new here plus a question...

[Don Tillman]

   Date: Thu, 18 Jan 2001 19:46:11 +0100 (MET)
   From: Bram de Jong <Bram.DeJong at rug.ac.be>

   On Thu, 18 Jan 2001, Happy Hairy Harry wrote: > The "tone controls"
   in the Duncan application are typical of > guitar amps.  If you
   model them, you will have a first-order > approximation of how they
   "sound".

   Aha! But, my question really was: how do I do this :)

Write out the equations for the current into each node of the circuit,
and solve those equations simultaneously.  If you'd like more details,
it's basically a full semester course in electrical engineering.
You'd need to get some textbooks on "linear circuit analysis".

   > But most of us think that there is still something missing from
   > the model. Maybe parasitic components of the circuit, or
   > non-linear processes that are or are NOT obvious.

I'll suggest that the parasitics and nonlinearities are not important
to the tone stack.  The problem is more fundamental.

   > The other thread was "Why does the Moog Ladder filter have some
   > quality that does not allow it to be modeled exactly" This is
   > probably way beyond what you are trying to get to right now.

   Hmmm. Isn't this allso because the straight s-lane to z-plane
   transform introduces delay-free feedback loops? (that is,
   additional to the 'unlinear' part)

The Moog Ladder is a separate case because it's nonlinear in a really
interesting way.  You're just interested in simulating a Fender tone
stack, right?  (Or the whole amp?)

(Of course I've got to wonder why anybody would go to the trouble of
simulation a simple circuit made from $10 worth of parts...)

I think the main issue is that translating from the s-plane to the
z-plane is a very rude approximation.  z-poles are inherently
different than s-poles, they won't sound the same as the original, and
I'll bet you would have no problem telling the difference between the
frequency response plots visually.

  -- Don

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