changing pot resistance?

[Stevie Nazarenie]

i was reading last week how adding a resistor to a pot can change it's value but now i can't anything on the net. any tips or web links out there? thanks.

[carverman]

i was reading last week how adding a resistor to a pot can change it's value but now i can't anything on the net. any tips or web links out there? thanks.

 

It's basically OHM's law, as applied to resistors in parallel.

Rule of thumb is..if you parallel two 500k resistors, the result is that the current

splits thus effectively reducing the resistance of each to one-half (250K).

 

If you have unequal values then the formula goes something like this..

Rt= 1 + 1

--- --- ......etc

r1 r2

 

Here some online info to explain it better:

http://www.tpub.com/neets/book1/chapter3/1-26.htm

[TWANG]

Seems odd though.. I guess a resistor is cheaper than a new pot, but we're only talking a few bucks for a new pot.

Why have extra circuitry just for a value change when you can buy pot with that resistance?

 

If you use a R to change a 500K to 250K. it'll sound like a 250K pot.

maybe not work as well.. !

 

lowering the resistance will reduce the output and the highs as well.. which is what your tone control is for.

Raising the resistance, like going from a 500K to a 1M will give you more stuff... but again, just buy the pot!

TWANG

[carverman]

TWANG; I wasn't suggesting this method becomes general practice to change a 500k pot to lower resistance.

 

The resistive element in the original pot is still 500k (+/- 10% to 20% depending on the quality

of the control and manufacturer). I was just suggesting this as TEMPORARY TROUBLESHOOTING technique

to see if too much "presence" in a pickup/control reconfiguration COULD be improved by changing the loading

on the pickup(s). One can do this very quickly by temporarily soldering a 470K resistor across the outer

legs of the pot..effectively (by virtue of OHM's law), you then have a "250k pot" impedance presented

to the coils of the the humbucker or SC.

 

If that works, and the OP that had this problem decided to go permanently

with 250k pot value, then the proper thing to do is to get 250K pots..but that involves a lot of

soldering and rewiring, and with hollow bodies..a lot of wire fishing as well.

 

As far as increasing the resistance, the only way to do that is to solder a resistor of some value in series

between the ground tap of the volume pot and ground. But then it won't completely cutoff the sound from

the pickup, so a 1 meg pot is more desirable. I had to do this with a t-o-m bridge piezo (LR Baggs) which

was 5 meg impedance and very finicky, resulting in the sound cutting off completely with the piezo volume

at 1/3 of the rotation still available. Installing the 1 meg resistor in series with the 5 meg pot changed the cutout

point down to almost the end of the pot travel..so that techique is useful in some cases as well.

 

The above methods are strictly for experimenting and IF you don't happen to have the right pot value around

but want to go ahead and prove what the problem is...as in the case of the master volume config,

the left over (and supposedly unused) pot could serve as a troubleshooting VARIABLE 500k resistor.

 

(IE: Temporarily solder this pot across the working 500k master volume to see if "loading up" the pickups to 250k

will help reduce the excessive treble).

Electronics formulas, such as OHm's law, can be useful (in these particular cases) on guitars.

[TWANG]

No, I didn't mean to imply you were! Sorry. *s*

 

And way cool of you to take the time to give more explanation.

You always come through, everyone sees that!!

 

TWANG