[sdiy] 10K Pot into 1MEG Pot?

[Scott Gravenhorst]

I'm curious, what would make you go to this trouble
when for about $5.00 (or less), you can get the real 
thing?

I've looked at OTA based VC resistors, but the single
ended one is AC coupled, and the floating one is
too complicated, using both OTAs in a dual package.

Also, these circuits are not potentiometers, they
are variable resistors (or rheostats).  They do not
have the equivalent of two end terminals and a
wiper.  To do that, you'd have to build two of them,
and drive the control voltages inversely.   This could
require up to 2 LM13700 packages and an opamp for 
control voltage inversion plus a small garden of 
resistors.  Add two more opamps for a voltage to
current converter to drive Iabc current if you want
linear operation (a resistor is a crappy current source).


<macbeth2600 at yahoo.co.uk> wrote:
>
>
>Hey, thanks, Crow, I'll give this a try!
>Regards, Ken 
>  The Old Crow <oldcrow at oldcrows.net> wrote: On Mon, 25 Mar 2002, Ken MacBeth wrote:
>
>> 
>> Hi, does anybody out there have any ideas how to turn a 10K
>> potentiometer into a 1MEG pot? I'm imagine using an OTA as a voltage
>> controlled resistor, but just can't figure this one out yet! Any help
>> here would be most appreciated- Regards, Ken
>
>NatSemi datasheet for LM13600 has examples of single-ended and 
>double-ended voltage-controlled resistors; see figs. 8 to 10.
>
>http://www.oldcrows.net/ota/datasheets/lm13600.pdf
>
>Hope this helps?
>
>Crow
>/**/
>
>
>http://www.macbethstudiosystems.com
>Home of the M3X Analogue synthesizer...


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