Optonica SM-4100 Controls

These wonderful controls are very elegant and understated. You can have two sets of front speakers, and choose between set a, and set b, from the switch control shown above. The sub-sonic function provides an extra low bass, which low frequencies provide. The dubbing switch allows one to copy a tape between two tape decks. The loudness switch brings some of the bass and treble to the front.

From the inside, the switchboard PCB and wiring looks like this. Thick shielded wires bring the signals from the input selector board at the back, to the front.

Here is a plan view of the switchboard. It has many holes for the multiple terminals of the switches.

The rotary potentiometers are stepped in small graduations.

The input selector knob at the front connects to the switch at the back of the amplifier through this metal connecting rod.

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