SERVO-COMPRESSOR // JC Maillet (c) 2024
The original circuit that I’m demo’ing here doesn’t exist on the guitar market today.
Unlike other compressor designs this one operates purely on a mathematical principles – that is, the servo principles of Control theory … as a result the steady-state transfer curves differ in this case from the ones usually obtained for (classic) COMP-LIMITER designs. In the SERVO-COMP the Ratio concept remains unchanged – but here it has a much wider range – while the idea of a Threshold is now replaced by one of Rotation Point, to borrow modern (THAT Corp) language. It is capable of producing levels of compression not achievable with ANY comp-limiter architecture; such as 1176, LA-2A, etc etc etc.
Two controls determine RATIO and ROTATION POINT values according to the theory that describes this kind of circuit … the SERVO-COMP is a hi-fi version of a mid-70’s lo-fi broadcast chip-set, configured to operate in either of two modes – in ALC (constant output) mode or in COMP mode …
this class of circuit was originally conceived as phase shift oscillator stabiliser, useful in shift keying applications … but on audio signals it can be used to produce brick-wall limiting and infinite-sustain effects – it’s very possibly THE compressor circuit everyone is looking for, going way beyond what any COMP-Limiter can achieve – a level up in extreme compression effects …
At modest RATIO levels the COMP mode shown in the video below sounds very natural and musical, very similar to the response of a COMP-Limiter when operating in COMP mode – here with much wider range of adjustment on the RATIO side.
At higher RATIO settings this circuit produces rubber-band-like super squash effects …
Next is an example of the circuit’s ability to rapidly adjust large amounts of gain
all while keeping distortion levels low …
HISTORICAL CONTEXT
Design flaws in a major manufacturer’s dynamic processor chip-set, one originally conceived solely for broadcast level signals, means very few people if any have experienced this AGC topology in a music “production” context … a longstanding engineering design shortfall that gets fixed with this work and paves the way for instrument level applications of the idea.
Very interesting approach, and the result can have very diverse usage.
What are your plans? Will you be making a version of it commercially available, or will you publish it in some form?
maybe this spring … 🙂