Substituting pot values

[audioguy]

What would be the effect of using a different value on a pot than what is listed in the schem? For example- I have a 50k linear- what would happen if I droped it in an effect that calls for a 100k linear?


ThANKS!

Audioguy

[nosamiam]

Hey, I'm still a newbie but I think I can answer this one.

If you did the above substitution, chances are you would not get the full range of desired effect you're looking for.  For instance if the pot were wired as a volume control, you would not be able to turn the volume all the way down.  With only 50k of resistance the pot would not "resist" enough of the signal to turn it all the way down.

If you used a 200k linear pot instead of a 100k, the knob would be done with its work only halfway through its travel; turn the knob halfway and the volume would be all the way down.  Continue to turn the knob and it wouldn't have any effect.

I get the feeling that's only half the story.  I'll leave it to the experienced folks to fill in the rest (or to correct me if I'm wrong).

[audioguy]

If you did the above substitution, chances are you would not get the full range of desired effect you're looking for.  For instance if the pot were wired as a volume control, you would not be able to turn the volume all the way down.  With only 50k of resistance the pot would not "resist" enough of the signal to turn it all the way down.

Thats kinda what I thought- I just wanted some 2nd and 3rd opinions as to how retarded I am.
In many cases this is the EXACT effect I'm looking for- for example- I built the Obsidian (which I love) but the distortion control goes all the way from full on noise to silence- I should be able to hear something with the distortion turned all the way down, just less distortion. It does a fine job of turning the distortion down, but then gets to a point where it turns the volume down and out.

Anyway... Im babbling...
Thanks for the info

[sir_modulus]

Look at my new TYOS fuzz for some examples. If you increase the value of the distortion pots, you get more max distortion, but less presicion over the rest of the range. For the EQ, you don't change the pots, as that will drastically change the EQing.  For volume, Nosamiam is right, as you will make the control unlinear.

[bioroids]

Hi:

I think this is wrong:
"if the pot were wired as a volume control, you would not be able to turn the volume all the way down. With only 50k of resistance the pot would not "resist" enough of the signal to turn it all the way down."

If you have a pot for the volume control, it's usually wired as a voltage divider, so changing from 50K to 100K would still give you the same effect (0 volume when you turn it all the way down and max volume all the way up). There could be some side effects regarding loading or impedance issues but that's another matter.

In case of a "drive knob" it depends on how is it used. It could be a simple volume control before some stage, so the above still aplies.
Or it could be a series variable resistor controling, for instance, the negative feedback on an opamp (tubescreamer?). In that case, changing for a greater value pot would give you less feedback in the max position, so increasing the gain (and distortion) of the effect.

Check out the forums, there are some great posts around on this subject.

Luck

Miguel

[Kent S.]

The effect of changing the pot value depends on how the circuit is set up, yes a volume control is set up as a voltage divider, as such it depedns upon the ratios of the two sets of resistances set up between it's full value,the cold terminal and wiper, and in some instances the wiper and hot terminal come into it also, filters are added between there.
Frequency resopnse can be effected by a load difference because of where the CCW andCW lugs are hooked in the circuit. The answer is maybe yes, maybe no ... it really depends upon the circuit itself and what that circuit needs to see as far as a resistance from the cW to CCW point.
I have changed out BMP style tone controls in order to get a more scooped center tone (at the cost of gain), say changing a 25k pot for a 50k pot, the end of the tone sweep remained the same, but the mids dipped more. Sounds like what you want is a different taper pot to even out the change, it almost sounds like you have a linear in there. Double check the taper first ... bTW EMG has 25k-audio pots if you need those.

[Kent S.]

Okay,...I'm an idiot ... :lol:  I just caught where you said you had linear pots, and a 50k (why would you want to go down to a 25k then ::::smakcs self in head::. Put in a 50k audio or log taper ... that will get you much more clean-up towards the lower side ...
Hence, your 5, will become 7.5 on the new pot;your 1, will become 5 on the new pot; and your 0.5 will become 2.5 on the new pot;your 0.1 will become 0.5 on the new pot... and so forth ... 10 will be 10, and 0, will be 0 of course. Put an audio/log in there.
Value change ...NO, Taper change ...yes!