proco rat mods for bass

I believe it is as simple as removing a single cap (or resistor??) in the signal chain whose purspose may be to filter out the lows so that the distortion won't get "muddy. A techie pal o' mine said that he could even a a "blend" knob to my old RAT II. Of course...the Juggernaut has all that

If the box has a small value input or output capacitor like .01uF, you can change the capacitor to a larger value such as .1uF and this will feed the unit more bass. If you change the input capacitor to a larger value, you will put more bass into the distortion circuit. If you change the output capacitor to a larger value, you will output more bass after the distortion.

Try a .1uF or .22uF and maybe a .47uF for increased bass response.

Originally posted by tplyons
If the box has a small value input or output capacitor like .01uF, you can change the capacitor to a larger value such as .1uF and this will feed the unit more bass. If you change the input capacitor to a larger value, you will put more bass into the distortion circuit. If you change the output capacitor to a larger value, you will output more bass after the distortion.

Try a .1uF or .22uF and maybe a .47uF for increased bass response.

Click to expand...

Interesting, could I get this done by any guitartech/repairman?

I don't see why not. It's personally something I'd do myself. A $5 trip to Radio Shack will bring you home all the parts you need.

I tried swapping out the input cap on my Rat2, but it never seemed to make much difference.

I ended up wiring an extra cap in with a switch as a treble cut when I wanted ultra-scooped-fuzz without the nasty feedback the Rat always gives me...problem was that I got it wrong somewhere and the cut works with the pedal on or off (well, good for an overall cut for smoother numbers I guess).

I modified a RAT once. My simple mod gives subjectively a bit more bass while scooping out some of the low-mid; turning the filter knob to the left lets in the upper mids and treble while leaving the lower mids scooped. It sounded pretty good, and could probably be improved with some more fiddling.

I could only find some of my old notes, so I dug out the original schematic and my modded box and the one page of notes I could find.

As others suggested, I thought of upping the value of the output capacitor (C12 which is 1 uF) but on closer examination it should be flat above about 30 Hz so I left it alone.

Then, through some torturous mental process that I can't now recreate, I figured out the following mod.

Beware that my mod requires breaking two connections on the original circuit board. I make no guarantees whatsoever. If you don't already know how to do this and how to get things working like normal if you later change your mend... then you should NOT attempt to do this mod. YOU HAVE BEEN WARNED! Read the whole mod description before making up your mind.

1. Replace C9 (0.033 uF) with a 0.022 uF capacitor.

2. Replace R9 (1.6k) with a 10k resistor.

3. Break the connection between C9 and C10.

4. Connect the now-disconnected ends of C9 and C10 with a 10K resistor.
I call this R12 since there are already 11 resistors in the circuit.

5. Break the connection between pin 1 of the Filter pot and D1,D2.

6. Solder a 0.01 uF capacitor between pin 1 of the Filter pot and D1, D2. I call this new capacitor C13.

That's it!

You can adjust the tone by playing with the values of R9, R12, and C9 and C13.
Unfortunately I'm not really sure what effect will result from what values.

I *think* what happens is this: the larger value of R9 means you can tune the filter lower, for more apparent bass. Meanwhile, adding C13 means that some treble and upper mids get through the circuit even when you're cutting some treble. So you end up cutting more lower mids than treble. However, turning the filter all the way still results in a heavy treble cut and leaves nothing but bass. I can't remember how R12 plays into this, but I remember that it was very important for some mysterious reason.

AARGH, sorry, I got the schematic & description wrong.
C13 was in the wrong place, which means that steps 5 and 6 of my directions were wrong.

Here's the correct version. Notice that C13 is really between the filter pot and R9.

So the complete, correct instructions are:

1. Replace C9 (0.033 uF) with a 0.022 uF capacitor.

2. Replace R9 (1.6k) with a 10k resistor.

3. Break the connection between C9 and C10.

4. Connect the now-disconnected ends of C9 and C10 with a 10K resistor.
I call this R12 since there are already 11 resistors in the circuit.

5. Break the connection between pin 3 of the Filter pot and R9.

6. Solder a 0.01 uF capacitor between pin 3 of the Filter pot and R9. I call this new capacitor C13.

---

Also, I don't know where the complete schematic I have came from originally. The part numbering is based on that schematic, and may not match other versions of the rat schematic. The relevant part of the circuit is easy to find - it's all right around the connections to the filter pot. There are numerous links to RAT schematics online, most of them dead... but here's one:
http://www.montagar.com/~patj/pcratb.gif

My rat is apparently the "B" version (earlier versions had another transistor before the IC).

the one I used was the basic RAT circuit from around 1990, It's not the "old" rat (different shaped box, two transistors instead of one), nor is it the "turbo" model.
But I have it in a crappy Radio Shack aluminum box because this one was actually made from a salvaged circuit board that a friendly guy on the net mailed to me many years ago. So I wasn't too worried about ruining anything

That tone mod looks cool.

I'd also be tempted to try a few different things, like...

Changing the value of those caps around the opamp... the 100pF cap in the feedback loop of the opamp... the 30pF between pin1 and pin8... the 0.001uf that goes from pin2 to ground.

Changing the value of the 0.022uF cap just before the output tranny.

Trying some different clipping diodes, like maybe LEDs or Ge or a combination.

~ Charlie

Nice information, thanks guys.

Gives me something to try out one evening! I'll let you know the results.

Originally posted by nil
I wanted ultra-scooped-fuzz without the nasty feedback the Rat always gives me

Click to expand...

Funny...I had always found that to be one of the RAT's sweetest of features. I loved the "violin" like quality of that sustain...very controllable (for me) and a wonderful tool. Dudes like Sonny Sharrock utilized that quirk to great extent.
I fired this jpeg of to the head of ProCo as a lark and the fellah politely mailed back a compliment and the first news of the Juggernaut; the box I will eventually score rather than goring my RAT (not that their is anything wrong with that.)


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I was a bit disappointed with the Juggernaut when I saw it (haven't tried one though) - looked like they had simply added a blend control and fixed the frequencies (for bass). I would've expected a more "marketable" (ie competing against the Sansamps, MXRs et al) pedal that had that extra wow!

While I like the rawk the Rat gives, I tend to play at a fairly high stage volume (plus the noisy Ric pickups) which can induce feedback if i'm not too careful (also makes purposely-induced feedback to be a little uncontrollable).

Finding a grind-box that gives up a controllable feedback tone is a very unique and personal quest. The RAT always worked best for me.
I only wanted a RAT with a blend so maybe the Juggernaut will do me..or no. Sure liked that Sparkle Drive I tried...wow.

wow,i didn't even know about the juggernaut! I might have to check that one out.

I forgot about this thread. A while after this discussion, I got an R. Keeley-modified Rat. This might be worth a look for Rat fans; it has noticeably more lows than the stock Rat, but still has the distinctive Rat tone.

I found that I ended up fighting its aggressive mids too much, and I exchanged it for the Keeley-modified Blues Driver.
(Very quick responses and no hassle at all, Keeley is one guy with impeccable customer service.)
The modded BD-2 gets the frequency response just about perfect for me, although the hard-to-describe "texture" of the distortion is not as nice to my ears as the Rat. The quest for the perfect bass overdrive is probably not over for me, but I've found a comfy place to stop for a while.

here's Keeley's BD-2 page...
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