[sdiy] somewhat sucessful f to v circuit

[Dan Snazelle]

just some info for those into F to V

notes:

first of all, thanks ian!
ian fritz had pointed me in the direction of the LM331 for a decent F TO V and i got one.
However, the circuits in the datasheet actually performed far worse than the lm2917 for converting a guitar to cv.
But knowing that he knows what he is talking about, i decided to look for more circuits involving the lm331. which led me to the 4ms Atoner Fx (anyone heard this?) device which uses the re badged version of the lm331, the XR4151. learning of this chip name, i did some looking.


i went to the exar site and got their datasheet. WOW

its not perfect but it blows away the lm2917 for both speed and pitch. ITs amazing how different their 2 datasheets are but the exar people really have a much better idea of how to get a square wave to track (at least for what i am doing)


now i am driving a 566 (in linear mode) using thomas henry's negative supply designs from the vco cookbook and TRYING to figure out how to best use this. the only thing I cant quite figure out yet is how to make the CV a higher pitch. in other words, right now, its putting out pretty low notes via linear cv.


QUESTION:


i am putting it directly into pin 6 of the Lm566 (not sure if it leaves the lm331 as a current or a voltage but when i hooked it up to a resistor and transistor before pin 6 it didnt work so well and only tracked one string) and this seems to work. If it IS coming out of the lm331 as a current, how can i add a current offset to it?? (for a lower or higher frequency) i would like to just add a freq knob somewhere in the path that will offset it but i am only used to adding a voltage offset.

thanks so much