[sdiy] DETERMINING FLOATING RESISTOR RANGE OF OTA??

[Harry Bissell]

The formula is on the data sheet, R (100K) and Ra (1K) are listed on the schematic.

as gm is the only variable possible, you need to limit its range to keep within 1 - 3K

That will probably be a pretty narrow range in your case (gm can usually go at least 1000:1
and you need 3:1)

Another way to go might be a vactrol based solution. Probably equal in complexity, and maybe
not fast enough, but it would not have any offset voltage troubles or extra noise.

imho this circuit is there to illustrate what ~might~ be done, not what is really pratical.

H^) harry

----- Original Message -----
From: dan snazelle <subjectivity at hotmail.com>
To: synth-diy DIY <synth-diy at dropmix.xs4all.nl>
Sent: Wed, 01 Dec 2010 09:05:03 -0500 (EST)
Subject: [sdiy] DETERMINING FLOATING RESISTOR RANGE OF OTA??

Hello there

Looking at the FLOATING RESISTOR in the lm13700/lm13600 datasheet, I am trying to figure out how one gets the right values when building this to specifiy a range of resistance

i am building a circuit which requires a variable resistance over the range of 1k-3k


thanks for any help!!




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-- 
Harry Bissell & Nora Abdullah 4eva