Two gain pots

[Venusblue]

So I lurk here a lot but never really post, but today I saw two posts about this... aaaand i'm making a third one.

Some one made a thread about using a 250k and megohm gain pot in their pedal. Why? What's the advantage? Couldn't you just turn the megohm pot up 1/4 of the way and have the same effect, or is there a different timbre involved?

Also are there any books or anything people could recommend that deal mostly with pedals, and what the components do? I'm trying to learn more about what they do in different configurations I guess, so I can look at schematics and pick out coupling, decoupling, filtering, ect. I've read a few things that dissect pedals, but not in too much detail. I'm studying to become an electrical engineer, but sadly i'm still taking my basics and haven't learned too much about this stuff yet.

[Galego]

I might be wrong but usually gain pots are used as variable resistors, and not as voltage dividers.
So choosing a 250k over a 1m pot, i think it's just to have two different channels where the first always has less maximum gain than the first.

[Venusblue]

I might be wrong but usually gain pots are used as variable resistors, and not as voltage dividers.
So choosing a 250k over a 1m pot, i think it's just to have two different channels where the first always has less maximum gain than the first.

So i'm confused. What would be the difference between the two?

And although it has less gain, couldn't you still just wind the pot back instead, or is the tone different? Sorry, i'm still kind of a noob... I can't wait to take more classes, though.

[flintstoned]

Check out indyguitarist's website for the books, they're exactly what your looking for.

[caress]

I might be wrong but usually gain pots are used as variable resistors, and not as voltage dividers.
So choosing a 250k over a 1m pot, i think it's just to have two different channels where the first always has less maximum gain than the first.

So i'm confused. What would be the difference between the two?

And although it has less gain, couldn't you still just wind the pot back instead, or is the tone different? Sorry, i'm still kind of a noob... I can't wait to take more classes, though.

it most likely depends on the application/schematic in question.  but...
it may be that if you use a 250k rather than a 1M, there will be a more useable sweep.
or maybe when you get past 500k it starts to oscillate.
or maybe the taper is weird with a 1M.
or maybe you find that you just don't need anything past 250k.
etc.

[petemoore]

  Resistive wafer has X resistance, we'll call that 100.
 Since it is even thickness and resistance across the wafer [ie linear], if you touch at the center, you now have 2 resistances of 50 each, 50 from wiper to left side, 50 from wiper to right side.
 Wiper is the variable center contact [literally what it is in a pot], the outside lugs of the pot are connected to the ends of the wafer.
 60/40, 30/70, 0/100, 1/99, resistances can be found [and everything inbetween, as long as the two numbers add to 100] by touching the wiper at various places along the wafer.
 Variable resistance: between the wiper and one end of the resistive wafer.
 Variable resistance 'mirror opposite' at the other end of the wafer.
 Using wiper to outside lug = variable resistor, the third lug 'open' [some like to tie it to the wiper in case the pot dies...R goes to 'default' pot R value] otherwise, either way works the same.
 Variable resistive divider: The wiper is a fraction of the resistance on one side and the other side is the inverse...60/40 for instance, when turning the potshaft [and moving the wiper to a different point along the Rwafer], both resistances change, one goes up and the other goes down in R value by the same X amount, which always adds up to the total value = pot wafer's resistance.
 In the case of typical 100k pot that might not be 100k...87k ? ..hopefully within the allowable component tolerance.
 So there's a buncha ways to apply potentiometers, each one deserves individual study to understand, opamp gain can be controlled with ''negative feedback'' for instance, and there are many ways to wire a circuit, pots can play any part that a fixed resistor or resistors play.
  'It' definitely depends on the shematic/ application.

[Kearns892]

Check out this thread. It's old, but has a wealth of information, just keep in mind that after 24 hours posts can't be modified so some things posted are corrected/ expanded upon later.
http://www.diystompboxes.com/smfforum/index.php?topic=47572.0

[Venusblue]

 Resistive wafer has X resistance, we'll call that 100.
 Since it is even thickness and resistance across the wafer [ie linear], if you touch at the center, you now have 2 resistances of 50 each, 50 from wiper to left side, 50 from wiper to right side.
 Wiper is the variable center contact [literally what it is in a pot], the outside lugs of the pot are connected to the ends of the wafer.
 60/40, 30/70, 0/100, 1/99, resistances can be found [and everything inbetween, as long as the two numbers add to 100] by touching the wiper at various places along the wafer.
 Variable resistance: between the wiper and one end of the resistive wafer.
 Variable resistance 'mirror opposite' at the other end of the wafer.
 Using wiper to outside lug = variable resistor, the third lug 'open' [some like to tie it to the wiper in case the pot dies...R goes to 'default' pot R value] otherwise, either way works the same.
 Variable resistive divider: The wiper is a fraction of the resistance on one side and the other side is the inverse...60/40 for instance, when turning the potshaft [and moving the wiper to a different point along the Rwafer], both resistances change, one goes up and the other goes down in R value by the same X amount, which always adds up to the total value = pot wafer's resistance.
 In the case of typical 100k pot that might not be 100k...87k ? ..hopefully within the allowable component tolerance.
 So there's a buncha ways to apply potentiometers, each one deserves individual study to understand, opamp gain can be controlled with ''negative feedback'' for instance, and there are many ways to wire a circuit, pots can play any part that a fixed resistor or resistors play.
  'It' definitely depends on the shematic/ application.

Wow, Thank you very much for your response, and everyone elses too.

I had to go over this several times to understand it a bit more fully. 

So I totally understand the use of a pot as a variable resistor... I'm pretty sure at least, I understand it enough. As for the voltage divider, how does it work without giving massive resistance? Hmmm maybe i'm missing out on a bit of basic theory here...

@Kearns

Oh wow, i'm reading through this, and it's great. Thank you very much!

@ Flintstoned

Hmmm cool, thanks, i'll bookmark this!