Potentiometer value change calculation - SOLVED

[Zduck]

Any of you smart people know if this C50K tone pot could be replaced with a 10K pot in this circuit and still keep the same sweep, by adjusting the component values around it? Or would it not work or be more work than it's worth? The reason is I'd like to add in a 10K expression pedal input so would need the pot to be 10K as well (I can live with it not being C taper)

(Taken from Cyborg Drive Pedalpcb project). Thanks.

 

[Feral Feline]

It's times like this I wish I knew how to use LT Spice, or similar.
I'd have to breadboard it and fumble and stumble until I found something that worked or got fed up and quit bread-boarding.

 

[finebyfine]

It's times like this I wish I knew how to use LT Spice, or similar.
I'd have to breadboard it and fumble and stumble until I found something that worked or got fed up and quit bread-boarding.

I threw it in LTSpice a few days ago and still couldn't figure out how the frequencies and Q are defined. Really curious the answer to this one. I know it's part of the Ibanez WH-10 Wah but can't find nail down the filter topology it uses.

 

[pricklyrobot]

Someone should sell expression pedals with easily swap-able pots!

 

[jwin615]

Just looking at it as an RC network, in current form it sweeps from 931Hz-~26k
Swapping to a 10k with the rest of the circuit unchanged would sweep 931Hz-4kHz

Swapping R14 to 260 ohms, C9 to 22nF and the pot to 10k would give you a sweep of
705Hz to 27.8kHz

Pretty close.

 

[jwin615]

Actually, do 16nf and 470 ohms
That gets you 950Hz-21.2khz
18nf or 20nf would work in a pinch, loosing a bit more high-end the larger the cap.

 

[Zduck]

Just looking at it as an RC network, in current form it sweeps from 931Hz-~26k
Swapping to a 10k with the rest of the circuit unchanged would sweep 931Hz-4kHz

Swapping R14 to 260 ohms, C9 to 22nF and the pot to 10k would give you a sweep of
705Hz to 27.8kHz

Pretty close.

Amazing, I'll give these values a try! thanks!

 

[jwin615]

Amazing, I'll give these values a try! thanks!

Did it work out for ya? See it's marked solved.

 

[Zduck]

It did! Just breadboarded things up and it works great! I actually tried a bunch of values and decided I liked the sweep best with 470ohm and 22nf.

@jwin615 what would the sweep freqs be for those values?

Also, as a mod I added a pot to ground before R17 so you can blend in the filter if you want more of subtle bandpass filter sound!

Thanks so much @jwin615! I appreciate the help with this project.

 

[jwin615]

It did! Just breadboarded things up and it works great! I actually tried a bunch of values and decided I liked the sweep best with 470ohm and 22nf.

@jwin615 what would the sweep freqs be for those values?

684Hz to 12.7k
No a whole lot lost above 12k.
Glad it worked out!