[LAD] simulating analog audio devices part II

Dominique Michel dominique.michel at citycable.ch
Mon Jun 18 21:57:41 UTC 2007

Le Mon, 18 Jun 2007 09:56:21 +1000,
"porl sheean" <porl42 at gmail.com> a écrit :

> hi Giuseppe
> would it be at all possible to provide a link to the ltspice file you made
> of the amp? i am having trouble finding out how to do things like output
> transformers well, and didn't even imagine the possibility of spice
> simulating a particular speaker. whilst i am eagerly watching the ngspice
> patchset i would like to play around with one that i know works so that i
> can make sure i'm doing things right.
> ps. where abouts did you get the models for the transformers, valves and
> speaker from? and how did you simulate the reverb section?
> cheers
> porl

I don't see this one before, sorry.

Free valves models are not so good at the exception of the diode (The Perugini
model is outstanding

For the other tubes, the result will depend of what you want to do with the
tubes. In pure class A without grid current, you will get very good results
from the simulation. With grid current or changing g2 current, the result will
be wrong most of the time because of inexact or non-existent modelisation of
those grids currents.

With triode, I get the best result with the Koren model. Ducan's ones are good,
but Koren's models are easier to setup and have a better convergence.

With tetrode and pentode, no one model I found was good for the kind of stuff I
want to simulate (mostly guitar amplifier with those tubes, that mean class B
with huge grid current and huge variations of Ig2).

You can get both Koren's and Duncan's model at

I recently find this:
Modeling and Simulation of the Power Amplifier for the
         RHIC 28 MHz Accelerating Cavity

It is high frequency but the tetrode model they made is without any doubt
superior to anything else we can find on the web. It use the constant current
series of curves to determinate the model. The problem here for the tubes used
in audio is at we cannot find such curves just don't exist for that kind of
curves and at we have to extrapolate them from the curves we can get or measure.

I begun to do that for the 807 (military grade 6L6 with outstanding audio
capability), but stopped by cause of lack of time. I will finish it later but
cannot give any delay. I just have other things to do for now. But I am sure at
such a model will be better.


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