Maxon CP101... sort of distorting?

[AC30Dirty]

Hey guys, I have a Maxon CP101 compressor that i love but i've been noticing lately that when I hit the low E string on my guitar rather roughly but not really it distorts. Im using it with my AC30 so i figured maybe its the Class A circuitry of the amp so I tried it on my mesa dual rec and it does the same thing. I have no idea what it could be. Any suggestions?

[MartyMart]

Strat/Tele or HB pups ?
Possibly battery, if not PSU powered ?
I have one, doesn't breakup with Les Paul at all, its PSU powered.

MM.

[AC30Dirty]

hey Marty, i play a PRS Custom 22 with duncans in it. The bridge pickup is around 14.7ohm's so i guess you could say it is a moderate output pickup. I usually use it with a power supply but if im not mistaken it happens with a battery as well. I'll check for sure and get back to you. Thanks

[Mark Hammer]

Sounds like envelope ripple, which can be expected to be worse at lower note frequencies.  I don't have a schem of it, but I imagine it won't be too terribly different than the Ibanez CP10, which isn't too terribly different from the Boss CS-2 and MXR Dynacomp.

There are a couple of approaches to take.  One is to aim for the slowest recovery/decay you can stand, which will smudge a lot of that envelope ripple together so you don't notice it.  Another is to aim for the shortest recovery/decay you can bear for the exact same reasons.  Another strategy is to make sure that the two complementary halves of the Dynacomp style rectifier are properly matched.  Finally, another strategy is to trim the low end off the signal path feeding the rectifier so that modulation at low frequencies is attenuated.

[AC30Dirty]

Thanks Mark, I dont really want to have to set it to settings i can put up with. I really figured that it would be a simple component change. I sould mention that i swapped out all the caps in the pedal to the same value but made the metal film. It cut down on the noise alot. As soon as I can get a pic of the PCB ill post it here. Thanks

[AC30Dirty]

I finally had a chance to mess around with the pedal today. I noticed a trim pot in the circuit. So i decided to do some teaking. Counterclockwise dumped more gain and clockwise less but not enough to stop the distorting noise i hear. It even does it with the sustain at zero. I really cant figure it out. 

[MartyMart]

Take some readings off the ic's perhaps one has gone bad or had a shot of too much juice at
some point.
I'm guessing there's a 3080 or similar and another dual opamp in there.
Mine is clean as a whistle, so I dont think that's "normal" behaviour for the CP101
I tried mine with a very loud HB gtr and there's no breakup at all.

MM

[AC30Dirty]

Hey Marty, it only has one IC in it and its a JRC4558D. I have some RC4558P and, BurBrown, chips left over from a tube screamer mod i did a while back. Will these work? I also have some TLO72's.

[AC30Dirty]

OK, this is what i've gathered so far. I replaced the IC with a RC4558P and it still does the break up. But, I noticed that it only does it on my bridge pickup. I using a Seymour Duncan SH-14Custom 5, and it only does it on the low E. I have a SH-2n jazz pup in the neck and no break up at all. The only thing i can think of is the interaction of the output of the pickup with the compressor and the amp at the same time might not be a good combination. I recall something about thier breing to much of a ripple. Can anybody elaborate and point me in a direction as to how i can check this. Thanks

[AC30Dirty]

Well i tweaked some more with the pedal and i finally setteled on a BURBROWN IC, which is the same ones the use in the tube screamers. Believe it or not this actually improved the pedal. It also doesnt seem to be distorting anymore. Hopefully this does it. Still if anyone has any suggestions please feel free to post them, just incase the problem comes back. Thanks everybody for thier point of view.

[MartyMart]

Hey, I'm glad that's helped some, sorry that I can't get more specific but although I have one
I dont have a schematic or the time to trace it all out right now ....
I presume that as it's opamp based, there will be an LED/LDR in there to control the amount
of compression, with some filtering and volume recovery after it.
It's probably not "damaged" but just reacting badly to your particular setup, headroom  - wise.
Did you use an OPA2134 ?
If you check that caps are all rated at 16v and above and there's not a current limiting diode,
then perhaps you could run it from a 12v DC supply .... may get you some more headroom ?
I've done this with other effects for "Bass" use it's helped .

MM.