Saturday, April 14, 2012

Simple CV/Trigger switch box

I like my Yamaha CS-30.
I like my Kenton Pro Solo Mk II.
I DON'T like that I have to plug the CV/Trigger cables in and out every time I want to switch between letting the Pro Solo control the CS-30 and playing the CS-30 keyboard myself.

Solution: Make a simple box that lets me choose which "mode" I want to use the CS-30 in.

Short description

The CS-30 has CV and Trigger inputs. That makes it controllable from external sources, such as another CV/Trigger keyboard, sequencer, or a computer via a MIDI converter.
In my case, I am using a Kenton Pro Solo Mk II (Hm, I realize it's not in my gear list yet) to control it from Steinberg Cubase Studio 4 or my little Behringer UMX49 MIDI keyboard.


The problem is that the internal CV/Trigger signals inside the CS-30 are routed from the keyboard, via the input jacks, to the "synth engine". The input jacks have breakers that disconnect the internal CV generated by the keyboard so you lose "local" control once you have anything plugged in in those input jacks.
Of course the jacks are on the rear and not very easy to locate with your fumbling fingers, trying to guess which jack is which. Every time you want to tweak a sound and play the keyboard of the CS-30 at the same time you have to pull those plugs out so you get local control of the CS-30. When you're done and you want to use your computer and MIDI/CV-converter you have to plug them in again. Very annoying...

Some useful features

Luckily, on the CS-30 there is also a CV output as well as a trigger output.
You could, for instance, plug a cable into the CV output and patch it straight back into the CV input.
The CS-30 would work just like normal and you have local control of it.
While that loopback by itself is pointless, it opens some possibilities.
Let's say you break the loop and insert another control signal instead coming from the MIDI/CV converter going into the CV input...
And let's say you put a switch there, letting you choose which signal you want to use...


I made a small box with 6 jacks and 2 SPDT switches on. It's actually a pair of 2-in-1-out selectors.
Here's what it looks like inside.
Not exactly rocket-science, but very simple and very useful!
The shields are just joined between all the jacks for each of the "2-in-1-out" sections.
The red switch just selects which of the two signals from the jacks on the left gets routed to the jack on the right. I guess I could have used DPDT switches and switched the shield as well, to reduce the risk of ground loops, but I don't think it matters in this case.

Also, I could have just used a single DPDT switch and switched both the CV and Trigger signals at the same time. As it is now I have to flip two switches to change between local and external control.
While this may seem stupid it may enable some interesting uses, such as letting for instance the computer trigger the CS-30 while I just change the pitch on the keyboard locally.
Or vice versa: Letting the computer change the pitch while I trigger the CS-30 locally.
Maybe not something I will use extremely much, but it seemed fun and didn't really add any complexity, so that's how I did it :)

I found a schematic I drew a while ago, which used the single DPDT-approach.
Excuse the silly Swedish comments, I'm too lazy to redraw it :)

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