Question about adjusting the max resistance of a pot and affecting taper

[Hangingmonkey]

Hi, Ive got a pot question.

Im building a Wampler Pinnacle on vero and one of the pots is a C50K, which I dont have.  I do have a C100k and I was planning to put a 100k resistor across lugs 1 and 3 but I wasnt sure of that would affect the antilog taper of the pot. 

Would it make a difference to the taper and if so would it make an audible difference?

Thanks

[DutchMF]

If I got my math right that would get you something close to a 50k lineair (B) pot... So yes, the taper is affected. As for how much you would notice it, I'm not sure, which pot is it?

Paul

[Hangingmonkey]

The pedal has 4 knobs, vol, tone, gain and contour. The pot is contour which is supposed to boost or cut mids.

[jimilee]

If I got my math right that would get you something close to a 50k lineair (B) pot... So yes, the taper is affected. As for how much you would notice it, I'm not sure, which pot is it?

Paul

Just because I don't know,how would a resistor reverse the taper Making an reverse audio pot  linear?

[DutchMF]

If I got my math right that would get you something close to a 50k lineair (B) pot... So yes, the taper is affected. As for how much you would notice it, I'm not sure, which pot is it?

Paul

Just because I don't know,how would a resistor reverse the taper Making an reverse audio pot  linear?

That has to do with the math behind calculating the total resistance of 2 resistors in parallel. That goes:
1/R₁ + 1/R₂ = 1/R_total

If you put this into an excel sheet, where R₁ is the value of the pot and R₂ is the value of the resistor across lugs 1&2, then output your results as a graph and see what happens! I'm sorry if this isn't clear enough, I have a good understanding of the math behind this myself, but explaining it to somebody else (and in a foreign language!!) is a whole other matter. If you like, I can try to phrase this a bit better and mail you the whole deal, including excel sheets.....

Paul

[DutchMF]

@Hangingmonkey:

What I would do is wire it up with a 50kB pot with some extra long wires and see if you like it. You can always include the correct Revlog pot in your next parts order and exchange them later!

Paul

[jimilee]

If I got my math right that would get you something close to a 50k lineair (B) pot... So yes, the taper is affected. As for how much you would notice it, I'm not sure, which pot is it?

Paul

Just because I don't know,how would a resistor reverse the taper Making an reverse audio pot  linear?

That has to do with the math behind calculating the total resistance of 2 resistors in parallel. That goes:
1/R₁ + 1/R₂ = 1/R_total

If you put this into an excel sheet, where R₁ is the value of the pot and R₂ is the value of the resistor across lugs 1&2, then output your results as a graph and see what happens! I'm sorry if this isn't clear enough, I have a good understanding of the math behind this myself, but explaining it to somebody else (and in a foreign language!!) is a whole other matter. If you like, I can try to phrase this a bit better and mail you the whole deal, including excel sheets.....

Paul

No no, that's ok. I was just curious, not a huge deal. That part that most intrigued me was how you could reverse the taper on a reverse taper pot. I'm a solder by numbers guy, so mailing me the formula would be like me reading Greek.

[DutchMF]

Well, reading Greek would be so cool! Might explain some of the financial problems they are dealing with  ! Anyway, if you ever feel the need to expand on your knowledge of Greek, contact me, we'll see what we can come up with! Cheers dude...

Paul

[Hangingmonkey]

Thanks Paul.  I was wondering why the resistor in parallel changed the taper also.  (I mentioned it in my first post because I remember reading it somewhere on one of the DIY forums)

I'll take some readings from the pot and log it on a graph and see what happens.

So, just out of curiosity, do you know what happens if I did the same thing to an audio taper pot? ie, would the same principle apply and change it to linear also?

[DutchMF]

Log taper (audio) and RevLog taper are two different beasts.... So putting a resistor on those different pots would result in different things! The math is actually quite difficult, let me sleep a night on how this would work out, I'll get back to you after I've gotten a day or two to think this through and translate it to english.... That's quite hard!!!

Paul