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If you just want a simple mixer VCA without the distortion, you could replace the bipolars with MOSFETs. That would allow a larger signal so a bit less noise<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of Jonatan Liljedahl <lijon@kymatica.com><br>
<b>Sent:</b> 07 April 2023 13:46<br>
<b>To:</b> René Schmitz <synth@schmitzbits.de><br>
<b>Cc:</b> synth-diy@synth-diy.org <synth-diy@synth-diy.org><br>
<b>Subject:</b> Re: [sdiy] what opamp for "warmth"? (I know, I know...)</font>
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<div dir="auto">How noisy is it, compared to an LM13700 for example?</div>
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<div dir="auto">I'm looking for a simple 2x4 channel waveform mixer so this two-transistor vca looks interresting. My waveforms are already unipolar (0 to -3.3v). I don't mind some distortion unless it turns my triangle into a sine or square :)</div>
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<div dir="auto">By the way, regarding VCA noise, there's a lot about minimizing distortion in LM13700 designs, but what about noise? I understand higher input level gives less noise for more distortion, but what about Iabc? Does lowering Iabc from say 500uA
to 250uA (and doubling the gain in the I-V opamp buffer) give better or worse noise performance? And how about other pros and cons? According to my sims, a lower Iabc at least gives less cv bleed-through.</div>
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<div dir="auto">Cheers</div>
<div dir="auto">/Jonatan</div>
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<div dir="ltr" class="x_gmail_attr">On Fri, 7 Apr 2023 at 13:57, René Schmitz <<a href="mailto:synth@schmitzbits.de">synth@schmitzbits.de</a>> wrote:<br>
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<p>You'll find the same VCA in the 909 in a few places. (Bassdrum , Toms, Clap..)<br>
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<p>Note how far the signal is divided down. <br>
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<p>It's noisy, and nonlinear, and has some control feedthrough. Show what you can get away with for a single monophonic signal.
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<div>The MS10 had the single transistor, the early "Korg35" MS20 had the same. <br>
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<div>The later MS20 had a second transistor, which makes things more linear/symmetrical and you can run larger amplitudes -> less noise.
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<div>According to the schematics the transistors shall be selected. jx3p also says "SEL".
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<div>Anyone would know what for? Equal gain? <br>
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<div>Best,</div>
<div> René<br>
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<div>On 07.04.2023 11:04, Adam (synthDIY) wrote:<br>
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<div>David G Dixon via Synth-diy pisze:<br>
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<blockquote type="cite" style="font-family:Helvetica">Whatever the VCA is in the Korg MS-20 really warms up the sound of that synthesizer. You can find the schematic on the internet. I have something redrawn by a fellow named Marjan Urekar that I looked at
years ago. It involves two transistors. It is evidently also the VCA used in the Roland JX-3P.</blockquote>
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<div>Interesting.... here's the JX3P version</div>
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<div dir="ltr" class="x_gmail_signature" data-smartmail="gmail_signature">/Jonatan<br>
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