Historical look at amps

Ayre's response. I asked Ayre the following question. Please not this is not hype but a reponse from Ayre's president and chief circuit designer.

My question........
> I’ve been corresponding with other
> audiophiles on Audiogon.com in the discussion forum under
> amps/preamps. Lots of discussion and disbelief about whether Ayre
> products are really zero feedback. May say no global feedback but its
> not possible to build an amp or pre without some local feedback and
> that Ayre’s claim is just a sales pitch. The thread is my (Keis)
> thread titled amp history.

Charles Hansen's reply

I briefly read through this thread, and this is basically an argument about semantics. (You will find that the people that argue about topic this generally have an ax to grind.)

The problem stems from the fact that there is no master dictionary that has a list of agreed-upon terms for circuits. So if someone calls a circuit a "current conveyor" or a "transconductance amplifier" or a whatever, you can probably find people that want to argue about the definition of those terms. These arguments can never be settled because there is no master dictionary that can be referred to.

The way Ayre uses the term "zero feedback" is in the context of a complete amplifier circuit and are completely consistent with the generally accepted terminology as used by major semiconductor manufacturers and experienced designers around the world (and not just in the field of audio). For example:

From the Burr-Brown data sheet for the BUF600: "The BUF600 and BUF601 are 3- stage open-loop buffer amplifiers consisting of complementary emitter followers with a symmetrical class AB Darlington output stage.... The amplifiers use no feedback, so their low-frequency gain is slightly less than unity and somewhat dependent on loading." (emphasis mine)

From the Maxim data sheet for the MAX4200: "The MAX4200–MAX4205 are ultra- high-speed, open loop buffers....Since these devices operate without negative feedback, there is no loop gain to transform the input impedance upward, as in closed-loop buffers." (emphasis mine)

Words are used to communicate ideas. (Remember that the map is not the territory.) The circuits in the Ayre products operate differently from the circuits used in other audio products. (This is obvious because they *sound* different than amplifiers that use feedback.) We use the term "zero feedback" to describe these circuits because this is the most accurate, generally accepted way to describe them.

If someone wants to argue about the definition of "feedback", they are welcome to. However, you will probably notice that those people have quite a bit less experience with circuit design than the engineers at Burr-Brown and Maxim.

Hope this helps,
Charles Hansen

Back to a subject touched by Bombay & Bigtee:

I always thought the "High end" was about accurate portrayal of a source. If it's not and it's about "Good sound" then I need to get out because it all becomes a moot point.

I agree -- yet, much of the time we see "pleasing" prime over "accurate". I.e. many audiophiles are searching for the most pleasing to the ears.
Case in point: lately we sat down with friends to audition equipment. As usual, the commentary edged upon "correct", "better", "more realistic" -- all relating to "accurate" rather than pleasing.
The music was electronic w/ some a'phile "girl with double-bass" thrown in. Quality of recording notwithstanding, how are we to gauge "accurate" or "precise" with electronic music??? A violin, say, (whether one listens to classical or not) offers some easy real-life reference -- as do many other sounds -- but electronic, or even electrical instruments???

Keis,
Thanks for posting the response from Charlie Hansen. His mostly detailed post does clarify his intentions & it is exactly what I envisioned his circuits to be - use mostly or only local negative feedback.

He is correct in writing that there is no standardized terminology for describing circuits. Often a circuit topology will acquire a certain name if it is used often enough & over a period of time. If one is in the business of creating electronic circuits, then, it is generally understood that 'feedback' pertains to 'negative feedback' unless otherwise stated & also that it pertains to some degree of 'global feedback' - either around the entire ckt or part of it. It is tacitly understood, once you graduate from EE school, that no device works w/o local feedback. so, if you are in the biz of making ckts, why even bother talking about it 'cuz it's a for-gone concl that it's omni-present.
HOWEVER, the audio market does not consist of merely EEs - it's got all walks of life. So, is it OK to assume that these people, non EEs, will know (& even care) about "generally accepted terminology as used by major semiconductor manufacturers and experienced designers around the world"? Under my breath I say "bullshit! they won't".
So........here you are, a well-known audio brand, selling seemingly good sounding equipment to many, many non-EEs BUT.........using "generally accepted terminology as used by major semiconductor manufacturers and experienced designers around the world"!!!
IMHO, the manuf (& I'm *not* singling out any 1 in particular 'cuz I feel that they are all guilty of this) is doing the minimum possible to enlighten the public about his/her product on his/her website. Hot issues within the audio community (& global negative feedback is one of them) are high-lighted in the marketing text almost the same way it would have been written in a technical data sheet.
Hell, the techincal data sheet is read by trained eyes (in the art of circuit design) while the marketing text is read by mostly untrained eyes!
It boils down to what is convenient to the manuf in the sale of the product. If you end up being less educated about, it's probably better for the manuf.
You fell for his "zero feedback" marketing stuff & really believed that he had no feedback in his circuits. If you had not asked for a more detailed explanation from the manuf, none would have been offered!
THAT IS my issue & is what I tried to highlight in my original post - Don't just eat what they give you hook, line & sinker. Ask for a more detailed explanation. They do not need to reveal any trade secrets or proprietary info for you to better understand their product & its benefits to you.
So, I'd like to ask - in this audio market, who is serving who? Is the manuf serving us the consumer or is the consumer serving the manuf?
I think, it's a bit of both - it has to be a closed loop (i.e. there has to be negative feedback between manuf & consumer. I'm almost laughing as I write this but I'm quite serious) system in that the manuf makes product to sell to the consumer so his/her tastes must be taken into account + the consumer should be able to feedback his/her preferences to the manuf & have the products evolve. However, in audio, where electronics is used to perform the signal processing, the consumer has to learn the appropriate language to have a meaningful conversation w/ manuf. To that effect, the manuf has a vested interest to teach the consumer some aspects of electronics. If that doesn't happen, the loop opens & you begin to get cr** electronics entering the market & marketing types taking ownership telling you what you should have & what you shouldn't have.
From a EE perspective I agree w/ Charlie but from a strictly consumer point of view I do not.
I have no ax to grind as I'm strictly a consumer & I'm free to choose which ever brand I like.
I might have less experience than the Burr-Brown engineers but the repetoire is fairly diversified.
(BTW, I've heard Ayre designs on several occasions & I have always liked Charles Hansen's designs tho' I have never owned one myself. I have no quarrels w/ Ayre or Charlie Hansen - just for the record. Ayre appears repeatedly in this post simply because you posted something about their latest product offering & for no other reason).

Charles Hansen should run for political office. He never did say for sure whether or not they use feedback. Only that

We use the term "zero feedback" to describe these circuits because this is the most accurate, generally accepted way to describe them.

A great non-answer.

Do you guys have any idea how hard it is to NOT use any (local) feedback, anywhere?

Thought so.........