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December 02, 2022, 10:48:28 AM

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Vox Pathfinder 10 - Tone stack experimentation

Started by dimkasta, May 30, 2022, 01:28:38 PM

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dimkasta

I am working on this as part of my other P10 thread, but I thought this deserved its own discussion.

I used the Tone Stack Calculator application to plot the frequency response of the tone stack, and compare it to those of Pathfinder 15r and an old school VOX stack. And then try to find values that could work and give a similar curve.

I do not know much about filters and plotting curves, so I would appreciate any feedback

This is the plot of a classic VOX. I tried different schematics like that of AC15c1, but the curve was very close to this one.

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This is the stock pathfinder 10. The bass pot is a bit off to compensate for the extra resistor in the circuit. And yeah it's quite off...

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This is pathfinder 15r. Still a bit off, but much better

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This is what I am planning to do on my pathfinder 10. I tweaked it to come as close to the classic Cox curve with values that I have. I plan to do this point to point on top of the pots. I know that the pots won't track the same as the original, and the curves won't be identical, but the starting point should be close enough to give a good approximation
R4 will be replaced with a single resistor. That's why it's shown at 100%.



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Any thoughts? Did I miss something?



phatt

I've not worked on this amp but have worked on similar small amps with some good results with improving tone efficiency.
Assuming I'm reading the right schematic you can raise the value of R14 which is 100k, up to 500k or even higher. (At pin3 of U2A,, after tone stack)
It should open up the tone a little better making it more effective at Boost and Cut.
100k might be loading down the tone section.
Hope it helps, Phil.


dimkasta

Courtesy of the nice folks at diyaudio

I don't know how feasible the 36R is, but here are some alternate values that can be used for the same curve

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