[LAD] Permafrost guitar amp, was Re: RDF libraries, was Re: [ANN] IR: LV2 Convolution Reverb

Giuseppe Zompatori siliconjoe at gmail.com
Sat Mar 5 17:55:19 UTC 2011

From: Stefano D'Angelo <zanga.mail at gmail.com>
Date: 2011/2/27
Subject: Re: [LAD] RDF libraries, was Re: [ANN] IR: LV2 Convolution Reverb
To: Giuseppe Zompatori <siliconjoe at gmail.com>
Cc: linux-audio-dev at lists.linuxaudio.org

2011/2/27 Stefano D'Angelo <zanga.mail at gmail.com>:
> Ciao Giuseppe,

Ciao Stefano,
Taking this email to a new thread.

>Well... they seem to have a lot of stuff there. :-)
>However, I wonder how they do it... I think they are probably using
>some black box modeling, since multiple nonlinearities+feedback in a
>single system is very hard to model.

They are very silent on this sadly, don't know what they are doing.

>The kind of stuff I'm trying to do is accurately model a class A amp
>with a single triode using white box techniques... to give you an idea
>of what it sounds like see this:
>http://www.youtube.com/watch?v=cdNtmaIdLdo - it is part of my MSc
>thesis presentation (100.000 lire guitar, dated and slow laptop, cheap
>speaker and cheap camera... only the sound card is good).
>I guess you speak Italian (at least your name suggests that), so enjoy
>my weird southern accent. :-P

Very interesting, I tried compiling your thesis with permafrost to try
this out (obtaining the source from the pdf has been hell BTW) but it
bails with an "m_pi" undeclared input/output function...

Anyway, are you limited to the simulation of a half triode with white
box techniques? I think you should model at least both halves of a
triode if you're after accuracy, a single triode amplifier won't even
work in real life (I build tube amps, I know) ;)
Also class A amplifiers aren't very popular amongst guitar players
(mainly because of their clipping behavior). You also want a
multi-stage preamp with different filtering/biasing points between
You might think I am crazy but that's what you'll discover yourself by
observing schematics to popular guitar amps.

Here's a simple (early Fender-like) amp topology:

                         Tube n. 1
                    Tube n. 2                           Tube n. 3 and
     |                                                      |
1st triode -> Tone stack -> post tone stack recovery triode -> P.I.
(Phase inverter) triodes -> (at least 2) Pentodes -> O.T. (Output
Transformer) -> Speakers




This is the easiest PP (Push Pull) class A/B amp I could come up with
(sounds pretty darn good in real life). It has got a tone stack, 4
tubes (2 triodes and two pentodes) and an OT/speakers, do you think
this is feasible computational-wise with permafrost?

>Well, they say guitarix has improved, yet the last time I was all but
>satisfied with it. You may want to take a look at invada plugins, if
>you haven't already.

Invada has a simple generic tube drive function AFAIK, I still prefer
the CAPS* amp over it as it's at least based on a real amp.

>Stammi bene,

Anche tu!


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