The Ultimate Boss CS-3 Mod

14 February 2009

Ideology Behind the Mod:

Another Boss pedal hits the chopping block!

The Boss CS-3 compressor stock is just a terrible pedal in my opinion. It is incredibly noisy; I mean it has a ton of noise! Yes compressors are high gain and noise is to be expected from them but this pedal design seems excessively noisey. The noise is really over powering and can seriously take away from one’s playing. I also find the actual tone of the pedal very bland and flat/boring sounding. Not that I particularly like using a compressor for rhythm guitar work but when you use the stock pedal for rhythm your tone turns to mush. All the notes blend together with no note separation, it sounds like one big mess. There is no twang or squish that excited me when the pedal is turned on like a good compressor should do. The attack is quite boring and it just seems to lack life overall.

I decided to come up with a fairly simple mod to take this cheap generic compressor and turn it into something more exciting sounding to address the issues above.

Before you Modify your Pedal:

Before you go slap happy tearing out components and “modding” away. Though this is not an intensive mod it still involves quite a bit of work. To make sure your pedal sounds great and works at the end I recommend testing the pedal after you finish desoldering and soldering in four or so new components. That way if your pedal doesn’t work it’s easier to find the problem. I did this but with every component. I did this when I was developing the mod and wanted to hear things rather than make sure they worked.

A hint for removing Boss’ industrial lead free (RoHs) solder. First heat up the joint so the solder melts, then heat again and apply a bit of your own lead solder (i.e. 60/40). After this is done you can go about removing the solder with your desoldering braid or pump.

The Modifications:


All part numbers refer to the schematic above (part numbers are printed on the PCB).


It should be noted all resistors part of the mod are metal film and all capacitors used for the mod are poly film (any film cap is fine though really).

C4, C6, C13, C14, C17: 1µF (tantalum)
C1, C2, C10, C16: 0.1µF
C9: 0.047µF
R5: 1.2KΩ
D2, D3, D6: 1N34A

IC1, IC2:
To really lower noise the cheap stock op-amps have to go. I replace both IC1 and IC2 SIP op-amps with two stacked DIP sockets. If To do this you will need to make a little conversion board. You can buy fancy little PCBs from Monte Allums which makes things super easy. In my mod I like to use a RC4558P and a Burr-Brown OPA2134PA op-amp for IC1 and IC2 respectively. This really increases the clarity and brings the noise level way down.

R36: 3KΩ (current limiting resistor for LED)
Replace stock LED with a water clear high brightness 5mm LED.

To further reduce noise all the cheap 1/8W carbon film resistors in the signal chain could be replaced with metal film resistors. This would help bring down the noise a bit more and you might notice a slight increase in clarity along with treble response. A long process but it can be worth it.


Was the modification worth doing? I’d say so; the pedal is now defiantly playable and sounds pretty damn fine in my opinion. It is not a super over the top compressor but it has a solid tone. I found the pedal to be one of those pedals where you love your tone when the pedal is on but the pedal is very subtle. It’s not till you turn it off do you realize how good it sounds.

The clarity and note separation has increased dramatically. Things are not dark and bland anymore. The tone has more “life” with tighter, rounder bass and more highs. Though I still don’t like compressors for rhythm playing the CS-3 does sound decent with chords now. With the increase in clarity you can hear individual strings and it’s not one big mushy mess when you’re playing. Dynamics have also seemed to improve, the pedal responds nicely to one’s playing and it just feels a bit more interactive.

Best of all the noise has gone down. No longer does this pedal sound swarm of one thousand angry bees. There is hardly any noise at all; the noise level is the same as a low gain OD pedal I would say. Much better than stock where if you took a break from playing the noise overwhelmed you.

{ 6 comments… read them below or add one }

Yacob July 12, 2015 at 14 h 32 min

Hi there.. Just curious.. What is the value of c13 ? 1uf or 0.047 uf


cmoir July 14, 2015 at 3 h 35 min

It should be 1uF


yacob July 13, 2015 at 8 h 38 min

hi there.. i’m very interested to mod my cs-3 with your mod..
but i think C13 had a duplicate value..
wich one is the right value?

thank you
best regards


Bob Rainey May 8, 2016 at 21 h 20 min

This is an outstanding mod. I’m 72, and I was ready to dump my CS-3 for a new pedal, but I ran across the Fromel kit and it saved a pedal. The LED is optional, but I came to appreciate it because I can now see the danged thing on-stage, which I couldn’t before. I just avoided using the original before the upgrade. I heartily thank whoever thought of this mod and put it on the market.


Erry October 20, 2016 at 15 h 26 min

Hi, i just curious, what is the function of D4 and D5. I disconnected both D4 and D5 from the ground, now my cs3 has less compression than before, more acceptable compression to my ear. Both attack and sustain knobs are still functioning,


Max February 28, 2017 at 21 h 12 min

Hello !

First of all, nice work with that mod! I had no problem changing the components and it really does bring the noise down a lot!

I have just a little question, now when I plug my CS3 it is always on. I checked the switch, and no wire has been cut or anything so is that a normal behaviour after the mod?

Thank you for your awesome work!



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