SV: Re: [sdiy] PAIA VCO, LM13700 diode temp comp.

[karl dalen]

--- Ian Fritz <ijfritz at earthlink.net> skrev:

> At 05:42 PM 10/17/05, karl dalen wrote:
> >Long time ago there was discussions on the PAIA
> >VCO temp drift compensation using the diodes of
> >the LM13700, how did that turned out?
> >
> >Was it a good idea of temp compensation?
> 
> I built a similar VCO a few months ago, as an aux VCO to use in my chaos 
> box.  My main trouble with this circuit involved the V/Oct tracking.  After 
> much experimenting and tweaking the best tracking I got was +/- 0.5% from 
> 100 Hz to 6 kHz.  Nothing even close to the 2 cents accuracy claimed in the 
> writeup.  I didn't check the temperature drift.  It shouldn't be too bad, 
> but I know from another active-compensation circuit that you need good 
> matching of the OTA pair.

Wich would be a pain! I have never found any pair that have matched each
other!!

BTW, there was previous discussion on the CV offset trim methods
the usless Serge - volt trim, and the typical National trim pot
app note, but i just realized i havent done the:
"Ground one of the inputs (no 330 resistor to gnd "just to gnd")
and apply a balancing voltage to the active input pin trough a resistor!!
Wonder if that would improve the CV feed trough problem a tiny bit?

KD