PAIA "Infinity+" Compressor/Sustainer
Re-design (c) '98
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The original PAIA Infinity Plus design had the envelope detector leaking turn-on currents into the output and also had (IMO) a slightly ill-distributed gain scheduling in the cascaded op-amp circuits that produced clipping in the second op-amp under hi-signal conditions ... the original circuit operated on a grain-of-weat bulb but I wanted to see what it would do with the NSL-32 opto-couplers I got from the Silonex rep a few years ago ...
I decoupled the detector circuit through a duplicate parallel side-chain circuit which then can be made sensitivity adjustable ... the signal-path gain is more equally distributed between the two op-amps so overload conditions are avoided ... also added extra filtering in the detector averaging circuit so that the gain doesn't bounce or suddenly drop "as much" when dealing with signal bursts ... the filtering capacitors can be toggled for Fast/Slow response ... I stuck a LED in series with the NSL-32 diodes to get external indication of how hard the compressor is working ...
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My stab at a revision of this basic circuit - it breathes and hisses like a bad compressor should ... I plug my tele into this thing and go straight into an old Sony tube reel-to-reel to get a devastating Marshall-like roar that's simply baffling ... [anyway (!)] ... btw, notice how the signal path is completely DC coupled from input to output - hence no phase shift and transient non-linearities from signal caps - the beauty of operating op-amps under dual supply ... not a danger provided the pedal preceeding it isn't giving off non-zero DC at its output ...
This is a "character" comp/sustainer - ie. it can easily produce an exaggerated non-linear envelope response - great for textured "squashing" effects ... when no signal is applied to the input the gain of the VCA increases to a value set by the gain limiter - I use a pot with a switch to open the circuit, yielding unlimited upper gain - great for sustaimed feedback effects ... this is quite different than the usual limiting circuits such as a DanElectro "Orange Squeezer" or MXR "Dynacomp", which are really limiters not compressors ... anyway, a cool experiment and a basis for other comp/limiter ideas and designs ...
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(c) 2006 JC Maillet
Greco Strat >> Infinity++ >> Yamaha DD20-MkII >> '65 Twin >> speaker line-out >> Korg D1600