Add VCOs to my CSY-1

[anders79]

Hello!

I've been watching this forum for a couple of years now and have learnt a lot from here. Since I'm a beginner and very interested in synth-DIY I became a member two days ago.

Ok, I hope this is the right place for questions about my project with my Yamaha CSY-1 monosynth/organ from 1974. It's a wonderful sounding synth, but a little bit thin in its sound, since it contains only a single VCO.
What I would like to do is to add some extra VCOs to it, so I've been searching around for schematics of simple linear VCOs, and this is what I have found on the net and from other discussions here on electro-music:

1: http://www.seekic.com/forum/22_circuit_diagram/19893_LINEAR_VCO.html

2: The linear version of Rene Schmitz 4069 VCO of Scott G.

3: Nicolas super simple V/Hz vco.

4. The square/triangle VCO on the LM13600 datasheet.

5. The LM3900 VCO showed in this thread: http://electro-music.com/forum/ntopic-26808.html

6. Multiple 4046 VCOs (pitch-tracked with the contained PLL) with different vibrato LFOs to get a slightly detuned effect. I know that the bad linearity of 4046 VCO makes it impossible to give them different CVs, the beatings between the VCOs changes too much for every note. So maybe different vibratos for each VCO is better since the phase relationship between the LFOs is always the same?

I want it simple because I want to build more than one.
I want the effect of multiple VCOs, slightly detuned, and of course I want it simple, but with good tracking in at least a couple of octaves. Will anyone of those VCOs I've listed be good enough for that?

The plan is to frequency-track the CSY-1 VCO with a LM2907 and use that voltage to the added VCOs (and fine-tune them) and route those to the filter together with the original VCO.
Any suggestions how it could be done more simple or more effective?

kind regards Anders

[Tim Servo]

Hey Anders,

Instead of adding another VCO to your synth, maybe you could try to get a "thicker" sound by experimenting with some waveshapers. I would think a suboctave (or two) would be a good place to start. You might also look at a Pulse Width Modulation circuit and/or a "wave folder" circuit. These would give you some more sonic possibilities, without the tracking problems of a separate VCO. Of course, you'll want to get the schematics or do some careful exploration with an oscilloscope to see what sort of signal levels are used in that synth. Of course, a second VCO would also be very cool, but the waveshapers might be a simpler place to start. Just a thought.

Tim (thinking, but not too much) Servo

[keyman2]

It's not a bad idea, you can have tracking 5th's, 7th's and octave's, the only thing is they are static but you could add some chorusing effect to liven things up as well.