Build Your Own Clone Message Board

I was wondering what's the general rule of thumb when replacing resistors with pots in circuits like the fuzz face. What's the relationship between the resistor rating and the pot rating? Which pot terminals are used when doing this? I asked the same question under the "super tricked out fuzz" topic but kind of got lost in the shuffle...I'd really like to see how the various resistor values affects the tone and response.

--Brad

It's one to one. So a 500k linear taper pot will be able to go from almost 0 ohms to 500k ohms. I try and get a pot that's as close as possile, but rated more than, the resistor I'm replacing. But if you want to experiment with a wide range of resistances use a larger value and tweak away.

Use the center lug (2) as your variable resistance output and either of the other two (3 or 1) should work fine for the input. I like linear pots (type "B" B100k for instance) for replacing resistors. Use a DVM to measure the resistance as you adjust the pot and then you'll know exactly which resistor value hits the sweet spot for that pedal. Then remove the pot and add that value of resistor in it's place and you done. Lots of pedal builders use pots to tweak designs to find the optimal resistor values for a given circuit.

So what happens with the used lug?

If you meant un-used lug then, nothing . It's not used. You could bend it up and solder it to the pot casing like on a guitar to ground it but I don't know if that's required. I never do it that way.

I'll bet that works for the un-used lug too.

is there any difference between a trim pot and the potentiometers that are used as the knobs for the pedals? could i switch out a trim pot for a larger potentiometer and just not turn it up all the way?

Awesome!

Thanks baj2k! I wanted to do some transistor tuning in rangemester circuit. Also was planning on looking for a control for that "gated" fuzz sound in a fuzz face.

--Brad

No, trim pots are just variable resistors too. You can remove a trim pot and wire in a regular pot in it's place. I do it all the time. Check the Mod's section of the forum. There's a Beavis Audio post there diagramming how, amoung other things, to remove a trim pot and use a regular pot. Here's a link, click on it and then scroll down and find the Beavis mods post.

Big list of verified mods

just a quick note:

some times (most times) when you are replacing a resistor with a pot, you don't really want the resistance to drop all the way to zero, so you can add a resistor in series with the pot.

for example, lets say you had a resistor that was like 100k and you wanted to replace it with a pot. in most applications you wouldn't want to directly replace it with a 100k pot. instead, you may consider replacing the 100k resistor with a smaller value resistor, say 47k, and using a 100k pot after that. this way you could get values that fell withing +/- 50k of the original value.

I agree with "dawg" about using the resistor with a pot if you plan you use the pot in place of a trimpot or resistor but what do you do when you don't know what resistor value to use and you don't want a pot there permanetly? Say in the case of the MK2 deciding between the 100k or 47k resistor.

What I'm making now from an old MXR style box where a paint job went horribly bad, is a variable resistance machine by connecting a B1000k, a B100k, and B1k pots in series. This way I can have from 0 to 1101k to play with. You can also think of them as course, medium and fine adjustments too. Say if you wanted to get a 575k resistance get 500k from the B1M pot, and ~75k from the B100k pot, and then dial in the last bit on the B1k to hit 575k exactly. The B1k is also required to get to values under 1k. That's why I chose a 1k instead of a 5k for sub 1k adjustment granularity.

Now add two female banana input plugs to the box so I could attach two male banana plugs from a DVM to it to measure the resistance at the PCB. Then there are two wires that come out another hole that you attach to PCB with a bit of electrical tape to where the resistor is question goes and you can adjust the resistance on the fly while playing. Now you can test virtually any number of values up to 1101k to find your sweet spot then you know exactly what resistor to use.

Yes, somewhat limited usefulness. Yes, you can do this with a breadboard... Have I tried it yet? Nope. Building it right now. I have the old box, some $2 pots and some time to kill so I'll make it to go with my "Mr. Keen" transistor tester.

Here's a diagram of the variable resistance machine.