[Audio Empire]

On Sat, 5 Mar 2011 11:17:39 -0800, Dick Pierce wrote
(in article ):

Audio Empire wrote:
For instance, I can design an all transistor amplifier and get all
of the component values right, and yet ruin the design sonically, just by
choosing the wrong kind of component. A high gain stage might call for
33,000
Ohm resistor. OK, fine. I'll use a 33,000 Ohm resistor. But if I choose a
carbon composition resistor instead of a metal film, that high gain stage
will be noisy. The maths and physics I used to design that amplifier didn't
predict that, and if I build TWO such amps, one with metal film resistors
and
one with carbon comp resistors, they'll sound different and anyone will
instantly tell them apart in a DBT!

Yes, you're right, if you use YOUR math and physics, as you
described you did.

But, no insult intended, your math and physics are rather
incomplete. The math and physics describing the non-ideal
behavior of resistors is rather much richer than that, and
has been for half a century and more. To your point: both
the observed behavior of various resistor formulations
such as carbon composition, carbon film, metal film and
so on is something that was well known and well understood
by bachelor degree level EE's graduating in the early 1970's.

I graduated in the 1960's, but that's neither here nor there. I'm trying to
make a point about how component choice can affect amplifier performance. I
realize that there are tools available today that a designer can use which
does take all of those things into consideration. There is also the
experience of the designer at work here. No competent designer is going to
use carbon comp resistors in an audio circuit these days, nor are they going
to use tantalum caps to couple between stages but some cheap mass-market
electronics were still using aluminum electrolytics to couple audio stages,
and not too long ago either (don't know about today). Heck the ubiquitous
Sony PCM-1610, 1620, and 1630 family of digital processors which were used
almost exclusively in the early days of CDs to master them, were full of
aluminum electrolytic capacitors between (741 op-amp) filled stages.

Had a more complete physical and mathematical model been
used in your design from the get go, the final properties
of the circuit, such as the noise, would have been far
more acccurately predicted.

Of course it would.

Further, once built and even before listeing, the detailed
noise properties of the circuit will have been easily
measurable, along with many other easily quantifiable and
trivially measurable properties far beyond the usual simple-
minded and largely irrelevant measures such as frequeny
response, THD, and simple broadband S/N.

Agreed.

But to indict the entire realm of audio "maths and physics"
based on what really is a very limited understanding of
the actual math and physics that are widely practiced in
professional engineering realm (admittedly, a fraternity
that is not as well represented in the realm of high-end
audio designers as eslewhere) is, well, ineffective.


Nobody's "indicting" anything. What you mischaracterize as a "limited
understanding of the actual math and physics that are widely practiced in the
professional engineering realm.." is, in reality, only an extreme, almost
hyperbolic example of how component choice "could", conceivably affect the
performance of a decent amplifier design.