Oddball One

[nickb]

Had one of these boutique amps to take a look at. Name and model removed to protect the guilty.

Some unusual things, none of it to my liking. Enjoy.

[Helmholtz]

Ouch!

Hard to believe.

[35L6]

Does it work ? How does it sound ?

[Helmholtz]

Apart from the highly questionable boost and fat switch wirings, the most fascinating part is the PI with the MV acting only on one phase.
So it's also an imbalance control.

[nickb]

Apart from the highly questionable boost and fat switch wirings, the most fascinating part is the PI with the MV acting only on one phase.

Actually the boost is one of the better ideas IMHO. It bootstraps the plate resistor of V1 to increase the gain.

[Helmholtz]

Actually the boost is one of the better ideas IMHO. It bootstraps the plate resistor of V1 to increase the gain.

Yes, that one makes sense.

[nickb]

Does it work ? How does it sound ?

Sure it works. With the pad ( bias) set hot, power to max, it's OK with a lot of second harmonics. Move away from those settings and it quickly sounds a a bag of gears mixed with sawdust being run over by a tank.

Out of deference to the designers, this is just my opinion. There are those that swear by the sound of this.

[J M Fahey]

Weird is a mild word to describe it .
The asymmetric clipping is used by Peavey, but they call it "texture", way more appropriate.

And here you have two of them, because "Pad" control also shuts down the other tube, by cutting it off.

Oh well.

[SoulFetish]

Doesn't this violate.... uh, either Mesa's (or Peavy's) patent that switches push pull & "class A" operation?
It's tough to keep track of which one of those 2 is winning, and who has what.

[SoulFetish]

Weird is a mild word to describe it .
The asymmetric clipping is used by Peavey, but they call it "texture", way more appropriate.

And here you have two of them, because "Pad" control also shuts down the other tube, by cutting it off.

Oh well.

right! Doesn't the Triple X use that circuit? I remember testing the output under load without realizing that control was heavily engaged, and I thought that one of the output tubes had lived it's best life and was on it's way out. It's interesting watching the waveform on a scope while adjusting that control, vs actually listening to the output. Sometimes, my eyes fight my ears when it comes to deciding what is "better".

[nickb]

Doesn't this violate.... uh, either Mesa's (or Peavy's) patent that switches push pull & "class A" operation?
It's tough to keep track of which one of those 2 is winning, and who has what.

That's a subject for lawyers to debate. The patents expired in 2002 and 2003 I think. Not that I ever thought that there was any merit to the concept of a single power stage being both class A and AB at the same time. If the aggregate or whatever power stage is conducting less than a full cycle then it's not class A. Just silly marketing hype is all it ever was IMHO.