Naim Audio Uniti Nova PE Streaming Integrated Amplifier Measurements

Link: reviewed by Roger Kanno on SoundStage! Simplifi on August 15, 2024

General Information

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

The Uniti Nova PE was conditioned for one hour at 1/8th full rated power (~18W 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 Uniti Nova PE offers four set of line-level analog inputs (two over RCA, two over unbalanced 5-pin DIN connectors), six digital inputs (two S/PDIF over RCA, one S/PDIF over BNC, two S/PDIF over TosLink optical, one over HDMI), an ethernet port for streaming, left/right pre-outs (RCA and unbalanced 4-pin DIN connector), one set of speaker-level outputs, and one headphone output over a 1/8″ TRS connector. A Bluetooth input is also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial (RCA), analog line-level (RCA), and the headphone output.

Most measurements were made with a 2Vrms line-level analog input and 0dBFS digital input. The signal-to-noise ratio (SNR) measurements were made with the default input signal values but with the volume set to achieve the achievable output power of 150W into 8 ohms. For comparison, on the line-level input, an SNR measurement was also made with the volume at maximum.

Based on the accuracy and randomness of the left/right volume channel matching (see table below), the Uniti Nova PE volume control is digitally controlled but operating in the analog domain. The Uniti Nova PE overall volume range is from -54dB to +27.9dB (line-level input, speaker output). It offers 2dB increments from position 0 to 27, 1dB increments from positions 28 to 84, and 0.5dB from 85 to 100. Also noteworthy is that not every volume step on the display offers a change in gain. That is to say, despite the display showing 100 “steps,” only 85 of those “steps” (default setting) offer an actual change in volume.

Our typical input bandwidth filter setting of 10Hz to 22.4kHz was used for all measurements except FFTs, where a bandwidth of 10Hz to 90kHz was used. Frequency-response measurements utilize a DC to 1MHz input bandwidth. Because the Unity Nova PE uses digital amplifier technology that yields considerable noise above 20kHz, THD vs frequency sweeps were restricted to 6kHz to capture the second and third uppermost signal harmonics with the 22.4kHz analyzer bandwidth.

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 Naim for the Uniti Nova PE compared directly against our own. The published specifications are sourced from Naim’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 was extended to 1MHz, assume, unless otherwise stated, 10W into 8 ohms and 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 line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the Uniti Nova PE was able to sustain 330W into 4 ohms (~3% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (33W) for 5 seconds, for 5 continuous minutes without inducing a fault protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the sides of the Uniti Nova PE were only slightly warm to the touch.

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms input/output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

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

In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the Uniti Nova PE is not flat within the audioband (+0.25dB at 30Hz, -1.5dB at 20kHz). The -3dB point is at roughly 23kHz, and the low-frequency response is -1.6dB at 5Hz. The Uniti Nova PE appears to be AC coupled. What is very unusual and must be pointed out is the (what we assume to be) purposeful tilt (bass boost/treble cut) to the response. We can only surmise that this was done to impart a “sound” to the Uniti Nova PE. Also noteworthy is the near brick-wall-type attenuation at high frequencies around 20kHz. 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.

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

Above are the phase response plots from 20Hz to 20kHz for the line level input, measured across the speaker outputs at 10W into 8 ohms. The Uniti Nova PE does not invert polarity and yields -20000 degrees of phase shift at 20kHz due to the extreme high-frequency filtering.

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

The chart above shows the Uniti Nova PE’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The two green traces are the same analog input data from the speaker-level frequency response graph above. The blue and red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, the purple and green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and the pink and orange traces are for a 24/192 dithered digital input signal. At low frequencies, the digital signals yielded the same response as the analog response, as well as the same overall bass-to-treble tilt. The -3dB points are: 20.9kHz for the 16/44.1 data, 24.8kHz for the 24/96 and 24/192 data, and 23kHz for the analog input.

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

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level pre-outputs of the Uniti Nova PE, where 0dBFS was set to yield 1Vrms at the pre-outs. The digital input was swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output was analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both data were essentially perfect as of -100dBFS down to 0dBFS. Both data sets were at roughly +2dB at -120dBFS. Below -120dBFS . . .

. . . both data sets grossly over-responded (beyond +10dB at -140dBFS).

Impulse response (24/44.1 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 line-level pre-outs of Uniti Nova PE. The Uniti Nova PE DAC uses a reconstruction filter that has no pre-ringing and sustained post-ringing.

J-Test (coaxial)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outputs of the Uniti Nova PE where 0dBFS is set to 1Vrms. J-Test was developed by Julian Dunn the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). 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 (the main peak). 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 -144dBrA 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.

Here we see a strong J-test result, with only a few peaks in the audioband, at the -130dBFS and below level. This is an indication that the Uniti Nova PE DAC may have good jitter immunity.

J-Test (optical)

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level pre-outputs of the Uniti Nova PE. The optical input yielded essentially the same results as the coaxial input.

J-Test (coaxial, 100ns jitter)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the Uniti Nova PE, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 12kHz cannot be seen above the -145dBFS noise floor. A strong result.

J-Test (optical, 100ns jitter)

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level output of the Uniti Nova PE, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The optical input yielded essentially the same results as the coaxial input.

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

The chart above shows a fast Fourier transform (FFT) of the Uniti Nova PE’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at -1dBFS fed to the coaxial digital input, sampled at 16/44.1. The roll-off around 20kHz in the white-noise spectrum shows the implementation of a reconstruction filter that is steep but not of the brick-wall-type variety. There are no aliased image peaks within the audioband above the -135dBrA noise floor. The primary aliasing signal at 25kHz is at -70dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at and below the same level.

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 line-level input swept from 5Hz to 50kHz. 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. Here we see that the deviations between no load and 4 ohms are relatively large at 0.4dB. This is a poor result and an indication of a high output impedance, or low damping factor, for a solid-state amplifier. With a real speaker load, deviations measured lower at roughly 0.3dB.

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

The chart above shows THD ratios at the speaker-level outputs into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level 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 just at 140W (near the rated output of 150W). The power was varied using the Uniti Nova PE volume control. The 10W THD ratios were the lowest, with a fairly constant 0.003% to 0.005% across the sweep. The 1W THD ratios were slightly higher with a fairly constant 0.005% to 0.006% across the sweep.  At 140W, THD ratios remained low, from 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 speaker-level outputs of the Uniti Nova PE 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). THD ratios into 4 and 8 ohms are remarkably close (within 2-3dB). Beyond 10W, the left channel outperformed the right by as much as 10dB. THD ratios into 8 ohms (left channel) ranged from 0.01% at 50mW down to 0.001% at 30W, then up to 0.002% at the “knee” at roughly 140W, and up to the 1% THD mark at 157W. THD ratios into 4 ohms (left channel) ranged from 0.01% at 60mW down to 0.0007% at 50W to the “knee” at roughly 210W, and up to the 1% THD mark at 261W.

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

The chart above shows THD+N ratios measured at the speaker-level outputs of the Uniti Nova PE 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). THD+N ratios into 4 and 8 ohms are remarkably close (within 2-3dB). They range from 0.1% at 50mW, down to 0.003% at the “knees.”

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 Uniti Nova PE as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 50W at the output into 8 ohms (and roughly 100W into 4 ohms, and 200W into 2 ohms) for the analog line-level input. All three THD plots are remarkably close, and in fact essentially identical at between 0.003% and 0.006% from 20Hz to 500Hz. From 3kHz to 6kHz, there is roughly a 5dB increase in THD every time the load is halved. At 6kHz into 2 ohms, the THD ratio is 0.02%.

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 Uniti Nova PE 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). THD ratios into the real speakers were higher than those measured across the resistive dummy load from 20Hz to 200-300Hz. The differences ranged from 0.3% at 20Hz for the two-way speaker and 0.02% for the three-way speaker versus 0.005% for the resistive load. Between the important frequencies of 400Hz to 6kHz, all three THD traces are essentially identical at 0.005%.

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 Uniti Nova PE 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 was 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). We find that all three IMD traces are essentially identical, ranging from 0.01% at 2.5kHz up to 0.15% at 20kHz.

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 Uniti Nova PE 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 was 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). We find very similar IMD ratios into all three loads, between 0.02% and 0.015% across the 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) harmonic dominates at -90dBrA, or 0.003%. The third (3kHz) and fifth (5kHz) signal harmonics can be seen at -110dBrA, or 0.0003%. On the left side of the signal peak, we find power-supply related noise peaks, with the third harmonic (180Hz) dominating at just above -110dBrA (left channel), or 0.0003%. Other noise peaks can be seen below the -120dBrA level.

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 coaxial digital input, sampled at 16/44.1. Here the second (2kHz) and third (3rd) signal harmonics dominate at -85dBrA and -90dBrA, or 0.006% and 0.003%. The fourth (4kHz) and fifth (5kHz) signal harmonics can be seen at roughly -110dBrA, or 0.0003%. Noise peaks are at and below the -120dBrA, or 0.0001%, level.

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 coaxial digital input, sampled at 24/96. We see essentially the same result as with the 16/44.1 FFT above.

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 coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, with signal harmonics visible (right channel) at the same level as the signal. The noise floor for the right channel is elevated, as high as -100dBrA, approaching the signal peak in amplitude. The left channel noise floor is much lower at -125dBrA to -145dBrA.

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 coaxial digital input, measured at the output across an 8-ohm load. We see essentially the same result as with the 16/44.1 FFT above.

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 line-level input. The X axis is zoomed in from 40Hz 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 second (100Hz) signal harmonic at a low -90dBrA, or 0.003%. Other peaks (both signal harmonics and power-supply noise related harmonics) can be seen at -110dBrA and below.

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 line-level 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 -80dBRa, or 0.01%, while the third-order modulation products, at 17kHz and 20kHz are just below the -70dBrA, or 0.3%, level. This is a poor IMD result.

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

Shown above is the FFT of the speaker-level output of the Uniti Nova PE with the APx 32-tone signal applied to the analog 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 at and below the  -115dBrA, or 0.0002%, level.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial 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 coaxial input at 16/44.1 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -90dBrA, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are at -95dBrA, or 0.002%.

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

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96 (-1dBFS). We see essentially the same result as with the 16/44.1 IMD FFT above.

Squarewave response (10kHz)

Above is the 10kHz squarewave response using the analog line-level 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 Uniti Nova PE’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Uniti Nova PE’s low 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. In this case, we only see the fundamental 10kHz sinewave, along with a 600kHz high frequency signal (from the switching oscillator in the digital amp) riding on top. 

Square-wave response (10kHz)—250kHz bandwidth

Above is the 1kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms, this time with a 250kHz bandwidth filter on the analyzer to filter out the 600kHz oscillator. We see a poor squarewave reproduction, with ringing in the corners.

FFT spectrum of 500kHz switching frequency relative to a 1kHz tone

The Uniti Nova PE’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 Uniti Nova PE oscillator switches at a rate of about 600kHz, 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 600kHz peak is quite evident, and at -50dBrA. There is also a peak at 1.2MHz (the second harmonic of the 600kHz peak), at -80dBrA. Those peaks--the fundamental and its harmonic—are direct results of the switching oscillators in the Uniti Nova PE 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 graph above shows the damping factor as a function of frequency. We can see here a constant damping factor of 46 through the audioband. This is a poor result for a solid-state amplifier.

Diego Estan
Electronics Measurement Specialist