# CEM 3340 simple VCO **URL:** \ **Category:** DIY STUFF\ **Created:** [November 29, 2020, 1:52pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405 "2020-11-29T13:52:06Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![daryll](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/daryll/32/10949_2.png) [@daryll](https://lookmumnocomputer.discourse.group/u/daryll)\ **Post date:** [November 29, 2020, 1:52pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/1 "2020-11-29T13:52:06Z")
On the Strip board layout it calls for a .1nf Cap , but on the BOM it states 1nf , which one is it ? Cheers Daryll ---
**Author:** ![CTorp](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/ctorp/32/15023_2.png) [@CTorp](https://lookmumnocomputer.discourse.group/u/CTorp)\ **Post date:** [November 29, 2020, 2:23pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/2 "2020-11-29T14:23:59Z")
![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/6/65a4987a98d29463e6733a849b052157607b7106.jpeg) Data sheet for the 3340 uses a 1nf in example schem ---
**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\ **Post date:** [November 29, 2020, 2:51pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/3 "2020-11-29T14:51:06Z")
Where do you see 0.1 nF? From [https://www.lookmumnocomputer.com/projects#/cem-3340-diy-simple](https://www.lookmumnocomputer.com/projects#/cem-3340-diy-simple) : ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/2/2198983eb711e3e99e0d4460fc6f1540f1166861.jpeg) ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/9/94a355219f5446b27c1498f3424168716dc152c6.png) ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/e/e06b70044d24c4a8a8dfc1d006ebe1309dc6e448.png) If it says 0.1 nF somewhere else that must be an error. That capacitor determines the frequency range: ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/3/3d3aa95c65f60e5da9c580e442b3f476eb478c3c.png) Presumably 0.1 nF would ~~drop~~ raise the range to ~~~0.5 Hz to 1 kHz~~ ~50 Hz to 100 kHz. ---
**Author:** ![eric](https://avatars.discourse-cdn.com/v4/letter/e/898d66/32.png) [@eric](https://lookmumnocomputer.discourse.group/u/eric)\ **Post date:** [November 29, 2020, 3:12pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/4 "2020-11-29T15:12:56Z")
> [@analogoutput](#): > > Presumably 0.1 nF would drop the range to ~ 0.5 Hz to 1 kHz. Smaller cap = higher frequency, no ? ---
**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\ **Post date:** [November 29, 2020, 3:13pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/5 "2020-11-29T15:13:55Z")
Oh duh. Is a complete sentence. … ---
**Author:** ![daryll](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/daryll/32/10949_2.png) [@daryll](https://lookmumnocomputer.discourse.group/u/daryll)\ **Post date:** [November 29, 2020, 3:39pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/7 "2020-11-29T15:39:07Z")
![CEM 3340](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/7/71da4c33f56319ff619725419a226817a1309576.jpeg) sure looks like .1nf to me ---
**Author:** ![Bas](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/bas/32/6908_2.png) [@Bas](https://lookmumnocomputer.discourse.group/u/Bas)\ **Post date:** [November 29, 2020, 3:48pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/8 "2020-11-29T15:48:19Z")
.1nF is not a thing. That would be marked as 100pF for sure. Typo? ---
**Author:** ![eric](https://avatars.discourse-cdn.com/v4/letter/e/898d66/32.png) [@eric](https://lookmumnocomputer.discourse.group/u/eric)\ **Post date:** [November 29, 2020, 3:56pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/9 "2020-11-29T15:56:12Z")
That’s already been pointed out. it’s the pin of the cap, not a decimal point, you can guess the second one on the ‘f’ of ‘nf’, that’s why that ‘f’ look strange. But it’s confusing for sure ! ---
**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\ **Post date:** [November 29, 2020, 4:31pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/10 "2020-11-29T16:31:05Z")
Looks like that dot was edited out in the basic version at [https://www.lookmumnocomputer.com/projects#/cem-3340-diy-simple](https://www.lookmumnocomputer.com/projects#/cem-3340-diy-simple) . ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/d/d004942c74368712ab14e5beab1a623b6be42e2a.jpeg) but in the images below it’s there. Yeah, confusing. But the BOM is right. ---
**Author:** ![SYNTHGUY57](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/synthguy57/32/14422_2.png) [@SYNTHGUY57](https://lookmumnocomputer.discourse.group/u/SYNTHGUY57)\ **Post date:** [November 30, 2020, 7:12am UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/11 "2020-11-30T07:12:53Z")
welcome daryll, to our lmnc synth group hug of interesting tidbits and suggestions ---
**Author:** ![lu.caas](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/lu.caas/32/12420_2.png) [@lu.caas](https://lookmumnocomputer.discourse.group/u/lu.caas)\ **Post date:** [December 18, 2020, 6:55pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/12 "2020-12-18T18:55:37Z")
So I was working on making a AS3340 VCO on protoboard but a problem came 😕 - On the electric druid schematic we have a 360k pull up resistor, - But on the Sam’s version there isn’t any. So is that normal? Or not needed? (I think it’s for tuning maybe?) Thanks for reading and helpinn ^^ ---
**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\ **Post date:** [December 18, 2020, 7:05pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/13 "2020-12-18T19:05:50Z")
It’s not a pull-up resistor, but another “control voltage”, one that’s constant. As such it offsets the oscillator pitch by a constant amount. In the 1222 oscillator (which I think that schematic is referring to, not the “simple VCO”) there are an octave switch and a center note pot which perform a similar function but can be varied. The simple VCO stripboard has a coarse tune pot which serves similarly. ---
**Author:** ![lu.caas](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/lu.caas/32/12420_2.png) [@lu.caas](https://lookmumnocomputer.discourse.group/u/lu.caas)\ **Post date:** [December 18, 2020, 7:08pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/14 "2020-12-18T19:08:29Z")
Ooh okay now I see thank you a lot. So I can just replace it with a pot so I can change the coarse? Yeah sorry I just wanted to use a similar topic so I chosen this one ^^ ---
**Author:** ![Jos](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jos/32/151_2.png) [@Jos](https://lookmumnocomputer.discourse.group/u/Jos)\ **Post date:** [December 18, 2020, 7:51pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/15 "2020-12-18T19:51:40Z")
Or maybe it is a wee fly taking a rest? ---
**Author:** ![BlackDeath](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/blackdeath/32/7644_2.png) [@BlackDeath](https://lookmumnocomputer.discourse.group/u/BlackDeath)\ **Post date:** [March 3, 2021, 7:58pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/16 "2021-03-03T19:58:45Z")
I don’t have a 10k trimpot… can I use a 100k instead? Will it break, or just make tuning more difficult? ---
**Author:** ![fredrik](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/fredrik/32/682_2.png) [@fredrik](https://lookmumnocomputer.discourse.group/u/fredrik)\ **Post date:** [March 3, 2021, 8:05pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/17 "2021-03-03T20:05:46Z")
It’s connected as a variable resistor (i.e. wiper is connected to one end) so it’ll work, but the target resistance for 24k + trimmer is ~30k so you’ll end up tuning at around 6% rotation. ---
**Author:** ![BlackDeath](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/blackdeath/32/7644_2.png) [@BlackDeath](https://lookmumnocomputer.discourse.group/u/BlackDeath)\ **Post date:** [March 3, 2021, 8:14pm UTC](https://lookmumnocomputer.discourse.group/t/cem-3340-simple-vco/2405/18 "2021-03-03T20:14:57Z")
Thank you for the quick reply… that sounds a little too precise. Guess I’ll wait, thanks.