Finding Potentiometers for Overdrive/Distortion Pedals?

[Steve Mavronis]

I'm working on making myself a few clones of some classic overdrive/distortion pedals like the DOD 250 Overdrive and MXR Distortion+. I know they are very close cousins to each other circuit design-wise yet have slightly different sounds. I'm starting with a DOD 250 as my first clone and want to get as close as possible to the classic grey spec version. I want to get some reverse log gain pots for building both pedals but not sure where to find to buy them? The DOD 250 uses a 500K reverse log gain pot and a regular 100K level pot. What else do I need to look for in the case of different shaft lengths/diameters, etc?

As a related side note my dad who is an electronics engineer has a bunch of parts he can get for me from his work but is having a disagreement as to why I even need a reverse log pot. I've read another thread here with a great dialog by Mark Hammer explaining how diode distortion in these circuits won't happen with regular gain pots until you dial through a substantial portion of the pots range, making you lose fine tuning control over the amount of overdrive and distortion. I will explain this to him next the best I can as the reason for needing the reverse log gain pot. He just doesn't understand that I want to make a "clone" pedal to original specs and he wants me to "re-engineer" it to make a general fuzz box or something. I tried to explain if I altered the parts called out in the original circuit design then it wouldn't be a true clone at all. I just think my dad's adversion to rock n' roll distortion use in general is part of the problem. I told him if I wanted to preserve a clean input signal without distorting it's output, I'd be playing acoustic folk music, LOL.

These first few clone pedals will be my study benchmarks towards making my own original pedals with any modifications and new ideas that I hope to come up with as I learn the subtle nuances that affect different sound effect results.

[caspercody]

I have gotten couple of reverse pots from Mouser.com. I think I have gotten 50k, 100k, and 500k. I do not have my packing slips here at work, but if you do need the part numbers I can look thru my packing slips later on?

[Steve Mavronis]

I have gotten couple of reverse pots from Mouser.com. I think I have gotten 50k, 100k, and 500k. I do not have my packing slips here at work, but if you do need the part numbers I can look thru my packing slips later on?

Yes that would be helpful, when you have the time - no rush.

Thanks...

[chi_boy]

I think Mouser has the reverse pots on the same page as the regular Alpha 16mm pots.

As for dad, just agree with him. But convince him that it it important to duplicate the original design to study it and THEN modify. You could also use a socket for the pot so you can A/B more easily. Then let him listen and help decide what really works better. Who knows, you may both learn something.

[rustypinto]

Mouser catalog page for 16mm pots:

http://www.mouser.com/catalog/catalogUSD/640/692.pdf

Note the reverse log selection is only available with PCB mount terminals.

Reverse log pots give you a slower change for the upper bound (in this case) of the gain. If you used a normal logarithmic taper, you get a much faster change when you approach the last 25% of a clockwise rotation (clockwise being the accepted convention for an increase of something). Reverse log is also used for rate controls, eg. tremolo, phase, etc. where you get a slower, more usable response over the faster rates, and a faster response of slower rates. With LFOs, the topology is sometimes dependent on the pot taper.

[Mark Hammer]

You can also get reverse log at Small Bear, which carries them expressly for projects like the one you are working on.

And Steve, I'm not trying to get you to "re-engineer" it.  The basic fact is that the original was produced during a period when pedalboards were small (2-3 pedals) and people wanted the pedal to do a couple of different things for them, one of which required being able to dial in low gain, and the other of which required being able to dial in much higher gain. These days, most people will only use the pedal for the latter, rather than the former, and simply supplement their pedalboard with a "clean" booster if they want a volume boost.  So why drive yourself nuts over the aspect you'll be seldom inclined to use?  That's all.  Realistically, all the things people want from a Dist+ or DOD250 these days (more than 3 decades after they were introduced) can be achieved with a plain vanilla 100k gain pot.

If making an exact replica is that important to you, then certainly go ahead and score yourself reverse-log pots.  While you're at it, use tantalum caps instead of electrolytic (MXR used them because they could be easily laid flat), and hunt around for 1N270 diodes (much harder to find than comparable 1N60 or 1N34A).  From where I stand, though, it's a bit like trying to replicate a sandwich that used 12-grain bread, and all you can find in town is 7-grain.  Is it an exact copy?  No, but it IS multi-grain bread, and that captures the essence.  Can you tell that the spelt or millet is missing from the bread, while you pick the flax seeds, crushed oats and cracked wheat berries from your teeth?  Not really.  Does it do the best part of what the original did?  Certainly.

I admire your industrious spirit, and enthusiasm for a newfound hobby.  Kudos.  Just be sure to spend it on the things that matter, and don't squander it on the things that don't.

[Steve Mavronis]

Thanks Mark, and the others who have chimed in to help me. I'm finding the DIY community (on this forum especially) is a great resource for people of all skill levels and experience. Yes, my goal is to try to build several classic pedals to spec to make it as authentic as possible to start a collection, and later I'll experient and make something new from scratch too. I'm an obsessed detail nut anyways so going for the easy or convienent route drives me nuts because I tell myself that's not how it could have been. Maybe others out there are like that too. This smallest details are given lots of thought, maybe too much. For example today I'm ready to order an enclosure or two and can't decide if they should be bare aluminum (Hammond 1590B) or pre-painted (Hammond 1590BLK) or one of each. I start second guessing myself right in the middle of the checkout screens! Isn't that goofy or what?