linuxaudio.org

From: Stefano D'Angelo

Date: 2011/2/27

Subject: Re: [LAD] RDF libraries, was Re: [ANN] IR: LV2 Convolution Reverb

To: Giuseppe Zompatori

Cc: linux-audio-dev@lists.linuxaudio.org
2011/2/27 Stefano D'Angelo :

quoted text
>

>

> Ciao Giuseppe,

>

Ciao Stefano,

Taking this email to a new thread.
>Well... they seem to have a lot of stuff there. :-)

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>

>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.
>

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>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

stages.

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

4

     |                                                      |

                        |

  |

1st triode -> Tone stack -> post tone stack recovery triode -> P.I.

(Phase inverter) triodes -> (at least 2) Pentodes -> O.T. (Output

Transformer) -> Speakers
                                    ^

                                                              ^
                                    |

                                                               |
           Presence

pot<--------------------------------negative-feedback---------------------------------------------
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

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>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,

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>

>Stefano

Anche tu!
-Giuseppe

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