The API 525 Compressor Module. A reissue of one of the most successful solid state feedback compressors in history.

The API 525, originally released in the 70's, is a feedback type compressor, such as the 1176 and 660, etc. An input (threshold) control and output (make-up gain) control are provided. An additional Ceiling fine tune function modifies threshold and make-up gain for precise changes in compression without changes in output. A compression/limit switch sets ratio at either 2:1 or 20:1. Attack time is as fast as 15u/s. Four auto release modes are offered via two switches, 0.1s, 0.5s, 1.5s, & 2.0s. A De-Ess function inserts an inverse vocal energy curve filter in the detector for effective sibilance/p-pop reduction. The API 525 is perhaps the most successful solid state feedback compressor in history. It delivers dynamics control behavior unlike VCA feed forward compressors so common today. A remarkable multi-function ceiling control can increase gain reduction (lower threshold) while simultaneously raising output level to match, so the user can alter dynamics on the fly without level changes. Release times vary with frequency, with high frequency/full bandwidth content released faster than just low frequency for natural envelope tracking. Attack time is fixed, chosen to catch the fastest peaks, without pumping. Equally useful as a tracking, mixdown or program compressor/limiter, the benefits of the API 525 are most obvious to those who use compression on a regular basis. Vintage dynamics control, an easy to use multi-function control set, and a wide range of 500 Series mounting options assure that the 525 will surpass your most critical applications. With the addition of a hard-wire bypass switch, a balanced input, and a pinout that is the same as all the other 500 series modules, the 525 is still, after 25 years—the sound. Two or more 525s can be linked for multi-channel compression. The 525 Feedback Compressor/Limiter makes use of the 2510 and 2520 op-amps and therefore exhibits the reliability, long life, and uniformity which are characteristic of API products.

The main features of the API 525 include:

• A reissue of one of the most successful solid state feedback compressors in history
• The API 525 is a module and requires mounting and power via the 500-6B 6 Slot Lunch Box or the 500VPR 10 Slot Rack w/PS
• Peak detecting "feedback" compressor/limiter
• Variable Threshold and Output levels
• Unique "Ceiling" control combines key functions
• VU meter for monitoring gain reduction
• 4 Switchable release modes
• De-Ess function
• Traditional API fully discrete circuit design
• Hardwire bypass