One of mictester’s circuits from FSB, very transparent compared to Dynacomp or Squeezer’s so definitely one to try for the compressor fans.
Mictester’s description:
The original idea was to replace the old fashioned way of getting
compression – connecting an LDR across the volume control of your
amplifier, then illuminating it with an incandescent lamp driven from a
tap on the output transformer. The louder the signal, the brighter the
lamp, and the more the audio was shunted to earth at the volume control!
It was the very simplest compressor, but along with some nice second
harmonic distortion introduced by slightly changing the bias voltage to
the screen grids of the output bottles, you ended up with a very “loud”,
very lovely sounding amplifier that would give fabulous sustain to any
guitar.
The Really Cheap Compressor is a minimum parts design
that was meant to be a replacement for the simple valve amplifier
modification outlined above. I’ve built several of them (which reminds
me, I need to make another one this week), and everyone who’s used them,
likes them. If you use a good quality dual op-amp (a TL072 is OK, but
the LM833 or NE5532 are slightly quieter), you won’t hear any added
hiss, and no added distortion. This compressor is entirely clean, and
doesn’t have any part of the LEDs (or any other diodes) in the signal
path, so there’s no clipping (unlike with the rectifier circuit in the
Dynacomp). The LDR is slightly slow to respond, so the attack of the
guitar note is retained, but the squeeze is nicely applied to the decay
portion of the note – just where you want it. This is one of those “is
it on?” effects, but you really miss it when it’s off!
and a version better suited for bass guitar:
