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That's fine then if the VCA also moves the frequency as you've proven. <br>
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Quite amazed at how much the pot, or VCA, moves the resonant frequency - I suppose one usually keeps it nearer the centre.<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 Ingo Debus via Synth-diy <synth-diy@synth-diy.org><br>
<b>Sent:</b> 12 February 2024 08:52<br>
<b>To:</b> SDIY List <synth-diy@synth-diy.org><br>
<b>Subject:</b> [sdiy] Cry Baby, was: Unique sounding modules that can't have voltage control?</font>
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<div class="">Am 09.02.2024 um 21:42 schrieb Mike Bryant <<a href="mailto:mbryant@futurehorizons.com" class="">mbryant@futurehorizons.com</a>>:</div>
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R5 C4 VR1 also form a variable frequency element as well as controlling the feedback level. Hence the waa effect.<br class="">
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<div id="x_divRplyFwdMsg" dir="ltr" class=""><font face="Calibri, sans-serif" class="" style="font-size:11pt"><b class="">From:</b> Synth-diy <<a href="mailto:synth-diy-bounces@synth-diy.org" class="">synth-diy-bounces@synth-diy.org</a>> on behalf of Ingo Debus
via Synth-diy <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a>><br class="">
<b class="">Sent:</b> 09 February 2024 20:28<br class="">
<b class="">To:</b> SDIY List <<a href="mailto:synth-diy@synth-diy.org" class="">synth-diy@synth-diy.org</a>><br class="">
<b class="">Subject:</b> Re: [sdiy] Unique sounding modules that can't have voltage control?</font>
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<div class="">Looking at this description of the Cry Baby:</div>
<div class=""><a href="https://www.electrosmash.com/crybaby-gcb-95" class="">https://www.electrosmash.com/crybaby-gcb-95</a></div>
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<div class="">It seems to me that the pot just sets the amount of feedback. This could be easily replaced by a VCA. Am I missing something?</div>
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<div class="">So I downloaded the LTSpice model of the Cry Baby here:</div>
<div class=""><a href="https://cushychicken.github.io/ltspice-dunlop-crybaby/" class="">https://cushychicken.github.io/ltspice-dunlop-crybaby/</a></div>
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<div class="">Here’s the frequency plot for various positions of the potentiometer:</div>
<div class=""><img id="x_99E833FA-3A34-4C36-B708-C846E35593A4" class="" width="320" height="177" data-outlook-trace="F:1|T:1" src="cid:ACFF5095-0F86-474D-9117-36E1831AD156"></div>
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<div class="">Then I replaced the potentiometer R14/R12 with a „voltage controlled voltage source“, emulating an ideal VCA. The gain was set to the same values the (unloaded) potentiometer would yield. Here’s the result:</div>
<div class=""><img id="x_B95C0AD9-D823-4D03-9981-E75E4BAB561E" class="" width="320" height="175" data-outlook-trace="F:1|T:1" src="cid:F7EB41B7-E3E9-4204-B6C2-959EAAB9C87B"></div>
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<div class="">Almost the same as the real thing. The peaks at the low frequencies are slightly higher.</div>
<div class="">So my conclusion is, the pot in the Cry Baby can be replaced by a VCA without altering the performance very much.</div>
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<div class="">Ingo</div>
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