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

[rburnett at richieburnett.co.uk]

Yes, the Dunlop Cry Baby is a neat circuit.  The variable feedback gain 
essentially magnifies the effect of one of the capacitors allowing the 
resonant frequency of the resulting LCR circuit to be swept over quite a 
large range.  It's very clever because it doesn't require a variable 
variable inductor or an actual variable capacitor!

It's also interesting how the Q factor is larger at the low frequency 
end of the range, and lower when the resonant frequency is at the high 
end.  This is a bit unusual.

-Richie,



On 2024-02-12 11:05, Mike Bryant 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>:
>> 
>> 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> on behalf of Ingo
>> Debus via Synth-diy <synth-diy at synth-diy.org>
>> Sent: 09 February 2024 20:28
>> To: SDIY List <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:
> 
> 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:
> 
> 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
> ________________________________________________________
> This is the Synth-diy mailing list
> Submit email to: Synth-diy at synth-diy.org
> View archive at: https://synth-diy.org/pipermail/synth-diy/
> Check your settings at: 
> https://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace at synth-diy.org