Looking for a way to boost treble in this compressor (Circuit Salad content)

[midwayfair]

I built this compressor recently:


It works spectacularly -- in fact, it's one of the best-performing compressors I've ever played -- but one thing I think would really put it over the top is some sort of treble boost. It compresses very hard at the highest settings and this gives it some "apparent" treble loss. Unfortunately, I don't see any way to do that that don't involve cutting bass. I reduced R1 to 22K, which was as low as I could go without getting some distortion. I didn't want to blindly increase the biasing resistors, though that's the only other place I really see as maybe having any effect.

Knowing whether there's a way to do this would help me with some other circuits, too.

[Seljer]

maybe try a capacitor (+ series resistor) in parallel with R1 to let is pass more treble

[midwayfair]

maybe try a capacitor (+ series resistor) in parallel with R1 to let is pass more treble

Thanks Do you know how I'd calculate the frequencies cut?

[Mark Hammer]

maybe try a capacitor (+ series resistor) in parallel with R1 to let is pass more treble

That was my instinct too.  R1 and Q2 are acting like a virtual voltage-divider, à la orange Squeezer.

If I am correct in assuming that the calculation of the "appropriate" capacitor value of a parallel network is akin to what one would calculate for the "pre-emphasis" network i an inverting op-amp, that wold point to something like a 2200pf cap and 47k parallel resistor for less attenuation in response to peaks for content above 1khz.  That's a bit of a shot in the dark, but gives one a starting point.

[Seljer]

My experience, is that for best results, you have to tweak these things by ear anyway. I'd probably start with 1nF or 2nF and maybe a 500kiloohm potentiometer in series to dial it in.

[midwayfair]

Thanks guys, I'll run some gigantic jumpers out of the pedal to the breadboard and see what comes out.

[merlinb]

Other options are:
Add an emitter resistor and bypass cap to the darlington pair.
Add a bright cap to the output volume pot.

[rring]

Yes emitter R with small bypass cap is the way to go! This changes the biasing though - You will want to probably increase the collector/base resistor up to 1 meg and add 100 ohm in the emitter with a .1 maybe up to a 1uF in parallel. Just a swag here. I will test and give you some better values .

[midwayfair]

100 ohm in the emitter with a .1 maybe up to a 1uF in parallel. Just a swag here. I will test and give you some better values .

Thanks. If I get to it before you do, I'll let you know the results.

[rring]

use the following:

1 meg in the collector to base circuit and add 100 ohm in the emitter with a 1uF in parallel. Simulation shows treble boosting at about 1K and up:


However since you are compressing- the treble boost might be bucked- you should get a little - I hope?