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Equipment Measurements

April 2010

Bel Canto Design e.One REF500M Mono Amplifiers: Measurements

All amplifier measurements are performed independently by BHK Labs. Please click to learn more about how we test amplifiers there. All measurement data and graphical information displayed below are the property of SoundStage! and Schneider Publishing Inc. Reproduction in any format is not permitted.

Additional Data
  • Measurements were made at 120V AC line voltage and on the unit with serial number R5-021. The Balanced input was used unless otherwise noted. The Audio Precision Aux-0025 low-pass filter was used on all measurements except for frequency response.
  • This amplifier does not invert polarity.
  • AC line current draw at idle: 0.22A, 11.5W, 0.45PF.
  • Input impedance @ 1kHz:
    • Balanced input: 197k ohms.
    • Unbalanced input: 91k ohms.
  • Output impedance at 50Hz: 0.034 ohm.
  • Input sensitivity for 1W output in 8 ohms, volume at maximum:
    • Balanced input: 129mV.
    • Unbalanced input: 129mV.
  • Gain (8-ohm load):
    • Balanced input: 21.9X, 26.8dB
    • Unbalanced input: 22.0X, 26.8dB
  • Output noise, 8-ohm load, balanced input, 600-ohm input termination:
    • Wideband, ~500kHz bandwidth: 1.63V, -4.8dBW
    • With AP Aux-0025 low-pass filter:
      • Wideband: 1.8mV, -63.9dBW
      • A weighted: 0.055mV, -94.2dBW
  • Output noise, 8-ohm load, unbalanced input, 1k-ohm input termination:
    • Wideband, ~500kHz bandwidth: 1.63V, -4.8dBW
    • With AP Aux-0025 low-pass filter:
      • Wideband: 1.8 mV, -63.9dBW
      • A weighted: 0.064mV, -92.9dBW
Measurements Summary

Power output with a 1kHz test signal

  • 8-ohm load at 1% THD: 235W
  • 8-ohm load at 10% THD: 291W

  • 4-ohm load at 1% THD: 424W
  • 4-ohm load at 10% THD: 533W


The Bel Canto REF500 utilizes a new ICEpower 125ASX2 stereo amplifier module strapped in mono-bridge mode. This unit, like recent previous models, places an extra rectifier and filter capacitor circuit ahead of the AC input to the ICEpower module. A sophisticated front end op-amp circuit delivers low-noise, equal out-of-phase signals to the ICEpower module’s input for both unbalanced and balanced signals.

Chart 1 shows the frequency response of the amp with varying loads. The high-frequency response is approximately 100kHz, depending on load. As usual with the ICEpower modules, the high-frequency response with varying loads is kept to reasonable tolerances with the exception of the open-circuit condition which does peak up a bit at about 90kHz.

Chart 2 illustrates how total harmonic distortion plus noise vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load. The THD+N is quite low over the power range, but the IM distortion is, not unusually, quite a bit higher.

Total harmonic distortion plus noise as a function of frequency at several different power levels is plotted in Chart 3. The amount of rise in distortion at high frequencies is quite high in this design.

Damping factor vs. frequency is shown in Chart 4 and is reasonably high and constant over much of the audio range and starts to decrease above about 4kHz, higher than most linear solid-state power amplifiers.

A spectrum of the harmonic distortion and noise residue of a 10W 1kHz test signal is plotted in Chart 5. The magnitude of the AC line harmonics are quite low and simple while intermodulation components of line harmonics with signal harmonics are quite absent. Signal harmonics consist of a dominant third order and a miscellany of higher-order terms.

Chart 1 - Frequency Response of Output Voltage as a Function of Output Loading

Red line: open circuit
Magenta line: 8-ohm load
Blue line: 4-ohm load
Cyan line: NHT dummy-speaker load

Chart 2 - Distortion as a Function of Power Output and Output Loading

(line up at 20W to determine lines)
Top line: 4-ohm SMPTE IM
Second line: 8-ohm SMPTE IM
Third line: 4-ohm THD+N
Bottom line: 8-ohm THD+N

Chart 3 - Distortion as a Function of Power Output and Frequency

4-ohm output loading
Yellow line: 400W
Cyan line: 200W
Blue line: 60W
Magenta line: 10W
Red line: 1W

Chart 4 - Damping Factor as a Function of Frequency

Damping factor = output impedance divided into 8

Chart 5 - Distortion and Noise Spectrum

1kHz signal at 10W into a 4-ohm load


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