Sonifex RB-SM1
Single stereo to mono converter, buffered and balanced mono output


The RB-SM1 converts a stereo input to a fully buffered and balanced mono line output, e.g. to supply cue in broadcast environments or to feed a mono PA system.

The connections, which are on the rear panel, are of an XLR-3 type. The input is electronically balanced with an impedance of 20kO bridging. This can be wired unbalanced to accept an output from domestic equipment.

The output is electronically balanced with an output impedance of <50O. The output can be wired unbalanced by grounding the non-phase signal, allowing you to feed both balanced and unbalanced equipment.

Output gain adjustment using a pre-set potentiometer for the converter allows a normalised mono output from domestic stereo equipment. This potentiometer is accessible through the rear panel.


  • Maximum input level:  +28dBu
  • Maximum output level:  +28dBu
  • Input Impedence:  >20ohms balanced bridging
  • Output Impedence:  < 50 ohms balanced
  • Frequency response:  20Hz to 20kHz +/- 0.1dB (600ohm lead, ref 1kHz)
  • Gain Range:  Adjust -8dB to +18dB gain, ref. 0dB input on L and R
  • Common Mode Rejection:  >66dB typically
  • Distortion:  0.01% THD @ 1kHz, ref +8dBu output
  • Noise: -100dB, unity gain, ref +8dBu output


  • Inputs:  2 x XLR 3 pin female (balanced, can be unbalanced)
  • Outputs:  1 x XLR 3 pin male (balanced, can be unbalanced)
  • Mains Input:  Filtered IEC, switchable 110-120v or 220-240v, fused, 6w max
  • Fuse Rating:  Anti-surge fuse 100mA 20x5mm (230VAC)/250mA 20x5mm (115VAC) 
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