Historical look at amps

Audio Girl, we all live inside our heads, don't you know? There isn't a thing you feel, touch, hear, that isn't a product of your brain activity. :)

Ar_t has said, repeatedly, tucked into his long winded lectures, ICE highs are wrong. I say, the ICE module is a chameleon. Actually, I'm borrowing that from another thrilled H2O owner. It can be made to sound like just about anything the designer wants.

Henry's amp has a full kilowatt high quality transformer, and over 70,000 mƒ of capacitance. These figures far exceed that of competing amps. There are other devices that I'll wager is unique in class D amp design.

Whether that is bad or good, one can debate. One thing is for sure, Henry builds amps his own way. No one should assume what they sound like.

It might be a little late to comment on this, but here at Atma-Sphere we use an old school means of defining feedback:

A cathode or emitter resistor is a form of negative feedback called *degeneration*. This form of feedback occurs in real time and also has the effect of increasing the output impedance of the circuit. A secondary form of degeneration is the type where a push-pull amplifier can cancel even-ordered harmonics in its output. In any case the feedback is characterized by being in exact real-time opposition to the output signal.

The second type, the 'bad' kind IMO, is *loop* or *global* feedback and is the more common variety referred to loosely as negative feedback. In this form, a portion of the output signal of an amplifier circuit is applied back to the input of the circuit (and can be tube, transistor or opamp). Due to propagation delays in the amplifier circuit itself, the weakness of this approach is to be increasingly less correct as the frequency increases, and/or less accurate as the propogation delay through the circuit is increased. IOW it is not in real-time opposition to the signal. Generally the output impedance is said to be lowered with this type of feedback.

I personally do not like loop feedback as it increases odd-ordered harmonics (depending to certain degree on the amplifier circuit too) in the range at or beyond *about* the 9th harmonic up the 17th- the area that the human ear (over millions of years) has evolved to use to detect loudness. Obviously we cannot change our ears! IOW, these harmonics make an amplifier sound louder and harsher, and they only need be in vanishingly small amounts to be noticed. Humans are *very* sensitive to this type of distortion.

I feel that the appearance of low and 'zero' feedback amplifiers ('zero' meaning zero loop feedback) in the last two decades is a good thing. Negative feedack is a character of the ruling Voltage test and measurement paradigm, which has been in place for some 50-60 years. It has been responsible for a lot of foolishness over that time, negative feedback's acceptance being one of them.

The opposing paradigm, the Power paradigm, uses slightly different rules of test and measurement, which conform more closely to the rules that the human ear has developed over the millennia. Horn speakers, ESLs and magnetic planar speakers all operate according to the power paradigm. So these zero feedback amplifiers that have appeared have some venerable company...

Back to our regularly scheduled flames, already in progress :)

Horn speakers, ESLs and magnetic planar speakers all operate according to the power paradigm

... another manufacturer (Mr Pass) also expressed an interest in this and actually played with a number of amp-spkr applications. The spkr units used were wide-rangers, with high magnetic fields (and correspondingly low q -- Lowthers, etc) and the results quite convincing.

A simple point of departure in considering feedback could be the very low output impedance achievable for the amp using (loop) f/back... Now, if we look at an amp alone and we concur that low output impedance is very impressive, then why not be impressed? But then we can likewise be imporessed by its horsepower, looks, engineering, etc.

If OTOH we consider the amp as ONE component of the amp-spkr interface -- i.e. we see it as an operational tool doing a specific job rather than a finality -- then the importance (or not) of its output impedance approaching zero may not be as impressive per se... we would be more impressed with 1st how the combo SOUNDS, and THEN (2nd), what the electrical and design attributes of the amp that sounds "good" are.
For example, we may conclude it's preferable to have an amp with absolute steady impedance fm 5Hz-1MHz, even if we only achieve say 1,5 ohms invariable o-impedance... (actually that's not bad). We might even decide that the keeping phase and minimising signal propagation delays due to loops may be useful: THEN, these (measurable) characteristics, rather than the previous ones, will be "impressive".

In my longwinded way, I'm suggesting that:
*quoted design, standard performance and measurement characteristics currently offered are mostly true and real -- BUT do not necessarily influence the resulting SOUND in a positive manner;
*other design..etc..characteristics may have a more immediate relation to the sound resulting fm amp-spkr interface, and those too are available -- but less standard;
*In older times, when amp+spkrs were part of a single package, there was very little problematic regarding this amp or that, etc...
*Ultimately, as atmasphere has already indicated, it's VERY difficult to design the amp that will do the best with ALL full-range (or otherwise) passive speakers. Indeed, IMO, this item will either be a statistical aberration or ridiculously expensive and experimental, or all of the above.
Cheers