[LAD] simulating analog audio devices part II

Giuseppe Zompatori siliconjoe at gmail.com
Mon Jun 18 19:59:25 UTC 2007

2007/6/18, porl sheean <porl42 at gmail.com>:
> 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?

Xformers, valves, pots and speaker models courtesy of duncunamps.com:


The ogg I linked to in my previous email has been processed with
LADSPA plugins for recreating the speaker filtering a bit more
accurately, and to add a bit of reverb and delay.
Sorry for not making it clear in my previous email.

You should keep in mind though that the speaker models are made out of
a simple network of resistors inductors and capacitors that only
roughly mimics the interaction or "impedance dance" that exists
between a power amp and a speaker.
The mechanical aspects, the interaction of the paper cone colliding
with air etc. can't be simulated in an ECAD program even though they
contribute a lot to the final sound.
For the theory behind the speaker models (reactive loads really) have
a look at this link:


My Carvin Legacy schematic is a bit borked right now since I am
messing around and experimenting on it by replacing the power section
with the one of an AX84's Firefly "open HW amp" (see
http://www.ax84.com under legacy projects).

In general there seem to be a lot of problems in simulating the power
section of push-pull NFB enabled amps in LTSpice... the NFB starts
oscillating producing really high frequencies even at modest volumes
eventually inflating the sim duration to infinity... garanted that's
also what happen in reality but only when the power section is
severely distorting...

Also keep in mind that by feeding a large number of high pitched notes
simulation times increases... i.e an F# fretted at the 2nd fret/low E
string is much quicker to simulate than an F# fretted on the 19th
fret/B string, I hope this makes any sense.



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