Mellotronists

...and this same Optigan has popped up several times on eBay in the past.

I'll just have to assume the seller never knew a disc was inside the
closed front tray...makes you wonder. "it made a sound" eh? A sound is
any vibration in the air than can be detected by an audio device or
the hearing of a living thing. Since it *is* an Optigan, probably
hiss, hum, and buzz...or the faint signal from a nearby AM radio station.

I think many an Optigan met a sad fate when they were dropped of at
Goodwill, Salvation Army, etc., and when people there plugged them in
and depressed the keys and buttons & heard no music, they assumed they
were broken and threw them away.