A fine Bass Distortion Pedal by Exar Electronix. New Old Stock, come with box. See photos.
From EffectsDatabase:
The BD-04 is a distortion-unit, which is mainly designed for use with a bassguitar. Like a conventional distortionunit` s mode of operation, the BD-04 cuts the peaks of the input-signal. The effect-signal can be mixed with the dry-/input-signal.