The Minimoog is a monophonic analog synthesizer, invented by Bill Hemsath and Robert Moog. Released in 1970 by the original Moog Music, it was among the first widely available, portable and relatively affordable synthesizers.
Design
At its most basic, the Minimoog control panel can be broken up into 3 sections:
The sound generator (the VCO or voltage-controlled oscillator)
The filter (the VCF or voltage-controlled filter)
The amplifier (the VCA or voltage-controlled amplifier)
To produce a sound, the musician would first choose a sound shape to be generated from the VCO. The VCO provides a choice of several switchable waveforms:
triangle wave
sawtooth wave
a combination of the sawtooth and triangle wave/reverse sawtooth or ramp wave in oscillator three
square wave
two different width pulse waves
The sound then travels from the VCO to the VCF (voltage-controlled filter) where it can be shaped and sculpted, adding resonance.
Next, the sound travels to the voltage-controlled amplifer (VCA). The term "amplifier" can be a bit misleading to novices who might be thinking of a stereo amplifier with a single volume knob. In a modern synthesizer, a VCA actually has 4 separate volume knobs that control four different stages of the sound. For example, the first knob - the Attack volume - controls how loud a sound is when the key is first pressed: does it start immediately like a string being plucked? Or does it fade in gradually like a violin being softly bowed? (See the "Sound Basics" section of the general synthesizer article for more information on this.)
Part of the appeal of this instrument over the early modular Moogs was the fact that the Minimoog required no patch cables. While this imposed the signal flow limitation outlined above (VCO -> VCF -> VCA), there are ways to tweak the sound. For example, in reality, the Minimoog has six sound sources. Five of these sound sources pass to a mixer with independent level controls:
Three voltage-controlled oscillators (see above)
A noise generator
An external line input
And the VCF can itself be made to oscillate, thus comprising the Minimoog's sixth sound source.
The voltage-controlled filter (VCF) and voltage-controlled amplifier (VCA) each have their own ADSD envelope generator (or Attack-Decay-Sustain-Decay). Musicians who are familiar with more modern synthesizers might expect the last letter to be R for "Release" (as in ADSR). However, on the Minimoog, the envelopes are ADSD as the Decay setting also sets the time for what's regularly known as Release. In other words, there are 3 knobs to control 4 sections of the sound (most modern synths have 4 knobs, one for each section) -- a "shortcoming" that doesn't seem to diminish the Minimoog's popularity in any way. There is also a switch above the pitch and modulation wheels to engage the final decay stage as well as a switch for engaging the glide circuit.
The VCF is of transistor ladder type, a design patented by Moog music and even defended in court.
The output of the third oscillator and/or the noise generator can also be routed to the control voltage inputs of the filter and/or oscillators. The amount of pitch or filter modulation thus realized is controlled by the modulation wheel, which is the right one of the two plastic disks located to the left of the keyboard. In this way the third oscillator is frequently used as a low-frequency oscillator to control pitch.
The Minimoog can be controlled using its in-built, 44-note keyboard, which is equipped with modulation and pitch-bend wheels or by feeding in an external one-volt-per-octave pitch-control voltage and triggering the envelope generators with an inverted trigger. External pitch control does not pass through the glide circuit, nor is presented to the VCF tracking switches and thus, the external inputs were not designed for external keyboard control. The lowest note played on the keyboard determines the pitch, a condition that is referred to as low-note priority. The envelope generators do not retrigger unless all notes are lifted before the next note is played, an important characteristic which allows phrasing. The modulation and pitch-bending wheels were an innovation that many instrumentalists found to be extremely playable. The pitch-bend wheel is on the left of the modulation wheel. It is normally kept in the centered position. It is not spring-loaded; the player must return it to the centered position to play in tune. There is a delicate detent mechanism to help the player find the center position tactually. In sharp contrast to later synthesizers that also have pitch-bend wheels, there is no deadband near the center of the wheel's travel; the wheel produces minute changes in pitch no matter how slightly it is moved in either direction. The wheel can therefore be used to introduce slight vibrato or nuance, as well as accurate pitch changes. However, Moog later recommended adding a deadband mod and published this mod in their factory service notes. The detent mechanism can be somewhat adjusted in its strength.
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