ASM-1 and Tempcos

Christopher_List at Sonymusic.Com Christopher_List at Sonymusic.Com
Tue Jan 28 21:21:01 CET 1997





> I've been building up the ASM-1 VCO so I thought I'd share one problem
> with you in case anybody else comes across this.
> The oscillator works fine but I had a problem when I put the 1K
> tempco in.  It made things worse.
> I didn't understand this at first but when I measured it it was
> slightly over 1K at room temp.  So I put my finger on it to warm
> it up and the resistance went down.
>
> So be warned: the Tempco's from Farnell have a negative coefficient
>
> If you put them in they will double the error rather than correct
> it.

You can probably still use these tempcos - if you stick them in a different
place.

Basically, a tempco with a + coefficient will cause the voltage at the base
of the tranny pair to INCREASE with increasing temp.

To get the same thing to happen with your tempco, you'd need to put it
where the 56K resistor is, and replace the 1K tempco with a little resistor
that'd give you the same voltage divider ratio as 56K/1K....

That'd be a 17 Ohm resistor.

Will this work - I'm not sure. Your op-amp need to drive into a 1017Ohm
load and that's a little low. Sounds good on paper though - you might wanna
try it. Anybody have any other thoughts?


- CList





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