initial preamp stage clipping

[loudthud]

Why not an OT set up like a variac (or Lionel train transformer) where the secondary winding is exposed on a torroid core and a wiper slides across it.

[Enzo]

Or actually USE a Lionel transformer as an OT. Or maybe not...

When Juan suggested a 100 tap OT and a rotary switch, for some reason my first thought was to motorize the switch et voila - instant tremolo.

[Diablo]

Well, a 100 tap OT + a 100 contact rotary switch might do the trick

Wouldn't the wildly changing reflected impedance play havoc with the output tubes?
Wouldn't each turn of the rotary switch send a voltage spike through the transformer because of the momentary interuption on the secondary?

[imaradiostar]

If you've got power to burn (and you likely do with a 100 watt amp) set it up with the transformer running into a 2 or 4 ohm load. Any variac and 8 or 16 ohm speaker downstream isn't going to effect the amp enough to cause any problems.

Sure, it'll work, but will it sound good? No idea.

I've built a few "airbrake" style attenuators for friends. I always leave off the lowest volume "bedroom" setting with the variable rheostat because, in my experience, it sounds like ass. I usually build them with -3, 6, 9, 12 and 15 db positions, all of which are pretty usable with minor tweaking of the tone on the amp. I'll usually bridge a few resistor positions with caps so the really highly attenuated settings have a little treble boost.

I tried to build (two years ago) but have since forgotten a "bedroom" amp with a cheap 8 ohm l-pad type attenuator after a small AC4 style circuit, wired as "master volume" on the front panel, in the chassis from some old solid state practice amp. I never finished it. Maybe I should. It'd be an interesting experiment if nothing else.

Jamie

[imaradiostar]

When I said "into a 2 or 4 ohm load" I meant a giant wirewound resistor.

jamie