This compressor replicates the operation and sound quality of a 1970s ROSS COMPRESSOR with SUSTAIN OUTPUT markings and serial number SN:14598, minimizing individual differences in the potentiometers. While remaining within the range of the original's individual variations, it subtly enhances the highs and deepens the lows, expanding the range for a more practical compressor. Condition: No issues with use Power: 9V center negative or 9V battery Accessories: Unit only