• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

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

Frank Dernie

Master Contributor
Forum Donor
Joined
Mar 24, 2016
Messages
6,491
Likes
15,898
Location
Oxfordshire
A single ended class A amp would be stupid to the extreme to use as the main amplification for powering a moderate to low efficiency speaker with traditional passive crossovers.
One of my friends has a Single ended class A Tron amp which he uses with Avante Garde horns.
My Goldmund speakers seem pretty efficient, about 10dB less on the Devialet for the same volume as Wilson Alexas so we gave it a try. I assume the load must have been pretty punishing or the transformer badly impedance matched because it could raise barely a peep out of the Goldmunds.
This was before I got my horns, I haven't tried it with them.
OTOH I have tried the Devialet D-Premier, programmed to its lowest power output, with his Avante Gardes and found a marked increase in clarity and detail over his valve amp, though it could have been a tad louder to explain that. He considers the Devialet too clinical and, in any case, terminally compromised by having any association with digital...
 
OP
watchnerd

watchnerd

Grand Contributor
Joined
Dec 8, 2016
Messages
12,449
Likes
10,418
Location
Seattle Area, USA
One of my friends has a Single ended class A Tron amp which he uses with Avante Garde horns.
My Goldmund speakers seem pretty efficient, about 10dB less on the Devialet for the same volume as Wilson Alexas so we gave it a try. I assume the load must have been pretty punishing or the transformer badly impedance matched because it could raise barely a peep out of the Goldmunds.
This was before I got my horns, I haven't tried it with them.
OTOH I have tried the Devialet D-Premier, programmed to its lowest power output, with his Avante Gardes and found a marked increase in clarity and detail over his valve amp, though it could have been a tad louder to explain that. He considers the Devialet too clinical and, in any case, terminally compromised by having any association with digital...

Is there some benefit to fiddling with this setting?

I've always just left it at default.

Or was this a speaker-protection effort?

In terms of sounding clinical, I thought my Expert sounded less "clinical" / "dry" than my previous IcePower based amps, but I'm quite possibly just imagining things.
 

SIY

Grand Contributor
Technical Expert
Joined
Apr 6, 2018
Messages
10,711
Likes
25,784
Location
Alfred, NY
please do not assume to understand what and how i hear.
i have been to many audio shows over the years and can usually spot a class A amp the minute i walk in to a room regardless if i am aware of the particular amplifier's topology or not.
Class A is not a topology, it's an operating point.

You haven't done the basic experiment. So seriously, your sonic claims have the evidentiary value of similar ones from Elsie Wright and Frances Griffiths.
 

Purité Audio

Master Contributor
Industry Insider
Barrowmaster
Forum Donor
Joined
Feb 29, 2016
Messages
9,555
Likes
13,184
Location
London
We had to use Tron for a few years in Munich, £27k 300Bs I think they were, one evening Thomas Woschnick plugged in a small valve amp of his own design, still valve but so much clearer, it was shocking.
I really object that an intrinsically poor product is marketed as somehow desirable .
Keith
 

Frank Dernie

Master Contributor
Forum Donor
Joined
Mar 24, 2016
Messages
6,491
Likes
15,898
Location
Oxfordshire
I noticed in the specs that one of the digital sampling frequencies is....

32 kHz

Whaaaaaat?

What the heck was that used for, given it would have a ceiling of about 16 kHz in the audible range?

Radio or some low bandwidth medium?
The NICAM system was used for transmitting radio from studio to transmitter here by the BBC for many years.
The SQ was way better than the analogue methods. FM stereo radio used an AM carrier at 18kHz iirc to carry the difference channel information, so the audio had to be filtered below this anyway.
The best quality audio I listened to in the early days was FM stereo broadcasts of live performances on BBC Radio 3.
It shows it is the recording not the equipment which is the limit for sound quality, as always.
IMHO of course.
It is also why I test myself with tones so I know what pitch the various frequencies are and ho loud, or indeed quiet I can hear them so I can work out for myself what sounds, noises and distortions are likely to be audible to me, and what are not.
 

ShadowFiend

Member
Joined
Dec 20, 2020
Messages
78
Likes
100
Class A and AB will not show any difference in both measurement and perception (hearing) if they have enough level of negative feedback. Problem is that most commercial amplifier (apart from Benchmark, Halcro, Soulution) does not use enough negative feedback.
 

MakeMineVinyl

Major Contributor
Joined
Jun 5, 2020
Messages
3,558
Likes
5,880
Location
Santa Fe, NM
Class A and AB will not show any difference in both measurement and perception (hearing) if they have enough level of negative feedback. Problem is that most commercial amplifier (apart from Benchmark, Halcro, Soulution) does not use enough negative feedback.
The SS amplifiers I work with have feedback up the wazoo, as I'd imagine would be the case in a lot of amps these days. But crossover distortion is still present, although at low levels, in most. ;)
 

ShadowFiend

Member
Joined
Dec 20, 2020
Messages
78
Likes
100
@MakeMineVinyl : how much negative feedback your amplifier has at 20kHz? I have access to many schematics/service manuals of well-known brands. Most of them still use the classic Lin circuit with only 20-25db NFB, and that's is not enough.

If your amplifier uses enough negative feedback, the distortion will be at ultra low level -130 db to -135 db like Benchmark AHB2, and I'm sure human can not hear that.
 

avanti1960

Active Member
Joined
Dec 31, 2019
Messages
121
Likes
70
Class A is not a topology, it's an operating point.

You haven't done the basic experiment. So seriously, your sonic claims have the evidentiary value of similar ones from Elsie Wright and Frances Griffiths.
the "experiment" would be a formality at this point.
 

MakeMineVinyl

Major Contributor
Joined
Jun 5, 2020
Messages
3,558
Likes
5,880
Location
Santa Fe, NM
Benchmark must think there is something to crossover distortion or they would not be paying licensing fees to THX
Contrary to rumors, crossover distortion is not a 'solved problem' in many consumer amps - there is compromise, mostly to keep heat and current consumption down.
 
OP
watchnerd

watchnerd

Grand Contributor
Joined
Dec 8, 2016
Messages
12,449
Likes
10,418
Location
Seattle Area, USA
Benchmark doesn't seem to be an advertising oriented company

Well, you could ask them if they think crossover distortion is audible.

I'd be curious to see what they say, given most on this thread think the answer is "no", at least when it comes to modern designs.
 

MakeMineVinyl

Major Contributor
Joined
Jun 5, 2020
Messages
3,558
Likes
5,880
Location
Santa Fe, NM
Well, you could ask them if they think crossover distortion is audible.

Ha! Do you really expect that they (or any manufacturer) would give an honest answer, even if they had one?
 

SIY

Grand Contributor
Technical Expert
Joined
Apr 6, 2018
Messages
10,711
Likes
25,784
Location
Alfred, NY
Ha! Do you really expect that they (or any manufacturer) would give an honest answer, even if they had one?

/notes MakeMineVinyl's "Manufacturer" tag

/giggles a bit at the delightful irony
 
Top Bottom