Sonifex RB-BL4
Dual Stereo Bi-Directional Matching Converter


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The RB-BL4 is a dual bi-directional stereo unit for interfacing domestic or semi-pro unbalanced equipment to professional balanced line levels, and vice versa.

The four XLR-3 electronically balanced inputs have an impedance of 20kOhms bridging and are routed to four unbalanced RCA (phono) outputs with an output impedance of <50Ohms.

The four RCA unbalanced inputs have an impedance of 20kOhms and are routed to four balanced XLR-3 outputs with an output impedance of <50Ohms. All connections are on the rear panel.

The output gain can be adjusted for left and right channels by using pre-set potentiometers accessible through the rear panel.


Audio Specifications

  • Maximum Input Level: +28dBu
  • Maximum Output Level: +28dBu
  • Input Impedance (RCA): >10kOhms unbalanced
  • Input Impedance (XLR): >20kOhms balanced bridging
  • Output Impedance (RCA): <50Ohms
  • Output Impedance (XLR): <50Ohms
  • Distortion: 0.01% THD @ 1kHz, ref +8dBu output
  • Noise: -100dB, unity gain, ref +8dBu output
  • Common Mode Rejection: >66dB typically
  • Frequency Response: 20Hz to 20kHz ±0.1dB (600Ohms load, ref 1kHz)
  • Gain Range: Unbalanced Output : -28dBu to 0dBu, ref 0dBu into balanced XLR input
  • Balanced Output: -15dBu to +15dBu, ref -15dBu into unbalanced RCA input


  • Inputs: 4 x RCA phono (Unbal), 4 x XLR 3 pin female (Bal)
  • Outputs: 4 x XLR 3 pin male (Bal), 4 x RCA phono (Unbal)
  • Mains Input: Filtered IEC, switchable 110-120V, or 220-240V, fused, 6W max
  • Fuse Rating: Anti-surge fuse 100mA 20 x 5mm (230VAC), Anti-surge fuse 250mA 20 x 5mm (115VAC)

Physical Specifications

  • Dimensions (Raw): 48cm (W) x 10.8cm (D) x 4.2cm (H) (1U), 19” (W) x 4.3” (D) x 1.7” (H) (1U)
  • Dimensions (Boxed): 58.5cm (W) x 22.5cm (D) x 7cm (H), 23” (W) x 8.9” (D) x 2.8” (H)
  • Weight: Nett: 1.3kg  Gross: 1.9kg, Nett: 2.9lbs Gross: 4.2lbs

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