[sdiy] expo converter /vco questions

[Dan Snazelle]

I have a few (well quite a few) basic questions about Expo Converters and VCO's


1. when i look at a vco and it has a PNP pair, can I replace that with an NPN pair?

2. Is there any advantage (other than cost) to using one or the other (npn or pnp pair?) it seems NPN pairs are cheaper and more common.

3. has anyone had good luck with the SSM2164? and once again, is it to replace an NPN or PNP pair?
at 6 bucks it seems like a good soloution (As you could get an expo AND a vca out of one chip right?)

4. Do you HAVE to use an lm311? could you use say an lm2903 or 339 or even a standard opamp?

5. in electronotes they had mentioned that using a discrete Schmitt trigger worked better than a 3080 or a 555...is there a modern best Schmitt trigger for vco use?

6. has anyone had much luck with those surface mount tempcos i have heard about?

7. what is a good replacement for the 3140 if i dont have one? electronotes said a 351 but that was a long time ago.


also...can anyone recommend a good NPN pair Triangle VCO?

thanks so much