Peavey Deuce/Mace Input Impedance, 220K? Mods? https://www.peavey.com/forum/viewtopic.php?f=19&t=44078
and
Peavey Deuce Repair and Clipping Diode Mod https://peavey.com/forum/viewtopic.php?t=44043
I was OK with the distortion, but it still didn't have a modern voicing and the clipping was a bit dull and fizzy. Also, to my ears the whole amp sounded muffled. (Listening is subjective, and my comparison is the range of blackface Fender amps I've owned. I know, there's little in common between the Deuce and a BF Bandmaster, but context influences perception and these old Fenders and early Mesas are my "gold standard" of amp tone.)
I decided to see if I could improve things. After a LOT of experimentation, I think I finally have an amp I can really enjoy. Below is a documentation of my changes.
1) Convert "normal" channel into "distortion" channel.
I'm not alone in thinking the overdrive on these amps is a bit . . . undesirable. My first attempt at adding TubeScreamer style diode clipping was to insert a pair of diodes (one LED and one ceramic) in the feedback loop of U2B. After that failed to impress me, I then added a single Ge diode across R36. Decent. A definite improvement improvement but . . .
I've finally got a great sound by adding asymmetrical clipping Ge diodes to ground between the first and second gain stage. I pulled C24 .01uF off the board and built a little perfboard with three Ge diodes (two going one direction and one going the other). The Ge diode forward voltage is a good match for this gain stage (just after the "pre-gain" stage), and adds a great sounding clipping effect. I'm really loving the sound of this distortion. A LOT more Tubescreamer'ish and a lot more tight. Huge improvement.
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I left the "normal" now "distortion" channel as-is. It sounds great overdriven. For the "effect" channel, I wanted a lot more highs. Here are the values I settled on:
C30 from 270pF to 450pF
R45 from 47k to 90k
C32 omit
I tried a million different combinations. Nothing really seemed to give me the high frequency "shimmer" I was after. I looked all through the schematic for the low-pass filter that was cutting out the highs. Never found it. So the above does it as good as I could get. It's similar to a Marshall voicing. The only disadvantage is a bit of volume loss. Well, I've never heard anyone complain about these amps being too quiet so, neither will I.
Last thing I did was make a couple cosmetic changes (saved the parts so I can go back if I sell). Removed the aluminum trim, and replaced the colorful knobs with black aluminum. I think it looks more like it sounds, dark and bad-ass.
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