Can someone help me with mods for a tonepad Ampeg Scrambler?

[monkeyxx]

I built this scrambler and it sounds great, I just think it could use a little more control.  I'm sort of just now getting a little more into actual circuit function topology

I want to add a "pre gain" control a la Fulltone's 69, or Devi Ever's various "controls" or "pregains", or Throbak's "pre-gain" switch, I find this pedal is too sensitive or not sensitive enough for some guitars with various output strength, since the scrambly effect varies based on this, and to my ears has definite "sweet spots".  Which resistor in the schematic would be most ideal to replace with a pot or switch to accomplish this?

if it's after Q1, what is the function of Q1 in this circuit?  I think I see the wet/dry path branching off after Q1

here's the tonepad schematic: http://www.tonepad.com/getFileInfo.asp?id=31

of secondary importance, I was thinking about adding an overall output level control.  You think I could just glom on a one transistor booster circuit, or the output section from a big muff or something on perfboard?  I wonder what the most elegant way to accomplish this would be.

lastly, both my pots gave me a hell of a time with this circuit until I found the solution to the "not working" behaviour was to wedge some guitar picks under the terminals of both pots to put constant pressure on them.  Is that just a sign of bad pots and I should replace them both?  I've never run into this one in any of my other builds.  maybe I overheated them or something?


this is my first post and I'm so excited to be a member of this forum!  there's going to be a lot of DIY stompboxes in my near future.  Thanks!

[Skruffyhound]

Can't help with your other questions since I am too lazy/busy to check out the schem (although I would guess a small pot to ground right after the input resistor/cap would do the trick for pickup sens, and an lbp-1 booster before the output would give you more gain for your volume control) but I would think the bad pots are more likely a bad solder joint since I've never met a bad pot and never seen one fried with heat.
       Anyways welcome to the addiction and good luck.
              -Aston

[Derringer]

Hello! And welcome to the board!

regarding boosting the output, I tried 3 different scenarios.

I tired a FET boost (uses 1 less resistor than a BJT stage like the LPB) after the blend pot. It boosted the output signal but it did something funny to the clean blend in the output signal. It seemed to boost the clean proportionally more than it did the octave up signal and I could not remedy the sound with the blend control. The clean sound mixed in was just "blatty" sounding to me and I did not like it at all.

So then I tried a boost before Q1, so that the input signal would be boosted. I did not like this result either. The outcoming signal did not really change much in volume, only more compressed and distorted.

The 3rd scenario is the one I stuck with. I boosted the output of the octave up signal only, right before the blend pot. This setup gave me the volume increase that I wanted and left the clean signal sounding the way I think it should sound.

I used the same PCB layout that you used from tonepad.
Did you spot that capacitor C3 is oriented the wrong way on tonepad's pcb layout? Make sure you have the positive end facing the trace that leads to Q1's emitter.