The VCO-555

[Thomas_Henry]

Hi all,

As alluded to previously, I have four projects that have been sitting around way too long and have been panting to get out the door for the past couple of years.

So, here's the first: a VCO using easy to find parts. If I may be so immodest, this is my best design to date. The waveforms look great and if you check the measurements, below, you'll see it's the most accurate I've ever come up with. If I were younger and had more energy, I'd turn this into an article and make some moolah from it. Unfortunately, my strength for such endeavors is ebbing, so instead I'll post it here for you to play with. All I ask is that you respect the rights and don't republish the design or rip it off for any commercial purposes. I'm not opposed to someone doing a PCB for noncommercial uses, but please secure permission from me first.

Okay, without that out of the way, here's the dope. My favorite VCO of all times is the CEM3340, and I've always wanted to approximate it somehow. After nearly thirty years, I finally have a design which comes the closest. The accuracy on my breadboard was very good.

There are ramp, triangle, pulse and sine outputs, all of which are decent looking. The sync is a real treat and basically comes along for free. And, of course, there are the usual VCO features such as coarse and fine tuning, exponential and linear FM, etc. If you're looking for cleverness, then be sure to check out how I did the sync, the ramp, and buffered the sine to keep the chip count down.

So there it is. Have fun with it and be sure to post your results here. Three modules are in the wings and should be out the door in the next week or so. And then school starts yet again and another year evaporates...

Thomas Henry

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VCO555_0001.jpg
Description:	Schematic - Sheet 1
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VCO555_0002.jpg
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Parts List.jpg
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Measurements.pdf
Description:	Measurements	Download
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[JingleJoe]

This is the kind of circuit I love simple and made with easy to find parts, this provides my favorite electronic circuit quality; longevity!
Jolly good work old chap

[v-un-v]

Nice one Thomas! Look forward to seeing the others too.

[Uncle Krunkus]

Elegant design Thomas.

[bubzy]

wooo!

if theres one thing i cant get enough of its vcos
and vcas
and vcfs
oh and sequencers
and.........
*goes off into a list of things you cant get enough of*


thanks thomas!

[EdisonRex]

Woot! And with standard parts too!

[bod]

this looks awesome!!

[Cynosure]

Wow! Very cool. Thanks for sharing.

[J3RK]

Nice work as always! VERY cool!!! Can't wait to give it a try!

[LFLab]

VERY nice!

[andrewF]

its great!
following the schematic it looks like a normal OTA based VCO and then suddenly there is a 555 in the middle

[Peake]

[frijitz]

[frijitz]

[LFLab]

Been busy to get the schematic into Eagle, definitely non-commercial effort. I make too much money in my day job and value my family too high to start a half assed commercial business off of the work of someone else

Let me know if you find any funny stuff (there will be plenty) or better yet, correct it yourself and post the file here

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untitled.sch
Description:	TH555 schematic Eagle file	Download
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[jojjelito]

Fantastic work! Clever and low parts count I can't resist experimenting with these. Like I don't have a ridiculous backlog. Grrr

Oh, and thanks Thomas!

[cleaninglady]

Excellent , can't wait to try this.

Thanks for posting it , Thomas !

[fonik]

i designed a PCB for this VCO end of last year, the prototype PCB is in my drawer since then.

i will start to build it this week in order to test it and to apply any changes that have been made to the original schematic i got in 2011.

i got thomas kind permission to do a PCB run for this project, which is really generous.

i will keep you posted on this, and will start a new thread when i am ready to take orders.

[andrewF]

[Designator]

Would like to mention that 'sync' (re-)sets the loading current here, not the entire waveform, so you don't have the usual hardsync.
If hardsync is desired some extension to the circuit would be nessecary.For inspiration have a look at the bassdrum of the TR909(sic!)!

[AlasdairMoons]

@fonik
if you do a run of the PCB's, please count me in

[vladosh]

Yuhoo )) i don't visit for two days and there is another VCO
Thank you Thomas for sharing it !

[fonik]

just wanted to give you an update (almost the same as for the verstaile LFO controller):
the timeframe is not set, yet. i could offer the PCB as i originally designed it very soon (will finish my build this week), however, quite a few people wanted an additional PCB for front panel components in eurorack format.
in order to achieve this, i have to re-design and modify the layout and design th eadditional front panel components PCB.
i will have to order another set of these new layouts for testing purposes befor i can offer the final product.
i will NOT offer front panels.

[AlasdairMoons]

[fonik]