[sdiy] LM13700 as VC resistor

[Tom Wiltshire]

Yes, I agree! So we’ve found two examples for you, Didier! Phasers and OTA filters both use the OTA like a variable resistance.

Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================

> On 9 Feb 2020, at 12:16, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
> 
> The OTA acts as a variable resistor here:
> 
> https://electricdruid.net/wp-content/uploads/2017/04/CEM3320LowpassFilterStage.png
> 
> -Richie,
> 
> 
> 
> -----Original Message----- From: Tom Wiltshire
> Sent: Sunday, February 09, 2020 11:40 AM
> To: Didier Leplae
> Cc: Synth DIY
> Subject: Re: [sdiy] LM13700 as VC resistor
> 
> OTA-based phaser designs are about the only application I can think of where the OTA functions like a resistor rather than a VCA. Even then it’s perhaps arguable.
> 
> Have a look at schematics for the EH Small Stone and the many subsequent derivatives.There’s also a good explanation on R.G.Keens page about phasers:
> 
> http://www.geofex.com/article_folders/phasers/phase.html
> 
> HTH,
> Tom
> 
> 
> ==================
>      Electric Druid
> Synth & Stompbox DIY
> ==================
> 
> 
> On 8 Feb 2020, at 09:58, Didier Leplae via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> 
> I am curious to know anyone’s opinions on using the LM13700 as a voltage controlled resistor.
> 
> The LM13700 datasheet has a couple schematics which I have tried building, with mixed results. I’m having a hard time knowing what sort of resistance I am getting as the multimeter gives strange and inconsistent readings.
> 
> The information on the datasheet is somewhat incomplete in my opinion and it is not easy to find much info online either.
> 
> It doesn’t seem like it is common practice to use these as VC resistors. Is that because it doesn’t work very well? Or use too many parts?
> 
> Any insight on this would be appreciated.
> I’m interested mostly in the single ended schematic at the moment.
> 
> Thank you,
> 
> Didier
> 
> 
> 
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