Tube Stereo Compressor, rev. 4. Designed to accomodate +14 to +24db operation. Matched Vactrol. Basic update for improved tube gain/noise. Improved Vactrol circuit and matched channels. Improved threshold, range compressor. Change of design to cathode feedback dynamic bias / tube harmonic. Engineering Sample (#9 condition). Volume levelling compressor (brings volume up, matched tubes).