Originally released in the 70's, the API 525 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 an identical re-issue of one of the most popular API products ever.

• Reissue of API's original 525 from the early 70's
• 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

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. This re-issue design has been taken from the original blue prints and spec control drawings from the API archives.

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.