Twenty Percent: modified drone machine

You know what is a Sony MX-555? Yeah, me neither, before buying one dirt cheap on ebay. There’s not a lot of infos on the web… it’s an hifi mixer with echo included.

I was attracted by the echo thing, and I thought I could bend it, but, you know, probing on a 220V powered device is not a good idea, so, after some cold sweat and shaking hands, I decide to mod it.

For sure you know Look Mum No Computer, and maybe you saw that video where he built a reverse avalanche oscillator, with just a pot, a transistor, a led, a capacitor and a pair of resistors. Easy, and I like it. The only non-standard parameter needed is a voltage between 12 and 18 volts, but the typical DC power adapter is 12V maximum, and that’s where the MX555 came to my mind.

I Opened the box, and with a multimeter I checked where I could get that voltage out of that board. PAY ATTENTION: for this probing the device has to be turned on, so there’s risk of damage (of the device, but also of the person with the multimeter), don’t do it unless you are sure of what you are doing!

Black probe on the ground, and red probe around looking for voltages. I found a nice 23V, that works well for the oscillators and gives also some space for some detune stuff. Perfect, I have the voltage, I have the box, I have the oscillator, I need a project.

I tried to wire together 3 oscillators with different capacitor value (1uF, 4.7uF, 10uF) without resistors between them. Doing this, there are only one signal in output influenced by the 3 oscillators. I planned a passive low pass filter after and 2 detune values before, one with a pot, and one with a LDR, activable by a switch.

I fit 5 of those “oscillator banks” into the box, and that’s the result (the mixer is still working, it’s possible to add another input or add and effect through feedback loop).

The name

Do you know… 555 + 20% = ?