I am curious about where to apply the "Jerry Garcia" mod or the preamp taps posted on www.wald-electronics.com/preampmods.html (alembic would be easiest, but it would be nice to know how to do both) in the hoffman ab763 build.
I skimmed much of that webpage, but only found non-tech explanations of what was done.
My sense of it was that the preamp signal was tapped from the Twin Reverbs and sent to ever bigger power amps and speaker cabinets. But that was also the late 60's, when you on-stage amp had to fill the stadium you're playing. Not so now with good-quality PA's.
Second thing that came to mind was that in '68 Allen Bradley resistors were not necessarily anything special. Even in the late-90's, I could buy then at an electronics whoelsaler in Nashville for about $0.10/resistor. Arguably, other american-made pots at the time would have had comparable quality to the Allen Bradley pots, though the RV4 series was nicer because it was sealed.
So bottom line, I'd say the likely place to add a "tap" is right before the ionput to the phase inverter. So that'd be where the 220k resistors meet up before going through a coupling cap and into the phase inverter grid. You could either have the preamp output go to a different power amp or a different preamp feed your AB763 power amp.
If your goal is to sound like Jerry, it seems a mid-late-60's Fender preamp, with enough output power to stay clean at whatever volume you're using, will suffice.
Oh yeah: Alembic preamps from the period are basically 100% Fender's preamp circuit minus any effects or phase inverter/output stage.
Topic: preamp tap hoffman ab763 circuit (Read 5290 times)