how to make a big pot act like a little one?

[marrstians]

what do you do when a schem says 100k pots but all you have are 250k ect... is it ok to put a resistor across the two outside lugs and it will act like a lower value pot? is there some kindof rule?

[Peter Snowberg]

It really depends on the circuit so there are no real hard rules. If the pot is a simple voltage divider, you may be able to just substitute without any other changes. If the impedance of the next circuit stage is high enough, you might be able to get away with just placing a single resistor across the pot (In your case try something like 220K). If the circuit relies on end to end resistance as well as proportional resistance, you may be able to add two resistors to obtain the desired effect; one end to end, and one end to wiper. You might also have to add three resistors to "normalize" the odd taper that will result from using two resistors.

This thread shows how to make a 100K act like a 25K:
http://www.diystompboxes.com/sboxforum/viewtopic.php?t=19846

To cut the pot value in half and keep the taper fairly linear try this:

Code Select Expand

1            2            3

|  Rpot*2.9  |  Rpot*2.9  |
+--/\/\/\/\--+--/\/\/\/\--+
|            |            |
|           \|/           |
+--------\/\/\/\/\--------+
|           Rpot          |
|                         |
+--------\/\/\/\/\--------+
         Rpot*1.5


This stuff applies to linear pots ONLY. If you want to fiddle with a log pot, you're on your own.

Take care,
-Peter