New Stroh Modular Stereo Pulse VCO

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New Stroh Modular Stereo Pulse VCO

Post by synthcube » Wed Aug 03, 2016 3:30 pm

courtesy of j3rk, the Stereo Pulse VCO is now available as a panel/pcb bundle and a full kit : ... e-vco-frac

assembled units coming soon

the BOM and schematic documents are available on the product page when you are logged in to the store...

thanks dustin! :hail:


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Post by KoryB » Sun Jul 30, 2017 4:24 am

What's this VCO sound like?!!?

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Post by thee ghost ov n_phay » Sun Dec 17, 2017 2:16 pm

KoryB wrote:What's this VCO sound like?!!?
I accidentally bought two of these recently, from Synthcube, Accidentally because I only meant to order one, but fucked up the order process somehow (my fault). They are very nice VCOs, the waves sound pleasing, especially the triangle wave, and the sync sounds great, really rich and strong. I'm glad I did get 2 of them.

They are a tricky build, and I think not for beginners, quite a lot of panel wiring to do, and a bit of inter-board wiring too. As supplied, they came with the trimmers to set the scaling as the type with the set screw on top, and these trimmers go on the VCO core board, which is sandwiched between the waveshaper board and the panel, so you can't set them without taking the 2 boards apart, and power comes in onthe other board, so... I'm going to replace these with trimers with the screw on the end. Probably possible to build it with the core board on the outside, but then the trimmers to set the waveshapes up correctly would be inaccessible.

The VCO is a bit quirky (which is OK, there are plenty of non-quirky VCOs out there) - There is only a linear FM input, not an expo one, also there is only a coarse tune knob, which is VERY wide-ranging, so it's tricky to tune them in accurately. I might see if a compact multiturn pot is available to replace the standard tuning pot, otherwise I might designe as Blacetesque panel in Front Panel Designer and repanel them. They are both Keepers, they sound so nice. The dual PWM outputs thing is unusual too, haven't quite got a handle on using this yet, I''m still experimenting with it.

Kit packaging by Synthcube was v good, made it easier to build.

Reccomend these, if you're an experienced DIY-er, and am looking forward to more of Dustin's designs making it to this delightful, but misfitish format.

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Post by J3RK » Tue Dec 19, 2017 11:56 am

Glad to hear about your builds! It's been a while, but I believe that I set my waveshapes up while the two boards were separate, and put the VCO board on the back, as it would need calibration more often. (at least I think I did it that way)

As far as FM goes, it was a panel-space consideration to have the V/Oct be the only exponential input. If you wanted to add another one, you could simply add a summing resistor to the CV summing op amp, and add a pot (if you do a repanel). It can be AC or DC coupled. If you go with AC, I'd recommend something in the 10uF to 22uF range, as it will allow much lower modulation speeds before getting filtered out by the cap.

Also, if you're not using a V/Oct signal on one of them, you can modulate it through the V/Oct input for exponential FM. Maybe run the modulation signal through an attenuator first. Then if you don't need V/Oct response, you should still be able to force some stepped voltages through to some degree on the linear. (or you could short across the AC coupling cap on the PCB, and have a DC coupled linear FM input)

For the dual PWM, there are a few things that I personally do with it. If you have a stereo output, you can put one PWM through one signal chain to one side, an the other through another to the other side. (wow, weird sentence :hihi: ) If you vary both of the pulse widths, you'll get some spacious sounding stereo fields.

The other is to combine them through a mixer, or a wave-splicer / precision rectifier or ring mod or XOR etc. You'll be able to get some somewhat complex PWM effects. I especially like the splicer, as you'll have one pulse-width below 0V, and another above 0V so you get a stepped wave more or less.

I'd love to do some more Frac modules at some point, and have some new circuits that would be fun to build I think. It would be up to Synthcube I think for the most part. If there's anything that people feel would be welcome in the format, I'm happy to consider putting something together.

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