F765 500 Series “Compex” Compressor/Limiter

The Q2 Audio F765 is the compression and limiting sections of the famous “Compex Limiter”™ built into a single 500 Series slot. The audio path contains the same blue Phillips type capacitors and BC series transistors as the original Compex.

Formatted after the vertical “N-Unit” with slight layout changes for enhanced usability, the F765 lives up to the reputation it’s big brother, the F760X-RS, has made over decades of being a “secret weapon” on countless records.

FEATURES

• Single channel level control offering simultaneous compression gain reduction with peak limiting
• Precision calibrated compressor/limiter threshold control which allows the user to “dial up” the amount of compression required before peak limiting occurs
• Switched Compression values from 1:1 (amplifier), 2:1, 3:1, 5:1, 10:1 & 20:1 (limiter)
• Auto dual platform release function – allows fast transient recovery on a “build-up” slow release

SPECIFICATIONS

• Input: 10K ohms Unbalanced
• Output: Transformer Balanced (Cinemag CMOB-3L) Max output: 20dBu, 18.5dBm
• Metering: Sifam Fast Responding analog meter
• Stereo Linking: Must order as stereo pair
• Power requirements: +/-16V DC @ 70mA per rail (brief 400mA turn-on surge).
• System Gain: 34dB with input/output attenuators fully open. Unity gain in Bypass mode
• Thresholds:
  • Peak Limiter: +14dBu maximum with unattenuated output. Referred to unattenuated input level 20dBu
  • Compressor: Calibrated with reference to Peak Limiter thresholds and marked 0 – 20dB in 2dB steps. (Reference to unattenuated input level this is -20dBu to -40dBu)
• Release:
  • Peak Limiter: 250mS,
  • Compressor: 25mS, 50mS, 100mS, 200mS, 400mS, 800mS, 1.6 secs, 3.2 secs + Auto release function
• Attack:
  • Peak Limiter: < 250uS for 100% control of overshoot – without any over limiting. (measured at 1KHz for 10dB gain reduction)
  • Compressor: 250uS, 2.5mS, 25mS
• Distortion: Measured at 1KHz for 10dB compression & 3.2 secs release time.
  • Compressor: at +10dBu threshold <0.1% (typically 0.04%)
  • Peak Limiter: at +14dBu threshold <0.3%
• Frequency Response:
  • Balanced: < -0.5dB at 20Hz & < -0.75dB at 20KHz
• Signal – Noise Ratio: Referred to Peak Limiter threshold level as set by output attenuator: better than -80dB (Measured with low pass filter -3dB at 25HKz)
• Stereo Matching:
  • Control volts matching on compressor to within ±1dB of each other, consequently no image shift during operation
  • Selectable Peak Limiter operation
  • Peak Limiter on – off or Pre-emph (50uS time constant)
• Indicators:
  • Overall Gain Reduction Meter scaled 0 – 20dB in 4dB divisions. White scale on black background with yellow pointer
  • Peak Limiter operating: Red indicator

ENHANCEMENTS

• Gold contact rotary switches
• Gold contact toggle switches
• Conductive plastic potentiometers
• PCB headers for possible future connection to E900 type EQ
• Sidechain Insert and Bus output functionality per Radial Engineering specs
• Sidechain insert is jumpered by default
• Sidechain insert send minimum external load of 10K