Watt Sucking Fireball Series

[kenpeter]

I like the way you think, really I do. But as usual, beware the curveball!
I don't know they work any similar, or merely drawn from the same bag
of parts?

[Roadbagger]

I think that's very cool. Its self bias feature is pretty tight <40 mv but it has to operate at a high watt bias current or all hell breaks loose at higher power. Input impedance has to be relatively low so the gate capacitance doesn't swamp the frequency response. Must work on split supplies to establish bias to the bipolar balancing act; I like self biasing methods, see Ref:2N4401-3-AMP; and the "gain pivot" for the amp is the transfer function of the lower MosFet. Zen kinda in a twisted way. This type of circuit convolution is exactly the type of thing that can nudge a change in thinking habit. Wierd, but cool. Below is what's left from optimising; Madman Muntz lives; the lower boot had little or no influence. There doesn't seem to be a convenient way to use the small bipolar devices in the signal gain path, the're busy balancing the output for all practical purposes. The intermods are a bit high but the circuit twist is interesting stuff.

[kenpeter]

OK... I see it now a little clearer how the simplified fireball worked.
Seems a concertina splitter around Q2? Q1 handles the feedback,
and the rest of it is all bias... Very much a tube circuit translated
over to the sandstate, was that a Williamson???

Mine's a Zen (Schaded MOSFET triode emulator) like you spotted
already. Then the SRPP above is a crazy hybrid of Nelson's Aleph,
Waveborne's servo'd CCS, and MJK (split SRPP resistor) style Anti-
triode. I claim nothing original.

The negative bootstrap was pretty pointless, I don't recall anymore
exactly why I thought it was necessary? Probably nitpicking idiocy.

You can loosen it up a little into AB by putting Schottky in series
with each of the output resistors. I'd suggest MBR745 to start.
Otherwise it tends to glitch a little hard when asked to do the
impossible. You noticed raising bias was another workaround.
You sho hooked on fireballs...

I had a more evolved version on my drive somewhere, but havn't
had time to go digging or reinventing that wheel. Maybe later...

[kenpeter]

This has the same issues (like pointless negative bootstrap) you noted....
But I post it for your entertainment, since I can't seem to find the one
I was actually looking for...

The challenge here was keeping the plate (triode feedback loop)
voltage high enough that the grid didn't start leaking. So I settled
for dumping only half the output swing back into Mu... I guess you
can call that a 50&#37; ultralinear strapping...

I remind that voltage gain from plate to cathode is roughly 1/(mu-1).
Which at this ratio is totally voltage attenuation, but current gained.
Concepts stolen from Smoking-Amp and OldEurope.

About as weird as you could possibly hope for.

[Roadbagger]

The Low Complexity Guitar amp follows a circuit that I've held true to form from the beginning. It is as described, a Sinclair/Peterson structured amplifier. Where this is dramatically different from Zen/Aleph is that both MOSFET output conductance elements are driven the same way, gate to source, in counterphase, no static current source or slave load. R9 is the load resistor of a Q1/Q2 composite NPN transistor whose emitter Re=R1+R21 not only serves as a V/R current modulator through this composite but also as the composite's local gain feedback loop. AC voltage developed across Re is mirrored across R9 and that voltage is AC referred to the M1 source by the bootstrapping cap C4. Divider R12/R13 simply sets a quasi Vdd/2 at the output while R16/R17 bias M2's gate to set a quiescent totempole current that tends to also hold the center in check by DC feedback. Four active parts, but as is, maximally utilized for multiple functions as coud be imagined at that time. If I can find the prototype I'll show a photo of the totally freeform hairball wiring method used, no board, just components wired in 3 dimentional space. Very few parasitics. Also, Simple can be finessed to a high order of performance if the balance of multitask elements is carefully ordered. "The simplest circuit will be one whose element count equals the number of internal nodal functions to be performed" Dr. Gene Slottow 1973

[Roadbagger]

Originally Posted by kenpeter

OK... I see it now a little clearer how the simplified fireball worked.
Seems a concertina splitter around Q2? Q1 handles the feedback,
and the rest of it is all bias... Very much a tube circuit translated
over to the sandstate, was that a Williamson???..

The difference between what the Sinclair/Peterson phase splitter does and a concertina is huge! Many early OTL amps used a concertina drive to the output stage which makes the upper tube of the output stage a cathode follower with less than unity gain while the lower half of the output stage has Gm x RL Gain. I think even one of the Futtermans was done this way. Though the classic RCA OTL amp used a balanced differential splitter, the upper portion of the output was, unsymmetrically, a cathode follower. This asymmetry is why so much gain prior is used and then thrown away with a feedback loop. The Sinclair/Peterson amp allows both tubes to operate linearly with gain the same way as a pair driving a push-pull transformer. There is no imbalance in the transfer function between the output conductance elements relative to their drives. Even a properly designed Williamson is very linear while requiring meager feedback.

[kenpeter]

Sinclair/Peterson huh? OK, got it...

For what its worth, I saw your bootstrap and knew you were
driving the upper device to have gain, and not merely to follow.
Williamson drives both devices to have gain, so maybe not that
different, except the transformer push pull rather than totem.

The presence of a bootstrap makes S/P not considered to be
a Concertina splitter? I'd never heard that distinction before,
but accept that I have not yet read the full history.

I guess Sinclair/Peterson is quasicomplimentary rather than
SRPP? As there isn't a series regulated follower thingie going
on upstairs... I tend to misuse SRPP to describe things that
maybe sometimes don't apply.

[Roadbagger]

Originally Posted by kenpeter

I guess Sinclair/Peterson is quasicomplimentary rather than
SRPP? As there isn't a series regulated follower thingie going
on upstairs... I tend to misuse SRPP to describe things that
maybe sometimes don't apply.

There's an excellent article that made me feel better about the ambiguity of perception that I've noticed relating to SRPP references by many who assume that the concept is clear. Ref http://www.tubecad.com/may2000/ I was even baffled by some of your abbreviated references earlier in this thread that I'm sure in some audience, a majority of people would have a common understanding of, however, living in a bubble, I find it more useful in first technical exchange to define all references, "not obvious to one familiar in the state of the art". Though I've been designing with everything including tubes for 44 years, I seem to have a less than current vocabulary incorporating many of the abbreviated things I see referred to with ease by others like yourself. " Zen, Aleph, Anti Triode, SRPP, etc. "quasicomp" to me means NPN and NPN/PNP composite or the inverse PNP and NPN/PNP composite. If an amplifier uses only one polarity of device in its structure then quasicomp couldn't apply, or am I out of touch here too?

[kenpeter]

Hell, I just make up words as I go. Everyone else does.

[Roadbagger]

Wadaya think, are we the only people in here?