Following on from my last post I’ve been trying to simplify the signal chain in my live setup even further. The main problem with using the Field Kit mixer was that it involved a lot of 3.5mm to 6.35mm adaptor cables. I also realised that if I used the extra input on the DI box, I could do away with the mixer altogether and run the instruments in parallel with two separate effects chains. I was also finding the latest addition of the Shruthi Sidekick to be a bit tricky to dial in, plus it was adding a bit too much weight to the case for my liking. So I decided to bring back the Monotron for filter duties, albeit in a modified form. This project became the Stickybox.
Basically, the Stickybox is a Raspberry Pi running Samplerbox, with a Korg Monotron velcroed to the top. The first major modification was to run the Monotron directly from the Pi’s power supply, as I was fed up with the batteries running dry at inconvenient times. This was easy from a soldering point of view, as there are Vcc and Ground pins marked on the Monotron’s circuit board. I connected these to the GPIO on the Raspberry Pi (pins 4 and 6) with a jumper cable. One thing to note if you perform this mod is that the standby switch no longer turns the Monotron off; it’ll be on as long as the Pi is powered. The switch still works in terms of selecting the lfo destination though, so there’s no real loss of functionality. I also thought that the output sounded a bit less noisy when powered in this manner, although I haven’t tested it in a high-volume environment yet so it may just be an illusion.
After the success of this mod we come to the ‘Mk.2’ modification. This one was a bit trickier and involved the addition of an expression pedal input. Again I tapped the Vcc and ground pins from the Monotron board, as well as the handily labelled Cutoff solder point. I ran the wires to a breakout box with a TRS connector. At this point I had to cut a small part of the case away on the Monotron to feed the wires through, as it was getting a bit tight in terms of closing it all up. If you’re doing this, make sure you feed the wires to wherever you need them to go before soldering anything on the end!
My thinking was to send 5 volts to the ring connector of the TRS socket, and the Cutoff input to the tip (& sleeve to ground). I’ll save you some time by saying *USE A RESISTOR* on the cutoff input signal. If you don’t, it’ll make all sorts of weird oscillation noises and won’t work. There are various different schematics floating around the internet but I found a 150K resistor to work quite well in combination with the Roland EV-5 expression pedal that I am using. I had to approximate the value, and 150k resistors were all I had to hand.
I’d also suggest if you’re doing this ‘properly’ that you add some sort of strain relief to the wires. In fact bare wires like I’ve used are probably a bit of a bad idea generally. If I had thought the whole project through before starting, I might have used pin headers on the Monotron so that I could actually remove the modded parts easily. When you factor in the speaker connector and ribbon on the Monotron itself, it can get a bit tangled when trying to disassemble the thing. Generally, I think it’ll be okay as the entire device is velcro-taped to the inside of a pedal case. That, and the fact that the unused connectors on the Pi are covered in slightly gooey electrical tape, is what gives the Stickybox its name.
In terms of further modifications, I think more breakout boxes would probably start to make the whole thing a little unwieldy. I said at the start of the post that I was trying to simplify the signal chain, and this mod- while removing the need to carry batteries- does give me one more thing to plug in (i.e the expression pedal). Make of that what you will.
However, if I ever end up making a Mk.3 model, I think there’s decent scope for either using a Monotron Delay instead of the classic Monotron, or linking both together, at which point I’ll have to start thinking about rehousing the whole thing into a bespoke case. If you were feeling really adventurous, you could feasibly build a Stickybox into the chassis of a suitably sized Midi keyboard. The Stickybox Mk.2 will need a proper run out on stage before I even think about doing that though.
Addendum: Whilst trying to work out a total spend for making this project (it’s not much), I have discovered that you can’t buy the original Monotron new anymore, which is a bit of a shame, but there are loads around second hand. The Delay model is still available new for £42.20 online, as of 31/07/18. As it turns out, both the midi keyboard (Akai MPK Mini Mk1) and the Raspberry Pi (2B) I used are both now discontinued as well. So much for cutting edge!