150.2 Stereo Amplifier: 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 with 120V AC line voltage with both
- All measurements, except for frequency response, were made
with the new Audio Precision Aux-0025 filter, that is especially designed to keep the
out-of-band switching noise out of the Audio Precision measurement system and thus prevent
inaccurate measurements due to input overload.
- Gain, unbalanced input: 23.3x, 27.3dB.
- Output noise, 8-ohm load, 1k-ohm input termination: wideband
29.0mV, -39.8dBW; A weighted 0.72mV, -71.9dBW.
- AC line current draw at idle: 0.56A.
- Output impedance at 50Hz: 0.047 ohms.
- This amplifier does not invert polarity.
Power output with 1kHz test signal
- 8-ohm load at 1% THD: 166W
- 4-ohm load at 1% THD: 300W
The Audio Research 150.2 is yet another of the new breed of
switching amplifiers utilizing the TriPath technology and controller chipset.
Measurements were made through the unbalanced inputs except
otherwise noted. Performance through the balanced inputs was essentially the same. Chart 1
shows the frequency response of the amp with varying loads. As can be seen, the output
impedance -- as judged by the closeness of spacing between the curves of open circuit,
8-ohm, and 4-ohm loading -- is quite low. However, the ultrasonic response past 20 kHz is
a strong function of the load, with strong peaking near 100kHz with an open circuit load.
The response with the NHT dummy load is reasonable, with a variation of about +0.6/-0dB
over the audio range. Some speakers utilizing dome tweeters, due to the high frequency
inductive nature of these types of drivers, may exhibit some fractional part of this
resonant rise above the audio range. Chart 2 illustrates how total harmonic distortion
plus noise versus power varies for 1kHz and SMPTE IM test signals and amplifier output
load. As can be seen, attainable power is greater for the 4-ohm load, as is usual for most
power amplifiers. Total harmonic distortion plus noise as a function of frequency at
several different power levels is plotted in Chart 3. The TriPath system has a peculiar
behavior at power levels approaching clipping. The output waveform starts to exhibit some
switching noise near the peaks that will get through the Aux-0025 filter and into the
distortion measurement when the bandwidth of the measurement is opened up to 80kHz.
Generally, I use the 80 kHz measurement bandwidth to more accurately let some of the
actual signal harmonics get through at frequencies at the high end of the audio band. This
shows up as the higher distortion at the 200W and 300W levels on the chart, and does not
indicate distortion that would necessarily be audible. Damping factor versus frequency is
shown in Chart 4. A spectrum of the harmonic distortion and noise residue is plotted in
Chart 5. The magnitude of the AC line harmonics is reasonably low for this amplifier. The
test signal harmonics are both even and odd harmonic, with the second and third harmonics
dominating the total distortion makeup.
- Frequency Response of Output Voltage as a Function of Output Loading
Red line: open circuit
Cyan line: NHT dummy-speaker load
Magenta line: 8-ohm load
Blue line: 4-ohm 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: 4-ohm THD+N
Third line: 8-ohm SMPTE IM
Bottom line: 8-ohm THD+N
|Chart 3 - Distortion
as a Function of Power Output and Frequency
4-ohm output loading
Green line: 300W
Cyan line: 200W
Blue line: 140W
Magenta line: 20W
Red line: 2W
|Chart 4 - Damping Factor
as a Function of Frequency
Damping factor = output impedance divided into 8
|Chart 5 - Distortion and
1kHz signal at 10W into an 8-ohm load