API Audio 527 500-Series Compressor  From API

Legendary API punch, tone, and build quality, the 527 is a staple within the 500 series compressor world - and for good reason.

API Audio


Retail:  $1,095.00

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What We Think

Modeled after the famous API 2500 Stereo bus compresor, the 527 offers a single 500 series channel of one of the punchiest, most forward compressors within the audio realm. While it's condensed 500 series faceplate offers half of the real estate of it's 2500 big brother, the 527 features nearly all of the unique controls that made the 2500 so powerful - API's patented THRUST circuit, NEW/OLD switch for feed-forward or feed-back compression, HARD/SOFT knee switch, and stereo linking capabilities. The well thoughtout layout of controls causes the compact faceplate to never impede workflow, which is quite an impressive feat for a 500 series compressor boasting so many additional tone and compression controls.
The tone is classic API punchiness that commands listener's attention with it's enticing, forward nature. Drums become alive and thunderous, guitars grow to unimaginable sizes, and modern mixes achieve that unmistakeable API "gloss" with the 527. Set more gently for compressing a direct signal or crushing your source for parallel blending, the API 527 is a modern classic for a reason. Set up a Try-Before-You-Buy demo to hear this impeccable 500 series compressor in your studio and understand what makes a classic, a classic. 

API 527 Compressor for 500-Series Introduced at AES, Oct. 2009

Todd Atlas of Sound Pure takes a quick look at the Brand New API 527 Compressor at the AES Convention in New York, October 2009. It is a single channel module based on API's 225L discreet channel compressor. The 527 features comprehensive controls including variable attack, release, ratio, and output gain controls. The unit also includes API's patented 'Thrust' circuit, first offered on the 2500 Stereo Bus Compressor. A 10 segment LED meter is switchable between gain reduction and output level. "Anyone who has used the 225L compressor found in API consoles has expressed a longing for the same kind of flexibility and control in the 500 Series for some time" said Larry Droppa, President of API. "We're delighted to now offer the 527 to complement our vintage 525 compressor, which has been many engineers' favorite compressor over the years. Call Sound Pure toll free at 888-528-9703 to discuss ordering one, or any questions you might have, or try sales@soundpure.com. Members of the Sound Pure Sales team are also experienced professional recording engineers that are glad to lend their sales experience with any of their prospective customers. Please give us a call, we are here to help!

  • Signal Chain
    • API Audio 527 500-Series Compressor

Manufacturer's Description from API


  • Audio circuit uses the 2510 and 2520 Discrete Op Amps with transformer output
  • Continuously variable detented Threshold control
  • Continuously variable detented Attack and Release controls
  • Continuously variable detented Ratio control
  • Output Fader level control
  • 10 segment VU/Gain Reduction meter with selector switch
  • Overload LED
  • "Link" switch for multiple unit interdependent compression linking
  • "New"/"Old" switch for feed-forward or feed-back compression
  • "Hard"/"Soft" compression curve knee switch
  • Patented THRUST® switch for frequency dependent side chain control
  • "IN" switch with hard relay bypass when in the "Out" position


The API 527 takes it's place alongside the family of API VCA based compressors, the 225L and the 2500 Stereo Bus Compressor. Anyone familiar with those units will immediately be at home with the 527. Features common to the line like "feed forward" (NEW) and "feed back" (OLD) gain reduction methods selectable on the front panel, provide a choice of "that old way", or "the new way" of compression, for the highest level of flexibility in signal gain control. The "old way" or Feed-Back method is what most of the classic compressors used for the gain control circuit. The "new way" gain reduction is more typical of the newer VCA type compressors that rely on RMS detectors for the gain control voltage.

There is a "SOFT"/"HARD" switch for an "over-easy" type compression resulting in a very natural, uncompressed sound or a typical sharp knee type that lends itself to a much more severe limiting effect.

The Threshold control sets the initial operating parameter. The 527 can be operated with signal input levels from +10 dBu to -20 dBu.

The 527 features an Output fader control that ranges from minus infinity to +10dB, and output capability is +28 dBu through our 2520 discrete amplifier and a large API output transformer. The output level remains fairly constant regardless of the threshold or ratio control, much like the "more/less" Ceiling control on the API 525 compressor. This allows for live adjustments without any noticeable gain changes in the program level.

The patented THRUST function can be switched in and out via the front panel as well, applying a high pass filter before the RMS detector circuit that preserves that punchy bottom end.

Attack and Release are fully adjustable on the 527. Release time can be adjusted by rotating the inner concentric RELEASE knob. Release time constants: .3 sec to 3 sec. Attack time is adjusted on the outer concentric ATTACK knob, which ranges from 1 millisecond to 25 milliseconds.

The 527 is designed for individual channel use or, through the use of the LINK switch, two units can be combined for Stereo applications via a motherboard bus connection.

The 527 Compressor/Limiter makes use of the 2510 and 2520 Discrete Op-amps and exhibits the reliability, long life, and signature sound which are characteristic of API products.

API Audio

About Manufacturer

API (Automated Processes, Inc.) is world famous for its all-discrete audio products: studio and broadcast mixing consoles, and a full line of rack mount mic preamps, equalizers and processors. It all began with a dream. It was 1968. The company: Automated Processes Inc., formed by men with a vision. Best known for their now legendary "2520 amplifier", this unique amp has been and will continue to be the heart of all API discrete products. It continues to provide reliability and sonic purity unmatched by the competition. The resulting console met the needs of the music, commercial and broadcast industry. API became the leading audio broadcast console manufacturer for radio and television networks and high profile stations. In addition, recording studios, large and small, began using API.....and receiving rave reviews from engineers and producers. There are over 700 API consoles across the nation and around the world, including the three major networks. Over thirty years later, many of these consoles are still in daily use in some of the most prestigious recording and broadcast facilities in the world because, to date, there are few, if any consoles of equal sound quality at a cost-effective price.



Input Impedance:

High Level In 160K ohms

Low Level In 80K ohms

Output Impedance:

High Level Out 85 ohms

Low Level Out 50 ohms

Nominal Operating Level:

-2dBu or +4dBu

Maximum Input Level:


Maximum Output Level:


Output Fader Control Gain:

-Infinity to +10dB

Attack Times:

1 millisecond to 25 milliseconds (typical)

Release Times:

0.3 seconds to 3 seconds (typical)

Compression Ratios:

1:1 to 1:Infinity

Threshold Control Range:

+10dBu to -20dBu


10 RED LED VU scale:

-20VU to +3VU (positive illumination


RED GR scale: -1.5dB to -23dB (negative illumination indicator)

RED Overload LED: +27dBu (clipping)

THRUST® Filter Action:

-10dB/Decade slope, unity @ 1kHz

Frequency Response:

+/- 1dB 20Hz - 20kHz

Total Harmonic Distortion:

< .2% THD, any level below clipping, any compression setting

Signal to Noise:

Unweighted -100dB below clipping (+26dBu@0.1% distortion,

no compression)

Power Requirements:

+/- 15-18VDC @130mA

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.


1.5" X 5.25" X 7.5" Deep

Size (Boxed for Shipping):

4.5" X 6.5" X 10"

Actual Weight:

1.75 lbs.

Shipping Weight:

2.15 lbs.






Set up sheet