[sdiy] 3000ppm vs 3300ppm tempcos/4069 VCO

[Seb Francis]

I've used these 3000ppm PTC resistors before ..

http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=732308
http://www.farnell.com/datasheets/60774.pdf
(available from Farnell in 1K, 5K1, 10K)

The TCR tolerance is actually 10%, so they could be anything between 
2700 ppm and 3300 ppm (actually I think it depends on the temperature - 
the response is probably not highly linear).

However, I've had good results with them (but have never used them for a 
VCO - only in non-critical apps like VCFs and VCAs).  Probably over a 
small temperature range they would be fine.

Seb






Dave Kendall wrote:

>Hi all. 
>A couple of questions.
>
>1/ A while back I got some 1K 3000ppm tempcos (manufacturer unknown) from
>Tom at EFM. I'm wondering if there's a significant difference between them
>and PT146s.
>I've used the 3000ppms in an EFM VCO3D, and am planning on using them in EFM
>VCO4D/Es, and VCF2Fs. I don't know how stable the VCO designs are supposed
>to be, and whether using 3000ppm is a problem or not.
>Anyone had experience of these before, or have any thoughts on this?
>
>2/ I'm thinking of building Rene Schmidt's VCO4069. Has any one tried an
>LM394 in one, and would it substantially improve stability? I got some
>teeny-weeny-weeny 10K thermistors that are small enough for all 3 to
>thermally bond to the transistors, so that should help too.
>Thoughts from the wise anyone?
>
>
>Festive Cheers,
>
>Dave
>
>
>
>  
>