[sdiy] Request brain dump on balanced lines

[Don Tillman]

   > Date: Sun, 13 Oct 2002 10:47:05 -0700 (PDT)
   > From: Tim Ressel <madhun2001 at yahoo.com>
   > 
   > The best explanation I have heard is this: all semiconductor
   > amplifiers add 3rd harmonic distortion, which is unplesant to the
   > ear. Transformers tend to add 2nd harmonic distortion (as do tube
   > amps), and 2nd harmonic distortion is pleasant to the ear.
   > 
   > There are as many opinions on this as there are people, but this
   > explanation makes sense to me.

Really?  

If a tube stage was exactly a square-law device it would only have 2nd
harmonic distortion.  But tubes aren't exactly square-law devices,
more like 1.5-law, so a single tube stage does contribute third
harmonic distortion.  And if there's feedback involved, that will also
change the distortion products.  Multiple stages changes the
distortion products more.

And a single transistor stage has significantly more 2nd harmonic
distortion than third.

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.

Further, this explanation assumes that our sense of hearing cares a lot
about harmonic distortion, which is not necessarily true.

So while this explanation is the popular one -- it comes from that
engineering math class where you get to derrive the Fourier spectra of
exp(sin(wt)) and (sin(wt))^2 -- I think it completely lacks
credibility.

  -- Don

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