B-Stock, API 2500 Legacy Stereo Bus Compressor - API 2520 op-amp, variable threshold between -20 and +10, selectable ratio/attack/release times, patented "Thrust" high-pass filter before RMS detector, variable link between left and right channels, old "feed back" or new "feed forward" compression, soft, medium or hard knee for easy to sharp compression auto or manual gain make up, 1/4" balanced side chain inputs, output clips at +30 dBm., B-Stock with full warranty, may have slight traces of use