Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jordan86 on January 17, 2021, 01:31:45 pm
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Sort of a tricky wording here... :)
I'm considering tweaking a JCM800 style preamp to dial back some gain. It's 4 stages: Stage 1 > cold clipper > gain stage > CF Tonestack > SE Power section. It's too much gain for me, and a little too crispy up top, so I am considering running first two stages in parallel instead of series.
My question now is what the net difference would be between paralleling the triodes at the tube socket vs having two separate "channels" in parallel that get mixed before the next stage. My current scenario can easily afford either. The first would be more Matchless DC30.
https://el34world.com/charts/Schematics/files/Matchless/Matchless_dc30_old.pdf
The latter would be more like Marshall 1959/JTM45. Two separate stages with mixing resistors after their gain controls. https://el34world.com/charts/Schematics/files/Marshall/Marshall_1987_mkii_jmp_50watt.gif
I presume the two separate channel approach would have less "gain", but together would slam the third stage harder? Creating more "distortion"?
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I like V1 paralleled, this is about the 4th iteration, and probably, for me, the best one. you have gain and tone control for each, a recovery stage then CF, your opinion may very :icon_biggrin:
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Thanks, Shooter! Here is my intentionally LAZY attempt to go from a series to parallel. Minimally invasive to the layout. (I only have one input jack on the front faceplate and plan to keep it that way). Connect pins 2 and 7 at V1. Then turned the front half of the voltage dividers in-between the stages into my mixing resistors. Would 220K be sufficient for that? I've seen Fender's with those values, but the JTM/JMP use 470K I believe.
EDIT: GRAYED OUT PARTS ARE THE ORIGINAL CIRCUIT. Left them for reference.