Zero feedback and class A,which is better?

That's a good question, and I'm hoping some of the amp manufacturers that lurk hereabouts will post a response.

Many SET amp manufacturers and at least one OTL amp manufacturer combine zero feedback and Class A operation in the same package (three of the six amplifier lines I carry have both characteristics, so obviously I voted in favor with my wallet). I think that Nelson Pass's "First Watt" solid state amps do as well.

I'm under the impression that the Aerius has a fairly nasty impedance curve, which can work against such amps. Can you tell us anything about the impedance?

Duke

You need some power with those speakers and VAC made some pretty high powered class A 300B push-pull amps that you can run with no feedback. There are probably others.

Ayre claims their SS amps are zero feedback designs but they mean no global feedback. Any SS amp has to use at least local feedback.

First Watt amps are current sourse amps and only work with high efficiency single driver speakers.

My Aerius speakers, are 6 ohms' but can dip down to 1.6 ohms.

My Aerius speakers, (...) can dip down to 1.6 ohms

Given that, you need an extremely well stabilised amplifier circuit to drive those speakers. Some map manufacturers do spec how difficult a load their product is designed to take -- so go with that.

"Class A" simply denotes the circuit biasing. If you like the sound (I for one, do like it) then go for ultra "stabilised" class A amp.
Why don't you ask Ralph from Atma (lurks around here s/times). He should know a thing or two -- he designs tube-based amps.

'Lurk' is hardly the term!

For a speaker like this, a zero-feedback amplifier will need a little help. Fortunately there are two things going for you- the first is that the speaker is an ESL and the second is that there is a way to deal with the impedance.

The ZERO is the way to deal with the impedance and will allow any zero-feedback amplifier to operate the speaker so long as the amp is able to make enough power into a benign load.

The fact that the speaker is an ESL means that the speaker is expecting the amp to make constant power regardless of the load impedance of the speaker (which is why transistors for the most part tend to sound bright on ESLs). The ZERO will present the amplifier with the benign load that we are looking for, and a zero-feedback amplifier will have the proper 'constant power' characteristic.

Class A is important here as a zero-feedback amplifier does not have feedback to reduce distortion. Distortion is reduced by other means- class A is certainly one of those ways as it is the lowest distortion class of operation known to man. Feedback oddly enough causes some types of audibly undesirable distortions and so you are seeing a good number of manufacturers, tube and solid state, that eschew the technique. To do so means that component quality and topology suddenly got a lot more important to the overall success of the amplifier!

So the answer to the thread is: both are almost equally important.