Rump Roast tone control question

[sdb guitars]

I just built a Rump Roast, and the tone control doesn't seem to be usable across it's entire rotation.  I get a high frequency peak from full CCW to about 80% of the rotation, and then in the last 20% before full CW it transitions to suddenly very dark.  Using the switch to add the additional capacitor darkens up the overall output, but does not change the behavior of having ho change across a large part of the rotation.  I used a 1MA pot for volume/gain and a 500KA pot for the tone control.

I have a Carmen Ghia homebrew amp and its control seems very usable across the entire spectrum, except for the last 5% or so at each end of the sweep.  Interestingly enough, the amp has the same pot values, but the sweep seems completely different.

Any thoughts on effecting a more gradual change in tone across the entire rotation of the pot?  I know the last bit at each end of the rotation will likely be unusable (too bright or dark) as the amp is the same way, but I'd like to find a way to make the tone more usable.

Thanks,

Shawn.

[Haberdasher]

Hey Shawn

I don't remember mine acting that way.  Did you build it as a boost, drive or hybrid?
I guess double check your component values or try a linear pot for the gain? ...

[sdb guitars]

Keefe -

I built it as a boost only, and the gain is working normally, it's just the tone that's acting up. I double checked my part values, and they're all to spec. Maybe a linear pot for tone would even out the curve. I'll give that a shot. Other than that, the build went very smoothly.

[madbean]

I would try this: bump up C5 to between 6n8 and 10n, and change the Tone pot to reverse audio (or wire the 500kA backwards).

In retrospect, the tone control on the amp doesn't port all that well to the pedal version. I believe I did suggest changing C5 at one point, but I don't remember if I included that in the build doc.

For the newer sub-mini version I'm working on I've ditched that tone control altogether and picked a simple cut knob which I think serves it better.

[sdb guitars]

I swapped out the 500K log pot for a 500KB linear and it has a nice even sweep now.  I'm really digging it.  Interestingly enough, it added nice brightness and liveliness to my Carmen Ghia clone amp, making it even more touch responsive and "hi-fi".