[sdiy] LM13700 as VC resistor

Richie Burnett rburnett at richieburnett.co.uk
Sun Feb 9 13:16:34 CET 2020


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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