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proco rat mods for bass

Discussion in 'Effects [BG]' started by mw, Sep 18, 2003.


  1. mw

    mw

    Jul 24, 2000
    Cali
    hello everyone.
    has anyone out there modded a proco rat to have more bass frequencies? my vintage rat sounds good, but it does lack some of the lows...

    i searched for this, but i mostly found references to paying someone else to do it and not a do it yourself modification...

    so... any info on how to mod this series of pedals (especially the vintage rat) would be helpful.

    thanks!
     
  2. 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
     
  3. tplyons

    tplyons

    Apr 6, 2003
    Madison, NJ
    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.
     
  4. Interesting, could I get this done by any guitartech/repairman?
     
  5. tplyons

    tplyons

    Apr 6, 2003
    Madison, NJ
    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.
     
  6. 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).
     
  7. slinkp

    slinkp

    Aug 29, 2003
    brooklyn, NY, USA
    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.
     
  8. slinkp

    slinkp

    Aug 29, 2003
    brooklyn, NY, USA
    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).
     
  9. mw

    mw

    Jul 24, 2000
    Cali
    wow, thanks for the specifics on the mod. that cutting of a trace kinda scares me tho... i'm gonna have to seriously think about this before cutting into the rat...
     
  10. slinkp

    slinkp

    Aug 29, 2003
    brooklyn, NY, USA
    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 :)
     
  11. 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
     
  12. Nice information, thanks guys.

    Gives me something to try out one evening! I'll let you know the results.
     
  13. 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.)


    [​IMG]
     
  14. 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).
     
  15. 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.
     
  16. slinkp

    slinkp

    Aug 29, 2003
    brooklyn, NY, USA
    wow,i didn't even know about the juggernaut! I might have to check that one out.
     
  17. slinkp

    slinkp

    Aug 29, 2003
    brooklyn, NY, USA
    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...
    http://www.robertkeeley.com/product.php?id=14