• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Stay tuned for the Pass F4 tube preamp


diyAudio Moderator Emeritus
2002-10-24 10:19 pm
Vix, Charles, I'm almost finished an article on my F4 preamp (just got all the schematics drawn this part weekend, always the toughest thing for me). I'll let you guys know when it's submitted to AX. The HV regulator is almost identical to the simplified Maida reg that I used for the screen supplies in the Red Light District amp posted elsewhere on the site. I thought it sounded pretty good (still does, in fact, I use it in my main system now), but I'm prejudiced.

There were indeed fundamental problems with the early Audio Research preamps, but the power supply came rather far down the list. I suspect that making the supply "too good" brought those problems more forward. I played around with those circuits back in the mid to late '70s and finally figured out that the fundamental flaws were too much to overcome. Once you have that topology and that tube choice, you're in a dead end.

And, of course, a wise tube designer will (IMO) make his circuits non-critical regarding the fine points of regulation. If I hear an improvement using a better regulator, I'm likely to rip my circuit apart to figure out what I screwed up so badly in the design that a couple of microvolts on the rails would be audible.

Sorry for the OT. Maybe some kind moderator who is not participating here will split off this part of the discussion.