Let me end the Premp/Amplifier sound debate ...

FWIW, I've never measured a tube amp output voltage into a loudspeaker that was anywhere close to what an SS amp delivered into the same load... going back to the 70's. Admittedly, it's a small sample, and largely irrelevant as measurements mostly don't mean diddly. 😎

Its not that the measurements don't mean anything, its that the measurements have to be performed correctly, and the important measurements have to be made (the latter rarely happens, which has lead to the myth that we can hear things we can't measure...).

Maybe I am simple fellow… but how can the sound (SPL) be the same, if the current (and voltage) are not the same?

 

Its a good question. If a given amp is making 10 watts into a certain speaker at a certain frequency and has an output impedance of 0.01 Ohms, and another amp can make the same power at the same frequency and into the same load, while having an output impedance of 1 Ohm, since both amps are making the same power, the voltage and current will be the same.

The output impedance can affect FR and distortion but it won't affect output power since the example has that aspect being the same. If it really is the same the current and voltage has to be the same too.

Pool size and sample variation play a role here.

If you had happened upon Amir’s site in the early days after he had measured just two amps (or DACs) the different measurements would be very noticeable when presented on a graph graphic. After eight or so component tests that graph would have an obvious curve to it.

But, take a look at that graph now (after dozens and dozens of tests) and what do you see: that graph has flattened out. If he continues and eventually tests thousands of boxes that curve will continue to flatten to the point that it will look like a straight line. 
 

One camp could then say “they still all sound alike”. And the other camp could say “they all measure alike”. 
 

Does this all matter? Perhaps only when doing small sample size comparisons, like direct A:B tests at home, which is really the ony practical way of evaluating purchase options…
 

This, on the OP’s leading post, says a lot:

Be true to yourself, but I find very little on earth less worthwhile than having arguments about measurements vs. sound quality and value. 

It is not like measurements are not largely correlated with preferences.
And it is not like engineers aren’t using measurements in the process of design and quality control.

They measure the living $hit out things, and they know which measurements to be doing.
If they were not, and if people did not care, then we would all be running Class-B amps. But people do not usually enjoy crossover distortion, so we have Class-A, tubes, and highly biased class-AB… as well as Class-D.

It does not matter how many measurements we do, people do not enjoy crossover distortion. And that number of people is linear with the pool size of people chosen.

Maybe I am simple fellow… but how can the sound (SPL) be the same, if the current (and voltage) are not the same?

There’s much more to sound than SPL.

Mostly, the measurements quoted in HiFi are THD and IM @ a power level.

Occasionally, a square wave or distortion spectra.

ALL into a resistor, not a dynamic loudspeaker load.

This series of frequencies into an 8Ω load resistor gives an idea of the Phase Shift in a tube amplifier output transformer @ 10W RMS. The ear is extremely sensitive to phase, but hardly anyone mentions it. Ideally all lines should look like 200Hz & 2kHz as 45° lines. Nobody publishes anything other simple meaningless measurements that the untrained can lap up.

20Hz.jpg (566×477) (ielogical.com)

200Hz.jpg (566×477) (ielogical.com)

2kHz.jpg (566×477) (ielogical.com)

20kHz.jpg (566×477) (ielogical.com)

200kHz.jpg (566×477) (ielogical.com)

A solid state amp would do much better.

This series of frequencies into an 8Ω load resistor gives an idea of the Phase Shift in a tube amplifier output transformer @ 10W RMS. The ear is extremely sensitive to phase, but hardly anyone mentions it.

The ear is only sensitive to phase when it covers a spectrum of frequencies. It cannot tell phase of a single frequency.

FWIW our OTLs have 0 degrees of phase shift at 20Hz to 20KHz. Phase shift at 200KHz isn't a concern. So a tube amp can do much better too 😉

Your answer does not appear to address the question posed.