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API 525 Compressor
API 525 Compressor Front
API 525 Compressor Box
API 525 Compressor Left
API 525 Compressor Right
API 525 Compressor Box

API 525 Compressor Used

HomeOutboard/Recording500 SeriesCompressorsAPI Audio

525 Discrete Compressor Re-Issue
API 525 500 Series Compressor From original owner, lightly used in private home recording studio. Excellent shape, fully functional. Retails for $1230 new, save some here. Sequential stereo pair available, listed price is for a single unit.

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.
- 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
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.
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.

API 525 Brochure
API 525 Compressor Control Sheet Diagram
API 525 Power Pin Layout
API 525 Setup Sheet
API 525 Compressor Box
API 525 Compressor Left
API 525 Compressor Right