Possible improvements for Aleph?
Maybe this is old hat to you, I don't know how much Aleph may
have evolved since the version of Nelson's Patent 5,710,522???
Anyways, we from the other side of the Sand/Glass curtain have
been abusing a current source we call "Anti-Triode" to the same
effect. Usually with a depletion Mosfet, and just two resistors.
A very simple totem topology as proposed by Michael J Kostner.
I like some things about both designs: Aleph and Anti-Triode
Simplicity: Advantage Anti-Triode
Direct Coupling: Advantage Anti-Triode
Enhancement Mode: Advantage Aleph
Consistancy of VGSon: Advantage Aleph
So, screwing around, I sorta blended the two...
Maybe I've ruined it, I don't know. You tell me.
And here's the LTSpice.
Using only default parts and symbols.
I had originally hoped for a 47K input
impedance, but had to settle for 600.
IRF530 gate capacitance, go figure...
I need to show you guys yet another
hybrid tube trick, The Triodlington.
where a bipolar transistor inherits
the Mu of a Vacuum Triode. Would
apply equally well to Zen, and allow
for a much smaller mosfet gate.
Another day perhaps.
This is the Anti-Triode. Its strength is simplicity.
There is also no coupling cap (C1 in Aleph patent),
aside from inherent gate capacitance...
A lack of choices in depletion mode Fettery seems
to be its main weakness. We typically abuse the
Supertex DN2540. But VGS-On varies from batch
to batch. Neither of which is a concern for Aleph,
with its bipolar junction for reference.
Aleph, Anti-Triode, Paraphase, SEPP, & H-bridge.
All trying to achieve basically the same exact
thing, with varying degrees of technical success.
Long term currents should be equal and in Phase.
Short term currents should be equal and out of Phase.
Here we simply hold the voltage across the two
resistors constant, and let the magic happen.
Without losing any advantages it holds now,
Aleph could learn this same trick, and ditch C1.
Thats all I'm saying.
You realize, of course, that both these go waaay back.
And here's the other thing I was talking about.
Get around for that huge gate capacitance.
Simply magnify a much smaller MOSFET.
To understand: First you have to know that a
Triode already has built in Zen. We call it "Mu."
The space charge between grid and plate is
an invisible distributed control surface, and
takes the place of R2/R3 in this schematic.
In either case, we give the bipolar's collector
an awareness of its standing voltage. It then
inherits the property of Zen or Mu, becoming
an amplifier of voltage, rather than current.
Its an odd bird, as it doesn't need resistance
below the emitter to be stable. The stability
comes from watching the collector. Go figure.
You could probably achieve similar results by
wrapping Zen around an IGBT. But so few
characterize for linear/audio, its hard to tell
from spec sheet how it might behave.
transform that turns a square law device into a Triode?
Without cheatin by strapping the screen to the plate.
1939 or something? I'd have to go digging to confirm.
Though he used transformer taps, rather than resistors.
The Pentode was a depletion mode device, and probably
no easy way to simultaneously direct couple and bias.
Still, he showed us the way.
Never fully understood Triodes or Zen till I read Schade.
Then it hits you: Its all the same thing, only different.
I'm not sure how far back an Anti-current source goes?
Probably some anchient variant of Paraphase. It keeps
getting re-invented and lost, over and over...
The graph is from "Beam Power Tubes" and shows how
an anode follower network transforms a Pentode into
a Triode. Very similar as Zen today does for a MOSFET.
Here we see ZeSizzler, configured as a Sziklai Pair.
Zen (or Mu) equally aware of VCE either way, and
thus, no need for emitter current awareness.
I tried several sim runs with different NPNs as a
Darlington. But every time, that pairing seemed
to kill Zen's 2nd harmonic. I've never seen it do
that with a real Triode tube. I'm not sure why
the mosfet is more sensitive?
If you like 2nd harmonic sterility, the Darlington
may bear some further investigation. Though
It does nothing to reduce the 3rd and higher.
But Zen was always about SE, and this Szikilai
pairing seemed to keep original spectra intact.
Do note: Because it is a SE amp that distorts
as such, ideal DC center isn't exactly at 25V.
Nor is it the same at quiescent, as full output.
Because I'm never certain the exact value of
VG-Bias for any given mosfet. I might need to
allow for R3 to be grossly wrong, and abuse
a servo'd CCS to pull this node up or down.
Probaby up, there's more working volts to
play with on that side.... More on this later.
Also tried the Szikilai pairing for Aleph. Works,
but no better or different than one big Mosfet.
Same/Same. I put it back the way it was.
Also tried JFET follower to buffer the gate of
Zen's MOSFET and fake input impedance up.
Works, but adds a resistor more parts, and
wants another quiet rail at maybe 12V...
ZeSizzler was much simpler, for the same
upgrade in input impedance and gain BW...
You can play with the sim, and decide for
yourselves. I'll post the .ASC momentarily.
Also threw in the model I used for the PNP.
You might have to hack it into "standard.bjt"
Its an easy cut-n-paste, once you find it.
Unless you've already built biploar lookalike
symbols that let you pick your own includes,
LT-Spice will force you to pick from Standard
If there's a better workaround, I'm all ears.
Something weird here. Not weird bad, just weird...
I believe it didn't matter Darlington or Sziklai, it was just
the relative strength of the transistor compared to the
zen mosfet that mattered. I forgot the curves of bipolars
bunch together with increasing current, as the mosfet's
spread further apart.
I didn't notice till I started throwing triangle waves at it.
My triangles had been distorted upside down of normal!
Not referring to inverted, just bent the wrong direction.
As its still wrapped in Zen (direct coupled local feedback
referenced to output voltage), it still has Mu and some
other Triodelike qualities. But its a whole different animal.
Possibly an anti-triode emulator? Which may then make
Aleph become the actual Triode emulator. Or whatever...
In any case, its not what I intended. Though it would
probably still sound similar. There's no denying the FFT
looks just like the normal Zen.
These FETs seem rather weak when choices are pared
down to those with arbitrarily ultra-low gate capacitance,
comparable with real Triodes. Ended up using way more
bipolar HFE to make up the loss in Gm. Thats probably
where all my elaborate plans got thrown the curveball.
Back to the drawing board.
all this has taken place while I was asleep?
I do seem to sleep more than I'm awake.
I see you have the similar bootstrap in ZV9.pdf
But still no direct coupling between amplifier and
Aleph, using C9 220uF to achieve that coupling.
At what point did Aleph update to direct coupling
that I might have missed the transition? Or still
using the original RC coupling?
|All times are GMT. The time now is 11:16 AM.|
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright ©1999-2015 diyAudio