Bluesound Powernode Edge Integrated Amplifier Measurements

Link: reviewed by Todd Whitesel on SoundStage! Simplifi on July 1, 2023

General Information

All measurements taken using an Audio Precision APx555 B Series analyzer.

The Bluesound Powernode Edge was conditioned for 1 hour at 1/8th full rated power (~5W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The Edge offers one combination analog/optical input (1/8″ TRS/mini-TosLink), an ethernet connection for streaming, a subwoofer output (RCA), and a pair of speaker-level outputs. For the purposes of these measurements, the following inputs were evaluated: optical (mini-TosLink) S/PDIF and analog line-level unbalanced (1/8″ TRS).

Based on the accuracy and repeatability at various volume levels of the left/right channel matching (see table below), the Edge volume control is likely operating in the digital domain. Consequently, all analog signals are digitized at the Edge’s analog input so the unit may apply volume, bass management, and tone controls. The volume control offers a total range from -51dB to +26dB. Below about 20%, volume increments range from 2.5 to 3.5dB, above 20%, mostly 1dB increments.

Most measurements were made with a 1.7Vrms line-level analog input, or a 0dBFS digital input. We avoided our typical 2Vrms analog input level, because this caused some sporadic noise issues with the Edge’s analog-to-digital converter (ADC). The signal-to-noise ratio (SNR) measurements were made with the same input signal values but with the volume set to achieve the rated output power of 40W (8 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum, but with a lower input voltage to achieve the same 40W output.

Because the Edge is a digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), our typical input bandwidth filter setting of 10Hz–90kHz for frequency sweeps was necessarily changed to 10Hz–22.4kHz for all measurements, except for frequency response and for FFTs. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted bandwidth setting.

Volume-control accuracy (measured at speaker outputs): left-right channel tracking

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Bluesound for the Powernode Edge compared directly against our own. The published specifications are sourced from Bluesound’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth is set at its maximum (DC to 1MHz), assume, unless otherwise stated, a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.

Our primary measurements revealed the following using the analog/optical input (unless specified, assume a 1kHz sinewave at 1.7Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the Powernode Edge was able to sustain about 53W into 4 ohms using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (5.3W) for 5 seconds, for 5 continuous minutes. While the Edge can output more than 53W into 4 ohms for short bursts, there is an aggressive thermal and current protection circuit that clamps the output, even if the user keeps increasing the volume. This protection circuit was active during our test.

Frequency response (8-ohm loading, line-level input)

In our measured frequency response (relative to 1kHz) chart above, the Edge is nearly flat within the audioband (20Hz to 20kHz). At the extremes, the Edge is 0.7dB down at 20Hz and 1.5dB down at 20kHz. The Edge cannot be considered a high-bandwidth audio device as the -3dB point is just past 20kHz. In fact, the Edge exhibits brickwall-type filtering just past 20kHz and appears to sample analog signals at 44.1kHz. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

Frequency response vs. input type (8-ohm loading, left channel only)

The chart above shows the Edge’s frequency response (left channel only) as a function of input type. The green trace is the same analog input data from the previous graph. The blue trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz, the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, and, finally, pink is 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same across digital input types: flat down to 5Hz, compared to the -2.5dB at 10Hz for the analog input. The behavior nearing 20kHz is identical for the analog input and the 16/44.1 digital input—about -1.5dB at 20kHz. The behavior for the 24/96 and 24/192 input data was identical, with a -3dB point just past 30kHz, indicating that 24/192 data is likely resampled at 96kHz.

Frequency response (8-ohm loading, line-level input, bass and treble controls)

Above are two frequency-response (relative to 1kHz) plots for the analog input, measured at 10W (8 ohms) at the speaker outputs, with the treble and balance controls set at both minimum and maximum. They show that the Edge will provide a maximum gain/cut of approximately 6dB at 20Hz, and a maximum gain/cut of approximately 6dB at 10kHz.

Frequency response with subwoofer-crossover engaged (120Hz, 8-ohm loading)

Above are two frequency response plots for the analog input, measured at 10W (8 ohms) at the speaker outputs, and at the line-level subwoofer output, with the crossover set at 120Hz. The Edge DSP crossover uses a slope of 18dB/octave, and the subwoofer output is only 0.5dB down at 20Hz.

Phase response (line-level input)

Above is the phase response plot from 20Hz to 20kHz for the analog input from 20Hz to 20kHz. The Edge does not invert polarity and exhibits a little over +40 degrees of phase shift at 20Hz, and almost +80 degrees around 20kHz.

Digital linearity (16/44.1 and 24/96 data)

The chart above shows the results of a linearity test for the optical digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the speaker outputs of the Edge. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both digital input types performed similarly and flat from -90dBFS down to 0dBFS. The 16/44.1 data overshot the ideal output signal amplitude by only 2-3dB at -120dBFS. The 24/96 data overshot by a significant 26dB at -120dBFS. This appears to be some kind of bug, as the 24/96 signal output amplitude remained at just below -90dBFS, despite the input signal decreasing below this value.

Impulse response (16/44.1 and 24/96 data)

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the speaker outputs (10W at 8 ohms) of the Edge. We can see that the Edge utilizes a typical sinc function reconstruction filter.

J-Test (optical input)

The chart above shows the results of the J-Test test for the optical digital input measured at the speaker outputs (10W into 8 ohms) of the Edge. J-Test was developed by Julian Dunn in the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24bit). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave. In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g., 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBFS and below.  The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

We see several and clear peaks in the audioband at -95 to 130dBFS. This is a mediocre J-Test result, and an indication that the Edge DAC may have poor jitter immunity. When sinewave jitter was injected at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection, no further peaks, or worsening of existing peaks, were observed up to about 700ns of jitter level, where the Edge lost sync on the signal.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (optical input)

The chart above shows a fast Fourier transform (FFT) of the Edge’s speaker outputs (10W into 8 ohms) with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the optical digital input, sampled at 16/44.1. The sharp roll-off above 20kHz in the white-noise spectrum shows the implementation of a brickwall-type reconstruction filter. There are a few low-level aliased image peaks in the audioband at -125dBrA and below. The main 25kHz alias peak is highly suppressed at -110dBrA.

RMS level vs. frequency vs. load impedance (1W, left channel only)

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms or 2.83Vrms) as a function of frequency, for the analog input swept from 10Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Zoomed in, we can see a maximum deviation within the audioband of about 0.005dB from 4 ohms to no load, which is an indication of an extremely high damping factor, or vanishingly low output impedance. The maximum variation in RMS level when a real speaker was used is difficult to decipher, because the variations we see (due to the extreme zooming in the graph) are inherent frequency-response variations, not due to the amplifier output impedance interacting with speaker impedance.

THD ratio (unweighted) vs. frequency vs. output power

The chart above shows THD ratios at the output into 8 ohms as a function of frequency (20Hz to 6kHz) for a sinewave stimulus at the analog input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 40W (rated power). The power was varied using the volume control. All three THD plots are relatively flat and similar, hovering around 0.005 to 0.01%.

THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms

The chart above shows THD ratios measured at the output of the Edge as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Although there are fluctuations below 3W, both the 4-ohm and 8-ohm data are essentially the same (0.002 to 0.006%) from 3W to the “knees” at about 43W (8 ohms) and just below 70W (4 ohms). As is typical, THD ratios were highest with the lowest signal amplitude, at just above (4 ohms) and below (8 ohms) 0.2% at 10mW.

THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms

The chart above shows THD+N ratios measured at the output of the Edge as a function of output power for the analog line level-input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). There’s a distinct 5dB jump in THD+N (also visible in the THD plot above) when the output voltage is around 1Vrms (i.e., 0.15W into 8 ohms, 0.3W into 4 ohms). This behavior was repeatable over multiple measurement trials. Overall, THD+N values before the “knee” ranged from around 0.02-0.01% (0.5 to 40W into 8 ohms and 0.5 to 70W into 4 ohms) to up to 1-2% at 10mW.

THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)

The chart above shows THD ratios measured at the output of the Edge as a function of load (8/4/2 ohms) for a constant input voltage that yielded 5W at the output into 8 ohms (and roughly 10W into 4 ohms, and 20W into 2 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find identical THD ratios between the 8- and 4-ohm loads, hovering around 0.005%. Since the Edge is not designed to drive 2-ohm loads, predictably, THD ratios were much higher into 2 ohms, at 0.2%, dipping down to 0.03% at 6kHz.

THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only)

The chart above shows THD ratios measured at the output of the Edge as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three results are similar enough to be judged identical, yielding THD ratios around 0.005% from 20Hz to 6kHz. This is an extraordinary result and a first since we have been conducting this test. Typically, fluctuations of 20dB or more are oberved between the resistive dummy load and real speakers. This is a testament to the Edge’s extremely high damping factor (see last graph).

IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only)

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the Powernode Edge as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three results are similar enough to be judged identical, yielding IMD ratios from around 0.005% up to 0.02%.

IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only)

The chart above shows IMD ratios measured at the output of the Powernode Edge as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three results are similar enough to be judged identical, yielding IMD ratios just below 0.02% across the frequency sweep.

FFT spectrum – 1kHz (line-level input)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second (2kHz) and third (3kHz) harmonics dominate at -90dBrA or 0.003%; the remaining signal harmonics are at or below -110dBrA, or 0.0003%. Below 1kHz, we see power-supply noise-related peaks at 60Hz and 180Hz, at -100 dBrA, or 0.001%, and -115dBrA, or 0.0002%, respectively. Other lower-level noise-related peaks can also be seen. There is a significant rise in the noise floor just above 20kHz, typical for many class-D amps.

FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the optical digital input, sampled at 16/44.1. The main difference compared to the analog input FFT above is the lower second (2kHz) harmonic peak at -110dBrA, or 0.0003%. Power-supply noise-related peaks are little worse here, reaching -90dBrA (right channel) at 60Hz, or 0.003%.

FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the optical digital input, sampled at 24/96. We see essentially the same signal harmonic profile as with the 16/44.1 FFT above, but with a slightly lower noise floor due to increased bit-depth.

FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sinewave stimulus at the optical digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and the second (2kHz) harmonic just barely peaking above the -135dBrA noise floor for the right channel. The 60Hz power-supply-related peak is at -120/110dBrA (left/right), or 0.0001/0.0003%.

FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the optical digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and the signal’s harmonics (2/3/4/5/6kHz, etc.) at -100dBrA, or 0.001% and below, with the fifth (5kHz) harmonic peak dominating.

FFT spectrum – 50Hz (line-level input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is the signal second harmonic (100Hz) at -90dBrA, or 0.003%, with other signal harmonics seen below -100dBrA, or 0.001%. Very small power-supply-related peaks can be seen, for example at 180Hz, at just above -120dBrA, or 0.0001%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -100dBRa, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are higher, at around -85dBrA, or 0.006%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, optical digital input, 16/44.1)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital optical input at 16/44.1. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -110dBRA, or about 0.0003%, while the third-order modulation products, at 17kHz and 20kHz are at -95dBrA, or 0.002%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, optical digital input, 24/96)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital optical input at 24/96. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -110dBRA, or about 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are at -95dBrA, or 0.002%.

Intermodulation distortion FFT (analog line-level input, APx 32 tone)

Shown above is the FFT of the speaker-level output of the Edge with the APx 32-tone signal applied to the input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 10W into 8 ohms. The intermodulation products—i.e., the "grass" between the test tones—are distortion products from the amplifier and are below the -125dBrA, or 0.00006%, level.

Square-wave response (10kHz)

Above is the 10kHz squarewave response using the analog input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the Edge’s slew-rate performance. Rather, it should be seen as a qualitative representation of its very limited bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (e.g., 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. Due to Edge’s very limited bandwidth, only the squarewave’s fundamental (10kHz) sinewave is reproduced here. In addition, we can see the 500kHz switching-oscillator frequency used in the digital-amplifier section clearly visible modulating the waveform.

Square-wave response (1Hz–250kHz bandwidth)

Above is the 1kHz squarewave response using the analog input, at roughly 10W into 8 ohms, with a 250kHz restricted bandwidth to remove the modulation from the 500kHz oscillator. We see more evidence here, in the overshoot and undershoot at the squarewave corners, of the Edge’s limited bandwidth with an analog input.

FFT spectrum of 400kHz switching frequency relative to a 1kHz tone

The Edge’s class-D amplifier relies on a switching oscillator to convert the input signal to a pulse-width modulated (PWM) squarewave (on/off) signal before sending the signal through a low-pass filter to generate an output signal. The Edge oscillator switches at a rate of about 500kHz, and this graph plots a wide bandwidth FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz sinewave. We can see that the 500kHz peak is quite evident, and at -60dBrA. There is also a peak at 1MHz (the second harmonic of the 500kHz peak), at -55dBrA. Those peaks are direct results of the switching oscillators in the Edge amp modules. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

Damping factor vs. frequency (20Hz to 20kHz)

The final plot above is the damping factor as a function of frequency. Both channels show deviations across the frequency sweep, but this may be due to a higher uncertainty due to the extremely small differences in voltages that were required to be measured for this test. Damping factors were as high as 8000 (left channel at 3kHz), and as low as 330 at 20kHz. These are the highest damping factors we have ever measured.

Diego Estan
Electronics Measurement Specialist