[159] Quick Rat pedal mod

Date: September 14th, 2008 | Comments : [18] | Categories: amps, DIY, power.

Rat2 schematicThe Proco Rat has become a classic pedal that has a legion of fans among guitar players. I have 3 of them, two Rat2 and a Turbo Rat.

The Rat is designed to have a large amount of gain and a significant treble boost. This is part of what gives it a characteristic sound, but also makes some players dislike the tone it produces.

The resistors R6 and R7 along with the capacitors C7 and C6, are the main determining factors for the low frequency rolloff.

The C7/R6 pair has a frequency corner of 1540 Hz., meaning that all signals below that point are filtered out.

The C6/R7 pair has a 60.5Hz cutoff.

We can see that the first easy mod is to remove C7, which will leave only the C6/R7 network determining the frequency response and gain. R6 is not in the circuit once C7 has been removed.

The capacitor is easy to find. Locate pin 2 of the opamp and follow the trace to the 47 ohm resistor. It will have bands of yellow-purple-black.  The 2.2uF will connect to it. Desolder the connections and remove the capacitor.  You could also remove the resistor.

Gain is now lower and the frequency response is flat across the band of guitar frequencies. This will give it a tone with much less treble boost, and somewhat like a Big Muff.

If the Rat has now lost too much bite for your rig with this mod, then it can be fine tuned by changing the value of C6. Remove the 4.7uF (C6) and replace it with a 0.47uF capacitor rated for 25v minimum (50v, 63v or any higher rating is acceptable too). This will give it a low pass corner of about 600Hz.

Make C6 smaller to roll off more bass – 0.22uF will have a 1292Hz corner. Use the AMZ Filter Calculator to work out a combination that you like.

Customize your Rat pedal for the best sound with your guitar and amp!

More custom mods for the Rat are available in the AMZ Muff-Rat eBook.

Update: You can apply these mods to the BYOC Mouse kit. Here is the parts cross reference:

  • RAT : BYOC
  • R7 = R4
  • R6 = R5
  • C6 = C5
  • C7 = C6 (remove this one)

18 Responses to “Quick Rat pedal mod”

[523] Yunus Emre TOKMAK Says: 8:20 am, September 15th, 2008

The mod you’ve told is similar like Dano’s (Beavis Audio Reseach) Lube mod.

Thanx anyway…

PS: Sorry for my bad English

[524] Kerry Maxwell Says: 8:39 am, September 15th, 2008

Looks like I’ll have to crack open my beloved RAT2 for another round of tinkering. I have a cap across the volume pot to trim the *hair* off the treble. This gives a more usable range to the filter knob. I also added a third clipping diode for asymmetric clipping, and replaced a 1 uf electrolytic or two with non-polar films. Now I may want to put C7 on a switch.

[525] admin Says: 3:35 pm, September 15th, 2008

>>>The mod you’ve told is similar like Dano’s (Beavis Audio Reseach) Lube mod.<<< Excellent, Dano is a good guy and we obviously think alike. I've been recommending this mod for years on the pedal forums, but the C6 mod is really what makes it stand out. I find the best sound is had by removing C7 and changing C6 to 0.47uF regards, Jack

[526] Kerry Maxwell Says: 6:58 pm, September 15th, 2008

FWIW, I have some pics of a RAT 2 board at my website:


When I get a chance maybe I’ll hilite some *modspots* on those pics. Right now I’m trying to work out the best way to implement these C6 / C7 mods via switching, as I really like the my Rat sounds right now.

[528] jonb Says: 9:40 pm, September 18th, 2008

this mod also works on the you dirty rat!!!
just tried it it really opened up the tone:)

[529] dano Says: 10:04 am, September 22nd, 2008

The Lube mod on my site is not novel, it originally came from the ruetz mod (google it) so I can’t claim credit.

Jack’s ideas will offer you a quite a bit more control because of the changes in cap values whereas the ruetz mod just makes a single resistor into a pot.

happy Monday!

[536] wgtp Says: 10:35 am, October 1st, 2008

I prefer to disconnect the low frequency leg, or add the 4.7uf cap to the 2.2uf cap for a mega rat.

[593] Erik Says: 11:55 pm, January 6th, 2009

This is a great mod. After reading over it a couple times, I decided to crack open my Rat II and do the deed. I just clipped the side of the 47 ohm resistor facing the op-amp but I will most likely desolder the rest of it and remove the 2.2uf cap as well. I didn’t mess with C6 yet but I’ll know if I’ll need to after a couple gigs this coming weekend. Thanks again, Jack. Your site is one I frequent when it comes to things DIY.

[600] Pekka Says: 5:00 am, January 17th, 2009

I did something similar couple of years ago. I also got the idea from the Ruetz rat. More here: http://kotipolttoinen.com/wanha/sisalto/kitara/rat_mod/index.php

[776] samsara Says: 10:05 am, August 21st, 2009

I want to add more bass to my Vintage Rat (witouth the losing-gain deal). Also have a Dirty Rat but I can’t use it because its noisy as hell. Even with the guitar volume rolled off. Could you help me, please?

[1544] jbmannon Says: 6:47 pm, November 22nd, 2010

I tried the ruetz mod it sucked tried with the c6 .47uf capacitor and it sucked.The only way it sounded decent is when it was maxed controls out out.
Settled for a switch with led clipping one side and stock clipping the other side.
If you want the ruetz mod just turn the gain down and the volume up it sounds better than the mod an does not lower thge value of the pedal. IMO leave it alone and adjust your pedal and amp to compensate.The clipping mod is the only one i would suggest.

[1980] LC Says: 4:46 pm, December 18th, 2010

I wonder what “sucked” means specifically. Anyway, what was the purpose of having two high pass filters on that part of the original circuit?

[2104] jim Says: 11:57 am, March 18th, 2011

Instead of seeing two seperate high pass filters could you not look at the filter frequency as the parallel of the two resistors, 43 ohms combined with the total of the capacitance, 6.9 micro farads, giving a corner freq of 536 Hz?

[2171] GGBB Says: 8:43 am, April 18th, 2011

I am curious about LC and jim’s questions also. I would think that it’s not quite as simple as the parallel/series values of the components, but I don’t really know. I think that the two resistor’s first act as a voltage divider, and the capacitor’s then determine what frequencies are filtered out according to the output levels of the voltage divider. And since there is a different cutoff frequency for each path to ground, the slope of the filter is greater where both paths to ground apply (below 60.5Hz). So there would be two knees on the frequency response curve as opposed to just one.

[2212] wackie Says: 8:03 am, May 26th, 2011

correct me if i’m wrong here. but if the resistor comes first and the cap comes second, doesn’t that make it a low pass filter and not a high pass filter?…….really new at this and trying to learn. thanx.

[2213] wackie Says: 11:09 am, May 29th, 2011

I’m trying to ‘tighten up’ the pick attack ‘low end’ of my turbo rat with no luck. i’ve reduced the r/c in the feedback loop to one set and tried a 100 ohm / .22 uf polyfilm corner fre. of 7,238hz but the lowed now crackles. should i put the r/c back to original and try messing with cap/resistor values before the op amp? or should i try a .22uf metal film cap instead?

[3017] jbmannon Says: 9:20 pm, July 21st, 2012

I replaced the .0033 tone/filter capcitor with a .0047
Then replaced the .022 capacitor that was right next to it to a .047

I really don’t know exactly what i did but it increased the bass response and made filter control more useable.
The pedal is incredible!!! It sounds and does exactly what i want it to do.Everything else is stock rat. I am like everyone else in search of the tone just thoght i would share my success with this pedal. Try it you will love it.I HAVE BOTTOM END NOW THAT THE PEDAL WAS MISSING!! ps i STILL HATE THE RUETZ MOD YES IT STILL SUCKS ASS!!!

[3935] kace Says: 11:14 pm, July 17th, 2013

Yup, had the same problem, with ruetz mod it’s just mild overdrive, maybe good for cleans, but it doesnt work as a boost well, not enough bite/cut – setting gain to almost 0 sounds better to me.


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