[sdiy] Harmonics Question

[Andrew Simper]

> ----- Original Message -----
> From: Amos <controlvoltage at gmail.com>
> To: Harry Bissell <harrybissell at wowway.com>
> Cc: David G Dixon <dixon at mail.ubc.ca>, synth-diy at dropmix.xs4all.nl
> Sent: Thu, 03 Nov 2011 10:48:51 -0400 (EDT)
> Subject: Re: [sdiy] Harmonics Question
>
> On Thu, Nov 3, 2011 at 9:19 AM, Harry Bissell <harrybissell at wowway.com>wrote:
>
> > A tube amp and transistor amp could in theory sound identical !
> >
> >
> Strangely, I only ever see this asserted as actually-the-case by transistor
> amp makers, not by tube amp makers...  :)
>

Perhaps it is better stated something like "a transistor amp can be
set up with the same class A biasing that you use in tube amps and so
produce a spectrum which includes strong even harmonics". Even two
different types of transistor won't sound "identical" when used in the
same circuit, I think Harry was just really talking about general
harmonic structure and not exact noise, and transient response, and
all the other things that go up to making "tone".

In class A amps there is always even and odd harmonics. For amps that
are deliberately distorted for effect it seems to me there is an
optimal amount of even to odd harmonics that sounds fullest and
richest, and that is where the second harmonic is around the same
amplitude as the third +-10% (in dB). This amount is usually in the
"middle" of the drive region. Below that the even harmonics become
more pronounced, and above that the odd harmonics take over since both
sides are in hard clip.