Optonica SM-4100 Back Sockets

Interestingly, all the inputs feed through an operational amplifier with FET inputs. Because of this, impedance matching errors never occur in this amplifier. There is a phono input for a record turntable providing high quality sound, and its input sensitivity is 2.7 mV / 47 kΩ. There are also inputs for Tuner, Aux, and Tape, and their input sensitivity is 150 mV / 47 Ω.

It is possible to mod this and replace these sockets with gold plated ones, however I would like to keep the amplifier in its original condition.

This amplifier allows one to connect two sets of front speakers labelled A and B. There is a switch at the front of the amplifier for selecting the speakers. When you use both sets of speakers, essentially you are connecting two speakers in parallel across each channel. Resistance in parallel reduces the effective load; therefore, the manual advises 16 Ω speakers for both sets.

The speaker terminal clips are the push type, and these are much easier to work with and are more reliable than the others are.

The back label reads, made in Japan.

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