Choosing a Pot Value

[bkanber]

I was wondering.. what exactly determines what value potentiometer should be used, for say, a level control at the very end of a circuit? Pretty much all level controls are the same--lug 3 to signal, 2 to output, 1 to ground-- so why choose 100K over 50K over 500K? Is there something about the specific circuit that dictates what the pot value should be? If so, what? And what are the possible effects of using a different pot value (ie, the schem says 500K, I use 100K) instead?

Thanks!
  Burak

[petemoore]

 Resistance of the wafer...
  Say 100k is used..
  You have a resistance to ground [with potential to load the signal] with the volume ATW CW [all the way up].
  When less than full 'on', resistance is introduced or 'spliced' in the signal path.
  If pots were perfect they would be voltage dividers and nothing else, because they use resistances between 'above' [signal path] and 'below' [ground] and output in the middle...
  500k turned down to half ... that's 250k resistor the signal has to pass through, certainly enough to rolloff high frequencies noticably in many cases. [a treatment for that is use a small value bypass cap across the signal lugs].
  500k turned up most all the way makes for a big resistor between signal path and ground...less signal loading.
  Sometimes 10k might be good for impedance reasons, of course you'll need something that can drive the larger load the small resistance to ground creates.

[kvb]

I'll tell you what I know from bread boarding. A higher value pot is going to send a bit more signal along to whatever is next. It is also like in guitars, in general, a higher value pot is going to sound brighter. A value that is too high could cause problems for the input of the next effect.

In a booster, or a sufficiently loud circuit, a 100K or even a 50K is a high enough value to keep from loosing too much signal to ground.

Also, the pot is functioning as a voltage divider. If you used a high value pot say 250K, then when you start turning it down the signal has to go through some resistance to get out. A 250k pot at halfway has the signal going through 125k and still has 125k between the signal and ground.  This situation would tend to kill more of your high frequencies than a 100K pot turned down halfway (through 50k to 50k from ground)


Me and Pete were typing at the same time - and since we said almost exactly the same thing, I'm leaving my post as is (besides this comment)
And, Thanks for teaching me something Y'all!