I was able to make some massive improvements in this amp this week after letting it rest for a bit (year).
My original plan involved deleting the stock FX loop and implementing Martin's presonance circuit, and my initial results were flawed. The clean was farty and the presonance wailed on half of the pot. My PI waveforms were also severely squashed, and so I deduced the problem was operator error, WHADDAYAKNOW. I removed the presonance and installed a presence circuit with a 5KL pot and .1 uF cap. That instantly sounded better. [edit: That’s no diss on the presonance mod, I just don’t think I did it correctly.)
But I still had that farty clean tone. I took a hard look at the schematic and decided to reinstall the components of the original loop that were deleted except for the jacks. Not having much room, I decided to use a .1 uF Solen fast cap I had in the drawer, along with the 100K/10K voltage divider.
The amp now sounds *glorious*. It has some very creamy rock tones on both channels with the right settings. It is characteristically dark like the stock amp, but sounds good with the gain turned up on the clean channel. The lead channel has excellent control with the additional lead gain knob (a la SDM 2550X), it sounds very controlled but lively with the lead gain down and the lead volume up.
I need to balance the PI plate voltages and work on the Metro Loop, but that should be a success.
The clipping diodes in this circuit are very harsh sounding (1N4007s). Any recommendations on how to smooth that out? I was thinking a clipper. See what I did there?
VIPERDOC 2550X 1.3 SCH.pdf
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Just plug it in, man.