question about modding a Chaquo.

moonagedaydream · Joined: Sep 28, 2011 Posts: 17 Location: Waco, TX

I have a elby Chaquo for eurorack. what i was wondering is if there is a way to add CV control over the oscillator. The chaos section is great, but it seems like the other section is just taking up space. is this possible?

synchroton · Joined: Mar 02, 2010 Posts: 20 Location: Milwaukee, WI USA

No, there's not much you can do without a major overhaul of the circuit. It's really there so that you've got a signal source which is already coupled to the chaos generator, which doesn't function without an external driving signal. If you want something that's more voltage-controllable, you should check out the Chaotica which Elby is now offering as well. Same size, way more voltage-controllable.

thermionicjunky · Joined: Dec 07, 2006 Posts: 90 Location: san francisco

The Yusynth quadrature LFO is a VC version of the ChaQuo oscillator. You could compare them and see if you could hack in the extra circuitry with some knd of daughter board.

moonagedaydream · Joined: Sep 28, 2011 Posts: 17 Location: Waco, TX

ok, thanks!

i'll try and dig that up a little later, i'm about to head back to school.

moonagedaydream · Joined: Sep 28, 2011 Posts: 17 Location: Waco, TX

well, i looked over the schematics. I can see where they are bringing in the CV, but i can't really tell where the cv section ends, and the normal circuit begins. would i have better luck just ordering one of these? http://bridechamber.com/VC_Res_PCB.html

thermionicjunky · Joined: Dec 07, 2006 Posts: 90 Location: san francisco

Or, if you're really interested in VC chaos, replace the module with Chaotica. It has a wide range of patterns, four CV inputs and a very useful reset/inhibit jack. If you have room for both, you could use it to drive the ChaQuo (and maybe modulate Chaotica with the quadrature LFO).

If you still just want to modify the ChaQuo, I think that an OTA would be a better VC resistor for this application, but that vactrol PCB might be easier to implement.

synchroton · Joined: Mar 02, 2010 Posts: 20 Location: Milwaukee, WI USA

Actually, yeah, your simplest bet would be to use two vactrols to voltage-control the rate of the oscillator - I'd replace R27 and R32 (not certain the parts designations are the same on the elby pcb) with a VTL5C4 each. The range switch would then enable/disable the voltage control.

There are schematics for driving these floating around... You'd drive them both with the same current source, putting the 2 LEDs in series.

Where to best put the jack & circuit board, I don't really know. I added a range switch on the integrators for the chaos generator, and it fit fine underneath the Z out jack. Looks like there's plenty of space underneath the range switch for a kobiconn jack, not that it's the most ergonomic spot for it

synchroton · Joined: Mar 02, 2010 Posts: 20 Location: Milwaukee, WI USA

didn't even bother to look at your link until now. Yeah, those would work fine but you'd need two of them driven from the same voltage - you can't use a dual vactrol in this application. But you can fit single vactrols on that board as well, i'm sure. To me, it'd just be much easier to build it on perfboard, with a single transistor and the 2 led's in series. You don't need most of that circuit.