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<div class="moz-cite-prefix">On 08.09.2024 17:01, Rutger Vlek wrote:<br>
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<blockquote type="cite"
cite="mid:CAJ2Txe2uuuY_JMiQiQtzXkBCGnrL1OZV5sbiNZkPRvZd9TWMdg@mail.gmail.com">
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<div dir="auto"><span class="gmail_chip gmail_plusreply"
dir="auto"><a href="mailto:rburnett@richieburnett.co.uk"
style="color:#15c;text-decoration:underline"
moz-do-not-send="true">@Richie Burnett</a></span><span> thanks!
I have found Spice to be cumbersome for more advanced data
analysis, so resorted to Python for most of it. There I am
studying non linearities using saw, ramp (inverted saw) and
sine test signals. The latter I use mostly for spectral
analysis, while the first are also informative about time
domain effects. I also created the option to put out wat
files so that I can audition them. Some effects that were
impressive in the time domain where irrelevant when
listening, and (more importantly!) vice versa. I had to make
a bad prototype to remind me of this... What resembled the
time domain of a Moog filter did not sound like one. As soon
as I studied the spectral domain data I understood why.</span></div>
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<div dir="auto">The spectral effects on a sawtooth pushed
through a non linear filter, without any resonance are
impressive by themselves by the way. I never knew the effect
of an analogue filter could be this substantial.</div>
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<div dir="auto"><span class="gmail_chip gmail_plusreply"
dir="auto"><a href="mailto:synth@schmitzbits.de"
style="color:#15c;text-decoration:underline"
moz-do-not-send="true">@René Schmitz</a></span> Thanks for
the explanation! It confirms what I already suspected. The non
linear effects are a combination of TanH and something else. I
have the feeling your answer also implies that the latter
effect is important for the character of the ssm2040.</div>
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<p><br>
</p>
<p>The tanh works on the input voltage to current translation, and
the clipping is on the cap side, so that's after the current was
integrated back to a voltage . </p>
<p>Hence it's not something you can lump together into one non
linearity. You only get so far if you look at it statically. <br>
</p>
<p>How fast the cap is charged to -0.6V depends of course on the
control current, the size of the cap, and how long it is applied.
Plus the initial conditions.<br>
</p>
<p>The input attenuation at the bases of the long tail pair together
with the input amplitude determine to what degree the tanh is
actually driven. </p>
<p>If it's below 25mV you don't have a significant contribution from
it, pretty linear.</p>
<p>(With the 10k/200 divider common to JHs and mine the 2040 cells
are driven quite beefy, for +/-2.5V input, resulting in +/-50mV
after the attenuation.)<br>
</p>
<p>And there is also a feedback loop that works to get things back
into balance at the bases, i.e. to reduce deltaVbe. <br>
</p>
<p>Then we could ask what effect does the darlington emitter
follower with it's two Vbes have? </p>
<p>Spoiler alert, it shifts the whole waveform voltage at the cap
upwards, away from the clipping. </p>
<p>Theoretically you could add more Vbe drops and steer it clear of
the clipping zone (but who wants that...).<br>
</p>
<p><br>
</p>
<p>There surely is a lot going on in that simple circuit.</p>
<br>
<p>Best,<br>
René<br>
</p>
<p><br>
</p>
<br>
<pre class="moz-signature" cols="72">--
<a class="moz-txt-link-abbreviated moz-txt-link-freetext"
href="mailto:synth@schmitzbits.de">synth@schmitzbits.de</a>
<a class="moz-txt-link-freetext" href="http://schmitzbits.de">http://schmitzbits.de</a></pre>
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