Audiolab 9000Q Preamplifier-DAC Measurements

Link: reviewed by Roger Kanno on SoundStage! Hi-Fi on January 1, 1026

General Information

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

The Audiolab 9000Q was conditioned for 30 minutes at 4Vrms in/out into 200k ohms before any measurements were taken.

The 9000Q offers a multitude of inputs, both digital and analog (balanced and unbalanced), as well as line-level analog balanced outputs over XLR and unbalanced over RCA. For the purposes of these measurements, unless otherwise stated, the following inputs were evaluated: digital coaxial S/PDIF (RCA), analog balanced (XLR), as well as phono (RCA, moving magnet MM), over the balanced outputs.

There is also a headphone output on the front panel over a ¼” TRS connector. Comparisons were made between unbalanced (RCA) and balanced (XLR) line inputs and outputs, and the unbalanced inputs/outputs offered an improvement of approximately 9dB in signal-to-noise ratio (SNR) and roughly 10dB less THD compared to the balanced inputs/outputs (FFTs for different configurations can be seen in this report, and SNRs can be seen for both configuration in the main table).

Most measurements were made with a 4Vrms line-level analog and 0dBFS digital input with the volume set to achieve 4Vrms at the output.  For the phono input, a 5mVrms MM level was used to achieve 2Vrms at the balanced output. The SNR measurements were made with the same input signal values and, 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 4Vrms output.

The 9000Q offers five different reconstruction filters for the DAC inputs; however, on our review unit, changing these filters made no difference (i.e., it appeared that Audiolab had not enabled the feature). This was verified over RCA, optical, and USB digital inputs. Based on the impulse response results, it appears the filter being used is Minimum Phase (Fast Roll-Off). The 9000Q also offers a range of gain settings, with the 0dB default setting used for these measurements. 

Based on the accuracy and random results of the left/right volume channel matching (see table below), the 9000Q volume control is likely digitally controlled but operating in the analog domain. The 9000Q offers 78 volume steps from -77dB to 0dB for the line-level inputs. Step sizes are between 1 and 2dB.

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

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Audiolab for the 9000Q compared directly against our own. The published specifications are sourced from Audiolab’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 set at its maximum (DC to 1MHz), unless otherwise stated, assume a 1kHz sinewave at 4Vrms or 0dBFS at the input, 4Vrms at the output into 200k 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 balanced line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 4Vrms or 0dBFS, 4Vrms output, 200k ohm loading, 10Hz to 22.4kHz bandwidth):

*due to low noise levels of DUT, analyzer self-noise has been subtracted

Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz sinewave at 5mVrms, 2Vrms output, 200k ohm loading, 10Hz to 22.4kHz bandwidth):

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 4Vrms input/2Vrms output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

Frequency response (line-level input)

In our measured frequency response (relative to 1kHz) plot above, the 9000Q is perfectly flat within the audioband (0dB at 20Hz/20kHz). At the extremes, the 9000Q is 0dB at 5Hz and 0dB all the way up to 200kHz. The 9000Q appears to be DC-coupled, as there is no attenuation at low frequencies, even at 5Hz. 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 (line-level input, bass and treble)

Above are the frequency response (relative to 1kHz) plots with the bass and treble controls set to minimum and maximum. We find a boost/cut of 5dB at 20Hz/20kHz.

Phase response (line-level analog input)

Above is the phase response plot from 20Hz to 20kHz for the balanced line-level input. The 9000Q does not invert polarity and exhibits essentially no phase shift in the audioband. This is as expected given the very high bandwidth of this preamp.

Frequency response vs. input type

The chart above shows the 9000Q’s frequency response (relative to 1kHz) as a function of input type. The green trace is the same (but limited to 80kHz) analog input data from the previous graph. The blue/red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, the purple/green traces for 24/96 from 5Hz to 48kHz, and finally pink/orange for 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same for all the digital sample rates, as well as the analog input—flat down to 5Hz. The behavior at high frequencies for all three digital sample rates is as expected, offering filtering around 22, 48, and 96kHz (half the respective sample rate). The 44.1kHz sampled input signal exhibits sharp but not “brick-wall”-type behavior, with a -3dB point at roughly 21kHz. The 24/96 and 24/192 signals show softer attenuation around the corner frequencies with -3dB points at roughly 36kHz and 80kHz.

Phase response (digital input, 16/44.1, 24/96, 24/192)

Above are the phase-response plots from 20Hz to 20kHz for the digital coaxial input at 16/44.1 (blue/red), 24/96 (purple/green), and 24/912 (pink/orange). Predictably, the 16/44.1 data yields the highest phase shift at -100 degrees at 20kHz. The 24/96 input signal is just shy of -10 degrees at 20kHz, and the 24/192 signal shows no phase shift in the audioband.

Frequency response (MM input)

The chart above shows the frequency response (relative to 1 kHz) for the phono input (MM configuration). What is shown is the deviation from the RIAA curve, where the input signal sweep is EQd with an inverted RIAA curve supplied by Audio Precision (i.e., zero deviation would yield a flat line at 0dB). Between 20Hz and 20kHz, we find strict adherence to the RIAA curve, within roughly +/-0.1dB from 30Hz to 20kHz, and -0.3dB at 20Hz. At 5Hz, the response is at -3dB. This is an example of exceptional RIAA tracking implemented in the analog domain.

Phase response (MM phono input)

Above is the phase response plot from 20Hz to 20kHz for the phono input. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about -60 degrees at 200Hz and -90 degrees at 20kHz.

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

The chart above shows the results of a linearity test for the coaxial digital input (the optical input performed identically) for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the balanced outputs of the 9000Q. For this test, 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. At -120dBFS, the 16/44.1 data overshot by only 1-3dB, while the 24/96 remained perfect. To verify how well the 24/96 data would perform down to -140dBFS, we extended the sweep in the chart below.

Here we can see that the 24/96 data only missed the mark by +/-1dB (left/right) at -140dBFS. This is an exceptional digital-linearity test result.

Impulse response (24/48 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 balanced outputs of the 9000Q. We can see that the 9000Q utilizes a reconstruction filter that favors no pre-ringing.

J-Test (coaxial input)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the 9000Q. 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.

The coaxial S/PDIF input of the 9000Q shows a near-perfect J-Test result, with only very small peaks observable at a vanishingly low -155dBrA.

J-Test (optical input)

The chart above shows the results of the J-Test test for the optical digital input measured at the balanced outputs of the 9000Q. The results here are essentially the same as the coaxial input above.

J-Test (coaxial, 2kHz sinewave jitter at 10ns)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the 9000Q, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The tell-tale peaks at 10kHz and 14kHz can be seen, but at very low -155dBrA. The optical input yielded the same result.

J-Test (coaxial, 2kHz sinewave jitter at 100ns)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the 9000Q, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. This time, the tell-tale peaks at 10kHz and 14kHz can be seen at a still very low -135dBrA. The optical input yielded the same result.

Wideband FFT spectrum of white noise and 19.1kHz sinewave tone

The chart above shows a fast Fourier transform (FFT) of the 9000Q’s balanced outputs with white noise at -4 dBFS (blue/red) and a 19.1kHz sinewave at -1dBFS fed to the coaxial digital input, sampled at 16/44.1. The gentle roll-off past 20kHz in the white noise spectrum shows that the 9000Q doesn’t use a brick-wall-type reconstruction filter. There is one aliased image within the audioband at -110dBrA at roughly 13kHz. The primary aliasing signal at 25kHz is barely suppressed at -20dBrA.

THD ratio (unweighted) vs. frequency vs. load (analog)

The chart above shows THD ratios at the balanced line-level output into 200k ohms (blue/red) and 600 ohms (purple/green) as a function of frequency for the analog balanced inputs. The 200k-ohm THD data are lower than the 600-ohm data by a full 20dB. The 200k-ohm data are around the 0.0001% level from 20Hz to 2kHz, then up to 0.0005% at 20kHz. The left channel did exhibit about 3dB lower THD compared to the right channel. Into 600 ohms, THD ratios ranged from 0.001% up to 0.002% at 20kHz.

THD ratio (unweighted) vs. frequency vs. sample rate (16/44.1 and 24/96)

The chart above shows THD ratios at the balanced line-level output into 200k ohms for a 16/44.1 (blue/red) dithered 1kHz signal at the coaxial input and a 24/96 (purple/green) signal, as a function of frequency, at 0dBFS. The 16/44.1 THD ratios ranged from 0.0006% from 20Hz to 1kHz, then up to beyond 1% at 20kHz. It’s important to note that the digital signals were at 0dBFS, and that this level sampled at 16/44.1 causes clipping at high frequencies. Had the sweep been done at -1dBFS, the 16/44.1 data would have looked nearly identical to the 24/96 data. The 24/96 data ranged from 0.0004% from 20Hz to 1kHz, then up to 0.001% at 20kHz.

THD ratio (unweighted) vs. frequency (MM phono input)

The graph above shows THD ratios as a function of frequency for the phono input. The input sweep is EQ’d with an inverted RIAA curve. The THD values vary from around 0.007% (20Hz) down to around 0.0006% (2kHz to 3kHz), then up to 0.0015% at 20kHz. 

THD ratio (unweighted) vs. output (analog)

The chart above shows THD ratios measured at the balanced outputs of the 9000Q as a function of output voltage for the balanced line-level input, with the volume control at maximum. THD values start at 0.07% at 1mVrms, down to a low of 0.00006% at 2-3Vrms, then a steep rise past 5Vrms to the 1% THD mark at 5.9Vrms.

THD+N ratio (unweighted) vs. output (analog)

The chart above shows THD+N ratios measured at the balanced outputs of the 9000Q as a function of output voltage for the balanced line-level input, with the volume control at maximum. THD+N values start at 0.7% at 1mVrms, down to a low of 0.0003% at 3-4Vrms, then a steep rise past 5Vrms to the 1% THD mark at 5.9Vrms.

THD ratio (unweighted) vs. output (16/44.1 and 24/96)

The chart above shows THD ratios measured at the balanced outputs of the 9000Q as a function of output voltage for the digital coaxial S/PDIF input, swept from -90dBFS to 0dBFS, with the volume control at maximum. Blue/red traces are for 16/44.1 data and purple/green for 24/96. For the 16/44.1 data, THD values start at 2%, and predictably, reach their low at the maximum output voltage of about 4Vrms, at 0.0005%. For the 24/96 data, THD ratios ranged from 0.1% down to 0.00015% at 1-2Vrms, then up to 0.0005% at the maximum output voltage.

THD+N ratio (unweighted) vs. output (16/44.1 and 24/96)

The chart above shows THD+N ratios measured at the balanced outputs of the 9000Q as a function of output voltage for the digital coaxial S/PDIF input, swept from -90dBFS to 0dBFS, with the volume control at maximum. Blue/red traces are for 16/44.1 data and purple/green for 24/96. For the 16/44.1 data, THD+N values start at 20% and reach their low at the maximum output voltage of about 4Vrms, at 0.002%. For the 24/96 data, THD ratios ranged from 1% down to 0.0003% at 2Vrms then up to 0.0005% at the maximum output voltage.

Intermodulation distortion vs. generator level (SMPTE, 60Hz:4kHz, 4:1, 16/44.1, 24/96)

The chart above shows intermodulation distortion (IMD) ratios measured at balanced output for 16/44.1 (blue/red) input data and 24/96 input data (purple/green), from -60dBFS to 0dBFS. Here, the SMPTE IMD method was used, where the primary frequency (F1 = 60Hz), and the secondary frequency (F2 = 7kHz), are mixed at a ratio of 4:1. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 16/44.1 data yields IMD ratios from 2% down to 0.003% at 0dBFS. The 24/96 data yields IMD ratios from 0.15% down to 0.0005% (right) at 0dBFS. The left channel at 24/96 saw a rise in IMD ratios beyond -5dBFS, up to 0.003% at 0dBFS.

FFT spectrum – 1kHz (analog line-level input, XLR in/out)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced outputs for the balanced line-level input. We see that the signal’s second harmonic, at 2kHz, is at -120dBrA or 0.0001%, with subsequent signal harmonics at and below -130dBrA, or 0.00003%. Below 1kHz, we see power-supply-related noise peaks at -130dBrA and below, dominated by the 180Hz peak.

FFT spectrum – 1kHz (analog line-level input, RCA in/out)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the unbalanced outputs for the unbalanced line-level input. We see improvements in signal related harmonic peaks (-130dBrA vs -120dBrA) and power-supply-related noise peaks (-140dBrA vs -130dBrA) compared with the XLR in/out FFT above.

FFT spectrum – 1kHz (analog line-level input, RCA in/XLR out)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced outputs for the unbalanced line-level input. Signal related harmonic peaks are similar to the RCA in/out FFT above, while the power-supply-related noise peaks are similar to the XLR in/out FFT above.

FFT spectrum – 1kHz (analog line-level input, RCA in/XLR out)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the unbalanced outputs for the balanced line-level input. Signal related harmonic peaks are similar to the XLR in/out FFT above, while this combination yielded the best results in terms of power-supply related noise peaks (all below -150dBrA, or 0.000003%).

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 balanced outputs for the coaxial digital input, sampled at 16/44.1. We see the third (3kHz) signal harmonic dominating at roughly -100dBrA, or 0.001%. The second (2kHz) and fifth (5kHz) signal harmonic peaks are at the -125dBrA, or 0.0006%, level. The noise floor is much higher (-140dBrA) due to the 16-bit depth limitation. Because of the elevated noise floor, no power-supply-related peaks can be seen.

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 balanced outputs for the coaxial digital input, sampled at 24/96. We see the third (3kHz) signal harmonic dominating at roughly -100dBrA, or 0.001%. The second (2kHz) and fifth (5kHz) signal harmonic peaks are at the -125dBrA, or 0.0006%, level. Higher signal harmonics can be below -130dBrA, or 0.00003%. We see power-supply-related noise peaks at -140dBrA, or 0.00001%, and below, with the peak at 180Hz dominating.

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 balanced outputs. We see the 1kHz primary signal peak, at the correct amplitude, and no signal or noise related harmonic peaks above the -140dBrA noise floor.

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 balanced outputs. We see the 1kHz primary signal peak, at the correct amplitude, and signal related harmonic peaks at 2kHz and 6kHz below -140dBrA, or 0.00001%. Power-supply related noise peaks can be seen at and below -140dBrA, or 0.00001%.

FFT spectrum – 1kHz (MM phono input)

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the balanced outputs across for the phono input. The dominant signal-related harmonic can be seen at 2kHz, at -105dBrA, or 0.0006%. Power-supply-related noise peaks can be seen at -90dBrA, or 0.003%, at 60Hz and at 180Hz, with subsequent peaks at and below -100dBrA, or 0.001%.

FFT spectrum – 50Hz (line-level input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the balanced outputs for the balanced line-level 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 that of the signal’s second (100Hz) harmonic at -120dBrA or 0.0001%. The third signal harmonic (150Hz) and third power-supply-related noise peak (180Hz) are both at -130dBrA or 0.00003%.

FFT spectrum – 50Hz (MM phono input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the balanced outputs for the phono input. The most predominant (non-signal) peaks are power-supply-related noise peaks at -90dBrA, or 0.003%, at 60Hz and 180Hz. The second signal harmonic (100Hz) is just below -100dBrA, or 0.001%.

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 balanced outputs for the balanced 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 -130dBrA or 0.00003%, while the third-order modulation products, at 17kHz and 20kHz, are at -120dBrA or 0.0001%. This is a very clean IMD result.

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

Shown above is the FFT of the balanced outputs of the 9000Q with the APx 32-tone signal applied to the input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 4Vrms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the preamplifier and are around the extremely low -150dBrA, or 0.000003%, 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 balanced outputs for the digital coaxial input at 16/44.1. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -130dBrA, or 0.00003%, while the third-order modulation products, at 17kHz and 20kHz, are at -110dBrA, or 0.0003%. We also see the main aliased peaks at 25.1kHz and 26.1kHz at around -30dBrA.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial 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 balanced outputs for the digital coaxial input at 24/96. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -130dBrA, or 0.00003%, while the third-order modulation products, at 17kHz and 20kHz, are at -110dBrA or 0.0003%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MM phono input)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the balanced outputs across for the phono input configured for MM. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -110dBrA, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are just below -120dBrA, or 0.0001%.

Square-wave response (10kHz)

Above is the 10kHz squarewave response using the analog line-level input, at roughly 4Vrms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the 9000Q’s slew-rate performance. Rather, it should be seen as a qualitative representation of its very extended 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. The 9000Q reproduction of the 10kHz square wave is very clean with sharp corners devoid of ringing.

Diego Estan
Electronics Measurement Specialist