Well, I really had no option but to order one, er, or two...
I had the idea that a modified Gakken SX-150 MarkII could provide the perfect accompaniment in my budding Telstar Attaché Eurocase, alongside the recently Eurofied Monotron Delay.
Now, there is a fair bit of advice online about modding the SX-150 MKI, but precious little about the MKII, which just happens to have a completely different PCB. However, with a little help from those good people at MuffWiggler, I drummed up the confidence to have a go. To be fair most of the Test Points on the board have their function marked (VCF, OSC, LFO, +5V, ENV, etc).
My dodgy soldering skills notwithstanding, it mostly does what I wanted it to. The oscillator kind of tracks to scale, the LFO's put out useable square and triangles and (with a bit of attenuation and amping, the envelope sends a signal and the filter receives one.
So here are a few demonstration videos. Just to be clear, these are in no way musical, simply a proof of concept type thing.
In the first, a gate is being sent simultaneously to the Gakken and the monotron from a homebrew battery powered sequencer. The raw oscillator from the monotron is also being fed into the SX-15o Line In and the raw oscillator of the SX-150 is being fed into the montron, so there's a bit of an uncontrolled mess going on. This is just an initial try out.
In the next test a scale is played from a minibrute, just to show the limit of the SX-150 range and then a simple arpeggio is played. In this, a CV is taken from the minibrute into the CV-in on the SX-150. Then the output from the SX-150 is passing through the minibrute (with filter wide open) just to use the VCA + VCA Envelope of the minibrute.
In the final test video, it all out oscillator war. There's lots of mutual modulation going on here between the SX-150 and the monotron delay. Towards the end a plain saw wave is also introduced from the minibrute. Apart from this though, the minibrute is only being used for it's VCA envelope.