Super Champ 1983 - Optimizing

ExpeditionElec

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Jun 6, 2018
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Pacific/Adriatic
I was thinking about adjusting the reverb mix resistor on my SC - can't use reverb over 3 - and then thought about the issue with tone suck with the pedal hooked up (Lead off), so I modelled the mixing node in Spice and tabled up some results. I used 150pF for the miller capacitance of the mix triode stage and assumed reverb was on zero through stock 470k. I was copying numbers off the graphs so they're not exact but close enough to see what's happening. Super Reverb is green line, stock SC is blue. They takeaways:

1.Yes, as everyone knows, there's a big change in tone and gain in the stock configuration with the pedal inserted.
2. If you can live with less max reverb, or that's something you actually want, reducing the dry mix resistor (3.3Meg) and using a shunt resistor to ground to have stock type gain is a better option than increasing the Reverb mix resistor value as reducing and shunting helps lower the impedance at the triode grid which lessens effect of miller capacitance and lessens the difference between pedal in and pedal out.
3. Also notable is that the gold standard AB763 circuits with the 220k shunt have a noticeable treble boost from the 10pF cap and so does the Super Champ, only more so.

Worth mentioning that I didn't consider what the changes will do to the Lead drive, since I don't care much about it. My guess is that it will reduce the Lead gain which might be a good thing.
 

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