Really I’ve had it for over a week now, but I wanted to live with it a bit before reporting. I bought it from @Melvin who found it too loud for home use. It’s a 1x15” combo, currently fitted with a Jensen Mod 15-120. I did get the original G15B-100 in the deal, but I haven’t tried it yet. Certainly, it gets loud fast. 1 on the master is too loud when any of the family is home. In stock form the Boost channel tone is a little dark, and I found the Normal channel a little harsh at low channel volume settings. I decided to tweak the circuit a bit.
Turns out this amp is sort of an oddball. I traced most of the preamp to figure out how to mod it, and it’s totally different from the available schematics. I even emailed Marshall, and they didn’t have a schematic that matches this amp.
Anyway, I ended up adding a cap to the Boost channel tone circuit to let a little more treble through, I removed the treble bleed cap on the Normal volume, and I replaced two of the op amps with fancy Analog Devices rail-to-rail op amps.
This amp is impressive! It really gets punchy when you turn the amp up a bit, and has a nice feel. I don’t know if the mojo is from the Hitachi mosfets or if it’s just the speaker compressing a bit. I don’t think the power amp adds any grit, but the LED clipping in the preamp responds enough like a tube amp for me. Nice smooth clipping that cleans up well from the guitar volume. I dig it, and it’s a keeper! Cheers!
