via this auction
Googlish: "vintage device for hobbyists - have the angschlossen synth at times of the system and also tested with headphones - the flash device (ie lamp lit) but there is no sound - I think the volume controller has no contact - that is only for people with the electronics know - unfortunately I do not -."

Update: Zoe Blade wrote in to let us know she found Thomas Bredenfeld who had the following to say: "@zoeblade yes, i've made it. ...looooong ago :-)" followed by "This 1st one was based on formant DIY synth. made a 2nd one later with curtis ICs from http://www.doepfer.de"
Formant was a DIY brand of synths. You can find more posts featuring Formant on the Formant channel here on MATRIXSYNTH.
Update: make that THB. I originally posted TBH.