DIY MPC's: Eliminating pots and compensating for different pot values

[ElectraMPC]

For those of you who are unfamiliar with Electra MPC's (which I will assume is pretty much everyone), they are guitars made in the 70's/80's that had terminals in the back for modules that you could buy for different effects.  For example, you could get an auto-wah module, put it in the back, flip a switch on the front and play, using a knob on the guitar to change the sensitivity.
(other examples are overdrives with a gain knobs and such)

Well that was then, this is now, and you have to shell out a pretty penny to buy a vintage module, so I was interested in making my own.  While figuring this out, I've encountered a few problems:
1) By nature of the design, only 1 pot is available, how do I eliminate pots in the design and replace them with a set resistance?
2) The pots are all 150k, how do I compensate for that if I'm using a design that specifies a different resistance?

I'm thinking of starting with the Run Off Groove Fetzer Valve to start with, so I only need 1 pot, but how would I compensate for using a 150k pot instead of a 100k, and what would the effect be in the end if I did nothing?

[Dan N]

You could mount trim pots on your board for all the stuff that needs pots and preset them to your hearts content.

I had an X-330. I seem to remember that the pickups go straight into the effect. Kind of a bad idea if you want to roll your guitar volume knob back with overdrives and fuzzes. Easy to rewire.

Lovely well made guitars!

[PharaohAmps]

I have an MPC Outlaw bass!  When I got it, I sold all my other basses ('75 Fender Precision, '79 Fender Jazz.)  It's a beast, but it has the tone.  Big ol' neck humbucker and a P-bass pickup, Rickenbacker bridge, neck-thru, the whole deal.  It currently sports a Red Llama-based CMOS fuzz module, and a Ross Compressor-based module.  Original modules were Treble / Bass Expander and Power Overdrive.

The Red Llama module has a preset 1M trimpot for gain, and the 150K pot adjusts output level.  On the Ross Comp module, gain is fixed and the onboard pot controls sustain.  I put a 220K resistor in series with the pot to make the range mroe useable.

I'd replace any useful pots with trimmers.  Fortunately the boards and edge connectors are single-sided, so it's not too hard to make PCBs to fit the MPC bays.  I made mine slightly oversize, and put small kitchen-cabinet drawer pulls on the end of the PCB opposite the edge connector to pull them out of the cavity.  My DIY modules do not have the plastic "cartridge" cases, but I did pot them with wax like the originals.

Matt Farrow

[Wild Zebra]

  Well I guess the cats out of the bag   I was experimenting with this as well, I made a post at the electra forum, but no one seemed interested.  I talked with Mark Hammer about the pot issues for a while.  I agree with trimpots.  I tried resistors in parallel also.

Kind of a bad idea if you want to roll your guitar volume knob back with overdrives and fuzzes.

This was an issue also.
  I have not messed with it for awhile but hope to get back into it soon.  I have an X-960 Ultima and its a f'n sweet guitar and a Electra Tele.
All Hail Electras!!!