"Rob" wrote in message
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Serge Auckland wrote:
"Trevor Wilson" wrote in message
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"Keith G" wrote in message
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"Trevor Wilson" wrote in message
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"Keith G" wrote in message
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"Trevor Wilson" wrote


I own a Marantz Model 18 Receiver, dating from 1968. It originally
cost US$1,200.00 and was the most power receiver on the planet, back
then. For it's time, it was quite a sophisticated product, employing
full complementary silicon outputs, relay protection system and
other nifty stuff. It was critically appraised by reviewers at the
time and when I purchased mine (ca: 1977) I was stunned at how much
better it sounded than many contemporary amplifiers of similar (60
Watts) or even more power. Just for yuks, I recently compared it to
a more modern Marantz amplifier (cost around AUS$1,000.00). No
comparison. The modern amp was somewhat better sounding. And,
allowing for inflation, the modern amp was MUCH less expensive.
Don't even get me started on loudspeakers. The technology for
designing speakers has improved in leaps and bounds over the last 40
years.


S'funny, we keep getting told how 'good amps' don't have a
sound....???
**Because that is a fact. The ideal amplifier has no 'sound' of it's
own. No amplifier is ideal.

Therefore no amplifier has no 'sound' of its own then?
**Nope. That's not what I said.


--
Trevor Wilson
www.rageaudio.com.au

The *ideal* amplifier has no sound of its own, and no amplifier is ideal.
However, for many years now, amplifiers come awfully close to the ideal,
and consequently, except for the nittiest of nit-pickers, I subscribe to
the view that no (half-decent) amplifier has a sound of its own, and
consequently all sound the same.

Certain conditions apply, like operation below clipping into loads for
which the amplifier was designed, using music signals.

S.

I simply don't get this. I've been using 5 SS amps of late (Quad 405, Rose
power amp, Cambridge AV, Behringer A500, and that within a Pure mini
system), as well as others on and off over the years, and I feel each has
'a sound of its own'.

But this has been done-to-death in this NG. One thing I was never clear on
is the definition of 'half-decent'. One definition (Stewart Pinkerton
IIRC) was double power into half impedance, down to 2 Ohms (50/8; 100/4,
200/2 or something, plus some other stuff), but I've never seen a sensible
money amp that could come close.

Could you name the cheapest available new amplifier that sounds the same
as (say) your own at medium-high volume?

Just curious!

Rob

Price of the amplifier isn't important. It is well recognised, at least
amongst audio professionals, that the ear's ability to hear differences has
a lower threshold. If an amplifier's performance is below that threshold,
then all differences between such amplifiers is not audible.

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.


If two amplifiers, whether SS or valved meet the above criteria, then their
sound will be indistinguishable.

As to what amplifiers meet these criteria, these days almost any modern
Solid State amplifier will do. SOme valve amplifiers will too, espcially if
they are Push-Pull Ultra-Linear with overall negative feedback. SET will
almost certainly *not* meet these criteria as their distortion is too high,
and their output impedance too high resulting in gross frequency response
errors.

Amplifiers *will* sound different if they are not gain-matched to better
than 0.5dB, ideally 0.1dB as the louder one will normally sound "better".
Also, if one or both amplifiers being compared are allowed to go into
overload, then what you will be hearing is their overload behaviour, which
could well be very different.

Finally, any sighted test will inevitably have the possibility of bias,
however inadvertent, so comparisons should be done blind, ideally
double-blind.

If you take two amplifiers and compare them properly, even two very
different amplifiers, provided they each meet the minimum audibility
criteria, and both are used within their output capacity such that neither
clips, they *will* sound the same.

S.