Limiting a Potentiometer - revisited

[phector2004]

Hi everyone,

Pasted bits of different circuits together and made a distortion I'm pretty happy with that I'm thinking of boxing/adding to current amp project. Now I have a pot I wanna limit, and I had a look at this: http://www.diystompboxes.com/smfforum/index.php?topic=79369.0 but my problem goes beyond that...

I'm trying to limit it to a specific WINDOW of values, not just a cut-off. I've wired a trimmer as a variable resistor limiting the drain voltage (controlling the headroom I'm guessing??) on one of my transistors changing it from crunch-->dist-->slight fuzz, but before the crunch, there's no signal (would too high a voltage on the Drain/Collector make the output small??) and after the fuzz, it becomes unstable and very gated, beyond any use I can think of.

Here's a colored ASCII diagram:  
[---------------CRUNCH----DIST--FUZZ-----]

I know I could chop off the first 1/4 of no signal by maybe putting a 25k in series with a 75k pot or something equivalent, but how would I be able to get rid of the 1st quarter and the last eighth? Tried making a calculator in excel, but it didn't work out too well... I'll try again and post if I get it working, but until then, any suggestions?

Thanks

EDIT:

Ok I feel really stupid now! I was overanalyzing it, and forgot it was wired as a variable resistor. Here's how its done:

1/8 * 100k = 12.5k

12.5k * 5 (5/8ths of useable potentiometration) = 62.5k

2 * 12.5k = 25k (high V resistor))
12.5k (low V resistor)

put a 168k resistor in parallel

[deadastronaut]

old thread but relevant to me today....

ive built a tonepad rebote 2.5...it calls for a 50k pot for delay time...but i want to just tweak a little more delay time out of it, before it gets dirty...

i know i can use a 100k and yep that works, but i want to limit that 100k to be around say 60k...ish

so going by phils example of 'limiting' should i whack a 10-20k on the 100k pot to achieve this???....thanks guys..

as a side note for rebote builders..change 33k to 10k for better volume on repeats...

[phector2004]

Hey rob,

Since the pot is being used as a variable resistor, you can just add a parallel resistor* to a 100k to decrease it to 60k. The taper would be different, though

adding a 10k in series with a 50k would make it go from 60k to 10k rather than 60k to 0 ohms

Doing the math,

1/Rt = 1/R1 + 1/R2

1/60k = 1/100k + 1/R2,
1/60k - 1/100k = 1/R2
10/600k - 6/600k = 4/600k = 1/150k

*R2 = 150k

[deadastronaut]

cheers phil, your a star!..

[phector2004]

No problem, let us know how it goes 

[deadastronaut]

will do....now to find a 150k resistor...hmmmm....

[deadastronaut]

great found one in a tray of odd bits...

yay!..it works...i did a sound test of the delay time before/after...now ive squezzed the max delay out of it , just to the point of breakup...much much better..and a better time too..

and with the 33k-10k level mod, its a much better effect all together...mods that i would thoroughly recommend...cheers man!!..

i'm a happy bunny!!...