Noob Question: Lower Pot/Elec cap values w/Resistors?

[Dingus]

Hey folks, I've been searching around trying to find a straight up answer on this, but couldn't.

I understand I can lower a potentiometer's value (ex. 500k to 250k) with resistors. I have no idea how you calculate what value resistor to use though. I was reading over this page (http://www.projectguitar.com/tut/potm.htm), which is rather informative on the matter (although I'll be using this for a pedal and not a guitar), but I have no idea how to guess at what value to use.

Anyone know?


Also, I need to make a 4.7uF electrolytic capacitor 4uF. Is that possible using resistors in parallel maybe?


Thanks!

[Berto]

that is really interesting. i would have assumed the opposite would have happened seeing as a pot is a variable resistor. cool stuff

[plesiosaurus]

you can't change the capacitance of a capacitor with resistors.

[Dingus]

you can't change the capacitance of capacitor with resistors.

Thanks man! I guess in this case, since I need a 4uF and the elec caps I have are a 20% tolerance I can just measure a bunch and see how close I can get. Cheers!

[plesiosaurus]

potentiometers are variable resistors, so you're basically putting two resistors in parallel

which means to determine the resulting resistance, you'll use this forumla



So if you have a 500k pot and you want it to be 250k,

solve
250 = (x*500) / (x+500)
250x + 125000 = 500x
125000 = 250x
500 = x

so use a 500k resistor

basically if you want to halve the resistance, use the same resistance resistor as the potentiometer.

if you're too lazy to do the math,

use this calculator

http://www.sengpielaudio.com/calculator-paralresist.htm

[Dingus]

Thanks again man! Btw I take it you've seen the performer Pleaseeasaur? I saw him in D.C. a few years ago, I'm still a sucker for the No Prob Limo sketch.

[SGJarrod]

anytime u put a resistor across the lugs of a pot it will change the overall value of the pot but it will not be a smooth taper across the pot, it will work but not the same as just using a 250k pot

[plesiosaurus]

anytime u put a resistor across the lugs of a pot it will change the overall value of the pot but it will not be a smooth taper across the pot, it will work but not the same as just using a 250k pot

this is true and relevant.

i don't know what pleseasarrr is or whatever. i just thought it was a cool dinosaur.