Can I use a 100k pot instead of a 250k for this?

[vanessa]

I've been meaning to build the crossover distortion section of the T.M.K. and tag it on to the end of a fuzz pedal. I have some 100k pots but the circuit calls for 250k. Would it still work with a 100k or am I missing something here? Does it matter that it's not being tagged on to a opamp circuit?

[markusw]

I suppose if you increase the 1µ input cap to 2,2µ it should be about the same frequency response. Don't know though how the lower input impedance will change the sound.

Regards,

Markus

[slacker]

I tried tagging that on to the end of a circuit and a 100k pot worked but not very well. As I understand it when the pot is on minimum resistance it shorts the LEDs so you get no distortion. As you increase the resistance at some point the path through the LEDs becomes "easier" than the path through the pot  so the signal flows through the LEDs giving you the distortion.
I found that with a 100K pot I only got any distortion with the resistance on maximum. I ended up using a 1Meg pot which gave a nice range of distortion and a lot more of it at max resistance as most if not all of the signal was going through the LEDs.
By the way the octave section of that thing is great

[vanessa]

I tried tagging that on to the end of a circuit and a 100k pot worked but not very well. As I understand it when the pot is on minimum resistance it shorts the LEDs so you get no distortion. As you increase the resistance at some point the path through the LEDs becomes "easier" than the path through the pot  so the signal flows through the LEDs giving you the distortion.
I found that with a 100K pot I only got any distortion with the resistance on maximum. I ended up using a 1Meg pot which gave a nice range of distortion and a lot more of it at max resistance as most if not all of the signal was going through the LEDs.
By the way the octave section of that thing is great

Do you think it's a matter of the use of LED's. I've read that Ge diodes sound great in this, I'm wondering if a lower pot value would work just as good with those as a higher value does with LED's?

[Mark Hammer]

100k simply only provides part of the full resistance range of a 250k unit.  The "missing" part can be easily subbed by a fixed resistor.  I don't know what portion of the possible resistance range provides the most interesting changes, or how much resistane change is needed to provide suitable variation, but you can always try a 150k resistor or something similar in series with the pot and see if it puts you in a sonically more interesting zone.

[gaussmarkov]

100k simply only provides part of the full resistance range of a 250k unit.  The "missing" part can be easily subbed by a fixed resistor.

like on P2 of this schem, where a 250K pot and a 10K resistor in series make a 10K to 260K range resistance.

[vanessa]

I'm thinking if you put a resistor in series to make a pseudo 250k it would not work the way you would want it to. Since you would want a path with zero resistance in order to short the diodes and have a clean signal. If you put a resistor in series with a pot a resistance will always be there.

[Mark Hammer]

Absolutely correct.  The question, however, is whether that zone between 0 and 100k is the most interesting, or overlaps with the most interesting range of sonic adjustments as far as your concerned, or whether it sits outside of it.  If it turned out that the most intersting sounds for you came when that resistance was between, say, 83k and 190k, then a 100k pot would only get you a small part of that, and a 250k pot would have a lot of wasted rotation space.  An 82k fixed resistor in series with a 100k pot, on the other hand, would nail just about all of that range, and make every degree of pot rotation count.  If the pot value Tim recommends is 250k rather than , say 100k in series with 22k, though, then I suspect the chances are pretty good that interesting sounds can be gotten all over that range.

Nothing to stop you from dividing it up in ranges, however, and allowing a 100k pot  to make its increased specificity (where, say, 10 degrees of rotation covers less ground than it would on a 250k pot) useful.

On the other hand, when something is called "Too Many Knobs", it's not like you're hungry for an additional range switch, are you?