Wrong value pots w/resistors

[philbinator1]

Hey guys, I'm wondering how I would go about using resistors with pots to get a desired value pot. 
I want to use a A500K pot w/resistor to get a A100K value...know what I mean?  How would I do this?
If so what lugs would I put the resistor across?


Cheers for any help.   
Phil

[Scruffie]

http://gaussmarkov.net/wordpress/parts/resistors/resistors-6-mods/ 

[philbinator1]

Thanks scruffie, lugs 1 and 3 got it.  Is there some calculation we can do for any pot value/resistor value?  I didn't
quite get some of the stuff in the link.

[frequencycentral]

http://www.diystompboxes.com/smfforum/index.php?topic=70732.0

[philbinator1]

http://www.diystompboxes.com/smfforum/index.php?topic=70732.0

That's much more understandable to my wee brain, thanks Rick!  But can you help me to understand the equation
used; 1/(1/R+1/P)...what does it mean by '1', why is the resistor and pot (and then the lot) divided by 1?

5 mins later..Ok i just tried some equations with it, one with 100K pot and 100K resistor, the result came up 50K.
then 250K pot and 100K resistor, resulting resistance was 71.4.  I also found a way to do the whole equation using
the scientific calculator in windows!     are my calculations right?  and in the equation, do the 1's in the bracket
just represent whatever number you're using?  maybe 'n' would be more apt?

[philbinator1]

bump

[Hides-His-Eyes]

You are aware that this will completely screw up the taper right?

[philbinator1]

Yip, I'm aware it will change the taper...from what I've read, yes it does change the taper but if one doesn't make to much
of a dramatic jump away from the original resistance of the pot, it wouldn't matter?  Say, from 200K to 100K via resistor.
I've also read it can actually help with some pedals (eg fuzz face) because it smooths out the way the gain pot bunches
up the fuzz towards the end of it's rotation.  I've yet to put it into effect yet, might be a chance for some experimentation!   

[Scruffie]

For what it's worth i've never felt the taper was bad after doing this when sticking to a maximum division of 10... infact it's felt alot nicer afterwards on some things.

And yes your calculation is correct... it's the same equation as this from the Gaussmarkov site that is perhaps laid out a little nicer.
   R1 R2
  R1 + R2

100k x 100k
--------------
     200k
    =50

[philbinator1]

Splendid!    Thanks man it's all very clear now.  Cool