C 940

Dual Headphone Amplifier / A440 Hz

2-channel headphone amplifier, 2 audio inputs with level controls, common loudness/master level control, 2 headphone stereo outputs.
this module contains a tuned A-440 Hz reference oscillator, on/off switch and level pot for adding to the outputs.

http://www.cluboftheknobs.com/pro_c940.html