From the Rain City Audio Repair Blog:
The first Bose® 402E Active Equalizer, for the Panaray speaker system, just came through the Rain City Audio repair bench. It’s a small speaker array system, designed around similar drivers in the 901, and uses an Active Equalizer for the same effect. They’re designed for a limited frequency response, 90 Hz – 16 kHz, up to 120W at 8 Ohms.
It’s a small box with two channels of 1/4″ TRS. There are no adjustments. Inside, there’s a power supply similar to that found on a Series III or IV, three op-amp chips, and a handful of electrolytic capacitors. This unit was noisy and had uneven volume when it came to the bench, and those should components should have it good as new again.
The board was produced in early 1985 in Atlanta, apparently.
It was time for some tests. It sounded pretty good, but how was it performing? I ran a frequency response sweep on the Audio Precision System One:
Both channels perfectly matched, in an interesting saddle curve rolling off sharply at 100 Hz down past -30 dB at 20 Hz, and a healthy boost to the high end. Comparing with the service manual,
Identical. This 402E Active Equalizer is performing perfectly and should work great for years to come.