Potentiometer value in Big Muff tone control

[RickL]

Hang with with me, this is an odd one.

I am trying to install a volume/tone control on an acoustic guitar. It has a preamp so I'm not worried about the volume loss from the tone control. Because of limited space (Washburn Rover if you're interested) I need to use a concentric pot. I have bunch of concentric pots that consist of: dual 50k (measured at about 38k), dual 100k and an on/off switch. So, separate control of the 50k dual section and the 100k dual section with the on/off operated in the CCW position of the 100k section.

I can use one section of the 100k part for the volume control and would like to use the 50k part for a tone control. I like the idea of scooped mids in the middle position, hence the Big Muff tone circuit, but I'll experiment with component values before the final install. I'll use a simple one capacitor treble roll off if this won't work. Or another option if someone has a suggestion. Keep in mind that this is a fairly thin sounding guitar to begin with.

Is there some way to wire the 50k sections so they operate as a single 100k pot? Or will the Big Muff tone control work okay with a 50k pot instead of a 100k, with, perhaps, changes of component values?

[RickL]

I just played with the Big Muff tone stack in the Duncan Tonestack calculator and using a 40k pot doesn't change the response much - slightly shallower mid scope. I think I'll be okay.

But I still welcome responses.

[amz-fx]

A couple of the values in the tone stack calc can be changed to see how it performs. The source impedance and the R4 load may need to be changed to match your preamp. These will have an influence on the response of the tone stack.

regards, Jack

[RickL]

So I did this and the tone control seems to work just fine. But I'm getting distortion when I plug into my amp (a JC 77 if it matters). The distortion is less when I plug into the low input so it may just be that I'm getting a hotter signal from the pre-amp than I expected.

I'm using this https://www.amazon.ca/Acoustic-Guitar-Classical-Adjustable-Performances/dp/B0CD3929NN/ref=sr_1_111?crid=KFUMDIEWBSP3&dib=eyJ2IjoiMSJ9.KNBM1_yPc_qvVIjobWrOEuKsxvbvbg0EU2BVDU5N9H4zDRJo1hGW0Uc5JKjvMZeUdDTiRPikS8KhZB_T7cCe7WBz7fY8zfP9d4LzeUVNXB17Q-Bts3YIHrG2UPTkjw69SYPbWACY9tsYS7CZmFvRVriE3WocDeheIYwkb9-ZmlHoVVSu1-sLvzgKiA1uuGE2VlO4bHInuDCHGwVQ0tJkQpriIQTzuqJTN6dTUY10fJvInYywPTsX85nlyS0Vxqld17eiGwMQrMgKIVXgsfl7scKOlY9S5qn2Jm-pC2Q6J0M.BplxEYHKNLaSeIt8YGuf3Brk725girnyW-QejZ_6mcc&dib_tag=se&keywords=acoustic+guitar+pickup&qid=1717859149&s=musical-instruments&sprefix=acoustic+guitar+pi%2Cmi%2C122&sr=1-111 as a pre-amp.

An idential unit (without the tone control inserted) worked fine on a classical guitar, with no distortion.

Is there something about putting the tone control after a pre-amp that would cause it to distort?

[Mark Hammer]

I might actually have some pots like that (one of those old Active Surplus finds).  The 50k and 100k sections are not ganged together, but the two sections for each individual value are?  And the switch is push-pull?  I gather these were used in early car radios, long before tone/volume adjustments required menu-diving and pushing buttons.

[RickL]

The 50k and 100k sections are not ganged together, but the two sections for each individual value are?

Yes.

Spring loaded pull to access the 50k sections, so, not consentric in the normal way with an inner and outer knob. Unless you're pulling on it you are turning the 100k sections. Unless you're pulling, full CCW  turns the switch off.