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.
 Measurements were made at 120V AC line voltage and on the
unit with serial number R5021. The Balanced input was used unless otherwise noted. The
Audio Precision Aux0025 lowpass 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 (8ohm load):
 Balanced input: 21.9X, 26.8dB
 Unbalanced input: 22.0X, 26.8dB
 Output noise, 8ohm load, balanced input, 600ohm input
termination:
 Wideband, ~500kHz bandwidth: 1.63V, 4.8dBW
 With AP Aux0025 lowpass filter:
 Wideband: 1.8mV, 63.9dBW
 A weighted: 0.055mV, 94.2dBW
 Output noise, 8ohm load, unbalanced input, 1kohm input
termination:
 Wideband, ~500kHz bandwidth: 1.63V, 4.8dBW
 With AP Aux0025 lowpass filter:
 Wideband: 1.8 mV, 63.9dBW
 A weighted: 0.064mV, 92.9dBW
Power output with a 1kHz test signal
 8ohm load at 1% THD: 235W
 8ohm load at 10% THD: 291W
 4ohm load at 1% THD: 424W
 4ohm load at 10% THD: 533W
General
The Bel Canto REF500 utilizes a new ICEpower 125ASX2 stereo
amplifier module strapped in monobridge 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 opamp circuit delivers lownoise, equal
outofphase 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 highfrequency response is approximately 100kHz, depending on load. As
usual with the ICEpower modules, the highfrequency response with varying loads is kept to
reasonable tolerances with the exception of the opencircuit 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 solidstate 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 higherorder terms.
Chart 1
 Frequency Response of Output Voltage as a Function of Output Loading 
Red line: open circuit
Magenta line: 8ohm load
Blue line: 4ohm load
Cyan line: NHT dummyspeaker load
Chart 2  Distortion as a Function
of Power Output and Output Loading 
(line up at 20W to determine lines)
Top line: 4ohm SMPTE IM
Second line: 8ohm SMPTE IM
Third line: 4ohm THD+N
Bottom line: 8ohm THD+N
Chart 3  Distortion
as a Function of Power Output and Frequency 
4ohm 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 4ohm load
