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

[Tom Wiltshire]

A typical wah pot can't physically reach the ends of its travel, so the simulation probably goes further at both ends than the reality.

So yes, one does usually keep it nearer the centre - you don't get much choice.

> On 12 Feb 2024, at 11:05, Mike Bryant <mbryant at futurehorizons.com> wrote:
> 
> 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.
>> 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 <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/ <https://cushychicken.github.io/ltspice-dunlop-crybaby/>
> 
> Here’s the frequency plot for various positions of the potentiometer:
> <Bildschirmfoto 2024-02-11 um 20.53.37.png>
> 
> 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:
> <Bildschirmfoto 2024-02-11 um 20.52.03.png>
> 
> 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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