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<div class="moz-cite-prefix">Hi Emily,<br>
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<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix">On 12.12.2022 11:14, Emily Straight via
Synth-diy wrote:<br>
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<blockquote type="cite"
cite="mid:CANA1Y6En40xBTF_8HsW27_XWyzBMAS0d00aFnCJHfNXMa3yZQA@mail.gmail.com">
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<div>i'm tweaking the <a
href="https://www.schmitzbits.de/ms20.html">rene schmitz</a>
implementation of the ms-20 filter for a project, and i was
hoping to use the emitter followers on the 13700 rather than
separate op amps if possible, it seems, like, vaguely wasteful
not to or something. in simulation this is resulting in
killing the resonance on the negative side of the waveform,
however. is this because of a mistake i made setting it up, or
is the 13700 buffer fundamentally unsuited for the purpose? i
found <a
href="https://aisynthesis.com/wp-content/uploads/2020/05/MS20v2.5.pdf">one
schematic</a> that appears to do the same thing so i'm
guessing the former, though idk maybe theirs sucks too lol. i
also put a vca in the feedback path rather than a
potentiometer, maybe that's causing problems? i have
essentially zero experience in analog electronics if you
couldn't tell</div>
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</blockquote>
<p>The original circuit from Korg used LM13600 and its buffers.
<a class="moz-txt-link-freetext" href="http://machines.hyperreal.org/manufacturers/Korg/MS-synths/schematics/KLM-307.GIF">http://machines.hyperreal.org/manufacturers/Korg/MS-synths/schematics/KLM-307.GIF</a><br>
</p>
<p>They used 4.7k and 10k for the emitter resistors (4.7k in the
highpass, 10k in the lowpass section), maybe try 4.7k too.<br>
</p>
<p>So there is in principle nothing wrong with using them. <br>
</p>
<p><br>
</p>
<p>I used the opamp buffers primarily because I was using CA3080s
which needs an extra buffer. <br>
</p>
<p>There are various mixed versions around because people built it
using 13700, some with the LEDs in the resonance like on mine.</p>
<p><br>
</p>
<p>With the darlington buffers there is a DC shift, this results in
more "thumping", i.e. the DC shifts with the frequency control. <br>
</p>
<p>Opamp buffers are the cleaner solution in this regard.</p>
<p><br>
</p>
<p>I would try lowering the amplitude in your simulation, maybe you
are exceeding the dynamic range of the right circuit. <br>
</p>
<p><br>
</p>
<p>Cheers,</p>
<p> René<br>
</p>
<pre class="moz-signature" cols="72">--
<a class="moz-txt-link-abbreviated" 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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