Originally released in the 70's, the API 525 is a "feedback" type compressor. An input (threshold) control and output (make-up gain) control are provided, along with an additional "Ceiling" fine-tune function which 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. 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/pop reduction. The 525 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 lower frequencies 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 525 utilizes "vintage" dynamics control and an easy to use multi-function control set. The 525 has a hard-wire bypass switch, a balanced input, and a pinout that is the same as all the other 500 series modules. Two or more 525s can be linked for multi-channel compression.

The API 525 Compressor makes use of the 2510 and 2520 op-amps and exhibits the reliability, long life, and uniformity which are characteristic of all API products.

Features:
Exact 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
Analog VU meter for monitoring gain reduction
4 Switchable release modes
De-Ess function
Traditional API fully discrete circuit design
Active Balanced Input/Output
Hardwire bypass

Technical Specifications:
Input Impedance:     > 30 K Ohms, Balanced
Output Impedance:     100 Ohms, Transformer coupled, Balanced
Operating Levels:     -15 dBu to +20 dBu
Maximum Gain Reduction:     25 dB
Noise:     98 dB below +10 dBu output, at 10 dB of Compression
Harmonic Distortion:     0.5% Max, 30 to 20 kHz
Attack Time:     15 micro seconds
Release Times:     .1, .5, 2.0, 2.5 seconds
De-essing:     Inversion of the Voice Energy Curve
Slopes:     Compression, 2:1, Limit, 20:1
Metering:     Compression or Limiting-Illuminated Analog dB meter, shows Gain Reduction
Frequency Response:     ±.5 dB, 30 to 20 kHz
Power Requirements:     ±12/18 Volts/DC, @80 ma.