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In Reply to: RE: Is there any real benifit sonically between class A, AB etc... posted by Tre' on June 28, 2016 at 14:17:05
but it's the topology of SET that causes the affect. Tube linearity can't fix it. Nothing can since the topology is set.
Follow Ups:
No it's the tube that causes the affect. Push pull masks it, but not entirely."Tube linearity can't fix it. "
More correctly stated "tube linearity can't be fixed". That's why it's so important to choose the most linear tube you can get.
If you load a DHT into a high impedance and don't drive it anywhere near the cutoff region or the saturation point you won't have much power but you also won't have much (if any) asymmetry.
All of the examples in the books of Class A operation show this type of operation, just using the "sweet, linear, center cut" of the dynamic curve.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/28/16
Sorry the asymmetry is there inherent in single ended topology. I checked with Nelson Pass who is a single ended fan and he confirmed what I knew. And in an imperfect world he did give the correct reason for using them. He likes the way they sound. I guess I just can't handle knowing that even a simple sine wave gets fouled up.
simple sine waves and all wave forms are always fouled up by amplification unless that amplification has no distortion.
I've never seen an amp without distortion.
and BTW this might just be semantics but the asymmetry is in the tube and SE has no way to hide that. Push pull hides it but not completely.
If you had a tube that could amplify in a truly symmetrical way then the output from a SE amplifier would be symmetrical. BTW a lot of preamp stages and input stages in power amps are SE, even input stages in push pull amps.
In this graph the input swing is symmetrical but the output voltage and current wave forms are not.
If a truly linear tube was used then the output wave forms would be linear (symmetrical).
A 45 or 2a3 or 300b operating only in the sweet spot in the middle (input signal limited) of the most linear operating condition (idle current, plate voltage, load impedance) are very close to being symmetrical.
So again, the tube used is what is causing the asymmetry in the output of a SE amp.
If you look at the output of each tube separately in a push pull amplifier you will see that same asymmetry.
A push pull amplifier combines the two out of phase outputs of the two tubes to form an output that looks symmetrical while at the same time creating other problems.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
This would suggest then that a single ended MOSFET or bipolar transistor would be even less symmetrical than a triode because their curves are actually far less linear than the triode.
If one wants a linear (low distortion) amplifier one has to start with linear parts.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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