Anyone done a low noise mod on a Pearl CO-04 Comp?

[TheBigMan]

A chap I know has asked me about this, and I'm not really familiar with the pedal.  Beyond looking at replacing the opamps with lower noise versions I'm not really sure what I can do.  Just wondered if anyone has any experience with this pedal?  :?:

[MartyMart]

I dont have one, but a mate does and yes it is a bit "hissy" !
Other than opamp and replacing any "signal" carrying electro's with good
quality poly caps, not sure what else would do it ... or if it would be
worth all that fuss ??
There are schemo's around here somewhere ....

Marty.

[TheBigMan]

Yeah, that's what I though after having a quick look at the schem.  The only other thing that occurred to me was the CA3080, I was wondering if anyone knows of a better quality alternative?  Perhaps a Rohm chip, I recall Mark Hammer saying they made the BA chips used by Boss in the CS-2.

[petemoore]

Any huge resistors could be replaced with low tolerance ones, I don't know...would need to look at the schematic, I suppose IF they were making noise it might help.
 I got some hiss out using an audio probe. Compressors don't compress whentheere's nothing coming in, basically speaking if it's turned up, whatever hiss noise is at the beginning of the circuit will get amped up.
 Audio probing needs to be taken with a grain of salt or very seriously, depending on how much gain 'that' point of signal tap has on it.
 I'd guess start near the beginning, maybe put an opamp socket in and see what if about caps resistors reducing noise near the input.

[TheBigMan]

Having analysed the schem in more detail I'm looking quite hard at IC1 (JRC4558DD) for replacement.  If the tone circuit before the compression stage is noisy then that will all be amplified.  Any further suggestions are welcome though...

[Paul Perry (Frostwave)]

About replacing the 3080..
Maybe something could be done using half a NE5517 (LM13700).
Notice there is a linearizing diode input in these (see the National Semiconductor data sheet). Whether activating the linearisign diode input helps with noise I do not know (it might allow a higher input signal, which should help). I believe it is intended to help make a lower noise VCA. But, I have no personal experience.

[cd]

I would triple check the actual pedal against the schematic.  If you do a search here, I tried breadboarding that pedal 10 times with that schematic, and it never worked properly, so I wouldn't trust it.

Noise-wise, a 3080 based compressor will always be noisy, especially if you have the compression turned up.  With the Pearl, this is exacerbated with that last opamp stage which applies a ton of gain (amplify the weak signal, and you amplify the noise).

[TheBigMan]

The schem I have does look like a factory schem, but then I've never actually seen the pedal, I was just asked if I could do this and with no experience of the pedal I thought I'd ask here.

Seeing as there's no "easy" way to replace the CA3080 with a better part it looks like the standard replace the opamps and any small value electrolytics with film.

[mrsage]

You might e-mail Keeley and ask him, as well.

I know people were saying that he had a mod for the Pearl Comp, and he's always good about sharing with the DIY community.

[Paul Perry (Frostwave)]

it looks like the standard replace the opamps and any small value electrolytics with film.

I'd be suprised if this helped here (unless, in the million to one shot, that there was a reverse biased electro, the leakage can give a noise signal).

[TheBigMan]

it looks like the standard replace the opamps and any small value electrolytics with film.

I'd be suprised if this helped here (unless, in the million to one shot, that there was a reverse biased electro, the leakage can give a noise signal).

I tend to agree, but the myth of replacing caps with different types for a better sound seems to have spread to the extent that I was asked to replace the electrolytics.