[sdiy] Request brain dump on balanced lines

[Don Tillman]

   > From: "jhaible" <jhaible at debitel.net>
   > Date: Mon, 14 Oct 2002 02:15:13 +0200
   > 
   > > Don:
   > > But more practically, most amps work in a balanced
   > > configuration that cancels out all odd order distortion
   > > products, depending on how well balanced things are.
   > 
   > If the 3rd harmonic would be so much more unpleasant than the 2nd
   > harmonic, there would be no such rule as trimming amps for
   > symmetrical clipping.

Hi JH!

Right.  A more direct example would be matching output tubes in a
push-pull power amp -- if you had the output tubes exactly matched you
would have more odd harmonics and fewer even harmonics, yet we've never
heard of folks intentionally mismatching output tubes.

By the way, my comments shouldn't be interpreted to mean that I hear
no difference between a typical tube amp design and a typical
transistor amp design.  I just don't think the difference lies in some
weird abstraction involving the second harmonic.

   > > Further, this explanation assumes that our sense of hearing
   > > cares a lot about harmonic distortion, which is not necessarily
   > > true.
   > 
   > I fully agree. But maybe the ear cares for a sudden change of
   > harmonics.

The dynamic response to a transient can be very important, because it
contains perceptual clues to the process modifying the sound.

In a post in August I mentioned that I believe our sense of hearing
has been optimized over tens of millions of years of evolution to
recognize mechanical processes by their sonic fingerprints.  Well the
typical tube amp process (gain stage, phase splitter, output tubes,
transformer) is very different than the typical transistor amp process
(diff amp, large voltage gain stage, drivers, outputs, lots of
feedback), and I think it's very reasonable that we should be able to
detect the difference.  

(To that end, I'll even claim that they typical opamp-style transistor
amp is not an amplifier at all, it's a servo.)

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com