Tuesday, September 26, 2017


All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Note: Unless otherwise noted, measurements were taken at the Devialet Expert 130 Pro’s left-channel Coax 1 digital input, at a sampling rate of 96kHz and with 120V AC line voltage, both channels driven.

Power output

  • Power output at onset of limiter: approximately 100W @ 8 ohms, 200W @ 4 ohms

Additional data

  • Input/output polarity (digital and analog inputs): noninverting
  • AC-line current draw
    • Standby: 6.0W, 0.13A, 0.40PF
    • Operating: 33.0W, 0.35A, 0.82PF
  • Gain: output voltage divided by input voltage, 8-ohm load (Lch/Rch)
    • Analog unbalanced inputs (volume full up at +30dB): 284.6X, 48.6dB / 262.3X, 48.3dB
    • Digital input (-20dBFS input with volume at 0dB): 2.483V / 2.480V
  • Input sensitivity for 1W output into 8 ohms (Lch/Rch)
    • Analog unbalanced inputs: 9.9mV / 10.8mV
  • Output impedance @ 50Hz: 0.01 ohm
  • Input impedance @ 1kHz
    • Analog unbalanced inputs: 16.5k ohms
  • Output noise, volume at 30dB (Lch/Rch)
    • Wideband: 6.44mV/5.82mV, -52.8dBW/-53.7dBW
    • A weighted: 0.063mV/0.060mV, -93.0dBW/-93.5dBW
  • Output noise, volume at 0dB (Lch/Rch)
    • Wideband: 6.28mV/5.55mV, -53.1dBW/-54.1dBW
    • A weighted: 0.040mV/0.032mV, -97.0dBW/-98.9dBW
  • Output noise, volume at -20dB (Lch/Rch)
    • Wideband: 5.76mV/5.47mV, -53.8dBW/-54.3dBW
    • A weighted: 0.071mV/0.063mV, -92.0dBW/-93.0dBW
  • Output noise, volume at -30dB (Lch/Rch)
    • Wideband: 5.81mV/5.49mV, -53.8dBW/-54.2dBW
    • A weighted: 0.075mV/0.063mV, -91.5dBW/-93.0dBW

Measurements summary

The Expert 130 Pro is an unusual and clever combination of class-A and class-D amplification: The class-A section swings the output voltage, and the class-D section supplies most of the output current. Unique among designs using class-D circuitry, there is no output low-pass filter. As a result, the Devialet’s high-frequency response is quite independent of load. The Expert 130 has a limiter circuit that prevents it from clipping, which meant I couldn’t run my usual test of clipping behavior along with the power output at 1% and 10% THD+N. The Devialet’s digital switching frequency noise was low enough that I didn’t need to use Audio Precision’s AUX-0025 external low-pass filter in my testing, as I usually do.

I tested the Devialet’s volume-control tracking using a 1kHz test tone with the reference volume being that of the 5W output with a 500mV signal input. Volume-control tracking was within less than 0.1dB with volume settings of +30dB to -30dB.

Chart 1A shows the frequency response of the Expert 130 Pro with varying loads and with my usual vertical scale: the curves of the open circuit and 8- and 4-ohm loads are direct overlays; that is, they’re identical. The analog input frequency response with a sampling frequency of 96kHz looks about the same. Chart 1B plots the Expert 130 Pro’s frequency responses for sample rates of 44.1, 96, and 192kHz. For these kinds of response curves driven by the Audio Precision digital generator, it’s not possible to follow the curves very far into the high-frequency cutoff region, due to those frequencies approaching one-half the sampling frequency.

Chart 2 illustrates how the Expert 130 Pro’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation test signals and amplifier output for loads of 8 and 4 ohms. The amount of distortion is quite low, and is dominated by noise rather than by distortion per se over much of the power range. This test yielded very similar results when taken at the Devialet’s analog input.

The Expert 130 Pro’s THD+N as a function of frequency at several different power levels is plotted in Chart 3. This amplifier’s levels of distortion are so low that measuring its THD+N with an 80kHz filter bandwidth, as I usually do, didn’t actually reveal the distortion, which remains largely below the level of the noise. To compensate for this, in Chart 3 I reduced the measurement bandwidth to 22kHz, at the cost of showing an increase in distortion in the last two octaves of the audio range. Nonetheless, the readings are still largely dominated by noise, and show the distortion’s tendency to rise at higher frequencies.

The Devialet’s damping factor vs. frequency is plotted in Chart 4. These data were taken as a function of the Devialet’s volume-control setting, and surprisingly showed this variation in the high-frequency shape. Note that is with the digital input signal set to Off, and the output of the channel measured driven differentially from a separate power amplifier. A regulated 1A of current as a function of frequency is applied to each phase of the tested amplifier’s output as a function of frequency.

Chart 5 plots the spectrum of the Expert 130 Pro’s harmonic distortion and noise residue of a 10W, 1kHz test signal. The line harmonics are visible but low in magnitude. The signal harmonics are mainly the second, with lower-level, higher-order harmonics above that. These data show just how low the Devialet’s distortion is, and the values in Chart 3 approach this.

Chart 1A - Frequency response of output voltage as a function of output loading

Chart 1A

Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load

Chart 1B - Frequency response of output voltage as a function of sample rate

Chart 1B

Red line = 44.1kHz
Magenta line = 96kHZ
Blue line = 192kHz

Chart 2 - Distortion as a function of power output and output loading

Chart 2

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

Chart 3 - Distortion as a function of power output and frequency

Chart 3

(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 30W
Cyan line = 60W
Green line = 80W

Chart 4 - Damping factor vs. frequency and volume control

Chart 4

Damping factor = output impedance divided into 8

Red line: +10dB
Magenta line: 0dB
Blue line: -10dB
Cyan line: -20dB

Chart 5 - Distortion and noise spectrum

Chart 5

1kHz signal at 10W into an 8-ohm load

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