Class A, B, AB.. explained and Amp Brand results

[OzzieAudiophile]

Hello.

The following link provides a technical explaination of each Class type.

Perhaps good food for thought, don't use the following information to necessarily
stay away from specific brands/models. This is "purely" for information purposes
only.

http://en.wikipedia.org/wiki/Electronic_amplifier

Just taking a look at the last few owners manuals that I've downloaded from the
official websites here are the Class Types for brands of amps/receivers :

Balanced Technology : does not mention in the manuals
Boulder 2060 : Class A (weights 332 pounds, shipped !!!)
Bursonaudio PI-100 : Class AB
Cambridge Audio Azure Series (840 etc) : Class A and Class AB
Denon : Class B (from manual of top of the range receiver)
Integra : does not mention in the manuals
Marantz : does not mention in the manuals
McIntosh : does not mention in the manuals
NAD Master Series Integrated Amp : Class A
NAIM : Class B
Parasound A21 : Class A and Class AB
Plinius P10 : Class AB
Primare : Class B
Rotel : One series confirmed as Class D
Yamaha : Class B (took a look at many manuals, all Class B)

It is highly recommended to read the full owners manual as other features within
the components should be considered and not necessarily take the class type
as the main reason to buy or not buy the component.

It is also recommended to read as many reviews of the products. As stated,
the above information is purely for information purposes only.

I hope you find the above information useful.

[Feanor]

Thanks for your research, OA. It's interesting to see the claims of manufacturers.

Quite a few imply a greater degree of Class A operation than is really accurate. In the first place, Class A operation is common among preamps or the first stage of amplification.So for integrateds, the manufacturer will proclaim Class A, but on close inspection you see this really only applies to the preamp circuitry. By the same token they claim "A/AB" operation where the pure "A" part is only the front end or first amplification stage.

Apart from switching amps, i.e. Class D and proprietary variants, almost all powerful amps are Class AB, that is, Class A at low power levels to avoid "notch" distortion, but Class B and higher levels. Pure Class A amps are rare and tend to be lower powered. Pure Class A wastes a low power which is dissipated as heat, the more powerful the amp, the more waste and heat.

Sophisticated ciruitry has be developed, e.g. by Nelson Pass, to automatically adjust the Class A "bias", (point beyond which the amps goes to Class B operation). Thus as low levels volumes the bias is set just high enough to ensure continuous Class A operation but not produce excessive heat; as volume increase, the bias is increased to the same effect.

A minor issue I have with my Monarchy SM-70 Pro amps is the degree of Class A operation and also the amount of feedback. At one time this model was advertised as "Class A, zero feedback". I addressed the Class A question to the principal, C.C. Poon, who was quite coy on the subject, he replied that the amp operates in Class A mode "most of the time". In fact these amps run quite hot. However they are no longer advertized as "Class A". And by the way, feedback is used in the front end circuitry though not in the final stage nor globally, (back-to-front).

[oaqm]

There is no way on God's grey earth the Denon, Naim, Primare, and Yamaha are straight Class B amps.

They would sound like old AM hand held transistor radios if they were.

I have a 20 ounce ice-cold coca cola that says they are all A-B amps.

[elapsed]

There is no way on God's grey earth the Denon, Naim, Primare, and Yamaha are straight Class B amps.

They would sound like old AM hand held transistor radios if they were.

I have a 20 ounce ice-cold coca cola that says they are all A-B amps.

Here's a posting from 1998 from Julian Vereker (1945-2000), founder of Naim. I can assure you my Naim stack doesn't sound like an old AM hand held transistor radio. But I'll take that 20 ounce ice-cold coca cola.


Date: March 29, 1998 03:55 AM
Author: julian vereker
Subject: Bias

All Naim power amps are class B and they have as low a bias as we
can manage, just a few milliamps.

There are two reasons for doing this, in order to make a good
push/pull power amp, the two halves need to match very closely
since there is only one common feedback loop - this applies whatever
the 'class' of the amp. If one achieves this degree of precision
then one only needs a very small bias current.

Also it is extremely wasteful of resources making class A power
amps, since they use large amounts of electricity even when they
are not playing music, this means the waste heat has to be dissipated
into the atmosphere without overheating the components and thus
shortening their lives, which implies large heatsinks, big heavy
and expensive in terms of resources pieces of equipment.

There are quite a few power amps about, that are called class A
for marketing reasons, but are in fact to all intents and purposes,
class B. (Save the planet - buy class B).

julian

[oaqm]

Naims are not pure Class B.

"one only needs a very small bias current"

That's the definition of an AB amplifier.

[elapsed]

That's the definition of an AB amplifier.

Touché..

[OzzieAudiophile]

Order , ORDER (bang bang bang, with gavel) haha.

Seriously, I have noticed that models which are AV receivers are more
class B than class A, or AB. The nicer amps are either A or AB, or
combination of A and AB. Well, I wouldn't use what class it is as
the most important factor in considering to buy to dismiss a specific
brand. How it is built, the reputation, reviews, cost, have to be
considered.

If you're unfortunate like myself, the choices are a bit thinner than
the Europe and USA. Still, the amp/receiver MUST be able to drive
your speakers efficiently and sufficiently, having much reserve power
does make a difference also.

It appears that Class AB and/or a combination of A and AB seem to
either have the best of both worlds, and best value for money.

[Ajani]

Well, I wouldn't use what class it is as
the most important factor in considering to buy to dismiss a specific
brand. How it is built, the reputation, reviews, cost, have to be
considered.

Ummm... and how it sounds, might be also be a consideration.....

[Feanor]

For me, solid state design is eputomized by Pass Labs XA.5 amplifiers which combine high-power, ultra-low feed back, balanced, almost exclusively Class A operation. They sound great by all reports. And, damn, they look gorgeous.

Read some not-too technical discussion of the XA.5 design here.
...

[OzzieAudiophile]

Ajani - if I had to include every obvious aspect of an amp, I'd be listing them all until
the end of time.

I thought we were not dealing with 5 year old kids, and had to be overly obvious.

[E-Stat]

Seriously, I have noticed that models which are AV receivers are more class B than class A, or AB.

I'm with oaqm about this. I think you don't really understand what a true class B amp would be like. Here is a design that only works well at full output. At anything less (which would be 99% of all listening), the distortion levels would skyrocket. The only integrated amp I've owned was an AR Integrated back in 1972 which was a class B design. Resolution went totally out the window at low levels. Even the least expensive components these days are AB designs.

Like balanced vs. unbalanced connections, you really cannot make any sweeping judgments on the output design alone. There is no one way to implement a class AB amp either. The better ones are not only biased further into class A, but they are simpler designs with little or no global feedback. They also have far larger power supplies. Whereas my 1981 Threshold Stasis 3 (100 watts/channel into 8 ohms) has 63 joules of storage (50,000 uf / 50 v), my VTL mono amps have 250 joules of storage each. The big brother VTL Sigfried amps have nearly 800 joules each. You just don't see that data in common specifications. Here's the formula if you know the total capacitance and rail voltage (not capacitor rating): J=CV(squared)/2. Thats capacitance in farads times voltage squared divided by 2. HT receivers have tiny power supplies by comparison.

rw

[OzzieAudiophile]

Thanks for the explaination E-Stat.

Well at least in Australia, the more expensive amps with the good reputation are more ClassA than not. Assuming one can afford it, it is better in general to purchase a Class A amp, than any other class ? I have not seen much bad reviews on Class A amps.

A lot of Class A (at least in Australia) are in a price bracket way above much else.

I'm still auditioning other amps at the moment, and out of my short list half of them
are Class A, the rest are not. I found out that McIntosh are Class A, but most of your
feedback has been negative, in terms of their design.

EG.