Via Collin Cunningham at MAKE, MrBook has a lovely rig with a modified Gakken SX-150, the synth kit that sells for US$50 in the States and has even been seen as a free add-in with Japanese magazines. He’s added MIDI control and a digital audio converter, and put it into a housing, which makes for a quite-playable instrument.

Really terrific work! Of course, a few thoughts:

  • We need an OSC-compatible synth. (Anyone out there?)
  • I love you, Live, but this looks like a perfect job for Numerology (for its modular sequencing) or Renoise (for tracking).
  • Looks like more controls would make this even more self-contained.

Gakken sx-150 arduino hack number two: Adding MIDI and Audio out

If you have synth projects like this, we’d love to see them.

  • pluton

    super nice !!

  • lekvar

    That sounds damned good for such a simple machine. You can see the schematic here. Its circuits are simple enough that even I can figure out what's going on. It just proves that you can't judge a synth by its package/price tag.

  • Yeah, there are some really brilliant hacks that make it sound as good as it does. A really impressive design.

  • Cool, I'm glad it made it to CDM. The whole design of the hack is based on Arduino, which makes it easy to program and customize. If there's enough interest, I'll post the schematics and code of the project as a whole.


  • dyscode

    <cite> "been seen as a free add-in with Japanese magazines."</cite>

    it´s not a free add on it IS the magazine 😀

  • dyscode

    besides that hack is REALLY nice!

  • I'd love to see schematics and code, mrbook. It's a seriously sweet mod.

  • Luke D

    I'd definitely be interested in schematics and code!

  • fran

    This is too cool for words. Makes me rethink synths in general. Also, props to Mr. Book for some really nice sequencing/tweaking, making me want to get up and shake my booty a bit. As a firm believer that less is so often far, far more, this video shows why. It's also really funny to see digital supercomputer wizardry acting as a glorified porter for a $50 noise box.

  • Hey CDMers, I added post with instructions, schematics and code for this mod. Make sure you let me know if you make something cool with it!



  • @mrbook: It seem to me that the 12-bit DAC, with 4096 possible output voltages, might have some tuning issues at the extreme ends of the piano range. 4096 steps / 88 keys = about 46 voltage steps per key, rather than the 100 or so you'd really want for tuning accuracy (not to mention avoiding zipper noise for pitch bends).The output voltage swing of the DAC matters, too, but can also be dealt with in the analog domain.

    Of course, the flip-side is that available DACs at 14 or 16 bits are rather expensive and harder to use compared to these cheap and easy 12-bit guys. But then again, my dream is an analog synth with no knobs, using only CV for control, and then using the computer for patching, envelopes, and LFOs.

  • Hrm, looking at the data sheet for the DAC you used:

    Output swing goes from .010V to Vdd, which can be as high as 5.5V. Let's go with 5 for now. So, with a 1V/Oct synth, that's about five octaves you can control. 4096 / 60 (5 oct) = about 68 voltage steps per note. Probably good enough for most applications. And the difference in price between 12-bit DACs and 16-bit ones is staggering.

  • Scott Flavin

    Awesome! I picked one of these up last year and over the past few months it's been collecting dust on my desk. Hope to change that in the next week 😀

  • Actually the magazine is called Gakken Otona no Kagaku (Gakken Science for Adults) and costs around $35 now. Obviously a chunk of that goes to paying for the synth, but since it only comes with the magazine and is most often sold in bookstores, it's fair to say it's similar to other magazines that also have toys or collectables inside. It comes with the disassembled synth in a box with the magazine glued to the box. I'd definitely consider it more an "assembly required" than a real kit since the PCB already soldered in, unlike say a Paia synth kit, (The Gakken SX-150 resembles the PAIA Gnome from the 1970s). The magazine always has some sort of invention in it. My favorite is a phonograph that records onto CDs with a needle and plays them back. They've also done a $24 Theremin in an earlier issue. Some years back I bought an $8 science for kids magazine that contained a simple Stylophone type synth, though instead of a speaker you needed to tune in a nearby radio, presumably a Japanese one.

    Anyway the Gakken SX-150 must now have the record as the analog synth produced in the largest numbers.

  • Just recently had a look at my stylophone, and realised that would probably be a very easy hack to add midi control to it. Have a couple of arduino minis laying around that I will experiment with as soon as I got time.

  • Regarding what Video Music said – a Stylophone puts out more or less just square waves, and an Arduino already can make square waves by itself so all you are getting is that little extra something from the old components that you can't do with just an Arduino… if you manage to scale it. The thing that's impressive about the SX-150 is it's undeniably a real analog synth, albeit a simplfied one. As I mentioned, it's much closer to a "lite" minimal version of Paia Gnome than a stylophone imho.

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  • lefthandedheroes

    The Gakken SX-150 stylus gets the CV and GATE information from the ribbon-like slider pad.
    I just connected the Novation BassStation Rack CV and GATE out to the stylus and voilà! – have my MIDI controlled Gakken.
    The cheapest way to do this is to cut a patch cable in half, took the plastic bits off the wire coming from the tips of the jacks, roll them together and stick the Gakken's stylus into.
    You may notice that it only works if the BassStation's CV type set to '00' (Roland/Sequential/Arp) – because of the voltage and plug the Gakken SX's out to a mixer rather than using the built in speaker – this is needed as the ground.

    I believe this works with other MIDI-to-CV converters too.

  • Toby Lynn

    Does anyone know where i can just buy a gakken already midi modded that i can just plug into Ableton and play?? I really struggle even with the simplest of circuits and soldering =( any help appreciated …thanks