API 525 Compressor (500 Series Module)
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  • Regular price $1,230.25

API 525 Compressor (500 Series Module)

  • 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

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.

"First off, it’s a fully discrete analog compressor, so it’s built to last a lifetime and there are no IC chips or other cheap electronics that will diminish the fidelity of your signal. Its sonic imprint can be described as adding warmth, size, and density to practically any signal going through it, which is a great asset in the world of digital recording." - Val Garay (Grammy Award-Winning Producer / Engineer)


Conforms to Automated Processes, Inc. VPR Alliance size and connectorization layout specifications.
This unit is made to install into the 500 Series frame VPR rack, lunchbox®, or any API console with 500 series slots.

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 .1, .5, 2.0, 2.5 seconds
De-essing Inversion of the Voice Energy Curve
Slopes Compression, 2:1, Limit, 20:1
Frequency Response ±.5 dB, 30 to 20 kHz
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.
Size 1.5" X 5.25" X 7.5" Deep
Size (Boxed for Shipping) 4.5" X 6.5" X 10"
Actual Weight 1.77 lbs.
Shipping Weight 2.17 lbs.