The 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 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)
The mod you’ve told is similar like Dano’s (Beavis Audio Reseach) Lube mod.
Thanx anyway…
PS: Sorry for my bad English
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.
>>>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
FWIW, I have some pics of a RAT 2 board at my website:
http://www.bwanasonic.com/html/sights_rat2_01.html
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.
this mod also works on the you dirty rat!!!
just tried it it really opened up the tone:)
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!
I prefer to disconnect the low frequency leg, or add the 4.7uf cap to the 2.2uf cap for a mega rat.
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.
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
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?