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02-18-2024, 04:43 AM
Quick update: Just installed net 200kΩ 4W flameproof resistors across the first filter caps to bleed off charge when the amp is off. I was looking for 220kΩ or 330kΩ but to get a high enough voltage rating I had to to put two 100kΩ in series. Some quick math shows that 220kΩ is close enough to 200kΩ with respect to power dissipation, time constants, and bleed current that I don't think it will matter, so in they went.
Also, it looks like someone modded the tone stack of the lead channel before I got it. R4 was replaced by a 68kΩ unit. The person didn't want to pull the board, so they just clipped the last one out and tack soldered in the new one. I have parts on hand to almost fully convert the tone stack to the london power standard's values (mid pot is the only one I don't have on hand) so at some point that will get done. I've also identified several places in the circuit I suspect are contributing to what I don't like about the sound, we'll see if I'm correct. In short, there are two interstage attenuators that roll off everything below 329 Hz and and 720 Hz respectively, which seem to suspiciously correspond to my dislike of certain mid characteristics of the amp. That 720 Hz roll-off in particular... it reminds me of tube screamers, and I'm not a fan of tube-screamers. The lead tone kinda reminds me of one too, so that seems like a good candidate for the snippers.
C103/R108 and C106/R112 below are the two filters mentioned. The first one I'm thinking I'll just remove R108 and short C103. The second I think I'll just remove C106 from so that there is no high frequency emphasis.
Also, it looks like someone modded the tone stack of the lead channel before I got it. R4 was replaced by a 68kΩ unit. The person didn't want to pull the board, so they just clipped the last one out and tack soldered in the new one. I have parts on hand to almost fully convert the tone stack to the london power standard's values (mid pot is the only one I don't have on hand) so at some point that will get done. I've also identified several places in the circuit I suspect are contributing to what I don't like about the sound, we'll see if I'm correct. In short, there are two interstage attenuators that roll off everything below 329 Hz and and 720 Hz respectively, which seem to suspiciously correspond to my dislike of certain mid characteristics of the amp. That 720 Hz roll-off in particular... it reminds me of tube screamers, and I'm not a fan of tube-screamers. The lead tone kinda reminds me of one too, so that seems like a good candidate for the snippers.
C103/R108 and C106/R112 below are the two filters mentioned. The first one I'm thinking I'll just remove R108 and short C103. The second I think I'll just remove C106 from so that there is no high frequency emphasis.
