Service manual

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The external pre-amp is a three transistor high-gain amplifier. The output of the pre-amp is
monitored by an overload indicator. The overload driver circuit is a Schmitt trigger which turns
the overload light on when external signal levels become excessive.
The first and second voltage controlled amplifiers are two nearly identical circuits. Their gain is
controlled by varying the voltage which supplies the current source transistors. A buffer or
output amplifier follows the second VCA stage.
The A-440 reference source is a highly stable Wein Bridge oscillator circuit. It produces a
somewhat imperfect sinewave which increases its harmonic content. These harmonics or
overtones assist in tuning to the reference, especially when the source being tuned is one or two
octaves away from the reference frequency. The output of this circuit is coupled to the VCA
buffer amplifier.
93-118 Rectifier Board
This assembly contains the input bridge rectifier diodes and the unregulated D.C. filter
capacitors.
93-060 Left Hand Controller
This assembly contains the PITCH wheel, MODULATION wheel, GLIDE and DECAY
switches, and two jacks for remote switching of glide and decay. The PITCH wheel has a
mechanical detent which allows it to be easily returned to a pre-set tune point.
To service this assembly, remove the two mounting screws and lift the unit out. All connections
to this assembly are through a 12 prong plug to simplify servicing and replacement.
93-061 Keyboard
The Mini-Moog keyboard is a standard three and one-half octave removable sub-assembly. All
electrical contacts are gold plated for high reliability. The keyboard is held in place by four (4)
mounting screws which are accessible when the bottom cover is removed. All connections to
this assembly are through a 6 prong plug to simplify servicing and replacement.