API Audio 527A 500 Series Single Channel Compressor Limiter

Since its debut over 12 years ago, the API 527 has continued to gain popularity with mixing engineers across the world. Designed with maximum user flexibility in mind, the 527 has always offered fast compression and a characteristically punchy tone coupled with the unmistakable sound of API’s analog warmth.

With thousands of 527’s currently in service, API is releasing an updated version of the original 527, now called the 527A. Carefully retaining the circuit structure and sound of the original, the new 527A offers the same outstanding performance but with an expanded feature set which includes:
• Improved LED Monitoring of Gain Reduction
• A Hard Bypass Option



The API 527A Compressor/Limiter takes its place alongside the family of API VCA based compressors, including the 225L compressor and 529, 2500, and 2500+ stereo bus compressors. Anyone familiar with these units will immediately be at home with the 527A.

• Feed-forward or feed-back compression
• Hard or soft knee compression
• Patented THRUST® switch for frequency-dependent sidechain control
• Continuously variable, 31 position detented THRESHOLD control
• Continuously variable, 31 position detented RATIO control
• Continuously variable, 31 position detented ATTACK and RELEASE controls
• Continuously variable, 31 position detented OUT (output) level control
• 10-segment gain reduction/VU meter (GR/Output)
• Overload LED
• IN switch with soft and hard relay bypass
• Audio circuit uses the 2510 and 2520 discrete op-amps

Features common to the line include "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" knee 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 patented THRUST® function can be switched in and out via the front panel as well, applying a filter before the RMS detector circuit that preserves that punchy bottom end.
Two or more 527A Compressor/Limiters can be linked together via a DC link allowing multiple units to be combined for stereo and multichannel applications.

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 527A 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.

• Connector : API 500 Edge Connector - VPR Alliance Compliant
• Input Impedance : 120 K Ohms, Balanced
• Output Impedance : 75 Ohms, Transformer coupled, Balanced
• Maximum Input Level : +26 dBu
• Maximum Output Level : + 30dBu
• Output Fader Control Gain : -Infinity to +10 dB
• Attack Times : 1 millisecond to 25 milliseconds
• Release Times : 0.3 seconds to 3 seconds
• Compression Ratios : 1:1 to 1:Infinity
• Threshold Control Range : +10 dBu to -20 dBu
• Metering : 10 Segment LED Meter showing either Gain Reduction (-1 to -24 dB) or • Output Level (14 to +14 dBu). Overload LED: +21 dBu
• Frequency Response : +/- 0.5 dB 20 Hz to 40 kHz
• Signal to Noise : 110 dB
• Power Requirements : 3.5 Watts - VPR Alliance Compliant
• Unit Size : 1.5" x 5.25" x 7"
• Shipping Size : 4.5" X 6.5" X 10"
• Unit Weight : 1.8 lbs.
• Shipping Weight : 2.2 lbs.

API 527A Manual