[linux-audio-dev] Diode wave shaper (LADSPA plugin)?

[Jens M Andreasen]

On mån, 2004-08-16 at 16:49, Stanley Jaddoe wrote:

> The 12k resistor is just an example, it would be nice if it would be treated 
> as a variable.
> 
> How can I incorporate the 1N4148 diode characteristics in the final equation?
> 

One interresting thing to consider is that the diode pair is mimicking a
valve preamp, possibly with some rude Marshall characteristics.

The exact same solution can be found in the upper right corner in this
schematics, just before the tone controls:

  http://home3.netcarrier.com/~lxh2/marshprb.gif

(The 1N914 share characteristics with the 1N4148)

So what you should be looking for is a valve overdrive/distortion
plugin, rather than a 1N4148 emulator. 

My guess is that the *exact* characteristic is not *that* important, as
long as it has a reasonably soft knee.

> ------------------------------
> 
> I did some SPICE emulation (Alfons: I know, I'm not a (real) engineer) and I 
> never saw a tangentfunction-like output... 
> Assuming one input and one output, (instead of the shown three inputs in my 
> first post), if the input signal is a triangle wave, I should get a (not  
> perfect) sine wave.

For some value of 'not perfect', yes :)) Crank up the volume and it
should transform into a square, apply a second channel with LFO and you
get pulse-width modulation.

Now please tell us, what is this synth of yours that you have
disassembled? Is this circuit part of the output-stage or is it part of
the individual oscillators? Inquiring minds wants to know!

/jens

> 
> ------------------------------
> 
> BTW: Does anyone on this list has any experience converting an analog hardware 
> synth to a softsynth using the synth's schematics?
> 
> 
> Stanley