ProCo Rat

ProCo Rat

Project description

One of the classic distortion boxes found in the Distortion Hall-of-Fame! Raw, fuzzy distortion and lots of volume can be pushed out of this sucker!

Verification status

Built it; sounds like a Rat ;)


There are lots of schematics out there to build the Rat. Som of them excellent, some really bad. I've chosen this schematic as it seemed 100% (vintage) correct.


I based this layout on this one found on the website of Aron Nelson and modified it to fit nicely in a B enclosure.


Ruetz mod: just remove R8 and/or C4, or replace R8 with a 1K pot.
Booster: remove the clipping diodes D2 & D3.
You can also experiment with different kind of clipping diodes like symmetric/asymmetric setups, LED's, Germanium diodes, etc.

Bill of materials

R1: 47R
R2: 100K
R3: 100K
R4: 1M
R5: 1M
R6: 1K
R7: 560R
R8: 47R
R9: 1K
R10: 1.5K
R11: 1M
R12: 10K
R20: 100K Log (A)
R21: 100K Log (A)
R22: 100K Log (A)
C2: 22nF
C5: 1nF
C6: 30pF
C7: 100pF
C9: 3.3nF
C10: 22nF
C11: 1μF
C13: 10nF
C1: 1μF
C3: 4.7μF
C4: 2.2μF
C8: 4.7μF
C12: 100μF
IC1: LM308
D1: 1N4002
D2: 1N914
D3: 1N914
Q1: 2N5458
6 jumper wires
17 trace cuts


Click here to see the bill-of-materials as a list or download it as a comma separated values file (.csv).


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I all,

Can anyone confirm if it is working?

Rat Problem

Finished my build but cant figure out the problem. All that's heard is ticking (motorboating). The filter and volume seem to be working, but no audio signal coming through. Any ideas will be greatly appreciated.

Not working?

I've got it all rigged up but R1 has turned into a burner...I'm not quite sure what the problem is? no noise, just a burning resistor. any idea why that might be? where i should i start debugging?


R1 's sole purpose is to burn up if there's a short circuit. If you measure between GND and +9v you'll get a very low resistance, which indicates a short circuit.

Check all components and tracecuts and scrape all tracks between the traces clean with the tip of a knife. If you can't pass through it easily with your knife, you should clean up the soldering.

Also check if the effect doesn't touch the enclosure!

8.2k Resistance across the

8.2k Resistance across the ground and positive power. Still a bit confused as to what i'v got wrong? Rechecked positioning to all components and trace cuts. Still have not a clue what i'v done wrong ha! I'll have to keep looking.


Built it and it works fine.


All 100k pots are equal, but the taper (lineair/logarithmic/etc) and/or durability may vary.


Im kinda new all to this so i have a question( may be stupid), but does 4mm Mono 100k pots work? :D

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