# 3340 VCO Schematic for PCB design

**URL:** <https://lookmumnocomputer.discourse.group/t/3340-vco-schematic-for-pcb-design/730>\
**Category:** DIY STUFF\
**Created:** [April 25, 2020, 2:24am UTC](https://lookmumnocomputer.discourse.group/t/3340-vco-schematic-for-pcb-design/730 "2020-04-25T02:24:13Z")\
**Posts on this page:** 1\
**Showing post:** 43

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**Author:** ![Dud](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/dud/32/610_2.png) [@Dud](https://lookmumnocomputer.discourse.group/u/Dud)\
**Post date:** [November 27, 2021, 10:41pm UTC](https://lookmumnocomputer.discourse.group/t/3340-vco-schematic-for-pcb-design/730/43 "2021-11-27T22:41:36Z")

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Personally I would also suggest adding the octave selection, really very practical  
On my VCOs that don’t have it I miss it a lot

 ![schematic2](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/3/3/338489f274c032207e3e7e11d0c830e46781a35f.jpeg)

 ![schematic3](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/2/8/28d84862662a0104779a38acebe26cf806664536.jpeg)

R42 must be changed, i don’t remember exactely maybe 2K (i ll searched and come back 🙂 )

EDIT : I found it, between 1K and 4.7K

> (By the way, R42 shown there is specified as 220 ohms but it really should be higher; 220R results in too much current through the voltage reference U4, potentially causing bad behavior and possibly damaging U4 permanently. If you used 220R this would be a good time to replace it with something between 1k and 4.7k. For more on this and other mods see [1222 Tuner VCO Module - #203 by antoine.pasde2](https://lookmumnocomputer.discourse.group/t/1222-tuner-vco-module/16/203) and [1222 Tuner VCO Module fixes/improvements - #6 by eric](https://lookmumnocomputer.discourse.group/t/1222-tuner-vco-module-fixes-improvements/2072/6) .)

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