CLASS A AMPLIFIERS

Atmasphere,

Careful here. The ability of the ss amp to "double down" is
really a function of the regulation of the power supply in
conjuction with its power reservers. This is not really
negative feedback.

Additionally, it's the feedback on the gain stages for the
signal that can have a deleterious effect on the sound
quality.

One can design a zero-feedback gain stage that is fed by
a well-regulated power supply that has, in essence feedback.
However, the sound of such an amp won't be compromised.

The only drawback is that the amount of headroom in such
an amp is not dynamic. As you pointed out, it doesn't
increase in power for short transients.

However, I'd wouldn't count on the dynamic headroom in any
case - I'd size the amp so that the continuous power level
meets my needs.

Dr. Gregory Greenman
Physicist

Calanctus, Your speakers are a good example of what I was talking about. ESLs in general, regardless of their particular impedance curve, want to see the same power for a given sound pressure regardless of what their impedance is at a particular frequency.

In effect, they are driven by power.

If an amplifier driving speakers like this puts out a different amount of power into different impedances, the effect is a shift in tonality. This is why transistor amplifiers (in general) tend to be very bright on ESLs, as their 'constant voltage' characteristic causes them to put out a lot of power into the low impedance of the ESL at high frequencies. Some speakers (for example B&Ws) are designed to expect a 'constant voltage' amplifier, and so will have flat response in the room. This is much trickier with ESLs!

In essense, there are two paradigms competing in high end audio today- the 'voltage paradigm' and the 'power paradigm'. No-one talks about this!- but we see it all around us:

The Voltage Paradigm is the reigning test and measurement paradigm. It is only concerned about voltage, and so when measuring an amp or speaker, voltage is the only thing considered. 'Constant voltage' output refers to an amplifier that puts out constant voltage regardless of load (contrary to morbious' comments, this does not require power supply regulation to accomplish this- merely enough feedback). Such an amplifier is regarded by these rules to be 'load impervious'.

The problem lies in the fact that negative feedback runs counter to how our ears detect volume (higher odd orders being the key- these are enhanced by negative feedback). Additionally there is the question of whether or not a speaker is driven by voltage or power, and of course the answer is power. So the 'power paradigm' says that the amplifier will have little or no feedback to reduce the odd ordered harmonic that the human ear dislikes, and that the amplifer will produce (or attempt to produce) constant power into all loads. This, BTW, is very nice for ESLs, horns and magnetic planars. Amps that fall into this category are SETs, some OTLs, transformer coupled push-pull tube amps and a very small number of transistor amps with zero feedback. Such amplifiers typically have higher output impedances, and nearly all will be unsuccesful at the goal of constant power (in fact many designers of such gear may not even acknowledge that they even *have* such a goal).

A parallel controversy is the subjectivist/objectivist debate. Roughly, the power paradigm is more subjectivist and vice-versa, but this is *not* by any means cast in concrete!

The power paradigm has its roots much further back than the voltage paradigm (1920s), and only seemed to resurface in the last decade or two. The obvious proliferation of advanced SETs (and tubes in general), horns, single driver full range speakers and the like are an indication that no-one has all the answers.

Atmasphere, thank you for your explanation. Although I'm no EE I think I understand what you're getting at. I will have to try a suitably high quality and high power SS amp on my panels to see what it does to the treble.

Yada, currently I am using the Odysseys; their midrange is simply excellent, and they have good dynamics, but (as mentioned) they are not the equal of my previous ribbon speakers in the topmost treble. (Overall a much more musical experience; it's the midrange that counts the most!)

If an amp is rated 200watts @ 8 oms and 400 watts @ 4 oms what is the 3oms rating.
The reason I ask is Im trying to match components with Thiel CS 2.4 speakers I just purchased.
Thanks,
Dave

It depends on the amp. In theory if it is a solid state amp we would hope to see 600 Watts @ 3 Ohms if the amp is rated as 200 watts @ 8 Ohms. This generally doesn't apply to tube amps. Not all (in fact few) amps are capable of this kind of power delivery. Don't assume an amp is capable of this.