On 5 Jan 2006 13:22:32 -0800, "Bret Ludwig"
wrote:


wrote:


I guess the peers were
also tubies. Either that or they were smokin' some gooooood stuff. Maybe
both. ;-)
I'd like to find some AES old-timers and get some straight answers about how
a POS like the Hamm paper made it through the JAES review process. The
guilty parties are probably dead and gone by now, so the truth might be
knowable despite the confidentiality of the review process.

Has anyone here actually READ The Hamm article. It woiuld appear
not, as it does NOT support any of the assertions made about.
Consider the precis of the article:

"Engineers and musicians have long debated the question of
tube sound versus transistor sound. Previous attempts to
measure this difference have always assumed linear operation
of the test amplifier. This conventional method of frequency
response, distortion, and noise measurement has shown that
no significant difference exists. This paper, however, points out
that amplifiers are often severely overloaded by signal transients
(THD 30%). Under this condition there is a major difference in
the harmonic distortion components of the amplified signal, with
tubes, transistors, and operational amplifiers separating into
distinct groups"

Let's look at the KEY points of the article:

* Previous attempts to measure this difference have always
assumed linear operation ...

* amplifiers are often severely overloaded by signal transients
(THD 30%).

The article ONLY deals with the amplifiers topologies AT THE TIME,
UNDER CONDITIONS OF SEVERE CLIPPING DISTRTION.

It makes NO claims about the operation under normal conditions.
The implications are quite clear: Clipping results in audibly
different
output from. An early 1970's tube amplifier sounds different than an
early 1970's transistor amplifier WHEN BOTH ARE BEING SEVERELY
CLIPPED SUCH THAT THEY ARE GENERATING 30% THD.

The solution to the problem is NOT to by tubes or transistors. The
answer to the problem is VERY simple:

DON'T CLIP THE AMPLIFIER!

Thus, Hamm's paper supports the reasonable assertion that a 250
watt sollid stats amplifier MUST sound better than a 20 watt tube
aplifier when both are being asked to try to produce more than 20
watts.


"Don't clip the amplifier" is easy to say, and tough to do. Totally
avoiding amplifier clipping under any and all circumstnaces requires
either active power compression control (i.e. "Power Guard") or a
really, really, really big amplifier, the very small signal performance
of which is usually suspect unless the amplifier is made extremely
heavy and hot and has a very high quiescent power draw. A 20 watt tube
amp that pulls 50 watts at full power is more efficient in practice
than a 250 watt solid state amp that pulls 80 watts quiescent and 500
at full power if either provides the same _subjective_ performance-even
though the solid state amp is more efficent for each watt it puts out.

Actually, it's a piece of **** if you're using CD as a source, since
you can set system gain to sit just below clipping for 0dB FS from the
CD. That's what I do with my '50 watt' Krell.


--

Stewart Pinkerton | Music is Art - Audio is Engineering