36 watt project with TMB tone stack and switchable cold clipper stage
Posted: Wed 11/08/17 6:27 am
Hi all.
My mate blew up his Marshall JTM30 (apparently problems due to overheating are common with these amps), so he has agreed to let me build something similarly powered in the chassis. I'm using a Vox AC30 reissue transformer (Hammond 290MX) and a Fender 35 watt output transformer with 4, 8 and 16 ohm taps and a 4000ohm primary (Hammond 1760J). The output section is pretty standard 36 watt as far as I can tell, but the preamp is a mash up of 18 watt, Plexi, JCM800, Mesa and Soldano.
I've attached the first draft schematic and layout drawings. I've never tried to design a 'high gain' preamp before, and whilst I've done a fair bit of research, I'd appreciate any tips if people spot glaring issues or mistakes, or perhaps something that just straight up won't work.
I'm also curious about adding a tube/SS rectification switch. The circuitry/wiring isn't too hard, but I'm wondering if I'll end up running the tubes too hard in SS mode. What are peoples thoughts? It seems like it would make sense to have the option of that firm response with this higher gain style amp.
One more question... Does anyone see any issues with my 'Saturation' control, which basically just varies the cathode resistor value on the cold clipper stage? It's designed to run from roughly 5k through to 40k or so, so warmer than Marshall, all the way through to SLO100 and Mesa Dual Rec territory. Also, the 'Gain' control, which is basically just a variable resistor between V2A and V2B that controls how much signal gets dumped to ground. Will it work?
Thanks as always.
My mate blew up his Marshall JTM30 (apparently problems due to overheating are common with these amps), so he has agreed to let me build something similarly powered in the chassis. I'm using a Vox AC30 reissue transformer (Hammond 290MX) and a Fender 35 watt output transformer with 4, 8 and 16 ohm taps and a 4000ohm primary (Hammond 1760J). The output section is pretty standard 36 watt as far as I can tell, but the preamp is a mash up of 18 watt, Plexi, JCM800, Mesa and Soldano.
I've attached the first draft schematic and layout drawings. I've never tried to design a 'high gain' preamp before, and whilst I've done a fair bit of research, I'd appreciate any tips if people spot glaring issues or mistakes, or perhaps something that just straight up won't work.
I'm also curious about adding a tube/SS rectification switch. The circuitry/wiring isn't too hard, but I'm wondering if I'll end up running the tubes too hard in SS mode. What are peoples thoughts? It seems like it would make sense to have the option of that firm response with this higher gain style amp.
One more question... Does anyone see any issues with my 'Saturation' control, which basically just varies the cathode resistor value on the cold clipper stage? It's designed to run from roughly 5k through to 40k or so, so warmer than Marshall, all the way through to SLO100 and Mesa Dual Rec territory. Also, the 'Gain' control, which is basically just a variable resistor between V2A and V2B that controls how much signal gets dumped to ground. Will it work?
Thanks as always.