Arp 2600 3620 Keyboard Service Manual
Contents
1. FOIL SIDE VIEW SOINOUL9313 ONVOGAJN 0296 uo 3620 PARTSLIST SECTION 9 REFERENCE ARP PART NUMBER ARP MFG NUMBER DESCRIPTION 1200301 2N4148 DIODE SILICON SIGNAL 1303001 2N3906 TRANSISTOR SILICON PNP 5600201 A2803 003 1 TRANSISTOR FET SEL 2N5459 ORN 5600202 2803 0032 TRANSISTOR FET SEL 2N5459 YEL 11 12 1302501 2N5461 TRANSISTOR FET P CHANNEL 92 5 1303901 IMF3958 TRANSISTOR DUAL J FET 21 2 3 4 6 5601801 A2801 008 AMP OPL TESTED LM1458 25 1400601 CD4011AE GATE QUAD 2IN NAND CMOS R79 83 26 5700702 82801 006 2 POT SLIDE AUD 1 3W 30 100K R21 5700701 82801 006 1 POT SLIDE AUD 1 4W 30 1M 5700703 2801 006 3 POT SLIDE LIN 1 3W 30 100K c12 13 1100609 0 001 6 20 0 CAP TANT 35V 20 1UF 2 4 1100901 WCRIP47 CAP POLYCARB 100V 10 0 470 1100205 2PsP10 CAP POLYESTER 200V 10 s 1900801 02 481 00018 SWITCH ROCKER DP3T 52 1902401 01 481 0006A SWITCH SLIDE s3 1900601 01 481 0004 SWITCH SLIDE DP3T FCN 005 RP FIELD CHANGE NOTICE MODEL 3620 DATES 1121673 PUETE 20 WITH EST TIME TO COMPLETE EFFECTIVITY ANY 3620 WITH ES FCN 005 REASON FOR CHANGE ARP INSTRUMENTS INC 45 To reduce control voltage drift by the use of 2N4392 LS 4392 FET instead of 2N5459 MATERIAL REQUIRED 2 2N4392 1542. CONTROL CIRCUIT FUNCTION MUSICAL USE PORTAMENTO ON OFF SWITCH Turns on portamento circuit Upper Voice memory is disabled when in the on position Allows notes to slide from one pitch to another PORTAMENTO Provides the same function as porta Allows momentary control of porta MEMORY PUSH mento on off switch mento effect BUTTON PORTAMENTO SLIDER Increases Portamento time from Manually controls speed of portamento 1msec to 2sec effect TRIGGER MODE SWITCH Multiple mode provides a trigger to the envelope generators for each key depression single mode provides a trigger for the first key depression only Single mode provides attack on first key down but not on second REPEAT SWITCH In the auto Repeat mode the LFO square wave is supplied to the en velope generator instead of the keyboard gate in the Keyboard Repeat mode the square output wave of the LFO is supplied to the envelope generator only while key is held Allows the envelope generators to be triggered by the LFO instead of by key depressions LFO SPEED SLIDER Varies the LFO speed from 25Hz to 25Hz Controls Vibrato rate and repeat speed VIBRATO DELAY SLIDER Delays the vibrato from 0 to2 5sec after key depression Allows vibrato to fade in after key is depressed VIBRATO DEPTH SLIDER Attenuates the vibrato signal sup plied to upper and lower control voltage
3. Garp MODEL 3620 KEYBOARD SERVICE MANUAL THIS SERVICE MANUAL SHOULD BE USED WITH THE ARP 2600 SERVICE MANUAL TABLE OF CONTENTS 1 3620 DESCRIPTION 1 1 Introduction 2 1 2 Specifications 2 1 3 Function Descriptions 2 2 CIRCUIT DESCRIPTIONS 2 1 Keyboard Current Source 2 2 Second Voice Memory 2 3 Upper Voice Summation 2 4 Control Voltage Memory 2 5 Master Summation 2 6 Gate Generator 2 7 Memory Control 2 8 Low Frequency Oscillator 2 9 Vibrato Delay amp Wave Shaping TRIMS amp ADJUSTMENTS BOARD TEST POINTS 3620 THREE BUS CONVERSION BOARD 3620 CONTACT MAINTENANCE ASSEMBLY DISSASSEMBLY 3620 DRAWINGS 8 1 Board Layout 10 8 2 Board Schematic n 9 PARTS LIST 13 10 REVISIONS ARP INSTRUMENTS INC 45 Hartwell Avenue Lexington MA 02173 617 861 6000 c 1977 ARP INSTRUMENTS INC DOCUMENT NO 9000400 SECTION 1 3620 DESCRIPTION 1 1 INTRODUCTION The 3620 keyboard replaces the 3604P keyboard for the 2600P synthesizer Features included are two separate memorized control voltages interval latch O repeat modes LFO delayed vibrato transpose and e pitch bend controls This manual should be used in conjunction with the 2600 service manual for complete understanding of the functions it contains 1 2 SPECIFICATIONS UPPER VOICE CV OUTPUT 3 volts to 10 volts 1V OCT LO
4. board The top end of the resistor string is connected to J1 5 and the low end to J1 6 The current source supplies a four volt drop across the entire resistor chain This provides a one volt per octave control voltage to the Control Voltage Memory circuitry via the KYBD CV bus Pin 1 of Z1A is 4 0 volts when no keys or one key is depressed When two keys are depressed the con tacts and bus rod short out a section of resistors in the divider chain which reduces the gain of Z1A thereby lowering the voltage on Z1A pin 1 This voltage drop represents the voltage difference be tween two held keys When the difference voltage is subsequently added to the control voltage from the CV bus a high note priority control voltage is pro duced 2 2 2ND VOICE MEMORY The output of Z1A is connected through Q1 to a storage capacitor C2 When a memory trigger pulse is supplied to CR3 from the memory control Q1 turns on which charges C2 to the voltage level on 21 pin 1 Q2 and 218 are an FET op amp with high input impedance to buffer the voltage on C2 The stored difference voltage on pin 7 of 218 is supplied to the upper voice inverter summer 2 3 UPPER VOICE SUMMATION The upper voice summation sums and inverts the control voltage from the Master Summation Circuit and the difference voltage from the second voice memory The combination of these two voltages yields a high note priority control voltage R8 the offset trim
5. on 3620 control panel with a digital voltmeter 4 Adjust R8 for 4 00 volts mv INTERVAL 1 Set controls to initial setting positions 2 low C on the keyboard 3 Moniter the Upper Voice CV output on 3620 control panel with a digital voltmeter 4 Adjust trimmer R11 for 0 00 volts 5mv R13 UPPER VOICE 1 Set controls to initial setting positions 2 Pin high on the keyboard 3 Moniter the Upper Voice CV output on 3620 control panel with a digital voltmeter 4 Adjust trimmer R13 for 4 00 volts 5mv BOARD TEST POINTS SECTION 4 TEST Function ser up SPECIFICATIONS L KYBD CURRENT 1 No keys depressed 4 0 volts SOURCE 2 High C and low C depressed 0 0 volts 2ND VOICE 1 Portamento Slide Switch OFF MEMORY 2 Depress and release any key 44 0 volts 3 Depress high andlow C then 0 0 volts release both keys UPPER VOICE 1 Portamento Slide Switch OF F SUMMATION 2 Transpose Switch MIDPOSITION 3 Pitch Bend Control CENTERED 4 Depress and release low C 0 0 volts 5 Depress and release high 4 0 volts LOWER VOICE SAME AS TP 3 INVERTER CV MEMORY 1 Portamento Slide Switch OFF 2 Depress and release low C Ovolts 1 volt 3 Depress and release high C Exactly 4 volts higher than low C voltage MASTER 1 Portamento Slide Switch OFF S
6. on 2 Sliders Fully Down 3 Trigger Mode Multiple 4 Repeat Switch Midposi 5 Transpose Switch Midposition 6 Pitch Bend Centered off CAUTION The trims and adjustments for the 3620 must be performed in the sequence presented for proper results REF NO TRIMMER TRIM PROCEDURE R38 cvi 1 Set controls to initial setting positions OFFSET 2 Moniter the CV output on the 2600 panel near multiple jacks with a digital voltmeter 3 Pin low on the keyboard 4 Adjust trimmer R38 for 0 00 volts Smv R39 cvi 1 Set controls to initial setting positions 2 Pin high C on the keyboard 3 Moniter the CV output on the 2600 panel with a digital voltmeter 4 Adjust trimmer R39 for 4 00 volts 5mv R30 PITCH BEND 1 Set controls to initial setting positions CALIBRATE 2 Put the Pitch Bend control fully clockwise Pin low C 3 Moniter the CV output on the 2600 panel with a digital voltmeter 4 Adjust trimmer R30 for 1 00 volts R34 TRANSPOSE 1 Set controls to initial setting positions CALIBRATE 2 Put the Transpose switch in the up 2 octaves position Pin low 3 Moniter the CV output on the 2600 panel with a digital voltmeter 4 Adjust trimmer R34 for 2 00 volts 5mv RB UPPER VOICE 1 Set controls to initial setting positions CV 2 OFFSET 2 Pin low and high on the keyboard 3 Moniter the Upper Voice CV output
7. 15 R63 R65 to pin 1 of 25 Pin 2 of 25 is simul taneously supplied with a 15v gate voltage so that 25 3 wil drop from high 415v to low 0 when C9 is pulsed The resulting pulse 25 pin 3 turns 010 which turns on the Control Voltage Memory 1st Voice Memory Control via and the 2nd Voice Memory 2nd Voice Memory Control through CR16 and When the Portamento Switch S4 is turned on pin 6 of Z5B is held high 415v by R66 Pin 5 of 258 is supplied with the keyboard gate signal so that pin 4 of ZB will be low which holds 010 on continuously during a key depression This is to enable Q4 in the Control Voltage Memory circuit to be on so that the memory capacitor has time to assume the correct voltage with the portamento control R21 in the cir cuit The voltage from R66 is also supplied through CR17 to reverse bias CR16 when the portamento is to continuously gate the Second Voice Memory circuit Board pins 16 and 17 are connected to the portamento foot switch jack and momentary push button These switches are in series and are normally conducting 2 8 LOW FREQUENCY OSCILLATOR The LFO produces a triangle and a square wave out put in a frequency range from about 1 Hz to 25 Hz 268 and C10 are an integrator which charges from current passing through R77 26 is hysteretic switch whose output switches from 15 volts to 15 volts when the output of Z6B reaches 5 volts This then reverses
8. 302 PARTS DISPOSITION Order 005 DETAILS OF CHANGE Change O1 and Q4 in the memory circuits from 2N5459 to 2N4322 or 154382 DOCUMENTS AFFECTED 3620 Service anual document number 9000400 pages 10 and 11 Ep xingten 02173 617 851 6000
9. UMMATION 2 Transpose Switch MIDPOSITION 3 Pitch Bend Control CENTERED 2 Depress and release low 0 0 volts 5 Depress and release high 40 volts KEYBOARD 1 All keys up 0 volts GATE 1 2 Any key down 15 volts TPS KEYBOARD GATE 1 All keysup 15 volts GATE2 2 Any key down 415 volts MEMORY TRIGGER 1 Depress any key nem me TRIGGER 9 Amsec typical TRIGGER 1 Depress any key mw OUTPUT 0 5 msec typical m GATE 1 All keys up 0 volts OUTPUT 2 Depress and hold any key 10 volts 1st VOICE 1 Portamento Slide Switch OFF 5v MEMORY Depress a key CONTROL Z Portamento Switch ON EZ key Depress a key T Key Up Key Down Key Up TPA3 2nd VOICE 1 Portamento Slide Switch ON m MEMORY ak CONTROL ov 2 Portamento Slide Switch OFF ETT Depress a key TEST POINTS CONTINUED TEST Function ser UP SPECIFICATIONS LFO 1 LFO Speed Slider Up fully e TRIANGLE OUTPUT 4 5V SOmsec typical TPAS LFO 1 LFO Speed Slider Up fully 10 SQUAREWAVE OUTPUT ov TPG DELAYED 1 LFO Speed Slider Up fully pem EE VIBRATO 2 Vibrato Delay Slider Down Fully OUTPUT SECTION 5 3620 THREE BUS CONVERSION BOARD The 3620 electronics is designed to be used with a two bus keyboard When the 3620 panel electronics is used with a three bus keyboard an interface board is inser
10. WER VOICE CV OUTPUT 3 volts to 7 volts Gane ese 1V OCT pr LFO TRIANGLE OUTPUT 25 volts 10 volts peak to peak PITCH BEND CONTROL 1 octave calibrated LFO SQUARE WAVE OUTPUT 10 volts 10 volts TRANSPOSE SWITCH 2 octaves calibrated peak to peak PORTAMENTO SPEED SLIDER 1msec to approx LFO DELAYED SINE WAVE OUTPUT 3 volts 2sec 6 volts peak to peak PORTAMENTO FOOT SWITCH Accepts only ARP EXTERNAL VIBRATO INPUT Accepts 10 volts foot switch maximum INTERVAL FOOT SWITCH Accepts only ARP foot VIBRATO DEPTH SLIDER 10 volts yields approx switch 1 octave shift GATE OUTPUT ON 2600 PANEL 0 volts keys up VIBRATO DELAY SLIDER Delays sine wave from 10 volts key down 0 sec to approx 2 5 seconds TRIGGER OUTPUT ON 2600 PANEL 10 volts LFO SPEED SLIDER 25Hz to approx 25Hz key depression Smsec duration 1 3 FUNCTION DESCRIPTIONS CONTROL CIRCUIT FUNCTION PITCH BEND CONTROL When turned clockwise or counter clockwise from center offset voltage is summed with the upper and lower voice control voltages The Pitch Bend control is calibrated to a maximum 1 octave MUSICAL USE Manually Bends the pitch of the oscillators sharp or flat Also can be used as a 1 octave transpose TRANSPOSE SWITCH Up and down two octave positions sum 32 V offset voltage with upper and lower voice control voltages Changes the playing range of keyboard
11. e to Q9 Q9 is turned on when the output of 25C is low 0 which supplies 15 to the gate volt age divider R61 and 62 When the repeat switch S3 is in the KYBD repeat mode CR13 clips the positive portion of the LFO square wave Then the output of 25 will only Change state when the gate voltage is supplied to 25 pin 8 via R51 and R53 when a key is depressed During the negative portion of the LFO square wave 15 volts through CR13 defeats the Keyboard gate 25 pin 8 to supply a square wave on pin 10 during key depression only TRIGGER When a key is depressed the gate bus voltage drops from 15 volts to 10 volts additional key depressions will drop the voltage still further These voltage transitions are coupled through capaci tor C5 R47 to Q7 which supplies 15 to the memory control circuit and the trigger generator circuit CR11 CR6 250 C6 is charged by Q7 on each key depres sion 250 is an inverter shaper Since 250 pin 13 is held high 15 and pin 12 is normally low pin 11 will be normally high Each key depression results in 15 and 0 VPP trigger 250 which is supplied to 25 and the LFO 25 pin 10 will momentarily Switch from low to high during the pulse from Z5D which is then coupled to Q8 through C8 Q8 shapes the pulse and R57 and R58 voltage divide the trigger to 10 VPP 2 7 MEMORY CONTROL When key is depressed a trigger pulse is supplied from the Gate Trigger generator circuit through CR
12. hould be cleaned Use a OQ tip and denatured alcohol or trichloretheline Be sure not to expose the keys and stand off mountings to any sol vent unsafe for plastic 6 3 CONTACT ADJUSTMENT The design of the 3620 requires that the control volt age contact meet the bus slightly before the gate trigger bus This is to insure that the memory circuits are provided with the voltage which is to be memo rized by the time the memory command signal from the gate trigger bus occurs The following two charts outline typical problems that may occur when the contacts are not adjusted properly Do not make any contact adjustments until they have been cleaned many problems which seem to be related to contact timing are actually caused by dirt for contact adjustment procedu THREE BUS KEYBOARDS PROBLEM CAUSE TWO BUS KEYBOARDS PROBLEM CAUSE CV contact meeting bus too late or Gate too soon Previous pitch heard before correct pitch on key depression Envelope is triggered twice on one key depression Trigger contact meeting bus too late Previous pitch or CV contact meeting incorrect pitch bus too late or Gate memorized on key 100 soon Clean contacts depression before adjusting ASSEMBLY DISASSEMBLY SECTION 7 DO NOT REMOVE THESE SCREWS OM BOARD HINGES DOWN 3620 LAYOUT gy EES FOIL SIDE VIEW
13. lies offset voltages to Z4A to be summed with the control voltage R34 calibrates the voltage to exactly 2 octaves 24 is unity gain inverter which sums the transpose pitch bend and keyboard control voltages R38 adds an offset voltage so that 24 is zero volts when Low C is depressed The control voltage on the output of Z4A is inverted Low C will be O volts high C will be 4 volts The upper and lower voice summation circuits will re invert these voltages to 0 and 4 volts 2 6 GATE GENERATOR Each gate contact on the keyboard is connected to a 2 2K ohmresistor to ground When a key is depressed the Gate Generator produces three different gate sig nals KEY UP KEY DOWN GATE BUS 15 10V KYBD GATE 1 ov 15V KYBD GATE 2 15v 15V The Gate Bus signal is supplied to the Gate Trigger generator Keyboard Gate 1 enables the Memory Control circuit and is supplied to the Auto KYBD repeat circuitry GATE When the repeat switch is in the off mid position Keyboard Gate 2 is supplied to the gate out put of the 3620 through CR14 and R61 R61 and R62 set the gate to 10 when a key is depressed REPEAT When the repeat switch S3 is in the Auto position the gate signal through CR14 is interrupted and a low frequency 30VPP square wave from the LFO is supplied to Z5C pin 8 via R54 25 pin 9 is high 15 except when a key has just been depressed 25 pin 10 then supplies a 0 and 415 inverted square wav
14. mer supplies voltage to the summed input to set the output of Z2A to zero volts when low C depressed The output of Z2A is connected to the Upper Voice control voltage output jacks on the front panel 24 CONTROL VOLTAGE MEMORY Control voltages supplied from the keyboard bus are buffered by a unity gain amplifier 23 The voltage is then supplied via the portamento slider R21 and Q4 to memory capacitor C4 Q4 is turned on during the pulse signal or gate signal when the portamento switch is on which is supplied to CR6 from the memory control circuit Q5 and Z3B are an FET follower with high input impedance to buffer the voltage on C4 urpeR umen eren Voice d voice b gt voice URRENT ev our SHORE tower were Lower MST Voice Lower Voice INVERT CONTROL VOLTAGE GENERATION Q3 is on when the portamento switch is off which shorts out the portamento slider Q3 is turned on by the 15 volts supplied from S4A memory control R2 then varies the time C4 takes to charge from one voltage level to another causing a sliding effect 2 5 MASTER SUMMATION Pitch Bend The Pitch Bend control supplies an off set voltage to Z4A to be summed with the control voltage from the CV memory and create dead zone when the control is centered and R30 calibrates the offset to exactly 1 volt Transpose The Transpose switch supp
15. s Varies the degree of frequency shift of vibrato EXT VIBRATO IN JACK Sums external signals to upper and lower voice control voltages through the vibrato depth slider Allows other low frequency wave forms to frequency modulate the oscillators through the upper and lower control voltages LFO TRIANGLE JACK Supplies the LFO triangle waveform for use outside the keyboard Provides additional control of other functions in the 2600 LFO SQUARE WAVE JACK Supplies the LFO square wave for use outside the keyboard Provides additional control of other functions in the 2600 PORTAMENTO JACK Provides same function with foot Switch as the portamento momen tary push button Allows momentary control of porta mento effect INTERVAL LATCH JACK 1 Latches holds second voice con trol voltage when foot switch is depressed Allows single notes to play preset intervals when foot switch is held down UPPER VOICE JACK Control voltage outputs for use outside the keyboard Allows the upper voice control voltage to be connected to any VCO or the VCF Patch to CV jack on any VCO k as SECTION 2 CIRCUIT DESCRIPTIONS 2 1 KYBD CURRENT SOURCE The Keyboard Current Source supplies a constant current through forty eight 100 ohm resistors con nected in series This resistor voltage divider chain supplies specific voltages for ach key on the key
16. ted on the molex pins of the 3620 electronics to make the keyboard compatible with the 3620 When the 3620 is used with a three bus keyboard the gate voltage from the bus is 0 volts with no keys de pressed and 15 volts when any keys are depressed The trigger function is totally separate from the gate 02 converts the gate from three bus keyboards to 15 volts with no keys depressed and 410 volts with any keys depressed Q3 and 04 add the trigger pulse to the gate voltage which is then supplied to the 3620 electronics 3620 CONTACT MAINTENANCE SECTION 6 6 1 TYPES OF CONTACTS Two types of keyboards have been employed in the 3620 keyboard The new two buskeyboard contains a gate and control voltage bus the older three bus keyboard has a gate trigger and control voltage bus The trigger function for the newer keyboard is genera ted in the 3620 circuitry It is important for both types of keyboards that the contacts be clean and properly adjusted Since the upper and lower control voltages are memorized by a pulse signal instead of a gate the contacts must be clean in order to provide correct voltages to the mem ory circuits Should the control voltage bus become dirty or corroded improper pitches or sour notes may occur from time to time due to the memorization of incorrect voltages 6 2 CLEANING Before any contact adjustments are undertaken the bus and contacts s
17. the direction of current through R77 and the rate control R79 and thus the direction of integration at the output of Z6B When the output of 268 reaches 5 volts the output of 26 switches back to 15 volts and the cycle repeats An LFO reset pulse is supplied from the ADSR circuit every time a key is depressed 011 is turned momentarily by the LFO reset pulse and discharges the integrating capacitor C10 thus resetting the LFO output to zero clips the negative portion of the square wave and R81 and R82 voltage divide the square wave to 10 VPP 2 9 VIBRATO DELAY amp WAVE SHAPING CR20 and CR21 clip the peaks of the triangle wave from the LFO 268 pin 7 to produce a sine wave When no keys are depressed 15 volts from Keyboard Gate 2 is supplied to CR19 which turns Q12 on 013 turned off and capacitor C11 is charged by the voltage from R83 vibrato delay slider When a key is depressed 15 volts is supplied to the gate 012 CR19 which turns it off Capacitor C11 can now be charged by the LFO sine wave to turn on Q13 gradually The more negative the voltage supplied by R83 through Q12 the longer C11 takes to charge thereby controlling the delay time Z4B buffers the delayed sine wave which is then supplied to the Master Summation Circuit via the Ext Vibrato input jack on the front panel SECTION 3 TRIMS amp ADJUSTMENTS ANITIAL SETTINGS 1 Portamento Slide Switch
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