what obvious perceived sound quality segments found in Class A compared to AB? - Page 2 - diyAudio
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Old 23rd December 2012, 02:00 PM   #11
dewardh is offline dewardh  United States
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Originally Posted by Pano View Post
There are other advantages, of course. Such as the lack of crossover distortion . . .
That's the one. Its absense is also why "Class D sound" is often compared to "Class A sound". And it's the very essense of the "first watt" concept . . . that's where crossover distortion is worst, and most noticeable, in most amps.

Simple harmonic distortion hardly matters, we don't hear it at the (low) levels that can be accomplished in any reasonably competent amplifier. It's a useful test only because it's a proxy for IM (which is easier to hear and harder to measure). Keep the IM low and the crossover distortion lower and all is good . . . (and never dirve any amp to clipping . . .).
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Old 23rd December 2012, 02:08 PM   #12
6L6 is offline 6L6  United States
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I'm not an audio reviewer so I might not be full of lovely prose and illuminating elocutions...

Simply put, the class-A amps that I have heard (mainly Pass designs) have a certain rightness about them - some have likened then to having all the advantages of a tube amp without the downsides of tubes, and also having the qualities of a good solid-state amp without their downsides.

You will like it, I'm sure!

One thing to remember, however, is that for some people and some systems 25W per channel might not be enough... so don't blame the amp in that case. (But most people are pleased as punch with their amps. Should you find it necessary, there are a couple ways to get lots more power in the Pass/Firstwatt series.)
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Old 23rd December 2012, 02:11 PM   #13
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With any amplifier worth using, speaker drives obvious perceptions.
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Old 23rd December 2012, 02:16 PM   #14
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Originally Posted by Barleywater View Post
With any amplifier worth using, speaker drives obvious perceptions.

Absolutely. Or you can swap speaker and amplifier in the quote and it still makes perfect sense
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Old 23rd December 2012, 02:24 PM   #15
6L6 is offline 6L6  United States
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Extremely true.

Philosophically speaking, it's not a bad way to choose speakers that you really love and build a system around them.
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Old 23rd December 2012, 03:08 PM   #16
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Originally Posted by analog_sa View Post
Absolutely. Or you can swap speaker and amplifier in the quote and it still makes perfect sense

Well designed AB is easy to bias crossover into linear region of output devices, extending range of greatest linearity. Within this region, crossover distortion is lower than non linearity in output devices across operating range. Further biasing into A range has rapidly diminishing returns of improved distortion v dissipation.

Single ended output performance is limited to biasing quiescent point to center of output device's most linear range.

All loudspeakers with efficiency suitable for low wattage amplifiers inherently distort at orders of magnitude greater than lowest distortion drivers.

So, no inherently different performance in signal output, lots more heat with class A.

Regards,

Andrew
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Old 23rd December 2012, 03:35 PM   #17
Zen Mod is offline Zen Mod  Serbia
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Originally Posted by Barleywater View Post
.......

All loudspeakers with efficiency suitable for low wattage amplifiers inherently distort at orders of magnitude greater than lowest distortion drivers.

.......
aha

say that to guys who made Altec 515
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Old 23rd December 2012, 08:02 PM   #18
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by Pano View Post
At the expense of heat, of course!
Class AB amps can theoretically be 78.5% efficient, but as they are often built with high maximum power output they are operated far below their maximum output power and require biassing to minimize cross-over distortion they tend more often than not, to achieve more like 50% to 60% efficiency.

A choke loaded single ended Class A amplifier can theoretically be 50% efficient. And since they are usually built for lower max power output they tend to make more use of their theoretical efficiency.

At some point I would guess that a low powered Class A amplifier is no worse for heat than a high powered Class AB amplifier ?
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Old 23rd December 2012, 08:14 PM   #19
6L6 is offline 6L6  United States
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Originally Posted by Bigun View Post
At some point I would guess that a low powered Class A amplifier is no worse for heat than a high powered Class AB amplifier ?
Yes, kinda... That would mostly be dependent on how high the AB amp is biased, and/or how hard you are running it.

It's not really apples to apples, but I know what you mean.
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Old 23rd December 2012, 08:17 PM   #20
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Bigun View Post
Class AB amps can theoretically be 78.5% efficient, but as they are often
built with high maximum power output they are operated far below their
maximum output power and require biassing to minimize cross-over distortion
they tend more often than not, to achieve more like 50% to 60% efficiency.

A choke loaded single ended Class A amplifier can theoretically be 50% efficient.
And since they are usually built for lower max power output
they tend to make more use of their theoretical efficiency.

At some point I would guess that a low powered Class A amplifier
is no worse for heat than a high powered Class AB amplifier ?
Hi,

A silly argument. Whilst AB efficiency varies so does its power draw.

Class A draws the same power regardless of level and it never gets
anywhere near like 50% efficiency for any real music programme.

Single ended class A can't get past 25% efficiency and in real life
with real music is horribly inefficient, especially if typical listening
levels are below clipping levels.

rgds, sreten.
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