PeterW. wrote:Mpffff.... Speakers are difficult loads altogether. Amplifiers treat them all pretty much the same within their design parameters. Well made amplifiers designed against this sort of thing will pretty much sound all the same within their performance limitations all other things being equal. Amplifiers....(..)....what they do is pretty basic and pretty simple. To the extent that they do it without adding or deleting artifacts from the original signal, they are successful.
So says the doctrine of the voltage amplifier driving positive resistive or reactive impedance loads, and to a large extent they do but not quite. Unfortunately, driving current
accurately into real speaker loads is at issue, as outined previously on this thread.
PeterW wrote:Take a _very_ difficult speaker for loading - the original issue AR9. A nominal 4-ohm speaker that drops well below 1 ohm at certain points. I know that, certainly.
OK, let's consider this example. The description of impedance, (1ohm) isn't adequate. That might be the magnitude
of impedance, but it lacks a necessary phasor to define a sense and time relationship between voltage and current. And without that, even for a sinusoid which has settled, it's impossible to know instantaneous current when driven by a voltage amplifier.
Secondly, it will be apparent that the magnitude of impedance (1 ohm) is significantly smaller than the dc resistance of the voice coil. This implies that the phasor contribution has an element of negative resistance, at minimum. And by logical extension, actually you don't know whether 1 ohm comprises nett positive or negative resistance overall, since you only know its magnitude. This ought to provoke some deep philosophical questions..........
Then you don't know that your voltage amplifier is not being asked to drive a negative resistance in combination with a reactance. And if you simulate most feedback circuits in voltage amplifiers under such conditions, you'll find stability problems and uncertainty. Quite possibly hasn't been considered in design. Same argument applies as to negative reactance. Instantaneously speaker impedance can be negative, speakers can store energy. Knowing magnitude
of impedance doesn't tell the whole story.
So no, conventional voltage amplifiers driving resistive loads doesn't describe it well, and not all voltage amplifiers cope similarly and therefore don't quite sound the same by any means. Even driving the same speakers with the same programme material.
PeterW wrote:Amplifier stability into such loads is critical - but again, well within easily achieved design limits.
Yes, stability is critical. And no, not necessarily easily achieved when one considers real loads and accuracy of current delivery as a criteria.
PeterW wrote:And *should* (hence the term 'well-designed') be able to handle at least a 20dB peak from on-board capacitance, with a 30dB peak not being out of the question. My only-mildly tweaked Dynaco ST120 can do that - and that is perhaps the least capable of my amps.
Being able to provide adequate current is but part of the issue. The distinction in action is really about being able to deliver current slew, I', and current jolt I'', and for that to be accurate under conditions where voltage, voltage slew V' and voltage jolt V'' might even be moving in the opposite direction.
I'm firmly in agreement about the proganda machine often being misleading, and would make it absolutely clear that I am not saying that audiophile amps necessarily embrace any of what I'm posting on about. I'm just pointing out one possible, unconventional explanation for why amps might accidentally sound different to an extent, and why speaker matching can be such an ad-hoc affair.
As to long umbilicals, the appropriate rider is 'with proper design considerations' then I agree there can be neither danger nor degredation of sound by doing it.
PeterW wrote: I took you for valve-challenged as you seemed to think that weight was not a valid issue.
If you search my posts here you'll see that I posted a tongue-in-cheek equation for evaluating power amp performance based on kg per Watt
I've designed, built and still use 150W + 150W rms valve monoblocks. But not exclusively, I also use SS amps.
PeterW wrote: Unless one is into OTL designs - again, another discussion,
I have a box full of EL36s and some sketch designs, maybe one day I'll do it, but transformers can be fine though generally large and heavy when good.