"Don Pearce" wrote in message
...
On Mon, 30 Jan 2012 21:16:09 -0000, "Woody"
wrote:

"Arny Krueger" wrote in message
om...

"Eiron" wrote in message
...
Browsing some amp specs, I find that one old Rotel amp has
ten
times the distortion of the others in the range.
Is this a typo or was the RA-960 specially designed for
people
who like valve (tube) sound?

Compare http://www.rotel.com/content/manuals/ra960bx_eng.pdf
with http://www.rotel.com/content/manuals/ra980bx_eng.pdf
(and the same for rb... power amps)

Most good SS amps can be speced for 0.03%, 0.3%, 3%, or 10%
THD by means of adjusting the rated power. Same amp.




You also need to remember that the majority of valve amps
produce
predominately second harmonic distortion to which the ear is
very
tolerant, whereas SS amps are usually third and odd harmonics
which the ear doesn't like at all.

But do bear in mind two things.

First, small valve amps generally produce an awful lot of
second
harmonics, while solid state amps produce bugger all of any
kind of
harmonics.

Second, harmonics are never the problem while listening to
music.
Intermod is the problem because it is generally unrelated
musically to
any of the wanted notes. For the production of intermods, it
makes no
difference whether the amp's distortion is predominantly odd or
even.

d



The point was that the ear is very tolerant of second harmonic
distortion so you can have what appears to be a high level of
distortion on a valve amp on paper - measured by figures in front
of the decimal point - but the brain doesn't object. Agreed SS
amps produce little or no distortion at any harmonic but what
they do produce is mainly odd harmonics which the ear finds
objectionable so it is easy to see why valves (or Class A SS
amps) somehow sound 'right.'

I seem to remember that the late great JLH (or was it Doug Self?)
did some testing many years ago to try to find out why SS amps
just don't sound the same as valves. What came out was that the
ear was not unhappy at as high as 1-2% or more second harmonic
distortion, but it could detect odd harmonic many times lower
that that - and I'm talking well less than 0.1% here. I'll have
to have a dig and see if I've still got the original somewhere -
I'm sure I kept it.


--
Woody

harrogate three at ntlworld dot com