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

@holmz

If a single frequency SPL is measured with the same terminal voltage, that SPL should be the same for any amp.

Since almost agree that tubes sound different than solid state, then what makes up the ’voltage’ must vary. So if you measure 1kHz 2.83v at the speaker, an SS amp could be 99.999% 1kHz. A tube amp may be 99.5% 1kHz, 0.25% 2kHz, 0.05% 3kHz, etc. Additionally, depending on the amp and system, there could be PSU or loop components. An FFT of the captured output could be revealing.

There fore, depending on the equipment and pertaining to the suggestion to measure the terminal voltage to match levels, is that the program SPL may not be the same with the same measured voltage assumed to be made at a reference frequency.

Since the early 70’s I’ve had time coherent speakers: Dalhquist DQ-10, KEF 105 MkII, BiAmp Magnepan Tympany IV. From 1987 to 2020, I used Spica TC-50, which were the speakers I carried around to studios. The TC-50 was the first box speaker I heard that more correctly presented the phase coherence that I first heard on Quad 57s. and were able to correctly produce what I heard on time corrected BIG monitors in recording studios. I bought the TC-50 without asking the price or knowing anything about them as they were the first small monitor I’d heard that came close to presenting the recorded sound field. Since 2020, I’ve used Eminent Tech LFT8b’s, triamped with time alignment via miniDSP. The speakers can produce a tolerable facsimile of a square wave. And then I screw it up with tubes.

The question was about current and voltage. The current and voltage cannot be the same if the harmonics are temporally shifted relative to the fundamental.

Since almost agree that tubes sound different than solid state, then what makes up the ’voltage’ must vary.

If you put a solid state amp and a tube amp on the bench, both might measure quite flat- the H/K Citation 2 is a good example. One amp might sound bright while the other does not. But if you measure the output at the frequencies where the bright amp sounds that way, you'll see that the power can be the same as the amp that is not bright (likely the tube amp).

The difference in sound is higher ordered harmonics which tend to be audible with most solid state amps (audiophiles have been hearing this problem for the last 60 years, which has kept the tube industry alive), and the ear is both keenly sensitive to these harmonics (it uses them to sense sound pressure) and assigns a tonality (as it does for all forms of distortion) of 'bright and harsh'.

Yet at any given frequency, for a given amount of power into a given load (8 Ohms for example) the voltage and current will be the same on account on the power formula (1 Watt= 1 Amp times 1 Volt). This is a simple fact that cannot be undone. The difference you hear isn't on account of power! Its on account of the distortion signature, which is simply too little energy to show up when measuring voltage and current.

The big reveal here is that distortion is always audible! The ear has over a 120dB range and since it uses higher ordered harmonics to know how loud a sound is, its sensitivity to those harmonics is paramount, but poorly understood by audiophiles and engineers alike. Yet that is the main difference you hear between tube and solid state.

The difference you hear isn't on account of power!

Yes it is.

It's not that the distortion signature is too small, it's that no one measures it. No SPL meter is going to be better than ±0.1db @ 85dB. It likely has a nonlinear response. In absolute terms, it's not even close.

Back in the 80's Bob Carver tweaked an amp to sound exactly like another: The Carver Challenge | Stereophile.com

FWIW, we gave up on matched level listening tests in the 70's simply because it's about as worthless reading the spec sheet. An amplifier is but one component in a system. Change one thing, change everything. I think it's stood me in good stead when a guitarist says "Joe Pass is sitting RIGHT THERE!"

@ieales , @atmasphere is absolutely correct. Debating opinion and supposition with facts presented by one of the foremost authorities on the subject is rather futile. You may wear down his willingness to contribute to educating others on the subject but you won't change the facts. @atmasphere is universally respected by amplifier designers, be they solid state or tube gear designers, who are universally respected.

It's not that the distortion signature is too small, it's that no one measures it. No SPL meter is going to be better than ±0.1db @ 85dB. It likely has a nonlinear response. In absolute terms, it's not even close.

It gets measured alright. But I think I see what the confusion is. An SPL meter is only useful if the speaker is making sound, whereas we've been talking about measured output power. The two are not the same, owing to tube amps having a slightly higher output impedance in most cases- that will cause minor FR errors. My prior statement in this regard is correct:

at any given frequency, for a given amount of power into a given load (8 Ohms for example) the voltage and current will be the same on account on the power formula (1 Watt= 1 Amp times 1 Volt).

Back in the 80's Bob Carver tweaked an amp to sound exactly like another: The Carver Challenge | Stereophile.com

I remember that. He failed too; a 35dB match was all he could get.

FWIW, we gave up on matched level listening tests in the 70's simply because it's about as worthless reading the spec sheet.

If one amp was making more higher ordered harmonics, it likely would have sounded louder. An SPL meter gets to the bottom of that pretty quickly.

Don't conflate the spec sheets with the measurements. Spec sheets are IMO the Emperor's New Clothes. Measurements are not.