The Ruetz Rat
The Ruetz Rat is a simple modification to the classic ProCo Rat distortion pedal that accomplishes two things. First, it lowers the overall amount of gain in the circuit, transforming the pedal into more of an overdrive rather than a distortion pedal. Second, it flattens out the frequency response of the circuit, resulting in a smoother tone and extended (but tight) low end.
The Ruetz Rat mod is as simple and easy-to-perform as can be. Anyone can do this mod: no electronics experience, soldering, or special tools required. Following the instructions and photographs below, all you need to perform the Ruetz Rat mod is a screwdriver (to take apart your Rat) and a pair of wire cutters or fingernail clippers (to perform the mod).
Don't underestimate the power of this mod because of its ease and simplicity -- the Ruetz Rat is a HUGE improvement over the stock circuit. Dozens of happy Ruetz Rat users have emailed me over the years to tell me how thrilled they are with their "new" Rat, and how usuable it is compared to stock. Try it: you'll like it.
Ruetz Rat -- Solderless Clip Mod
Some years ago, my uncle, Ron Wayton, asked me if I could mod his Rat pedal for a smoother tone and better low-end. At the time, I was unfamiliar with the Rat circuit, but (of course!) I accepted the challenge.
After locating a schematic and checking out the circuit, the first thing I tried turned out to be all that was necessary. Here is a close-up schematic detail of the relevant portion of the circuit:
Here you can see two resistor/capacitor pairs. As part of the feedback loop, this pair helps set the gain of the op-amp stage. But also, because of R/C interaction, not only does this pair affect the gain of the circuit, but also the frequency response.
The only mod I performed was snipping one of the leads of the 47 ohm resistor, effectively cutting that R/C pair out of the circuit. This leaves the 560 ohm/4.7uf pair to set the gain and frequency response of the op-amp. Here is a photo of the guts of my uncle's pedal and the snip that I made:
There are several different versions of the standard Rat pedal -- here's an example of one with a different layout inside. I've circled the 47-ohm resistor:
Here is a photo that someone kindly emailed me of yet another version of the Rat:
Here is a photo of a very recent Rat -- notice the blue 3PDT footswitch:
Here is a very rough explanation of what this mod accomplishes. The value of the resistors sets the gain of the circuit: the lower the value of the resistor, the higher the gain. But notice that in the original circuit there are two resistors, of widely different value. This would suggest two different values of gain. But, of course, the circuit as a whole is going to exhibit only one overall gain value. This is where the caps come into play. The 2.2uf cap has a certain low-end cutoff frequency; above this frequency, the gain will be set by the 47 ohm resistor. But the 4.7uf cap will have an even lower cutoff frequency: the gain for these lower frequencies will be set by the 560 ohm resistor. But since the 560 ohm resistor is a much larger value than the 47 ohm, the gain for these lower frequencies will be much lower. The overall result is: the gain of the circuit is less for the bass response, and more for the midrange and treble response.
Cutting the 47 ohm/2.2uf pair out of the circuit means that the gain and frequency response of the circuit is determined solely by the 560 ohm/4.7uf pair. This lowers the overall gain of the circuit, but also smooths out the overall frequency respone of the circuit: the amount of gain is flat across low-end to high-end.
This simple mod suited my uncle perfectly: he loves it! Now, you might want to try this mod in the other direction: you might want to cut out the 560 ohm/4.7uf pair, for a higher overall gain and even tighter low-end. Or, install a switch to make one or both of these mods switchable for even more versatility.
Ruetz Rat -- Trim pot mod
Here is a more challenging Ruetz Rat mod, for those of you who would like more versatility. Instead of clipping out the 47-ohm gain resistor, this mod involves replacing that resistor with a 1k trim pot. I've circled the trim pot in this photo:
This time around, Ron performed the mod himself. Here is what he had to say:
The new Rat mod was a huge success. I took my time and did it right. Took me longer to get the thing apart than it did to do the mod!! Certainly now with a fourth parameter there's plenty of tweaking to be done but at first listen it was definitely worthwhile. With the pot wide open it sounds slightly hairier and warmer than with the resistor clipped. As you dial in the pot you get closer to stock Rat and can in fact REALLY hear when you get to the stock value. Almost like the pedal wakes up and is reborn to what it was (not necessarily a good thing) but just before that is the TONE!! As I said. There's plenty to learn yet. The filter control and the trim pot are highly interactive so there are lot of tones to be discovered! The best part is that the trim pot is conveniently accessible just by opening the battery compartment door!! A 500-ohm pot would have been ideal but this 1K from Radio Shack works fine.
If you're really ambitious: instead of using an internal trim pot, why not remove the "Filter" pot and replace it with a full-size 1k pot, so that the gain resistor is now externally adjustable?