Potato Cakes
Well-known member
Hello, Everyone,
On another thread I documented a build for a Dumble inspired champ which at the end I commented on how it was very dark sounding. I wound up rebuilding it to the amp layout below and had the same tone results. I recently went back to try to solve this issue and took some measurements. I found that the normal channel with the 470pF bright cap has an EQ response that matches one of the frequency plots for the E3 tone control. With the lead channel in use, the tone control works the same till the halfway point (tone = 5) on the potentiometer. When I turn it up past this point, the high shelf increases but simultaneously there seems to be a low pass filter (or a wide bandwidth parametric) that yields the mid frequency bump you see on tone = 10. I removed the bright cap thinking that the return created to the normal channel's plate connection was causing this but there was no change. I added a 470pF bright cap to the lead channel it seemed to help but then the normal channel would only get to a flat response with the tone control at 10.
Is there a way to get both channels to behave the same way or is this the cost of doing business with two channels sharing the same tone knob. I had thought about using a dual gang pot for the tone and then 1k summing resistors to feed both channels into the preamp stage before the phase inverter but I am not sure if that will yield the desired results either.
Thanks!
Paul
On another thread I documented a build for a Dumble inspired champ which at the end I commented on how it was very dark sounding. I wound up rebuilding it to the amp layout below and had the same tone results. I recently went back to try to solve this issue and took some measurements. I found that the normal channel with the 470pF bright cap has an EQ response that matches one of the frequency plots for the E3 tone control. With the lead channel in use, the tone control works the same till the halfway point (tone = 5) on the potentiometer. When I turn it up past this point, the high shelf increases but simultaneously there seems to be a low pass filter (or a wide bandwidth parametric) that yields the mid frequency bump you see on tone = 10. I removed the bright cap thinking that the return created to the normal channel's plate connection was causing this but there was no change. I added a 470pF bright cap to the lead channel it seemed to help but then the normal channel would only get to a flat response with the tone control at 10.
Is there a way to get both channels to behave the same way or is this the cost of doing business with two channels sharing the same tone knob. I had thought about using a dual gang pot for the tone and then 1k summing resistors to feed both channels into the preamp stage before the phase inverter but I am not sure if that will yield the desired results either.
Thanks!
Paul
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