Dinky little 2-valve Chinese pre-amp

[Nick]

... I've attached the mind boggling circuit of the Optonica RP114. It's certainly a well engineered and very complex bit of kit and I think they're still quite sought after. Top end stuff I imagine, given that it was produced more than 40 years ago

Actually, it was released in 1983, so 31 years ago - still a decent amount of time!

The microprocessor, an NEC uPD650C, is a CMOS 4-bit processor that was basically suitable for running washing machines and stuff like that - the clock ran at only 100kHz with 2Kbytes of ROM and only 48 bytes (96 4-bit "nibbles") of RAM. The same CPU was also used in early Roland machines...