John Curl's Blowtorch preamplifier part II

[Jakob2]

@ vacuphile,

the simple answer would be, " we are measuring the same things as ever, with better measurment gear thus higher resolution, but these measurements obviously do not fully reflect the way our perception works"

Of course a good amplitude linearity is mandatory and low THD+N too, but beside that the relationship between perception and usually measured numbers becomes more and more "unstable" .

An additional factor is the somewhat artifical arrangement for measurement which does not really reflect the normal usage. As mentioned already often in the cable discussions, measuring a single amplifier with an audio analyzer on a bench with transformer coupled inputs (and maybe isolated mains connections) is a quite different condition.

Some combinations with other preamplifiers, loudspeakers and sources might be less ideal than others.

But, despite the overall good measured performance, the slope of the THD+N curves in the upper frequency region could be a hint why the results in real world setups might be different.

[SY]

Originally Posted by ThorstenL

Can you actually tell me which of these measurements is the one that shows that the Amplifier will sound good? Because this is what potential customers want to know.

None of them. As usual, you're attributing statements to me that I never made.

[ThorstenL]

Dear Sy,

Originally Posted by SY

None of them. As usual, you're attributing statements to me that I never made.

I attributed nothing to you. I asked a question to clarify your statement.

Sy: ".... the measurements .... quite nicely show the capabilities of this amp."

T: "Can you actually tell me which of these measurements is the one that shows that the Amplifier will sound good?"

Sy: "None of them."

To me at least now everything is very clear and there is no possible misunderstanding.

Ciao T

POST SCRIPVM: the .... above indicate cutting out a sub-section of the statement that is superflous to the point, however to avoid being accused of editorialising, here the full quote:

Originally Posted by SY

PMA's comment is irrelevant- the measurements provided go well beyond a single-number THD/IM measurement and quite nicely show the capabilities of this amp.

[PMA]

Originally Posted by Jakob2

the simple answer would be, " we are measuring the same things as ever, with better measurment gear thus higher resolution, but these measurements obviously do not fully reflect the way our perception works"

This is IMHO very well said. THD and IMD measurements cover very long time period of settled non-changing signal. The ear is most sensitive to transients, to the rising part of transients. Thus the methodology of THD and IMD is wrong regarding human perception. And it does not explain differences in sound of amplifiers at all, as the speaker distortion is about 20x higher at any level than that of well engineered solid state amplifier. Only some tube amps and poorly designed solid state have higher non-linear distortion than the speaker.

The only reason why THD/IMD is so popular is that it is easy to measure. Engineers love simple measurements that can be simply evaluated and compared. But, the ear is the judge and engineers tend to overlook principles of human hearing, or they rather do not know it at all and simply do not care. They usually use the equation lowest THD = best amp. Not many changes since 1970-ties.

[SY]

Originally Posted by ThorstenL

I asked a question to clarify your statement.

What was unclear? The output replicates the input to a high degree of accuracy even at the high powers needed to show any artifacts. The power is high enough that the amp is unlikely to clip. Frequency response does not vary with load.

[ThorstenL]

Dear Sy,

Originally Posted by SY

What was unclear?

To some the term "capabilities of an Amplifier" may be taken relating to the resulting sound quality. I wanted to clarify if there was anything of the like in your statement.

And I thank you that you made clear that for you "capabilities of an Amplifier" does not relate to sound quality.

Ciao T

[SY]

Unless transformer laminations are loose or capacitors are defective, amplifiers make no sound, good, bad, or indifferent. When they do, it's generally a rather boring 60 or 120Hz humming noise. They are electronic devices, not transducers or instruments.

[Pano]

FWIW, and if anyone cares - I've measured amps that have a changing harmonic structure depending on frequency and impedance. E.G. the forth harmonic might vary depending with load while the others don't change much. H3 might change more depending on frequency than other harmonics.

Not things that show up in the typical FR & THD specs. Maybe IM.

[jlsem]

Originally Posted by scott wurcer

Cool, I've never had a chance to listen to them in fact the only big name SS amp I spent any time with were some Krells but the friend who owned them insisted on playing everything at 11 with lots of window rattling bass. An all Cello/Theil set up at a local hifi salon had me putting my hands over my ears as folks like to say. Do you like Cary?

I don't remember if I ever listened to a Cary amp. Krells are pretty lifeless, but I do like the solid state amps designed by the guys who haunt this forum, namely Parasound, Ayre and Pass. Siegfried Linkwitz used Pass amps this past RMAF and they improved his system considerably.

Most tube amps have distortion so low that you never hear it, when paired with speakers of sufficient sensitivity. It's really hard to say what amps sound good and which ones don't because a lot of systems on the whole are not set up properly. Local hi-fi salons are usually a poor place to assess performance of an amp.

John

[DF96]

Originally Posted by PMA

There is almost no correlation between THD/IMD measurements and subjective assessment of sound quality.

There clearly is some correlation. Two snags though:
1. the line is fuzzy
2. it might not go through the origin

People who deny snag #2 are sometimes forced to exaggerate snag #1.