[sdiy] Cry Baby, was: Unique sounding modules that can't have voltage control?

[Mike Bryant]

That's fine then if the VCA also moves the frequency as you've proven.

Quite amazed at how much the pot, or VCA, moves the resonant frequency - I suppose one usually keeps it nearer the centre.
________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Ingo Debus via Synth-diy <synth-diy at synth-diy.org>
Sent: 12 February 2024 08:52
To: SDIY List <synth-diy at synth-diy.org>
Subject: [sdiy] Cry Baby, was: Unique sounding modules that can't have voltage control?



Am 09.02.2024 um 21:42 schrieb Mike Bryant <mbryant at futurehorizons.com<mailto:mbryant at futurehorizons.com>>:

R5 C4 VR1 also form a variable frequency element as well as controlling the feedback level.  Hence the waa effect.
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From: Synth-diy <synth-diy-bounces at synth-diy.org<mailto:synth-diy-bounces at synth-diy.org>> on behalf of Ingo Debus via Synth-diy <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>>
Sent: 09 February 2024 20:28
To: SDIY List <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>>
Subject: Re: [sdiy] Unique sounding modules that can't have voltage control?

[…]
Looking at this description of the Cry Baby:
https://www.electrosmash.com/crybaby-gcb-95

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?


So I downloaded the LTSpice model of the Cry Baby here:
https://cushychicken.github.io/ltspice-dunlop-crybaby/

Here’s the frequency plot for various positions of the potentiometer:
[cid:ACFF5095-0F86-474D-9117-36E1831AD156]

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:
[cid:F7EB41B7-E3E9-4204-B6C2-959EAAB9C87B]

Almost the same as the real thing. The peaks at the low frequencies are slightly higher.
So my conclusion is, the pot in the Cry Baby can be replaced by a VCA without altering the performance very much.

Ingo
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