Tempco's pos or neg

[Werebear]

Hi, yet more siiliness from the Bear.

Tempco's. Which ones would we want to use in a log conveter for a vco? Positive - PTC - or negative - NTC?

Or is it a matter of the design? You see I can get NTC from anywhere, well Mouser UK and Rapid and so on and have - possibly mistakenly - bought some. Not cheap for someone who has to buy his components a handful at a time.

So, do we want PTC for all designs that currently exist? Or - *dumb alert* - are they perchance interchangeable with NTC? I assume that we use one or the other to meet conditions from the log pair trannies.

And no, I won't be attempting to re design the log amp converter doofer to use NTC.

[Sebo]

Most designs uses NTC, I think because they are more precise.
I know only a few designs that uses PTC:
http://www.uni-bonn.de/~uzs159/vco4069.html
http://www.aleph.co.jp/~takeda/radio/farmVCO4069E.html
Also there is a mod of the Yusynth VCO that uses PTC (this VCO originally uses an NTC):
http://yusynth.net/Modular/EN/VCO/index.html

[wmonk]

For VCO expo converters you need a PTC with a temp coefficient of about +3300 ppm/K
There is some excellent reading on this on the website of Ian Fritz.
http://home.comcast.net/~ijfritz/sy_cir7.htm

[Sebo]

Sorry, I mixed PTC and NTC.
What I mean is:

Most designs uses PTC, I think because they are more precise.
I know only a few designs that uses NTC:
http://www.uni-bonn.de/~uzs159/vco4069.html
http://www.aleph.co.jp/~takeda/radio/farmVCO4069E.html
Also there is a mod of the Yusynth VCO that uses NTC (this VCO originally uses an PTC):
http://yusynth.net/Modular/EN/VCO/index.html

And, as the links I posted prove it, not all expo converters for VCOs uses PTC.

[Werebear]

Yeeaah...

I had a feeling I had the wrong ones. Bugger.

Thanks for the help chaps. I'm looking into Thomas Henry's VCO 1 design as a sound source for a stand alone instrument so I may just have to stump up the pennies to Music From Outer Space for the 2K.

Thanks.

Bear