Some circuits are more sensitive to these.
Many circuits are not sensitive to this. For example, CFP circuit.
You can query the results in the self book.
Of course, if you are interested, you can send information, and I can verify it for you.
I have APSYS two2722
https://www.diyaudio.com/community/threads/l20-5-ap-sys-test-data-my-design.323965/
CLASS B L20.5 CFP THD<0.0015%
I did this only once with a fully restored Realistic STA2250 with much better transistors and caps as its bias pot allowed for a wide range .Class A ...very hot, but sound was awesome.Unfortunately I had to revert it back to class AB as active cooling was too noisy.
That's not really fair comparison, as you could have applied the same amount of feedback to the class-A amplifier and then it would still outperform the class-AB amplifier. In fact, you may be able to apply a bit more feedback to the class-A amplifier because the poles of its output stage vary less with signal.
On top of that, the currents through the output devices in a class-B or class-AB amplifier are always distorted (ideally half-wave rectified waveforms). When these magnetically couple into the signal path, you get extra distortion that you ideally don't get with class A.
Nevertheless, my non-switching class-AB amplifier is good enough for me.
I have one of those. Nice little amp. At one point a cat peed in it, it was redone, and has probably been tweaked up a bit.
dave
Class AB, some NAD were acceptable for my budget. But surprised noone cites Hafler ?!
My main is a class A on few watts then class AB : Chord. Neutral to my ear and say all from the sources connected to it.
My main is a class A on few watts then class AB : Chord. Neutral to my ear and say all from the sources connected to it.
Last edited by a moderator:
Yesh! That cat knew how to get to you! From what i understand the Sony TA-F808ES runs pure class A until a certain volume level. To my ears those class A and AB amps sound a lot better than Class D.. Hopefully I am ok saying that! Class D can still be nice if an analog source is hooked in.
I have a NAD than I recaped with my voodoo as it was 30 yo. It is a class AB and it sounds very more nicer colorfull than the Chord. However the Chord is as clear as a scalpel that looks under the skin and virtually not here but can drives any load, so the source must do the colorfull job and be chosen or tuned accordingly. Choose your poison.
Both are nice but opposite philosophy. The amps having a nice harmonic signature may help all the cold sources you can see today.
Both are nice but opposite philosophy. The amps having a nice harmonic signature may help all the cold sources you can see today.
Every amp biased in AB runs "pure class A until a certain volume level". Whatever pure might mean in this context.
It gets really vague with non-switching class-AB amplifiers.
For example, suppose the quiescent current is 100 mA and the current through one side tends to 50 mA when the current through the other side gets large. Both sides are then conducting current during the entire cycle, so if you take the definition very literally, you could call it class A. However, during the peaks, the side that conducts 50 mA is not contributing much to the signal transfer, so in that sense it's class B or AB. The transition from the region where both currents are varying to the region where one side is just conducting 50 mA is usually gradual, so there is also no clear transition from class-A to class-AB operation.
For example, suppose the quiescent current is 100 mA and the current through one side tends to 50 mA when the current through the other side gets large. Both sides are then conducting current during the entire cycle, so if you take the definition very literally, you could call it class A. However, during the peaks, the side that conducts 50 mA is not contributing much to the signal transfer, so in that sense it's class B or AB. The transition from the region where both currents are varying to the region where one side is just conducting 50 mA is usually gradual, so there is also no clear transition from class-A to class-AB operation.
I think in this question it all depends on what you define as best. Measuring the best is not necesairly sounding the best for everyone. The ACA is measuring very bad, but sounds very good for instance. I take the question as subjective the best.
Anyway, my subjective favorites (of those i know):
Class A:
Pass Labs XS series (i know, ridiculous expensive, but it sounds also like that).
First Watt SIT3
Sugden A21 (the original, i don't know about the recreation).
Solid state:
Marantz 1030 (and that whole series) when in good shape because they are old and often not in good shape.
PrimaLuna's EVO 400 (tube amp)
Benchmark AHB2
Anyway, my subjective favorites (of those i know):
Class A:
Pass Labs XS series (i know, ridiculous expensive, but it sounds also like that).
First Watt SIT3
Sugden A21 (the original, i don't know about the recreation).
Solid state:
Marantz 1030 (and that whole series) when in good shape because they are old and often not in good shape.
PrimaLuna's EVO 400 (tube amp)
Benchmark AHB2
DEF amplifiers.
DEF stands for Depletion / Enhancement Follower, with First Watt SIT-3 as an example and several DIY projects as SissySIT and LuDEF available.
It’s a crazy breed where both positive and negative rail output semiconductors increase current with signal, not by the same amount depending on transconductance difference, and output is difference between two currents.
DEF stands for Depletion / Enhancement Follower, with First Watt SIT-3 as an example and several DIY projects as SissySIT and LuDEF available.
It’s a crazy breed where both positive and negative rail output semiconductors increase current with signal, not by the same amount depending on transconductance difference, and output is difference between two currents.
Most of them are, but not necessarily all. For example, the usual CFB input stages can operate in class AB when the signal rate of change is very high.
Thank you for clarifying. I was mistaken because AB amps do run class A until a certain level.
A lot of knowledge in this thread. My Mark Levinsons ran on Max when switched on and was using a Rotel pre amp to attenuate the power. Low or high volume the 20.6 sounded better than my 808. It’s pretty clear who won in sound quality, but the 808 ain’t no slouch either. The power stage of the 808 is good once you get the volume up. No loudness switch in either model
There are a lot of great amplifiers in this thread and have been looking at the models listed. Even though there are many more modern amps, they cost a fortune and mostly run Class D which is quite sterile on it’s own. I’m concerned about getting a dry sounding amp if I opt for a newer one
A lot of knowledge in this thread. My Mark Levinsons ran on Max when switched on and was using a Rotel pre amp to attenuate the power. Low or high volume the 20.6 sounded better than my 808. It’s pretty clear who won in sound quality, but the 808 ain’t no slouch either. The power stage of the 808 is good once you get the volume up. No loudness switch in either model
There are a lot of great amplifiers in this thread and have been looking at the models listed. Even though there are many more modern amps, they cost a fortune and mostly run Class D which is quite sterile on it’s own. I’m concerned about getting a dry sounding amp if I opt for a newer one
Last year I had 2 Threshold 400 for reapair in my workshop, one from -78 with simpler VAS-stage and one -79 with totaly different VAS and driver.
Both of them had blown outputstages, burned emitter resistors and drivers.
After a lot of matching and soldering they worked lovely. I must say that the -79 was one of the best sounding amps I've heard, smoth details, and brutal power.
BR
Figge
Both of them had blown outputstages, burned emitter resistors and drivers.
After a lot of matching and soldering they worked lovely. I must say that the -79 was one of the best sounding amps I've heard, smoth details, and brutal power.
BR
Figge