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Moog Music Minimoog 204D Synthesizer
Minimoog 204D


Specifications SOUND SOURCES NO. OF SOUND SOURCES: 5 (3 Oscillators, 1 Noise Source, 1 External Input /Microphone Pre- OSCILLATOR FREQUENCY: 0.1 to 20kHz (cycles/second) in six overlapping ranges. SHORT TERM OSCILLATOR STABILITY: Better than 0.25%. OSCILLATOR WAVEFORM OUTPUTS: Triangular, Sawtooth, Triangular-Sawtooth Mix (Oscillators 1 and 2 only). Reverse Sawtooth (Oscillator 2 only), 3 widths of Rectangular. NOISE SOURCE OUTPUTS: White or Pink random waveforms. PREAMPLIFIER INPUT: 10 millivolts minimum; 2 volts maximum. PREAMP INPUT IMPEDANCE: 100K ohms or FILTER FILTER CHARACTERISTIC: Wide-range low-pass filter with variable-height resonant peak at cut-off frequency, and 24dB/octave cutoff slope. RANGE OF CUTOFF FREQUENCY: Continuously variable from 40Hz to 20kHz (9 octaves). VOLTAGE CONTROLLED AMPLIFIERS NUMBER OF AMPLIFIERS: 2 (one controlled only by its Contour Generator: the other controlled by optional external controller). DYNAMIC RANGE OF EACH AMPLIFIER: 80dB. CONTOUR GENERATORS NUMBER OF CONTOUR GENERATORS: 2 (one controlling filter through an attenuator; the other controlling the first voltage Controlled Amplifier). RANGE OF ATTACK TIME: 10 milliseconds to 10 seconds. RANGE OF DECAY TIME: 10 milliseconds to 10 seconds. RANGE OF SUSTAIN LEVEL: 0 to 100% of contour peak. WIDTH OF SWEEP OF FILTER BY ITS CONTOUR GENERATOR: Continuously variable from 0 to 4 octaves. AUDIO SIGNAL OUTPUTS HIGH LEVEL OUTPUT: 0.5 volts typical, with 3K ohms nominal output impedance. LOW LEVEL OUTPUT: 15 millivolts typical, with IK ohm output impedance. HEADPHONE OUTPUT: 0.3 volts maximum, into standard 8-ohm stereo headphones. CONTROLLERS Keyboard FUNCTION: Permanently connected to (a) control Oscillators 1 and 2, and (b) trigger Contour Generators. Keyboard may be switched to control Oscillator 3 and Filter. DESCRIPTION OF KEYBOARD: Standard 44 key (3-1/2-octave) Organ Keyboard. Only lowest key depressed has effect in controlling Oscillators and Filter. Contour Generators are activated whenever a single key is depressed. RATE OF Keyboard GLIDE: Continuously variable from 1 millisecond to 1 second/octave. PITCH BENDING RANGE: 5 semitones mini- MODULATION INJECTION RANGE: 0 to 1-1/4 octaves. CONTROL AND POWER CONNECTIONS EXTERNAL PITCH CONTROL INPUT CHARACTERISTIC: 1 volt change produces 1 octave frequency change, + 2 percent. EXTERNAL FILTER CONTROL INPUT: 1 volt change produces 1 octave change in cutoff frequency, + 5 percent. EXTERNAL Amplifier CONTROL INPUT: Linear control voltage/gain relationship. Gain range spanned by 0-4 volts. EXTERNAL TRIGGER INPUT: Switch-closing activates both Contour Generators. AUXILIARY DC POWER SOCKET: +10 volts and -10 volts at 50 mil!amperes. DIMENSIONS AND WEIGHT OVERALL SIZE (with Front Panel down): 28-5/8 inches (72cm) wide, 17-1/8 inches (41cm) deep, 5-3/4 inches (14cm) high. NET WEIGHT: 28 pounds (12.7kg). SHIPPING WEIGHT: 45 pounds (20.5kg). POWER REQUIREMENTS 100-135 and 200-270 volts, 50-60Hz, 40 watts maximum. major differences in the two boards is that common summing is used on the new board while individual summing is used on the old board. All three oscillators have individual octave switching signals applied to three adjustable potentiometers providing precision octave switching of the individual oscillators. 2.2.2 MODULATION MIX Amplifier A modulation mix Amplifier selects the output of oscillator 3 or noise, or both, sums and routes them to the amount control in the left hand Controller. 2.2.3 NOISE GENERATOR The Minimoog contains a noise generator using a transistor generating white noise in the range of -60dB which is amplified to produce white, pink or red noise, selected by the noise Selector switch. White or pink noise is used for audio and pink or red for modulation. 2.2.4 HEAD PHONES An Amplifier is provided to supply sufficient current to drive standard stereo headphones. 2.2.5 POWER SUPPLY A dual output Power Supply with the rectifier on Board 3, the filter on Board 5 and the transformer on the chassis, provides + 10 volt regulated power. The input is either 115 or 230 volt as selected through a switch on the top of the panel. 2.2.6 KEYBOARD CIRCUIT The Keyboard circuit consists of a temperature compensated current source, the actual Keyboard and a track and hold amplifier. The Keyboard voltage is routed to a track and hold Amplifier where, with no keys depressed, the circuit is in a hold mode. With a key depressed, the pitch voltage occurs before the trigger and the trigger goes off before the pitch voltage is released. 2.2.7 A-440 REFERENCE OSCILLATOR The A-440 reference oscillator is based on a standard Wein Bridge oscillator design. The bridge has a phase shift of zero degrees at approximately 440Hz, supplying a positive feedback and causing the circuit to oscillate. The frequency of the oscillation is set by a resistor. Three capacitors and a resistor limit the signal amplitude to a transistor collector resulting in a clean sine wave output. 2.2.8 EXTERNAL Amplifier The external preamplifier is fed to the EXTERNAL INPUT VOLUME control where the output is fed through a 200 gain Amplifier and in turn routed to the EXTERNAL INPUT ON/OFF switch. This switch allows an external source to be summed with other signal sources. 2.2.9 OVERLOAD LAMP DRIVER The output from the 200 gain Amplifier is also fed to the overload lamp driver circuit. The amplitude envelope of the signal is detected and fed to a voltage divider. When the AC input voltage reaches approximately 1.2 volts, the OVERLOAD lamp illuminates and is held for a suitable period. 2.2.10 VOLTAGE CONTROLLED FILTER “Audio” signals are summed and a differential signal current is generated and applied to a filter ladder. Cutoff frequency of the filter is controlled by the standing current through the ladder. The higher the standing current, the higher the cutoff frequency. A differential signal is created and fed to a gain Amplifier which converts the differential input to a single ended output in tum fed to a transistor in the voltage control Amplifier. The FILTER EMPHASIS control is also connected to the gain Amplifier providing positive feedback at the cutoff frequency. As the amount of emphasis is increased, the Q increases and the filter starts a sine wave oscillation at the cutoff frequency. The cutoff frequency control current originates in an exponential voltage to a current Converter. Control voltages from the external input, Keyboard switches, modulation and the contour generator are summed and fed to the exponential convertor. A resistor sets the Keyboard scale at one volt per octave and in turn the front panel filter CUTOFF FREQUENCY control is calibrated in a similar manner. 2.2.11 VOLTAGE CONTROLLED Amplifier The input signal from the voltage controlled filter is AC coupled to a differentia) transconductance multiplier. The gain of the transistor is current controlled; the greater the current, the higher the gain. 2.2.12 CONTOUR GENERATORS Separate contour generators are provided for both filter and loudness contours. Each contour generator has its own controls consisting of ATTACK, DECAY and SUSTAIN. Contour generators are triggered by an internal voltage trigger from the Keyboard and/or the rear panel S-TRIG jack. The amount of contour control adjusts the sweep of the voltage controlled lowpass filter.

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Service Manual
Manual type:
Service Manual
9.19 Mbytes (9636281 Bytes)
Scanned document, reading partly badly, partly not readable.
Upload date:
01 November 2017


SPECIFICATIONS ... INTRODUCTION ... 1.1 GENERAL ... 1.2 PRECAUTIONARY MEASURES ... CIRCUIT DESCRIPTION ... 2.1 GENERAL ... 2.2 GENERAL CIRCUIT DESCRIPTION ... 2.3 "D" OSCILLATOR PRINTED CIRCUIT BOARD ... 2.4 MODULATION MIX Amplifier ... 2.5 NOISE GENERATOR ... 2.6 HEADPHONE Amplifier ... 2.7 POWER SUPPLY ... 2.8 VOLTAGE CONTROLLED FILTER ... 2.9 VOLTAGE CONTROLLED Amplifier ... 2.10 CONTOUR GENERATORS ... 2.11 A-440 REFERENCE OSCILLATOR ... 2.12 EXTERNAL PREAMPLIFIER AND OVERLOAD LAMP DRIVER ... 2.13 OLD MINIMOOG OSCILLATOR BOARD ... 2.14 -5 VOLT REFERENCE SUPPLY ... 2.15 OCTAVE SWITCHES ... 2.16 OSCILLATOR ONE ... 2.17 OSCILLATOR TWO ... 2.18 OSCILLATOR THREE ... 2.19 KEYBOARD CIRCUIT ... TROUBLESHOOTING ... 3.1 OVERALL QUICK REFERENCE TROUBLESHOOTING ... 3.2 OSCILLATOR PRINTED CIRCUIT BOARD NO. 1 TROUBLESHOOTING (SERIAL NUMBERS 10175 AND ABOVE) ... DISASSEMBLY PROCEDURES ... 4.1 DISASSEMBLY ... ADJUSTMENT AND TUNING ... 5.1 PRINTED CIRCUIT BOARD REPLACEMENT ADJUSTMENTS ... 5.2 VOLTAGE ADJUSTMENTS ... 5.3 TUNING OSCILLATORS (SERIAL NUMBER 10175 AND ABOVE) ... 5.4 TUNING THE OSCILLATOR (SERIAL NUMBERS 8ELOW 10175) ... 5.5 DETAILED ADJUSTMENT PROCEDURES ... 5.6 POWER SUPPLY ADJUSTMENT ... 5.7 A-440 ADJUSTMENT ... 5.8 SIGNAL FLOW ... 5.9 MAIN OUTPUT ... 5.10 PHONE OUTPUT ... 5.11 LOW MAIN OUTPUT ... 5.12 EMPHASIS CALIBRATION ... 5.13 FILTER CUTOFF ADJUSTMENT ... 5.14 FILTER SCALE ... 5.15 KEYBOARD 1/3 ... 5.16 EXTERNAL FILTER CONTROL ... 5.17 AMOUNT OF CONTOUR ... 5.18 FILTER CONTROL ... 5.19 AMOUNT OF MODULATION ... 5.20 FILTER CONTOUR ... 5.21 DOUBLE TRIGGERING ... 5.22 LOUDNESS CONTOUR ... 5.23 EXTERNAL LOUDNESS CONTROL UNIT ... PAGE NO. 5.24 NOISE ... 5-10 5.25 CONTOUR GENERATOR BALANCE ... 5-10 5.26 EXTERNAL SIGNAL INPUT ... 5-10 5.27 AUDIO NOISE GENERATOR ... 5-10 5.28 GLIDE ... 5-10 5.29 KEYBOARD PITCH CONTACTS ... 5-11 5.30 OSCILLATOR ADJUSTMENTS FOR BOARD ... 5-11 5.31 OSCILLATOR RANGE ... 5-11 5.32 OSCILLATOR 1 TUNING ... 5-11 5.33 OSCILLATOR 2 AND 3 TRACKING ... 5-11 5.34 OCTAVE ADJUST ... 5-11 5.35 RANGE OF TUNE, PITCH AND FREQUENCY ADJUST CONTROLS ... 5-11 5.36 OSCILLATOR 3 WIDE RANGE ... 5-12/6-0 5.37 MODULATION OF OSCILLATOR ... 5-12/6-0 5.38 EXTERNAL CONTROL OF OSCILLATOR ... 5-12/6-0 6 KEYBOARD MAINTENANCE ... 5-12/6-0 6.1 CLEANING ... 5-12/6-0 6.2 KEY80ARD ADJUSTING PROCEDURE ... 6-1 7 REPLACEMENT PARTS LIST ... 7-0 7.1 ORDERING ... 7-0 8 MODIFICATIONS ... 8-1 8.1 SERVICE BULLETINS ... 8-1 8.2 OSCILLATOR BOARD ASSEMBLY ... 8 1 8.3 CONTOUR GENERATOR ASSEMBLY ... 8-1 8.4 POWER SUPPLY ASSEMBLY ... '8-1 8.5 FILTER ASSEMBLY ... 8-1 8.6 KEYBOARD CIRCUIT PRINTED CIRCUIT BOARD NO. 2 ... 8-1 8.7 MINIMOOG OSCILLATOR TUNING ... 8-2 8.8 OSCILLATOR BOARD NO. 1. Power Supply CONNECTION AND OCTAVE 8UFFER ... 8-2 9 SCHEMATIC DIAGRAMS AND PRINTED CIRCUIT BOARDS ... 8-8/9-0 LIST OF ILLUSTRATIONS 2-1 Simplified Block Diagram ... 2-11 2-2 Subassembly Location Diagram ... 2-12 2-3 Printed Circuit Board Socket Location ... . 2-12 2-4 Left Hand Controller ... 3-1 5-1 Power Supply Adjustment Location Diagram ... 5-2 5-2 Rear Panel Tuning Control Location Diagram (Serial Numbers 10175 And Above) ... 5-2 5-3 Filter Adjustment Location Diagram ... 5-2 5-4 Front Panel Control Settings (Serial Numbers 10175 And Below) ... 5-2 5-5 Front And Rear Panel Location (Serial Numbers 10175 And Below) ... 5-2 6-1 Use Of Keyboard Adjusting Tool ... 6 1 7-1 Front Panel Control Diagram ... 7-1 8-1 Printed Circuit Board 2 Modification ... 8-3 8-2 Rear Panel Modification Diagram ... 8-4 8-3 Front Panel Controls Diagram ... 8-5 8-4 Rear Panel Adjustment Location Diagram ... 8-5 8-5 Connector Modification Diagram ... 8-7 8-6 Octave Buffer Schematic ... 8-8/9-0

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