from such engineering dedication comes the F 2 pe ym ee pye r a J a A gt 8 5 Vu o a Mcintosh reputation for highest sound quality with greatest long term reliability The MC 752 incorporates seven protection circuits to insure its total reliability These circuits are described in the Technical Description on page 8 Two circuits Power Guard for the left and right channels deserve special mentioning here POWER GUARD Power Guard a unique and patented feature of Mcintosh power amplifiers assures that each chan nel of the MC 752 will deliver full power free of clip ping distortion Clipping is caused when an amplifier is asked to produce more clean power out put than its design characteristics can deliver Con ventional amplifiers that are overdriven are capable of delivering large quantities of power when they are clipping but the output will also have up to 40 har monic distortion The sound will be grossly distorted and the extra energy content of the clipped signal will damage most loudspeakers particularly high frequency drivers The McIntosh Power Guard circuit protects your ears and speakers from this kind of damage INPUT Use shielded cables to connect the signal from the preamplifier
10. in application is received by McIntosh Laboratory Incorporated in Bingham ton New York Units in operation outside the United States and Canada not covered by the McIntosh Factory Service Contract irrespective of the place of purchase Nor are units acquired out side the U S A and Canada the purchasers of which should consult with their dealer to ascer tain what if any service contract or warranty may be available locally Introduction FEATURES The MC 752 is a direct coupled stereo power amplifier designed to operate with loudspeakers having a nominal impedance of 4 ohms to 8 ohms The amplifier is rugged and reliable The mechanical and electrical design of the MC 752 is the result of the many years of engineer ing and manufacturing experience of the designers at Mcintosh This know how combined with meticulous attention to design and production details makes the MC 752 one of the finest products ever produced by Mcintosh Laboratory Some manufacturers of power amplifiers adver tise that their products do not require or use protec tion circuits and that such circuits compromise per formance It is indeed possible for such circuits to cause substantial amounts of distortion and undesirable listening effects But this is true of almost any and every design The real genius of good design recognizes these problems and cir cumvents them while retaining the real merits of the protective circuits T
11. limit the power output available from the amplifier nor does it have any effect on normal signals passing through the amplifier All power amplifiers which do not use output transformers to bypass DC direct current can destroy loudspeakers should there be a failure within the amplifier Safety circuits are necessary to protect loudspeakers The MC 752 has a DC detec ting circuit connected to the output of each channel Should there be DC present this circuit reacts in milliseconds to open the speaker relay The speakers remain disconnected until the cause has been corrected Under normal operating conditions the DC protective circuit has no effect on the opera tion of the output circuit POWER GUARD POWER GUARD a unique feature of McIntosh amplifiers assures that each channel of the MC 752 will deliver full power free of clipping distortion Clip ping is caused when an amplifier is asked to produce more clean power output than its design characteris tics can deliver with low distortion Amplifiers that are overdriven are capable of delivering large quan tities of power when they are clipping but they have more than 40 harmonic distortion In this mode the sound is grossly distorted and the extra energy con tent of the clipped signal will damage most loud speakers particularly high frequency speakers The Mcintosh POWER GUARD circuit protects your ears and your speakers from this kind of damage The MC 752 has a built i
12. m wide by 9 5 8 24 4 cm deep by 5 9 16 14 1 cm high FINISH Chrome chassis with black ventilating cover WEIGHT 21 pounds 9 5 kg net 25 pounds 11 3 kg in a shipping carton Technical Description POWER AMPLIFIER The MC 752 requires 1 4 volts RMS to drive the amplifier to rated output The input impedance is 22 000 ohms The input stage of the amplifier uses two transistors connected as a differential amplifier The two input signals to the differential pair are the input signal and the negative feedback signal from the power amplifier output The differential amplifier permits the best use of negative feedback to enhance low noise and low distortion performance The outputs of the differential amplifier are com bined in a current mirror to form a single output This combined signal feeds a linear voltage amplifier which drives two medium power driver transistors The driver transistors feed the output stage The output stage is arranged as a fully complemen tary direct coupled push pull amplifier The power transistors used are selected for their high power dis sipation capability wide frequency response and large safe operating area All power transistors have limits for the maximum amount of heat they can tol erate The MC 752 uses a highly efficient amplifying circuit which produces relatively little heat for the output power produced The amplifier has 4 oversized heat sinks to dissipate transistor generat
13. n waveform comparator that compares the waveshape of the amplifier out put signal to the input signal If the distortion con tent between the two signals exceeds 0 5 the POWER GUARD circuit operates automatically to prevent the normal increase to 40 or more distor tion Operation is indicated when the amber left or right POWER GUARD lamps turn on At the same time an electronically controlled attenuator reduces the gain of the amplifier just enough to prevent clip ping As long as the amplifier operates without overload the indicators remain off POWER GUARD assures that you get the maximum undistorted power output available from the amplifier and it makes sure that you hear the full rated power of the amplifier at low distortion TURN ON DELAY The MC 752 has transient free turn on and turn off characteristics A heavy duty relay time controlled by a transistor switch connects the output to the speakers The control to the transistor switch is derived from a long time constant capacitor charg ing network that turns the relay on approximately one second after the power switch is turned on The Same circuit has a short turnoff time constant and the relay drops out before the amplifier s main power supply has a chance to discharge LAdLNO AV1ad NO NYNL HOSNAS 90 H3AIHO HVYND YAMOd dWV1 wovedass YSISIId WV YAMOd 03H31S 2SZ DIN HSOLNIPA ASL ABL A8P 8 YAMOd 53199
14. tosh preamplifiers have been designed to deliver 2 5 volts output with their rated inputs For best system signal to noise ratio when using McIntosh source equipment set the MC 752 input LEVEL controls to the 2 5 volt position For source equipment other than McIntosh set the level controls nearest to the stated output rating of the source equipment POWER GUARD INDICATOR LAMPS POWER GUARD assures that the power output section of the MC 752 cannot be overdriven and amplifier clipping is eliminated The amber POWER GUARD lamps turn on when the amplifier reaches its maximum distortion free output well above the rated power If the POWER GUARD lamps come on continuously lower the volume control on the preamplifier slightly to retain the full dynamic range of the program material AC POWER The red POWER lamp indicates whenever AC power is supplied to the amplifier The MC 752 is rated for 120 volts 50 60 hertz There is no power switch on the MC 752 as it is designed to be sup plied with power from one of the switched AC out lets on the rear panel of a McIntosh preamplifier The rear panel AC outlet is provided to supply power to an accessory unit that may be used in the system It turns on and off with the amplifier UiaMVAdS E 45 A9HN0S INVHDOHd 9001129000 210000094918 Performance Limlis and Ratings PERFORMANCE LIMITS McIntosh audio power ratings are in accordance with the Federal Tra
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