jh6you said:
He is over half way through his sentence, and has caused no more trouble, so hopefully he will be back in a few weeks😉
Mr. Pass,
What do you think about the schematic and graphics I posted above? It is not the same circuit as the one that Circlotron posted.
Note that the distortions on the outputs of the op-amps are gon when R5 and R7 are increased to 391k. I don't why does this occur, maybe some simulator imperfection?
What do you think about the schematic and graphics I posted above? It is not the same circuit as the one that Circlotron posted.
Note that the distortions on the outputs of the op-amps are gon when R5 and R7 are increased to 391k. I don't why does this occur, maybe some simulator imperfection?
Well, basically the circuit's a squirrel. If distortion occurs
in amplifier A, this will show up at the output of B, cancelling.
Unforunately, the distortion will then be fed back again to
A and be reproduced (legitimately) again at A's output, so
it doesn't go away.
Also, this circuit is close to instability. The 391K value puts
you just into semi-stability and less than 390K definitely
will make the circuit fly away. If one side's input is not an
identical mirror of the other, the gain figures go to hell in
a handbasket.
pass/ - I'm a professional: don't you try this circuit at home 😉
in amplifier A, this will show up at the output of B, cancelling.
Unforunately, the distortion will then be fed back again to
A and be reproduced (legitimately) again at A's output, so
it doesn't go away.
Also, this circuit is close to instability. The 391K value puts
you just into semi-stability and less than 390K definitely
will make the circuit fly away. If one side's input is not an
identical mirror of the other, the gain figures go to hell in
a handbasket.
pass/ - I'm a professional: don't you try this circuit at home 😉
Hadley 622c
The Hadley schematic djk linked to above is similar to the Pass X
circuit in using balanced shunt negative feedback around a
differentially-driven bridge circuit. But the Hadley includes a third
corrective loop that feeds common-mode error from the output
stage back to the differential pair's CCS for cancellation.
The presence of this third corrective loop suggests to me that the
designer did not recognize the "supersymmetric" behavior of the
balanced differential feedback, inasmuch as he took some pains to
eliminate a common mode artifact that, as such, does not appear
differentially across the the load.
The Hadley schematic djk linked to above is similar to the Pass X
circuit in using balanced shunt negative feedback around a
differentially-driven bridge circuit. But the Hadley includes a third
corrective loop that feeds common-mode error from the output
stage back to the differential pair's CCS for cancellation.
The presence of this third corrective loop suggests to me that the
designer did not recognize the "supersymmetric" behavior of the
balanced differential feedback, inasmuch as he took some pains to
eliminate a common mode artifact that, as such, does not appear
differentially across the the load.
The 200R pot is for DC off-set, these were built in the days of 10% carbon composition resistors. Note that the bases must be pulled to the negative rail as there is only one voltage gain stage.
The 25K pot is to adjust clipping symmetry.
The 25K pot is to adjust clipping symmetry.
The Hadley 622 is the closest predecessor I've seen to an
X circuit, but I agree; it doesn't appear that Dawson Hadley
recognized what he had.
X circuit, but I agree; it doesn't appear that Dawson Hadley
recognized what he had.
just a few explanations about my second shematic
I don't like this shematic, because it's not 100% based on the idea I had
I wanted to use an op amp, with it's feedback resistor, it's resistor to V- and V+ to ground, this whole thing (a classical inverting op amp) as a single block to work with
do you see what I mean? Using inverting opamps, like the basic components, things we can't modify internally
And here, the crossed feedback comes on V+, that is what annoys me
I don't like this shematic, because it's not 100% based on the idea I had
I wanted to use an op amp, with it's feedback resistor, it's resistor to V- and V+ to ground, this whole thing (a classical inverting op amp) as a single block to work with
do you see what I mean? Using inverting opamps, like the basic components, things we can't modify internally
And here, the crossed feedback comes on V+, that is what annoys me
The King of Siam would have said “X-tetra, X-tetra…”
So then, does this long tailed pair driven tetrahedron amp qualify as an “X” amp? Either half of the LTP receives it’s feedback from the opposite fet’s source so I think it does, but it also receives it from it’s own side fet’s drain via the electro so it doesn’t qualify, even though the drain and source are at the same AC potential. One definite thing though, the output lines cannot swing common mode, so any cancellation of nonlinearity by that mechanism won’t work.
/Circlotron – works for the Department of Tricky Circuits.
So then, does this long tailed pair driven tetrahedron amp qualify as an “X” amp? Either half of the LTP receives it’s feedback from the opposite fet’s source so I think it does, but it also receives it from it’s own side fet’s drain via the electro so it doesn’t qualify, even though the drain and source are at the same AC potential. One definite thing though, the output lines cannot swing common mode, so any cancellation of nonlinearity by that mechanism won’t work.
/Circlotron – works for the Department of Tricky Circuits.
Attachments
Re: The King of Siam would have said “X-tetra, X-tetra…”
common mode is not an intrinisc feature of the X circuit.
(but it can be bolted on later...)
pass/ - not above bolting.
Offhand, I would say it qualifies, and the cancellation ofCirclotron said:
common mode is not an intrinisc feature of the X circuit.
(but it can be bolted on later...)
pass/ - not above bolting.
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