AW: Re: Germanium Diode Filters?

[Don Tillman]

   From: Paolo Predonzani <predo at dist.dist.unige.it>
   Date: Mon, 11 Nov 1996 11:45:12 +0100 (MET)
 
   Yes, smoothness is not the whole story. There has been a lot of discussion
   on Hi-Fi magazines about tube distortion but I've never seen a good
   explanation. Second and third harmonics issues are particulary confusing.

Most explanations I've seen in print are clueless because the writer
is almost always paraphrasing something he heard.  There are a number
of issues and they're all pretty interesting and someday I'm going to
write up a paper on the topic.

   I think the nature of the components alone (vacuum or solid-state) cannot
   determine the sound; the circuit schematic is much more important.

Absolutely true.

   For example: does open-loop and closed-loop designs affect the sound?

Lots.  Imagine an amplifier stage with some gain and some second
harmonic distortion.  Only second harmonic.  Add some feedback around
this stage and note what happens: as the amount of feedback increases
the gain is lowered (expected), the level of second harmonic
distortion decreases (also expected), but other harmonic distortions
appear (3rd, 4th, 5th, all of 'em) and their amounts increase as the
amount of feedback increases.

(You can model it yourself with a little program or a spreadsheet.
It's really interesting!)

So we have a situation where, as the amount of feedback increases, the
level of distortion decreases, but the character of the distortion
changes drastically.  

  -- Don