Circa 1970s there were bands touring (e.g. Yes) with music synthesizers that were made by wiring up voltage controlled oscillators, ring oscillators, filters and similar analog components.

That sort of musician was really an electronics technician who had to keep a fiddly piece of hardware working on the road. And that kind of synthesizer was often monophonic or not very polyphonic.

Yamaha's DX-7 was a digital simulation of that kind of synthesizer which was absolutely reliable and a musical instrument really has to be because you're going to put it in a case that is going to get banged around in shipping and expect it to work just fine wherever you go.