Feedback Master is a portable notch filter small enough to be body-worn using the supplied belt clip. Designed to help acoustic musicians avoid feedback when playing at high volumes, the all-analog Feedback Master is sturdily constructed in a metal chassis and powered by a single nine-volt battery. For both passive and active guitar pickups, operation is simple with main controls located on the top of the unit and 1/4-inch unbalanced input and output jacks on the bottom. Included also on the bottom are: a gain pot for matching the unit to your instrument's pickup and an invert or phase flip switch.

The two adjustable notch filters are called Null 1 and 2. Both filters are identical and are sweepable from Off to 320Hz. For most uses, a single filter "tuned" to the offending feedback frequency will allow you to play louder without any chance of howling from your amp or from the PA/floor monitor wedges. As extra insurance, the second filter will remove more of the same frequencies or another frequency slice if you encounter severe problems sometimes brought on by other amplified instruments on the same stage.