This device is realized with 2 specialized IC KA2284 /AN6884/.
Two entrances: for left and right channels.
Built-in amplifier input.
Trimmer to adjust the level.
Logarithmic indicator:-10dB,-5dB, 0dB, 3dB, 6dB
Constant output current: 15 mA
Power supply: 9~15 V
Overall PCB dimensions: 105x37 mm