Moog Micromoog 2090 Operating manual

TECHNICAL SERVICE MANUAL
for
MICROMOOG
and
MULTIMOOG
synthesizers
MICROMOOG
MODEL 2090
MULTIMOOG
MODEL 326A
James L. Scott • BSEE
(Author)
MOOG MUSIC INC.
2500 Walden Avenue
Buffalo. N*w York 14225
Copyright October. 1979

CONTENTS
SECTION
1
2
3
PAGE NO.
Title Page / Frontispiece .
Contents .
List of Illustrations .
List of Tables.
INTRODUCTION.
1.1 ORGANIZATION OF THE MANUAL
1.2 GENERAL SYSTEM DESCRlP“ION .
1.3 MODEL MODIFICATIONS.
CIRCUIT DESCRIPTION.
2.1 POWER SUPPLY.
2.2 KEYBOARD CIRCUIT.
2.2.1 DC Operation (Cortrol V/nlugo Generation)
22.2 AC Operation (Trigger Generation) .
2.3 CONTROL VOLTAGE SUMMEHS AM) DUAL
EXPONENTIAL CURRENT SOURCE . .
2.3.1 Oscillator Control Summing.
2.3.2 Filter Control Summing.
2.3.3 Dual Exponential Current Source .
2.4 OSCILLATOR. WAVESHAPER AND DOUBLER.
2 4.1 Oscillator.
2 4.2 Waveshaper.
2.4.3 Doubler.
2.5 VOLTAGE CONTROLLED IQWPASS FILTER .
2.6 VOLTAGE CONTROLLED AMPLIFIER.
2.7 DUAL CONTOUR GENEHATOP.
78 MODULATION.
2.9 NOISE SOURCE SAMPLE AND HOLD.
2.9.1 Noise Source.
2.9.2 Sample and Hold.
2.10 MISCELLANEOUSOFF BOARD COMPONENTS
Top Boord 2 .
Tandem Board 3 .
2-1
2-1
2 2
2-2
2-3
2-5
2-5
2-7
2-7
2-8
28
2-9
29
2-11
2-13
2-15
2 15
2-17
2-17
2-17
2-17
66
66
DISASSEMBLY PROCEDURES ...
3.1 OPENING THE SYNTHESIZER .. .
3 2 KEYBOARD REMOVAL.
3.3 MAIN PC BOARD REMOVAL ....
3.4 LEFT HAND CONTROLLER (LHC
3-1
3-1
35
35
3-10
TUNING AND ADJUSTMENT PROCEDURES.
4.1 EXTERNAL AND IN TfcHNAL ADJUSTMENTS.
4.2 EXTERNALLY ACCESSIBLE ADJUSTMENTS.
4.2.1 Oscillator Tuning.
4.2 1.1 Oscillator Range.
4.2 1.2 Oscillator Scale.
4.2.1.3 Oscillator High Frequency Compensation
4.2.1.4 OsciMotor Octavo Stop.
4-1
4-1
4-1
4 1
4 2
4-2
4 2
4 2
iv

CONTENTS (Continuod)
SECTION
4
5
4.3 FILTER TUMING.
4.3.1 Emphasis.
4.3.2 Filler Scalo.
4.3.3 Filter High Frequency Compensation.
4.3.4 Filter Octave Step.
4.4 OTHER ADJUSTMENTS..
4.4.1 VCA Balance.
4.4.2 Trill Trim.
4.4.3 Ribbon Centering.
4.5 INTERNALLY ACCESSIBLE ADJUSTMENTS.
4.6.1 - 16V ADJ.
4.5.2 Current Source Chip Temperature.
4 53 Filter Balance .
4 5 4 Filter Rang© ..
4.6 MULTIMOOG OSCILLATOR TUNING PROCEDURE .
4.6.1 Oscillator ' A" Temperature Adjustment . .
4.6.2 Oscillator "A" Tuning.
4.6.3 Interval Tuning Adjustment. .
TROUBLESHOOTING GUIDE.
5.1 SOUND CHAIN.
5.2 PITCH DRIFT AND TUNING.
b.2.1 Oscillator Drift.
6.2.2 O scillator and Filter.
5.3 KEYBOARD.
5.3.1 C leaning Key Contacts.
REPLACEMENT PARTS LIST.
MOTE: This lection also contains Multimoog circuit description and schematic diagrams
PAGE NO.
6 1
r

LIST OF ILLUSTRATIONS
FIGURE
1-1
1-2
1-3
1- 4
2 - 1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2- 9
2-10
3- 1
3-2
3 3
34
3-5
36
3-7
3-8
3 9
3-10
3-11
3-12
3-13
3 14
3- 15
4- 1
4-2
4-3
44
6 1
6-1
6-2
6 3
Rcor Panel, Early Version.
Rear Panel. Latest Version.
Control Panel, Early Version.
Control Panel, Latest Version.
Simplified Regulator Schematic . .. .
Keyboard Control Voltage Generation.
AC Equivalent of Keyboard String.
Equivalent AC Amp O/P Circuit.
Simplified Oscillator Circuit.
Waveshaper Output Shape Versus Waveshape Control Voltage.
VCF Frequency Response Curves tor Zero and Full Emphasis.
Equivalent Filter Ladder C rcuit.. • • • • ..
Envelope Shape (Either Section) at Timing Capacitor C705 or „706 .
Loudness Limiting.
Removing Case from Base.
Unplugging Audio Output Connector.
Unlocking Cable Clomp..
Base Assembly.
Installation of Grommet Strip.
Removing Ivor os.
Levelling Key.
Keyboard Mounting.
Servicing Switch Contacts.
Keyspring Replacement.
Knob Removal.
PC Board Removal.
PC Board In Service Position.
Left Hand Controller Removal.
Left Hand Controller Assembly, Part No. 93-603 .
Position for Making Externally Accessible Adjustments.
Oscillator Tuning Sound Chart.
Filter Tuning Sound Chart.
VCA Balance & Trill Trim Sound Chart.
Sound Chain Check .
Micromoog Block Diagram.
Micromoog Interconnect Harness Assembly.
Micromoog Schematic Diagram.
PAGE NO.
1-2
1-2
12
1-2
2-1
2-3
2 4
2-4
2-8
2-10
2-11
2-12
2-14
2- 15
3- 1
3-2
32
3-3
3-3
34
3-4
3 6
36
3-6
3-7
3-7
3-8
3-8
3- 9
4- 1
4- 2
4 3
4 4
5- 1
6- 3
6-5
6-7
LIST OF TABLES
TABLE
5-1 Sound Chain Troubleshooting Guide. .....
5 2 Oscillator and Filter Troubleshooting Guide
5-3 Keyboard Troubleshooting Guide.
5-4 Pots and Switches Troubleshooting Guide..
5-5 Control Circuits Troubleshoot ng Guide . ..
5-6 Power Supply Troubleshooting Guide ....
5-7 Noise, Etc. Troubleshooting Gu dc .
PAGE NO.
5-1
5-4
5-6
5-7
58
5-9
5-10
vi

SECTION 1
INTRODUCTION
This manual provides servicing and parts infor¬
mation for tho Micromoog/Multimoog Synthesizers.
11 ORGANIZATION OF THE MANUAL
The manual is divided into 6 sections. Section 1
provides general system description and model
modifications; Section 2 describes the circuit. Section
3 gives step-by-step procedures for disassembly of
the keyboard, main PC hoard and the left hand
controller. Section 4 describes the tuning and the
external and internal adjustment procedures. Section
5 contains the troubleshooting guide. To facilitate
ordering replacement parts, see .Section 6.
12 GENERAL SYSTEM DESCRIPTION
tSee Block Diagram — Figure 6-1)
The Synthesizers consist of several circuit blocks.
The POWER SUPPLY converts AC line voltage into
precisely regulated ±15 volts DC to operate all other
Micromoog circuits. A single VOLTAGE CON¬
TROLLED TONE OSCILLATOR (VCO) generates
the audio frequency waveforms that serve as the
source of pitched soundn. The wuveshaped output
of this oscillator passes through the VOLTAGE
CONTROLLED LOWPASS FILTER (VCF) which
strongly modifies the timbre ot the oscillator tone.
Tho NOISE SOURCE produces a pitchloa; hitting
sound that also may be fed into the filter. The outpu:
of the VCF pases through the VOLTAGE CON¬
TROLLED AMPLIFIER (VCA) to the Instrument
audio output. The* gain of the VCA is dynamically
shaped during a note by one section of the DUAL
CONTOUR GENERATOR. The VCA and contour
generator operating together constitute a loudness
ARTICULATOR The other section of the DUAL
CONTOUR GENERATOR dynamically shapes the
timbre of the VCF during a note. The contour
generator action is initiated by a trigger generated
within the KEYBOARD each time a key is depressed
The KEYBOARD also generates a control voltage
that increases as successively higher keys are depressed
This control voltage establishes the VCO pitch and
at the same time causes the VCF to track the VCO
to maintain constant timbre. The MODULATION
OSCILLATOR generates subaudio waveforms used
for control (not audio) purposes. This oscillator also
triggers the SAMPLE AND HOLD which samples the
noise circuit to yield control voltage that randomly
changes levels at a tempo sot by the RATE control.
The source of modulation is set by the SOURCE
switch and the circuit it will modulate is chosen by
the ROUTING switch. The MODULATION AMOUNT
wheel controls the level sent to the selected circuit
The Micromoog provides DC power to operate
auxiliary equipment. Through the rear panel the
Micromoog interfaces with external equipment such
as auxiliary controllers, other synthesizers, modular
equipment and other musical instruments.
1.3 MODEL MODIFICATIONS
This manual refers to the current production
model as of July 1976 - Serial Number 3300 and
above. Since the Micromoog was introduced to the
music world, several major and numerous minor
improvements have been incorporated. Some of
the modifications are discussed and illustrated in
tho following:
1) As of July 1976, the keyboard was modified.
It functions identically to and is interchangeable with
oirlior model::. Tho discroto rosUtorB and vortical PC
Board have been replaced by resistor packs and a
horizontal PC Board.
2) A direct audio output cable has been provided
to eliminate a slight, bleed thru. The cable is now
available as a field retrofit kit
3) A small rear panel PC Board and a control
pot (R261) has been added to provide variable
keyboard output control voltage. See Figures 1-1 and
1 - 2 .
4) As of October 1975, the nomenclature or the
main control panel. Serial Number 1500 and above,
was revised with no functional changes. See Figures
1-3 and 14.
1-1

FIGURE 1 1 REAR PANEL, EARLY VERSION
FIGURE 1-2 REAR PANEL, LATEST VERSION
FIGURE 13 CONTROL PANEL, EARLY VERSION
NEW
NOMENCLATURE
FIGURE I 4 CONTROL PANEL, t A TEST VERSION
1-2

SECTION 2
CIRCUIT DESCRIPTION
2.1 POWER SUPPLY 115 VAC. IC101 has been observed to survive the
1/4 second overvoltage that occurs at its inputs in
The supply druws 160 mA from a 115 VAC such ar. instance.
60 Hz input (or 75 mA from a 230 VAC 60 Hz input)
when the + 15V and - 15V outputs are 200 mA each.
Cl and C2 decouple RKI that may be riding in on the T1 steps the input AC down to 36 VAC cemer-
lino. SW1 connects the primaries of T1 in parallel for tapped The diode bridge CR101-CR104 rectifies the
115V operation and in series for 230V operation. FI AC to roughly ± 25 VDC. At a normal full load of
and 2 are in parallel for 115 VAC operation (250 mA ± 150 mA (Micromoog with 1125 Sample and Hold
blowout point) and in series for 230 VAC operation plugged into back), C101 and C102 provide sufficient
(125 mA blowout point). The fuses protect against filtering to keep the raw DC ripple around 2Vp-p. Dual
fire hazard should a short occur in the secondary of tracking regulator IC101 operates with external pass
Tl. They will not blow if the regulator outputs short transistors Q101 and Q102. These transistors drop the
out. (The legulator will current limit instead.) They ruw DC voltages to £ 15 DC. C103 and C104 stabilize
will blow i:' 230 VAC is applied and SW1 is set for the regulator against high frequency oscillation.
FIGURE 2-1 SIMPLIFIED REGULA TOR SCHEMA TIC
2-1

Since ihe base-emitter drop of external pass
transistor Q101 is about 0.6V, R101 will feed about
(0.6V/47 ohm - 12.5 mA) into IC101 pin 7, which
is more than sufficient to supply the 5 mA required
to operate internal chip circuitry. Qa passes the
balance of this 12.5 mA. Q101 forms n PNP-NPN
Darlington configuration with the internal pass
transistor Qa. Q101 passes mosl of the positive
current 1+ and therefore dissipates most of the heat
allowing IC101 to run cooler.
Pin 4 senses ♦ 15 V and causes the internal
circuits to drive Qa to maintain the output very
procisoly as the line and load vary. The sense input
provides another service; if 1+ reaches 250 mA, the
drop across R103 will rise to 0.7V and Ihe supply will
go into the current limit mode. If the output is
shorted to ground, Q101 will dissipate several times
normal power. However, Q101 will not burn out no
matter how long its output remains shorted due to
the attached heat sink. The negative regulator works
in exactly the same fashion as I he positive regulator.
Here are some important specs:
Input Voltage
Output Accuracy
Lcng Term Output Drift
Output Load Keg.
Output Lin* Reg
Output NoUe
Output Temp. Stab.
Output Current Limb Value
♦ 30V Max.
+ 10 mV (-1SV trimmed)
+ 300mV(+ 16 V ur.trimmedi
♦ 3 mV/1000 hours typical
30 mV Max. (0 to 230 mA)
20 mV Max. (SO VAC to
130 VAC 60Hz)
1.0 MV RMS Max. (100 Hz
to LOO kHz B.W.i
0.016%/°C Max.
250 mA
C105 and C104 are solid tantalum types to
effectively filter high frequency noise. CR105 and
CR106 protect the regulator against accidental con¬
nexion to it supply of an opposite polarity. RIOfi
sets the - 15V supply to - 15.00V. It must be se.
accurately since it is the reference for the Keyboard
String, Octave Buffer, Oscillator Range and Chip
Tomporaturo. The + 15V supply new! not he extremely
accurate so no trim is provided for it. It still must be
precise — i.e.: it must not drift or be noisy,especially
since the - 15V supply tracks the - 15V supply.
Cl09 and Cl 10 decouple the power supply lines on
tho main PC Board to forestall parasitic oscillations
The 1468 regulator is a ceramic encapsulated
device (non-hermetic glass frit type) rather than u
plastic device. The use of a plastic package would
result in a chip temperature of 125°C (not necessarily
worst case).This is dangerously close to the maximum
allowable chip temperature of 150°.High temperatures
cause shortened chip life, more rapid long-term drift,
and greater thermal (warm-up) drift. With ceramic
encapsulation the chip temperature is about 85°C -
a much more comfortable figure.
2.2 KEYBOARD CIRCUIT
Tho KEYBOARD CIRCUIT produces a control
voltage (to determine pitch) that increases linearly as
successively higher keys are depressed. The control
voltage increases from 0.00 volts at LO F (lowest, key)
at tho rate of one volt per octave (83.3 mV'semitone)
to a maximum of 2.58V at HI C (highest key 2-1/2
octaves above LO F). The keyboard has low-note
priority. If the performer holds down several keys
simultaneously, the lowest key determines the control
voltage.
The GLIDE control allows adjustment of the
control voltage transition rate from a 0.3 msec time
constant, (effectively instantaneous pitch change) to
a 1.0 second time constant, (effectively several seconds
before the pitch catches up to the controlling key and
stops changing). The Keyboard possesses a memory
that maintains tho control voltage at precisely the level
of the output at the instant the last key is released.
2.2.1 DC OPERATION (CONTROL VOLTAGE
GENERATION! (FIGURE 2-2)
IC202A applies constant current IK (set to
833 pA by R238) to the keyboard resistor string. The
1,0 F end of the string remains at ground potential
no matter how many or how few keys are closed.
Note that the I-R drop across the remainder of the
string below ihe lowest closed contact establishes
VOUT applied to the buss If more than one contact
closes, I K flows onto the bus at the highest closure
and returns to the string at the lowest closure. The
intervening resistors are simply shorted out.
2-2

FIGURE 22 KEYBOARD CONTROL VOLTAGE GENE RATION
When a key contact closes, holding capacitor
C212 charges (or discharges) at tho rate set by R251
to the level established on the buss. R250 sets a
minimum charging time constant of TCH (min) =0.22
pF x 1.5K “ 0.33 msec. R250 decouples the 25 kHz
pilot, oscillator signal (spp below) from the DC control
voltage on C212. R250 also filters key contact scrape
and bounce that occurs when a lower contact closes
while an upper contact is being held closed. When all
keys are released, no further charging of C2I2 is
possible and it holds the last instantaneous value of
control voltage. Dual J-FET Q201 in conjunction with
R252, R253 and IC204A comprise an extremely low
input bias current unity gain buffer. The buffer
provides substantial control voltage output drive
capability while draining C212 at less than a 200
pA rote.
MAX.MUN mSCHAROE ^ ^
NOTE
The output side of the buffer guards the
input side. This vastly reduces on-board
eakage since a potential equal to the value
being held surrounds tho entire holding
circuit.
C213 nnd C214 decouple RFI pickup by the
main PC Board. C214 also shunts capacitive audio
pickup by the keyboard control voltage output line.
CR203 and CR204 protect Q201 and 1C204A from
static discharge coming In via J3. R257 does not affect
the output li'vol normally (it. is inside the loop) but it
docs allow control voltage to be forced into J3 for
testing purposes, or for introducing external control
voltages to override the keyboard control.
22.2 AC OPERATION ITRIGGER GENERATION)
Since the keyboard uses a single-buss contact
scheme, nn AC pilot, signal (generated by IC201)
must he injected onto the buss so that detection of
contact opening and closing can occur. When closure
occurs, IC203 and IC202B amplify and detect the
signal and develop a clean DC trigger output.
Oscillator 1C201 generates the 25 kHz ± 5 kHz
triangular AC signal. 25 kHz lies above the audio
range which reduces the chance that unwanted signal
pickup by other Micromoog circuitry will be audible.
The 3080 transconduclance amplifier was chosen
as IC201 because it has very fas: slew rate, does not
delay coming out of input or output saturation and
does not draw current slugs from the supply lines
while slewing or while saturated. The output of a
3080 is a bilateral current source the magnitude of
which is given by:
lOUT _ 0-02 pA/ni» ( I npu t) . [ OCT (Mix.) - I BIAS
UA t bias)
R235 sets IFUAS (into pin 5) to 0.5 raa which
keeps the total package dissipation at 30 mW. well
below the absolute maximum of 125 rrW.lOUTwill
tend to alternate between + 0.5 mA and - 0.5 rnA,
2-3