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In Reply to: Is there any real benifit sonically between class A, AB etc... posted by airtime on June 26, 2016 at 07:53:14:
OK, I guess I'll bite on the original topic. I know this thread has wound up in east bumfukt Egypt somewhere but maybe ...
There is no discussion of single ended here because class A is the only way. So it is push pull.
What class A means is more bias. Some amps are only in class A up to a certain output. For true class A you need bias even at clipping. That means the amp will get hotter than if you ran it continuously on a sine wave at one third power. Why can't the new class A power amps do that ? Because they're not really class A. A class A amp dissipates the same power at idle as at full power.
Most of your amp is already class A. Biasing higher does eliminate some distortion, and provides better speaker cone damping, but that does not always make a huge difference.
I agree with (I forgot who) said about shifting the harmonic distortion to the higher octaves. The ear is alot more sensitive, that is why you can hear a piccolo in an orchestra with over 100 other instruments.
Having a high distortion design with alot of feedback to get rid of it can do just that. Because the gain is higher the feedback it higher. But then the feedback has to be limited somehow by frequency so the feedback cannot always be flat response. Flat enough, but not perfect.
The global feedback is not always capped off. Sometimes they use more Miller caps (or capacity) in the voltage stages. this reduces the open loop gain and the feedback is less because of it. This would also tend to shift the harmonic distortion to the higher ranges.
But power transistors usually have a terrible Hfe curve. And in push pull this causes odd order distortion. Biasing them harder helps. Just look at the datasheet for a... ... nevermind I would have to find two, one acceptable and one not ant it is late. Suffice it to say is that no transistor or tube is completely linear.
And you can build a tube amp with good damping, you just need the gain and know how to keep it stable using the output transformer. About a year or so later I am sorry I sold the pair of Chicago BO-15s. They had response into the subsonic. I could have built a hybrid to set the world on its ass.
And speaking of bias, at my last job (I could go back but the dude pissed me off ad I got a gig even closer to home now) I noticed some tube amps need bias adjusted or tampered with somehow. They were redplating. Some are old and people like them, but they say "110V" on them. Nominal voltage in the US is 125 now.
And the lowering bias (current) is not OK in a tube amp because the voltages are too high. It is over the ratings of the tubes, sockets and transformers. Luckily they were overbuilt, made to last. Well they might not now.
Single ended is always class A and favors even order harmonic distortion. the ear finds this more tolerable. One of the reasons is like, musical in a way. When you play one octave up on a musical instrument is sort of harmonizes. It is double the frequency. You play middle C it is 440 Hz. You play the next C up it is 880 Hz. You play them together it is pleasing to the ear. Even if you play a very low C and a very high C it is pleasing to the ear. But it is harmonious.
But if you play 3, 5, 7, 9, 11, and so forth, harmonics of the original note, that is not harmonious.
I think that is behind the allure of single ended. There might be a hair more distortion, but it doesn't kill you.
Never pooh pooh shit like this. I knew people who could not stand the LCD TVs. Something wrong with the color and bothered their eyes. Stuck with CRTs or bought plasmas, that is the two choices. Then I run across this old article says that some people can see a slightly wider spectrum. Hmm, whaddya think ? Not proven by any means but possible. Why not ears ? There are people out there who have perfect pitch and can tune a piano by ear. In fact how was the first piano tuned ?
The answer in the end (I wrote a song with that title) is that class A, all other things being equal, will be better. But true class A with the power (not green at all) and the heating of your components, I deem it simply not worth it. Maybe if you have a pair of Quad ESL-63s in perfect condition you might consider it.
Everyone is entitled to my opinion. Take it or leave it, or argue it or shove... no don't do that... LOL
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Follow Ups
- RE: Is there any real benifit sonically between class A, AB etc... - JURB 23:46:52 07/14/16 (1)
- RE: Is there any real benifit sonically between class A, AB etc... - A.Wayne 09:17:11 07/15/16 (0)
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