Class A vs AB -- Do They Really Sound Different?

[Ken Tajalli]

Rare, but yes. Some opamps work in AB close to their maximum output.

Thanx.
I meant in a hifi amplifier , not anything battery powered .

 

[mocenigo]

Thanx.
I meant in a hifi amplifier , not anything battery powered .

Yes. IIRC the TI LM4562 is one such example.

 

[Ken Tajalli]

Yes. IIRC the TI LM4562 is one such example.

Just glanced over data sheet, no mention of mode of operation.
however being an ultra low noise, high output current with rapid rising distortion values at lower output voltages, perhaps it is.
thanx

 

[pma]

People are gonna come at you with measurements of numerous class AB amplifiers beating the results above.
However, on a like for like test, your results are valid.

Yes, however it would beat the measuring system and probably not the amp . Soundcard is a bottle neck, not the amp. Measured on SYS-2712, it has had THD 1kHz/8W/8ohm = -129dB (0.000035%) and THD+N vs. freq at 8W/8ohm as below

Later, even the rise at 12kHz was fixed by improved PSRR. However this is not important at all. The goal was to show that the transition from class A to class AB inevitably brings rise of high order harmonics and distortion, no matter what is the number. And that the transition to class AB depends on idle current of the output stage and load impedance. Every discontinuity in transfer function, should it be because of Gm doubling or dead zone results in this rise of high order harmonics which is moreover frequency dependent and gets worse at higher frequencies. CCIF IMD 19+20kHz is a good indicator however not used here.

 

[GXAlan]

https://www.audiosciencereview.com/...marantz-pm-90-review-vintage-amplifier.26724/

Amplifier linearity graph in this review shows that Class A might be better up to about 3W only. That’s not horrible since a lot of music happens in the first watt if you are listening at moderate levels with high efficiency speakers but the A-bias in AB is pretty good and you gain all of the powerful benefits of the Class B mode as needed for transients.

 

[restorer-john]

Time to get the PM-95 to Amir for testing then!

I'm not shipping 27.5kg of amplifier from Australia to the US and back again! And, it's not like I could give/sell it someone over there, it's a 220/240V model. And, I have the CD-12/DA-12LE player/dac and matching tuner. It's a set. Not that I use it.

I can do whatever tests here anyone wants to see, just not with an AP.

 

[restorer-john]

When I did something like this in the primordial past, I kept the power output the same, and adjusted the output stage bias. When crossover distortion appeared, it added higher harmonics and some HF noise stuff, but did not seem to affect the primary distortion all that much, although second-order terms rose since crossover glitches appeared at every zero crossing. I had a hard time isolating crossover distortion in the FFT though it was clear on a 'scope.

Primordial past... I do it all the time on vintage restorations, except I feed the output of the THD meter into the scope (x60-80dB). Am I that old?

 

[DonH56]

Primordial past... I do it all the time on vintage restorations, except I feed the output of the THD meter into the scope (x60-80dB). Am I that old?

Not going there...

HP 331?

 

[Doodski]

Not going there...

HP 331?

Rolling eyes. We had a HP 331 on the shelf to satisfy the service agreements and we never touched it once. We collected Tektronix, Power Designs, Sorenson, Lambda etc and some HP gear but the 331 was a no-go.

 

[Art Vandelay]

The Cambridge's distortion was below the AP's residual. The Parasound wasn't quite as good, though still reasonably decent.

Parasound is an interesting AB design, with jfet LTP and mosfet vas stage, which isn't 'technically best', and looking at the distortion numbers the amp probably doesn't employ a huge amount of NFB, particularly above mid frequencies where compensation kicks in.

Overall though they're a 'nice' sounding amp in my experience, having listened to the JC1's quite extensively.

"Balanced in" on the JC1 simply drives the LTP differentially, but there's an additional jfet on the -ve input to buffer the input from the low impedance feedback network, and the JC5 is probably identical, which will explain why the distortion is slightly higher and with an identical signature.

 

[mocenigo]

See a recurring spike at the zero crossing? No? Then there's no crossover distortion.

Isn't the Edge W the Cambridge design that adds a bit of DC to the signal before the Class B stage and then removes it after amplification to push the crossover distortion where it should be less dangerous (at least in theory)? Quite an obvious idea – once one has seen it. But, in fact, genius.

 

[mocenigo]

Ears are wet transducers. The signal processing is done in the wet CPU.

I am often wet when I listen to music I like a lot.
(And before you think this is a SBAF-y sexual innuendo, of course I mean that some music makes me cry ;-) )

 

[mocenigo]

Mac & Linux user here, no Foobar for me.

Otherwise, I'd love to.

Can foobar work in a wine bottle?

EDIT: it seems so.

 

[SIY]

Overall though they're a 'nice' sounding amp in my experience, having listened to the JC1's quite extensively.

Comparison to two good class D amps on hand resulted in no audible difference below overload. I guess that's 'nice'?

 

[Art Vandelay]

Comparison to two good class D amps on hand resulted in no audible difference below overload. I guess that's 'nice'?

If it's measurable, it's potentially audible though. Assuming your ears are good enough.

 

[SIY]

If it's measurable, it's potentially audible though. Assuming your ears are good enough.

Not necessarily. We can measure way beyond any human auditory capabilities. And all of those amps perform orders of magnitude beyond what even the sharpest ears can hear- assuming no peeking!

 

[Ken Tajalli]

Not necessarily. We can measure way beyond any human auditory capabilities. And all of those amps perform orders of magnitude beyond what even the sharpest ears can hear- assuming no peeking!

So we have perfected the art of measurements and their audible effect for audio equipments? ?
Since the begining of Hifi history, that statement has been claimed, I wonder how true that is.
We (humans) can easily tolerate and enjoy a tube amp with a 1% THD, yet argue that another amp (mostly SS) with a 0.1% THD has way too much distortion, and 0.00000000001% (!) is better than 0.0000000001% .
Why does @amirm even bothers to measure SINADs over 90dB?
What gives?

 

[SIY]

So we have perfected the art of measurements and their audible effect for audio equipments? ?
Since the begining of Hifi history, that statement has been claimed, I wonder how true that is.
We (humans) can easily tolerate and enjoy a tube amp with a 1% THD, yet argue that another amp (mostly SS) with a 0.1% THD has way too much distortion, and 0.00000000001% (!) is better than 0.0000000001% .
Why does @amirm even bothers to measure SINADs over 90dB?
What gives?

Yes, we can measure every aspect of electronics routinely to the ppm level. And no-one has EVER demonstrated that they could hear things that the measurements don’t show. Lots of empty claims and handwaving for sure, but no actual evidence.

 

[Ken Tajalli]

....... Lots of empty claims and handwaving for sure, but no actual evidence.

Exactly!

 

[mocenigo]

Yes, we can measure every aspect of electronics routinely to the ppm level. And no-one has EVER demonstrated that they could hear things that the measurements don’t show. Lots of empty claims and handwaving for sure, but no actual evidence.

I can tell whether the mains fuse of a power amp has been removed! Blind!