Rack version of the GAP COMP-54 MKII single-channel vintage style compressor with some additional features and signal path that utilizes only discrete components like resistors, capacitors and transistors. Its line input and output are transformer balanced and the unit also has a third inter-stage transformer. The class-A circuit used in the unit is similar to the one in the classic 2254 compressor. The controls are very flexible covering broad ranges of Ratio, Attack and Release times, including two Auto positions. All controls except the Gain make-up one are stepped for easy resetting and stereo matching. There are three selectable side-chain high pass filter frequencies available to handle special situations and three flexible side-chain options (Internal, Insert and External). The external side-chain I/O is electronically balanced @ 4dBu and appears on the right slot rack connections. The compressor provides separate switches for hardware bypass and compression out, two insert connectors for inserting the EQ-573 in the main audio/or side-chain signal path and meter selectable for output (two reference level, +4 and +12 dBu) and gain reduction. It is also possible to link two units for stereo operation. Other features include three-position Air EQ switch (Flat, +3 or +6 dB @ 30 kHz), two-position output termination switch for different tones and a soft start circuit that ramps up the supply voltage slowly (about 10 sec.) to avoid a power-on current surge.