Pot/resistor question

MrBump

How do variable resisters work in series?  I mean, in a strat, if I have a pickup wired first to a 500k tone pot, and then to a 250k volume pot, what's the overall resistance/effect?  I'm trying to balance out resistance in a HSS build - I know that I can wire in a resister but I'm not sure about the effects of the pots themselves.

Alegree

Usually you wire resistors in parallel to the pot.  I believe the formula is 1/total R=1/R(1)+1/R(2).
1/TR = 1/250k + 1/500k = 167k 

EG 500k resistor in parallel with 500k pot gives 250k

If you use a series resistor with your pickup cable then you build up the capacitance in the coil, which makes your pickup darker. That's can also be good if you were to use 500k with singles that you pre-darken. 

ICBM

There are two different ways of using them.

Tone pots are connected as a variable resistance to determine how much signal can go through the tone cap to ground. (2 terminals used.)

Volume pots are connected as a potential divider to determine the ratio of the output to pickup input signal that the amp sees. (3 terminals connected.)

The overall *DC* resistance of a 250K volume pot and a 500K tone pot is still 250K, because the DC doesn't go through the tone cap.

Generally if you want a 250K/500K setup for single coils and a humbucker, you need to add a 500K (470K is the closest normal value) resistor in parallel with a 500K volume pot when the singles are selected. It's easiest to do this on a standard Strat setup by having the upper tone control (250K) working on both single coils, with the resistor directly to ground across it bypassing the cap, and the lower tone control (500K) for the humbucker. That also means you can use different tone cap values for the singles and the humbucker, which is useful.

MrBump

ICBM said:
Generally if you want a 250K/500K setup for single coils and a humbucker, you need to add a 500K (470K is the closest normal value) resistor in parallel with a 500K volume pot when the singles are selected. It's easiest to do this on a standard Strat setup by having the upper tone control (250K) working on both single coils, with the resistor directly to ground across it bypassing the cap, and the lower tone control (500K) for the humbucker. That also means you can use different tone cap values for the singles and the humbucker, which is useful.

Yes, that's exactly what I was planning to do - 2 SCs to the top tone pot, and the 1 HB to the second, with respective values ot 250 and 500.  I just wondered if I still needed the additional resister wired in, or if the pot itself provided the resistance.  Sounds like it doesn't and I do!

Thanks.