Noise from compressor - overdrive

[ghiekorg]

R21 connects to the Bias voltage (Vdd) and so does R2. 
[...]
A similar cap between the output of IC1a and lug #1 of the Blend pot might also be called for.

Thanks Mark i had finally time to read it through. It all made sense. As soon as i will be working on the new pedals and i will have tool in hands i will check if this mod is easy to do without messing up the board (the  pedal itself is already a mess inside).
Thank you very much, that's really useful infos

sorry, but that's just a bunch of non-sense
[...]
of course, you need good low-noise op-amps if you go that route

Thank you Eb7+9, that's also really interesting but, for me, still rocket science I also still don't quite get exactly how compressors work... I mean i know what it does but sometimes it behaves in ways i can't predict and/or understand (2 examples happened just recently:  when using a 1-knob compressor it was lowering the overall volume when i was playing the bass with the bass EQ knob all the way up. I still don't quite get why. Another example was a kind of clipping/grunt  due to the release/attack set wrong)

[Mark Hammer]

It is the duty and obligation of EVERY compressor to make everything it receives equally audible. 

sorry, but that's just a bunch of non-sense

I'll distinguish between "nonsense" and my use of mere hyperbole to make a point.  Yes, all compressors produce limiting in one form or another.  Unlike true peak limiters that leave most of what's below the threshold unaltered (i.e., linear transfer-function), stompbox compressors will increase gain when the input signal drops.  The "breathing" we hear from simpler guitar compressors IS from slow gain-recovery amplifying residual input noise, and whatever noise the circuit itself adds (though my experience is that this is usually less than what it has unintentionally let in).

Are low-noise components necessary for a stompbox compressor?  Depends on the intended application and rig.  If a compressor is going to be followed by a hissy high-gain pedal, then I'm not sure it is worth anyone's while to go "deluxe" on the component choices.  Yes, a hissy compressor, followed by a high-gain pedal will amplify that hiss in objectionable ways.  But, like I say, my experience is that much of that hiss is coming from outside the compressor, and amplified by it, rather than any shortcomings in the composition of the compressor itself.  My sense is that reducing the amount of compression applied, and opting for a faster gain recovery time will go some ways towards avoiding the sort of compressor noise artifacts that a high-gain pedal will only make worse.  Clearly studio applications, where low noise is an important objective (if only because one can hear it), demand additional considerations.

This is actually one of the reasons why I like the SSM2166-based compressor-pedals.  The unit includes downward expansion which can be used to provide "gentle" noise gating early in the signal path.

Hi JC, do you have ferry service to the island during these bizarre times?