# Polykit Octo VCO

**URL:** <https://lookmumnocomputer.discourse.group/t/polykit-octo-vco/2710>\
**Category:** DIY STUFF\
**Created:** [January 16, 2021, 9:36pm UTC](https://lookmumnocomputer.discourse.group/t/polykit-octo-vco/2710 "2021-01-16T21:36:34Z")\
**Posts on this page:** 1\
**Showing post:** 7

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**Author:** ![jaradical](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jaradical/32/12069_2.png) [@jaradical](https://lookmumnocomputer.discourse.group/u/jaradical)\
**Post date:** [February 13, 2021, 4:19pm UTC](https://lookmumnocomputer.discourse.group/t/polykit-octo-vco/2710/7 "2021-02-13T16:19:13Z")

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That’s sweet! Sounds fat and the github is a nice touch.

Some question on your use of the NTC - firstly, they’re the 4k7 resistors in your BOM? What kind of temp coefficient do they have? I used PTCs in my VCO, but they’re in a negative feedback path - so I guess it has the same effect as an NTC? Any particular reason you did it that way?

If you’re working on VCAs, here’s an lm13700 linear VCA I recently built - two ICs and two transistors for two channels. It seems to more or less work:

[lm13700 vca schematic](https://lookmumnocomputer.discourse.group/t/gain-using-the-lm13700/2929/8)

I’ve got a JFET variant that’s a single IC and two transistors I can share if you’re interested.

Cheers,  
Jared

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