API 527 Microphone Preamp

500 Series Discrete Compressor

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.

Part No:
Usually Ships in 1-2 Days
£975.00 £812.50
Did you find this item priced lower than £812.50 somewhere else? Yes

Anyone familiar with API VCA based compressors will quickly be at home with the API 527. This compressor offers an outstanding degree of adaptability in signal gain control because of qualities recurrent to the line: "feed forward" (new) and "feed back" (old) gain reduction methods, both of which are selectable on the front panel. Most established compressors use the "old way" or Feed-Back method for the gain control circuit, whereas it's more typical of newer VCA type compressors, that rely on RMS detectors for gain control voltage, to use the "new" method of gain reduction.

Innate uncompressed sounds or a typical cutting knee type that lends itself to a much more extreme limiting effect can be generated by utilising a Soft/Hard switch. The initial operating parameter is set by the Threshold control and the API 527 can be managed with signal input levels from +10dBu to -20dBu.

A sizeable API output transformer and 2520 discrete amplifier offer output capacity of +28dBu and the API 527's output fader control spans from minus infinity to +10db. Regardless of the threshold or ratio control, the output level remains at a relative equilibrium - much like the More/Less ceiling control on the API 525 compressor, making live adjustments possible without any noticeable gain changes in the program level.

A high pass filter is implemented before the RMS detector circuit, preserving a punchy bottom end, by the patented THRUST function that can be alternated in and out via the front panel as well.

The API 527's Attack and Release are completely changeable. Swivel the inner concentric Release knob to change release time with constants from .3 sec to 3 sec. The outer concentric Attack knob adjusts Attack time which ranges from 1 millisecond to 25 milliseconds.

Two API 527 devices can be integrated for stereo applications via a motherboard bus connection through the use of the Link switch, but the API 527 is also built with the intended purpose of individual channel use. The API 527 Compressor demonstrates the dependability, longevity and uniformity characteristic of all API products and makes use of 2510 and 2520 op-amps.

  • 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
More Information

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: +26dBu

Maximum Output Level: +26dBu

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 indicator)
  • 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 ([email protected]% distortion, no compression)

Power Requirements: +/- 15-18VDC @130mA


Dimensions and Weight

Size: 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.