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In Reply to: RE: Is there any real benifit sonically between class A, AB etc... posted by hahax@verizon.net on June 28, 2016 at 15:10:14
"But I believe that dynamic linearity, accurate changes in level from micro to macro may be the most significant factor in sounding 'real' and an amplifier that must compress the negative half of a waveform can hardly be called linear."
While I would agree with you a zero distortion amplifier would be the ideal, no such thing exists. Therefore, you decrying this compression issue on one half of the cycle (and I think this is only an issue as you approach clipping) and claiming this is a worse problem than those generated by other topologies is not completely logical. One has to look at the outcome of what the topologies produce in terms of distortion products and how these affect human hearing.
For sure if you put a SET on a low impedance insensitive speaker you will get gross distortions that are easily audible. But if you let the amp run in its preferred power range then good ones that don't have transformer core saturation (a big problem with SET but also with many PP tube amps) will sound strikingly natural and uncolored. This is because then the distortion products are reasonably low in level but most importantly low in order and largely monotonic (most still have too many higher order components though). It certainly won't sound compressed despite what you think the scope is showing you.
I don't worry about low power as there are plenty of very good high sensitivity speakers on the market. Since there is no stereo system on the planet that I have heard that can truly do a full orchestra justice, I am not so concerned with reproudcing this kind of music at true concert level at home...it just can't be done by any system, anywhere in the world at this time...maybe someday, maybe not.
What I do care about is can it realistically do a jazz ensemble or chamber music. This is possible with a very good system and a SET with a good horn does it just about the best. Some planars with SETs, OTLs or a good push/pull triode amp can also get pretty realistic sound from this kind of music.
I am an analytical chemist, so making measurements is my living and I believe in analyzing data to reach conclusions. What the data is saying up to this point is that for what listeners generally prefer (it is always statistical...there will always be exceptions...such is the nature of humans) will be a pattern that "hides" in the ear/brain distortion and tone masking. This pattern is specific and the closer an amp gets to this pattern the more chance it has of sounding right to the largest number of listeners.
"
In deed the Berning BA150(really about 225 watts by the way) sounds best in its highest distortion(no feedback) format because in spit of added distortion that's where it's most linear."
I have yet to hear an amp actually improve when feedback was added on amps with variable feedback settings. Probably those that have a lot of feedback probably need the feedback just to work properly. In the Cheever thesis, he bypasses the feedback loop in a Hafler DH500 and gets something like 25% THD! With feedback I think it was 0.05%. So for an amp that is grossly non-linear without feedback then perhaps it at least makes the amp listenable. I would imagine a majority of Class AB SS and tube amps fall into this camp.
Funny enough, Nelson Pass shows how it is possible to make quite interesting, extremely simple designs with a few transistors that apparently sound really good. His SIT-1 and SIT-2 are the simplest possible amplifier...just 1 transistor. Very limited in power, but again high sensitivty speakers are now pletniful. I would love to hear this. Distortion is simple and acceptably low.
His white paper is interesting as he explores what happens when you add multiple active elements and then feedback to the distortion components.
Of course we cannot ignore execution of a design. This is where a lot of SETs fall short. Often there the output transformer is inadequate and saturates...this makes audible distortion of the "warm and wooly" kind. Often the driver stage is inadequate and distorts...and so on.
Same though for push/pull. That is why the VAC 30/30 is an intersting amp. It is Class A, makes around 30 watts, uses 300Bs and has variable feedback (0 to 6db). It is quite heavy thanks to the well proportioned output transformers and bass is deep, tight and controlled but well textured (no one note thud here). Mids are smooth and resolving with nice natural tone...same for the highs. However, in head to head competition with a number of SETs it is found wanting in realism...not easy to say why but the word coherence keeps coming up in conversations with friends about it ( I used to own it as an experiment, I sold it to a friend who sold it in favor of a KR Audio and then to another friend who has now relegated it to a second system in favor of 845 SET monos).
We also compared against the Lamm M1.1, which is a Class A push/pull hybrid and considered to be one of the better amps with a transistor output. That also falls short in believability.
I haven't heard the Berning amps but would love to one day.
Follow Ups:
If you believe Morricab you will spend the rest of your life throwing money away buying different tubes & amplifiers never being satisfied and not enjoying the music.
If you are satisfied with the level of fidelity you have achieved with your system then that is great for you.
I am actually satisfied right now listening to youtube and apple earbuds while at work but that doesn't mean I don't want maximum quality at home.
Morricab : I get maximum fidelity at home with my excellent system a well designed class AB amplifier with THD 0.005% @ 1 kHz , damping factor 200 at 40Hz can be considered blameless. I have been involved with many tests of speakers for comparing Live v recorded sound and the technicians involved would never consider using antique tube amps.
Edits: 06/29/16
I have no idea what you think is maximum fidelity but based on my experience to date all I can say is that I am doubtful of your claim. Very doubtful.
maximum fidelity means closest approach to live sound.
Now I am even more doubtful of your success.
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