Jim Lesurf wrote:
In article , Rob
wrote:
Jim Lesurf wrote:
In article , Rob
wrote:

snip

and surprisingly (to me) there doesn't seem to have been many
rigorous tests to underpin the 'little if any difference' thesis.
You would need to clarify what you mean as I am unsure of the point
you are making.

I'll try.

1. It is maintained that most amplifiers sound the same;
2. I haven't see many tests that support (1)

That does not seem to me to be the same point as you made above. :-)


Point 1 is the 'little if any difference' reference. It's related to a
reference Serge Aukland made applicable 'most modern amplifiers'(1).
Point 2 is a reference to 'many tests'. There are two points - not one.

Nor it is clear to me who "maintains" this as it isn't something I've
said. :-)

I would never attribute you with anything quite so unequivocal :-)

I've seen various people say variations on "well designed
and appropriately used" amps give indistinguishable results. But that
isn't statement (1). So are you asking for evidence for a claim no-one
has made?

Nope - see above.


Is your concern simply that the evidence is based only on all the cases
tried? If so, it is open to you or anyone else to collect more evidence.
i.e. to carry out more comparison tests of appropriate kinds.


My concern (such as it is) is simply this: I maintain different modern
SS amplifiers can sound different. They are particularly affected by
load (speakers) in my extraordinarily humble opinion. Others (on this
NG, not you explicitly so far as I can tell) maintain this is highly
unlikely. For example, I'm pretty sure I could hear the difference
between a Cambridge audio power amp, a semi-pro power amp, and a Quad
405 power amp.

To do this you would have to define what you mean by "most". i.e.
do you mean more than half of all amps in use, or more than half
the designs, or more than half of those ever used, etc? e.g. can
we ignore the amps in TVs and portable radios and cheap 'music
centers'? If so, we have to define the line that rules in/out
a given amp, and give a plausible basis for doing so.


Again, Serge guided me on this. This issue has been mentioned many
times. 'Most' means virtually all modern SS amps that meet certain
criteria (1).

You would then have to devise a performable test/experiment and do
so on a basis that deals with why you feel all the tests thus far
have somehow been 'unrepresentitive' of "most" amplifiers. This means
giving a plausible and testable reason for why the previous tests
all 'selected' amps such that none of them were in the same alleged
catagory as "most" according to your claim.

You would then have to *perform* the tests and collect the evidence.
There would have to be a statistically significant number of tests
and you'd have to be able to establish the level of significance.


Yes, I understand that's necessary if you're going to take notice of
anything I say.


Then a decision could be based on that *evidence*.

If the above isn't done, then your idea is a speculation which the
current evidence seems not to support. This puts it into the "teapot
orbiting the sun" class. i.e. a fanciful speculation which can't be
tested and which the evidence we have shows no sign of supporting.

It is easy to make up speculations that remain untested or are
essentially intestable. However this means we can invent an infinite
number of them which may all conflict. Given this, it seems to me
to be a waste of time to take them seriously *unless and until*
someone does the above process to find evidence from a test whose
outcome had the ability to either conflict or support the idea.


I can only point out that "most" (indeed all) the relevant tests I know of
showed no sign that those who listened could distinguish one amp from
another - given a fairly basic set of requirements like level matching.

I find this virtually impossible to do, even (or because of?) the crude
sound meter I have. I assume the idea is to match levels between 20-20K Hz?

Interestingly, this includes cases where I and others were quite surprised
that those involved *couldn't* distinguish as there were quite large,
easily measureable, differences. Indeed, in more than one case the
amps compared were deliberately chosen with the aim of being able to find
clear differences. Some of the participants chose them for this reason,
but then failed when tested to tell one from another.

This means that we have in audio a history of people who are confident
they can 'hear differences', but when tested fail to show they can hear
what they believe. In this context it seems reasonable to be wary of
claims - although it is quite clear that some differences are indeed
audible, and hence are not contentious. So, for example, tests generally
proceed on the basis of level matching as it is generally accepted that
a change of level can be audible if reasonably large.


That I maintain there's a difference doesn't mean there is one.

It's quite simple - if I didn't think there was a difference I wouldn't
have so many SS amplifiers! Until about 10 years ago I only ever had one
at any one time (with a bit of overlap) - heightened awareness has
arisen with Dynaudio speakers.



Given this, I'd be interested in *evidence* to the effect that it isn't the
case that 'most' amps *don't* sound indistinguishable in an appropriate
comparison - excepting for reasons which are uncontenious and already
understood/accepted. Alas, arguments, discussing the meanings of words,
opinions, speculations, etc, aren't evidence

Of course, if your point is that 'most' exhibit problems in use like
obvious distortions, changes in response, etc, then I can see why you would
be concerned. There may well be 'many' amplifiers that produce audibly
different results - indeed there are various ways to cause audible
changes if we wish. However note the qualifications I have made about
what was being compared, and how.

However in the absence of evidence I can't see much point in what you are
now saying.


Okeydokey.

Rob

(1) This was Serge's reply to my question 'what's necessary to ensure
two amps sound the same':

Here is my understanding of the threshold levels:-

Distortions - all types, THD, IMD 0.1%
Important Note: This distortion is measured from 20Hz to 20kHz with a
bandwidth of 100kHz, and must be maesured into the loads declared
suitable
by the designer. For example, the QUAD 405 is rated at 100watts into any
load 4-8 ohms. Consequently, I would expect it to work with loudspeakers
rated at 6 ohms upwards. Note that 4 ohm rated loudspeakers can drop
to 3.2
ohms, and would consequently fall outside QUAD's specification for
the 405.

Frequency response +-1dB 20Hz-20kHz
Important note: This frequency response is measured across the
loudspeaker
load, *not* across a dummy load. This requires the amplifier to have
a low
output impdeance as otherwise, the loudspeaker's impedance
characteristic
will modify the frequency response.

Hum and noise 80dB measured on a bandwidth of 20Hz-20kHz, and no worse
than -60dB outside that band. It is important that the amplifier have no
instabilities at sub or supersonic frequencies.

Crosstalk: 60dB
In practice, crosstalk below -40dB is unlikely to be audible under
programme
conditions. It is important that the distortion of the crosstalk be
below
0.1% as otherwise, the crosstalk distortion could swamp the speaking
channel's distortion. This is a rare condition, but not unknown with
poor
designs with poor power-supply rejection.