API 525

Discrete Compressor Limiter Re-Issue for the 500-Series Rack

An exact replica of the legendary 70's-era workhorse, the 525 was (and still is) a sophisticated and transparent-sounding compressor/limiter.
Featuring a fixed, very fast attack time, variable release times and a killer de-esser, the 525 also boasts a one-knob ceiling control which automatically adjusts output gain -- very musical, and very useful for people who like to work fast.
Works with all 500-series powered racks.

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Features Specifications Downloads

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 525 is an identical re-issue of one of the most popular API products ever.

API 525 Features :

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.