VCO-1 Stripboard Layout with 12V mods

[warpeggio]

Hello fellow nerds!

I'm Warpeggio, first time posting here. I've set out to build a synthesizer, and having completed a build of Ray Wilson's Wall Wart Power Supply, I was ready to try my hand at a VCO.

I come from the 9v world of guitar effects pedals, so i was thrilled that Thomas' design called for such simple parts that I already had in my war chest. I was a little concerned about the CA3080, but i had LM13700 at hand, and others have written positively about it as a sub / replacement. Another design goal was working off +/-12V, so my part values reflect that. I have to thank Osal for his wonderful post here on those 12v modifications.

I've come to share my stripboard layout for VCO-1. I've built it up to the point that i'm comfortable calling it "verified", although i have not the rack to test the FM or PWM functions yet. The triangle, sine, and pulse outputs are working as described.

Problems that i am currently working through:
1) With stable or no CV input, there is significant oscillator frequency instability over the course of seconds. My Rigol DS1054 won't give a clean frequency count. I *believe* this is because i have a poor power supply transformer but haven't tracked it down yet.
2)I can't test the 1v/Oct trimmer functionality because i didn't have any 100Ohm trimmers. Small-bear will be shipping some to me shortly, so until then I can't comment on how this particular build tracks.
3) I've "parked" the unused half of the LM13700, but I'd like to use it somehow. I'm currently investigating a very simple VCA, since those are always welcome.

Thanks for all the information y'all have shared on this site. Your feedback is appreciated.

Changelog:
V 2020-10-15:
* R47 was not correctly tied to the positive rail, instead misplaced on a bus with the R02 wiper. Fixed.
* C7 tied to lower ground rail to better fit capacitor pin spacing. Allows tidier jumper nearby.
* Color coded resistors involved in choosing +/-12V or +/-15V, provided table for 15V values
* Credited Osal directly in image

V 2020-11-20:
* Updated values for C13 & C14 to be displayed in the BOM
* Some minor opacity adjustments for clarity
* Fixed the extra copper strip that was displayed at the bottom of each board

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Description:	Thomas Henry's VCO-1, on stripboard, modified for +/-12V
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[warpeggio]

Hello again! An update on the issues i was working through:

1) Instability: The scope revealed that my CV input signal wasn't as stable as i thought, and this was compounded by my poor power supply transformer responding to varying loads elsewhere in the house. Overall, the oscillator is as stable as designed.

2) Tracking over 3 octaves is excellent, although tuning can be tricky. I went back and forth between the scope and a clip-on instrument tuner. My build DOES go flat on the fourth octave - i believe it's because i used 2x 2N3906 that i didn't even try to match for current or Vbe. I assume this would be improved with a matched pair or dual IC. Personally, 3 octaves is pretty dang musical for a first VCO so i'm not sure i care to make any changes.

3) I've drawn up a version that implements a simple VCA on IC1B, but i haven't built it yet. It's based on a design that Kristian Blåsol shared on his Youtube. This would be a "no-frills" design, to say the least.

[mikeb]

[quote="warpeggio"
3) I've drawn up a version that implements a simple VCA on IC1B, but i haven't built it yet. It's based on a design that Kristian Blåsol shared on his Youtube. This would be a "no-frills" design, to say the least.[/quote]

If you do use the other half of the 13700 for something, I suggest closely watching the frequency of your VCO as you operate the shared VCA. From my experience using it in a very similar way about 10 years ago, my oscillator fluctuated around 5-10 cents.

[Gingoism]

agreed, in an earlier design i used the 2nd half as an FM VCA and it messed with the osc core majorly...now the vco sits on my desk as a test osc.
However in a more recent design i used the 2nd half as a sine shaper instead...which is a better use of the spare ota imo.

[warpeggio]

[R_Gol]

Thanks for sharing this!

My I ask you regarding two things:
All pots are in back view? lugs are from top to button is 3 2 1 ?

Can I omit the c12 (0.22uf) if I would like to make that input dc coupled? (same as the exp fm input?)

[warpeggio]

[JimRead]

Hello,

I really like this build fair play to you for doing it, I use 12v so it would be a boon to me.
I wondered if I made two of them is there any way to synchronise them?

Cheers - Jim