I just once listened to the Plinius Class A SA-100 amp and was blown away by its dynamics but it was almost a dacade ago never had a chance to listen to class A. I am in the process of building a 25W class A push pull amp but after reading the passgroup I was so curious that what actually is the perceived quality in class A.. Its said to be pure but what are the obvious sonic differences either in mid or High can anybody put a comparision in some listening instrument wise or whatever to describe in simple statements...
Hi,
Not a bad analogy. A sense of effortless power, but unfortunately only
at low power. I tried a class A in my system, sublime at low volume,
but it simply couldn't cut the mustard at reasonable levels with bass.
Pity, as it was oustandingly good otherwise. Kelvin Labs I recall.
God awful phono MC/MM stages though, very nice power amplifier.
rgds, sreten.
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well you can get Class A amps at higher power level too, some that stay Class A for lower Z loads - gets noticed on your power bill
Class AB can have low level crossover artifacts - like a sticky clutch
Class AB can have low level crossover artifacts - like a sticky clutch
I've heard Class-A at very high levels and they had no problem at all, quiet the contrary.
Depends on the amp - and the power supply. 🙂
Since a Class-A is burning up at least at much power at idle as it will supply to the speakers, the power supply doesn't see much variation in draw. That, IMO, is much of what adds to the sense of stability and power that Class-A amps tend to have. As Zen said about Steve and his Mustang.
There are other advantages, of course. Such as the lack of crossover distortion - you can read about that in many articles across the web.
Depends on the amp - and the power supply. 🙂
Since a Class-A is burning up at least at much power at idle as it will supply to the speakers, the power supply doesn't see much variation in draw. That, IMO, is much of what adds to the sense of stability and power that Class-A amps tend to have. As Zen said about Steve and his Mustang.
There are other advantages, of course. Such as the lack of crossover distortion - you can read about that in many articles across the web.
Hi,
The amp I tried was 20W proper push pull class A, of course you can go bigger.
At low power it sounded immense, like it had unlimited power, but it doesn't.
rgds, sreten.
The amp I tried was 20W proper push pull class A, of course you can go bigger.
At low power it sounded immense, like it had unlimited power, but it doesn't.
rgds, sreten.
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obvious problem in Sreten's system is usage of wrong speakers 
whatever - when one can say that A class amp is really good , usually amp in question is simple in construction , having pleasant THD spectra.
that , besides lack of xover distortion , almost constant PSU loading/modulation ..... is resulting in nice sounding amp
I had opportunity to listen PL SR1 , driven with pair of PL XA60.5 ; SR1 aren't in league of efficient spks , even if having benign impedance module ; sound was flawless - maybe not exactly my cup of tea , but certainly sound which I want for one of my rooms
something to read : http://www.firstwatt.com/pdf/art_leave_classa.pdf
whatever - when one can say that A class amp is really good , usually amp in question is simple in construction , having pleasant THD spectra.
that , besides lack of xover distortion , almost constant PSU loading/modulation ..... is resulting in nice sounding amp
I had opportunity to listen PL SR1 , driven with pair of PL XA60.5 ; SR1 aren't in league of efficient spks , even if having benign impedance module ; sound was flawless - maybe not exactly my cup of tea , but certainly sound which I want for one of my rooms
something to read : http://www.firstwatt.com/pdf/art_leave_classa.pdf
Funny thing that the OP talked about Plinius. I once heard a model which could switch between class A and class AB... short story, the AB had correct timbre, while in class A mode it was colored. Really strange behaviour.
For a general purpose amp, a heavily biased AB push-pull is probably the most "sound" (pun intended) option. With a bias as high to reach the crossover point only on the strongest music transients. The PSU would be a real challenge, especially if we want to regulate it or use chokes.
For a fixed class A operation psu while expensive is much easier to make, and we have several good examples in this very forum.
I have no idea what Plinius did wrong in its class A mode, but it's definitely not my reference.
Note that I find some coloration in all mosfet class A amps I heard, included PL and my little F3. My tastes are more for paralleled BJTs with very high current and a more neutral sound. YMMV.
For a general purpose amp, a heavily biased AB push-pull is probably the most "sound" (pun intended) option. With a bias as high to reach the crossover point only on the strongest music transients. The PSU would be a real challenge, especially if we want to regulate it or use chokes.
For a fixed class A operation psu while expensive is much easier to make, and we have several good examples in this very forum.
I have no idea what Plinius did wrong in its class A mode, but it's definitely not my reference.
Note that I find some coloration in all mosfet class A amps I heard, included PL and my little F3. My tastes are more for paralleled BJTs with very high current and a more neutral sound. YMMV.
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 . . .).
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.)
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.)
Absolutely. Or you can swap speaker and amplifier in the quote and it still makes perfect sense 🙂
Extremely true.
Philosophically speaking, it's not a bad way to choose speakers that you really love and build a system around them.
Philosophically speaking, it's not a bad way to choose speakers that you really love and build a system around them.
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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Joined 2009
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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 ?
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.
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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