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Electronics => Beginners => Topic started by: jpalicke on December 31, 2014, 01:44:49 am

Title: What to do with an unused half of an LM13700 OTA?
Post by: jpalicke on December 31, 2014, 01:44:49 am
Hey guys, quick question.

I'm building a clone of a guitar compressor pedal, specifically an MXR Dynacomp/Ross Compressor, and instead of using the CA3080, I'm using an LM13700.  What's the proper way to deal with the unused half of the OTA?  Tie the inputs and control pin to ground?  0 differential voltage and 0 control current should equal 0 current coming out right?  Or is there a better/safer way to do this?
Title: Re: What to do with an unused half of an LM13700 OTA?
Post by: c4757p on December 31, 2014, 02:19:02 am
Tying unused inputs straight to ground isn't always a good thing, but it looks like if you tie the transconductance control pin (1 or 16), the diode bias pin (2 or 15), both inputs (3/4 or 14/13) and the buffer input (7 or 10) all to V-, you should be able to shut off the whole amplifier and reduce its current consumption to practically zero.

Hooray for devices with the internal schematic in the datasheet! :-+
Title: Re: What to do with an unused half of an LM13700 OTA?
Post by: jpalicke on December 31, 2014, 02:44:26 am
Excellent, many thanks!
Title: Re: What to do with an unused half of an LM13700 OTA?
Post by: zmix on January 01, 2019, 04:19:45 pm
Hey guys, quick question.

I'm building a clone of a guitar compressor pedal, specifically an MXR Dynacomp/Ross Compressor, and instead of using the CA3080, I'm using an LM13700.  What's the proper way to deal with the unused half of the OTA?  Tie the inputs and control pin to ground?  0 differential voltage and 0 control current should equal 0 current coming out right?  Or is there a better/safer way to do this?

I realize that this thread is quite old now, but since the OTA is a current output device have you considered paralleling the two halves? 
I have a Chinese Dyna-Comp clone that does just that, presumably for lower noise and distortion.
I'd like to experiment with this as well, does anyone have any thoughts about it?
Title: Re: What to do with an unused half of an LM13700 OTA?
Post by: Lee Leduc on January 01, 2019, 05:47:59 pm
Hope this helps.

I contacted a TI application engineer with this question a while back:

"I need to properly terminate an unused OTA section of an LM13700.
I'm thinking that connecting the amp bias input (pin 1 or 16) to V- (pin 6)
should disable the input. I also plan to leave the buffer inputs open.

Is this a good approach or is there a better way to do this?

Thank you."

This was the response.

Lee,

That will work well. Pin 1 or 16 can be open, but connection to pin 6 ensures no bias current.
Regards,
Ronald Michallick
Linear Applications