Quad Artera Solus integrated amplifier/CD player Measurements

Sidebar 3: Measurements

I measured the Quad Artera Solus using my Audio Precision SYS2722 system (see the January 2008 "As We See It"). I precondition amplifiers by running them at one-third power into 8 ohms for an hour. (One-third power results in the maximum dissipation in the output devices.) The Quad survived this demanding test, though the side-mounted heatsinks were very hot, at 141.3°F (60.8°C). The front panel was cooler at 124°F (39.1°C).

Looking first at the Artera Solus's performance as a preamplifier and headphone amplifier, both sets of outputs preserved absolute polarity, ie, were noninverting. With analog input signals, the maximum voltage gain at the headphone jacks was a modest 1.6dB, that at the preamplifier outputs was 1.02dB, balanced, and –5.6dB, unbalanced. The headphone output impedance was appropriately low, at 5.5 ohms at low and middle frequencies, dropping to 2.75 ohms at 20kHz. The preamplifier output impedances were 119 ohms, unbalanced, and 234 ohms, balanced, both figures consistent across the audioband.

Plugging headphones into the front-panel jack mutes the preamplifier and power amplifier outputs. To avoid damaging the amplifier with high-level digital signals, therefore, I examined how the Quad performed as a CD player and D/A processor from the headphone output. With the volume control set to its maximum ("90"), a 1kHz tone at –20dBFS resulted in output levels of 250mV (balanced preamplifier output), 266mV (headphone output), and 3.63V (speaker output). The latter implies that with the volume control set to its maximum, a full-scale digital tone will drive the amplifier 3.4dB into clipping. Even so, the Artera Solus's gain architecture is much better arranged than I usually find with integrated amplifiers with digital inputs.

The CD transport's error correction was one of the best I have encountered—there were no glitches in the player's output with any of the torture tracks on the Pierre Verany Digital Test CD. Looking at the performance of the digital inputs, the optical and coaxial S/ PDIF inputs locked to datastreams with sample rates up to 192kHz. Apple's USB Prober utility identified the Quad as "QUAD USB Audio 2.0" from "QUAD" and indicated that the USB port operated in the optimal isochronous asynchronous mode. Apple's AudioMIDI utility revealed that, via USB, the Artera Solus accepted 16- and 24-bit integer data sampled at all rates from 44.1 to 384kHz. Both CD playback and the digital inputs were noninverting.

Four digital reconstruction filters are available for S/PDIF and USB digital input signals—Fast, Narrow, Smooth, and Wide—though not for CD playback. With the Fast filter selected, which I understand was what HR had preferred in his auditioning, the Quad's impulse response with 44.1kHz data was a time-perfect pulse (fig.1), with the only pre- and post-ringing associated with the single high sample due to the Audio Precision's A/D converter, this sampling at 200kHz. The Smooth filter is the default and was also used by HR for most of his auditioning. This has a time-symmetrical, linear-phase impulse response, with a significant amount of ringing before and after the single high sample (fig.2). The Narrow filter's impulse response was very similar, but the Wide filter response had just a single cycle of pre- and post-ringing (fig.3).

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Fig.1 Quad Artera Solus, digital inputs, Fast filter, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).

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Fig.2 Quad Artera Solus, digital inputs, Smooth filter, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).

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Fig.3 Quad Artera Solus, digital inputs, Wide filter, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).

With 44.1kHz-sampled white noise (fig.4, red and magenta traces), the Quad's response with the Fast filter rolled off very slowly above the audioband, with sharply defined nulls at 44.1kHz and 88.2kHz. While the harmonics of a full-scale 19.1kHz tone are low in level, the aliased image at 25kHz of this tone (blue and cyan traces) is hardly attenuated at all, and the higher-order images at 63.2kHz (44.1+19.1) and 69.1kHz (88.2–19.1) are very high in level. With the Smooth filter, the Quad's ultrasonic output reached full stop-band attenuation at exactly half the sample rate (fig.5, vertical green line), and no aliased images of the high-frequency tone can be seen. The rolloff was a little slower with the Narrow filter but a lot slower with the Wide filter (fig.6).

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Fig.4 Quad Artera Solus, digital inputs, Fast filter, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan) into 100k ohms with data sampled at 44.1kHz (20dB/vertical div.).

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Fig.5 Quad Artera Solus, digital inputs, Smooth filter, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan) into 100k ohms with data sampled at 44.1kHz (20dB/vertical div.).

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Fig.6 Quad Artera Solus, digital inputs, Wide filter, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan) into 100k ohms with data sampled at 44.1kHz (20dB/vertical div.).

Playing a test CD, the Artera Solus's frequency response was flat almost to 20kHz, and the player correctly applied deemphasis to preemphasized CDs. The digital-input frequency response varied with the reconstruction filter chosen. With data at 44.1, 96, and 192kHz, the response with the Smooth filter followed the same basic shape, but with a sharp rolloff above half of each sample rate (fig.7). The behavior was similar with the Wide and Fast filters, but when I measured the response with the Narrow filter, the output rolled off sharply above one-quarter of each sample rate (fig.8). With 44.1kHz data, for example, the output was down by 9dB at 10kHz (fig.9, red trace). These measurements had been taken using optical S/PDIF data. I therefore repeated the response measurements with the four filters using the USB input, as well as at the preamplifier and loudspeaker outputs. The Fast, Wide, and Smooth filters behaved correctly at all three sample rates, performing identically as they had with S/PDIF data. But with the Narrow filter and USB data, the output now extended two octaves higher in frequency (fig.9, blue trace). I suspect there is a coding error with the Narrow filter when fed S/PDIF data.

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Fig.7 Quad Artera Solus, digital inputs, Smooth filter, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left channel cyan, right magenta), 192kHz (left blue, right red) (1dB/vertical div.).

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Fig.8 Quad Artera Solus, S/PDIF inputs, Narrow filter, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left channel cyan, right magenta), 192kHz (left blue, right red) (1dB/vertical div.).

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Fig.9 Quad Artera Solus, USB input (blue) and Toslink input (red), Narrow filter, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz. (1dB/vertical div.).

When I increased the bit depth from 16 to 24 with a dithered 1kHz tone at –90dBFS (fig.10), the random noise floor dropped by 12dB, meaning that the Quad's digital inputs offer 18 bits' worth of resolution. With undithered data representing a tone at exactly –90.31dBFS, the three DC voltage levels described by the data were resolved but the waveform was overlaid with high-frequency noise (fig.11).

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Fig.10 Quad Artera Solus, digital inputs, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with: 16-bit data (left channel cyan, right magenta), 24-bit data (left blue, right red) (20dB/vertical div.).

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Fig.11 Quad Artera Solus, digital inputs, waveform of undithered 16-bit, 1kHz sinewave at –90.31dBFS (left channel blue, right red).

Intermodulation distortion via the digital inputs was very low, with the second-order difference product produced by equal-level tones at 19 and 20kHz with the combined waveform peaking at 0dBFS, lying below –100dB (0.001%). However, with the Fast filter, low-level image energy appeared in the audioband (fig.12), which was absent with the Smooth filter (fig.13). Tested for its rejection of word-clock jitter with 16-bit CD data, all the odd-order harmonics of the LSB-level, low-frequency squarewave were at the correct levels (fig.14, sloping green line) and there were no jitter-related sidebands present. Repeating the jitter test with 24-bit TosLink and USB data gave the same good result (fig.15).

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Fig.12 Quad Artera Solus, digital inputs, Fast filter, 24-bit data, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).

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Fig.13 Quad Artera Solus, digital inputs, Smooth filter, 24-bit data, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).

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Fig.14 Quad Artera Solus, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit CD data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

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Fig.15 Quad Artera Solus, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

Turning to the analog inputs and the Quad's behavior as a conventional integrated amplifier, the maximum voltage gain into 8 ohms was 24.3dB and the amplifier preserved absolute polarity. The single-ended input impedance was close to 21k ohms across the audioband. The output impedance was a very low 0.098 ohms at 20Hz and 1kHz, increasing slightly to 0.16 ohms at 20kHz. (All figures include the series impedance of 6' of loudspeaker cable.) Consequently, the response with our standard simulated loudspeaker varied by less than ±0.1dB (fig.12, gray trace). The audioband response into impedances of 8 and 4 ohms (fig.16, blue, red, cyan, and magenta traces) is flat up to 20kHz, and the two channels match very closely. The output into 2 ohms (green trace) was down by just 0.5dB at 20kHz. This graph was taken with the volume control set to "90," and the frequency response didn't vary at lower volume-control settings, or from the preamplifier and headphone outputs. The Quad amplifier has a wide small-signal bandwidth, and its reproduction of a 10kHz squarewave (fig.17) featured very short risetimes and no overshoot or ringing.

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Fig.16 Quad Artera Solus, analog inputs, frequency response at 2.83V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green), and simulated loudspeaker (gray) (0.5dB/vertical div.).

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Fig.17 Quad Artera Solus, analog inputs, small-signal, 10kHz squarewave into 8 ohms.

Channel separation was excellent, at 90dB in both directions at 1kHz and below. The wideband, unweighted S/N ratio, ref. 2.83V and measured with the volume control at "90" and the input shorted to ground, was 75.1dB (average of both channels), which improved to an excellent 83.8dB when the measurement bandwidth was restricted to the audioband, and to 87.1dB when A-weighted. Spectral analysis of the Quad's low-frequency noise floor (fig.18) revealed that power supply–related spuriae were all very low in level. That the even-order harmonics of the 60Hz power-line frequency were lower than the odd-order attest to the circuit-board layout.

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Fig.18 Quad Artera Solus, analog inputs, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms with volume control set to "80" (left channel cyan, right magenta) and "100" (left blue, right red) (linear frequency scale).

The Quad's maximum power is specified as 75W into 8 ohms, equivalent to 18.75dBW. I found that the Artera Solus slightly exceeded its specified power, even with both channels driven. With "clipping" defined as when the THD+noise reaches 1%, the amplifier clipped at 80W into 8 ohms (19dBW, fig.19) and 128W into 4 ohms (18.1dBW, fig.20). Fig.21 shows how the Quad's THD+N percentage varied with frequency at a fairly high output level, 15.49V, which is equivalent to 30W into 8 ohms and 60W into 4 ohms. The distortion into 8 ohms (blue and red traces) is very low, as is the increase in distortion into 4 ohms (cyan, magenta). Commendably, the distortion in the top audio octave is only slightly higher than it is at low frequencies, which suggests that the circuit has a wide open-loop bandwidth.

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Fig.19 Quad Artera Solus, analog inputs, distortion (%) vs 1kHz continuous output power into 8 ohms.

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Fig.20 Quad Artera Solus, analog inputs, distortion (%) vs 1kHz continuous output power into 4 ohms.

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Fig.21 Quad Artera Solus, analog inputs, THD+N (%) vs frequency at 15.49V into: 8 ohms (left channel blue, right red) and 4 ohms (left cyan, right magenta).

The distortion is predominantly third harmonic in character (fig.22), though the second harmonic is almost as high in the left channel (fig.23, blue trace). High-order intermodulation products with an equal mix of 19kHz and 20kHz tones at a peak level of 50W into 4 ohms were very low in level (fig.24), and the second-order difference product lay at –90dB (0.003%).

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Fig.22 Quad Artera Solus, analog inputs, 1kHz waveform at 30W into 8 ohms, 0.003% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).

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Fig.23 Quad Artera Solus, analog inputs, spectrum of 50Hz sinewave, DC–1kHz, at 50Wpc into 8 ohms (left channel blue, right red) (linear frequency scale).

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Fig.24 Quad Artera Solus, analog inputs, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 50W peak into 4 ohms (left channel blue, right red) (linear frequency scale).

Other than that anomalous behavior with S/PDIF data and the Narrow reconstruction filter, the Quad Artera Solus offers excellent measured performance both as an amplifier and as a CD player. It's well-sorted, as they say in the UK.—John Atkinson

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COMMENTS
Bogolu Haranath's picture

HR said Artera Solus' CD player sounded superior ........ May be HR could compare that CD sound with the Denon DCD-1600NE CD/SACD player ($1,200) and/or compare with the new Mark Levinson No.5101 CD/SACD player/DAC ($5,500)? :-) .........

JHL's picture

...you could compare the half of Fidel's last Cohiba Esplendido found wedged between the wall behind the desk and a tattered copy of Imperialism, and Clinton's sodden version of same found under the Resolute desk four days into the subsequent administration.

Because we're all in the market.

Bogolu Haranath's picture

One of them involves a 'blue dress' in the mix :-) ........

Bogolu Haranath's picture

I may choose a 'Wide Churchill' instead :-) ........

tonykaz's picture

Wasn't it QUAD that assured us that they came closest to the original?

While I was flying-in ( importing ) Air Containers of Quad 63s ( back in the day ), Quad people were bragging about "musical fidelity", Reviewers were supporting Quad's assurances. My customers bought all the Quads I could get into the Country. I wasn't a believer.

I do have the "Feeling" that Mr.Derda takes care to only represent high performance gear and that Mr.HR's evaluation is probably valuable, just not for me, this time.

For this 21st Century Quad to have genuine credentials it'd have to be made in the same place Quad was original, the place where "closest to the original" hung on the Production wall, the place where the Postman brought the day's mail on a Raleigh Bicycle.

As it stands, matching this device with Chinese loudspeakers seems appropriate.

So I ask the missing question: Why not just buy a bunch of Schiit?, Stoddard & Moffat are "our" newest Peter Walkers.

Tony in Venice

ps I've always felt Mr. Derda was a good person.

Bogolu Haranath's picture

HR said, Artera Solus CD playback came 'closest to the original', almost :-) ........

The Times They Are a-Changin' :-) ........

Bogolu Haranath's picture

The promise of 'perfect sound forever', finally fulfilled? :-) ........

Ortofan's picture

... will excel on a null test?

Do most audiophiles really want an amplifier whose objective performance exemplifies what QUAD's Peter Walker termed a "straight wire with gain"?

Or, would they rather have one that sounds, in some subjective manner, more "pleasant"?
https://www.stereophile.com/content/manufacturers-comment-0

tonykaz's picture

That test must have value to someone, for an important reason.

I can't answer any Schiit questions. I do realize that Schiit make dam good gear. ( what is dam good? seems like oppisotes )

A Null test for me is reading unenthusiastic & uninspiring reviews about another Chinesium, does-it- all, Best Buy Shelf siting SKUs.with legendary Brand Names.

What sings significant is that Mr.Dedra scored a product review by the reviewing industry's Poet Laureate. I'm hoping for a QUAD 11 Classic integrated 4_ KT66s & 4_12AX7s Review by someone.

Fingers Crossed

Tony in Venice

Ortofan's picture

... used to demonstrate the extent to which the performance of QUAD amplifiers resembled a "straight wire with gain."

As for a QUAD II Classic integrated review, Art Dudley did that deed nearly a decade ago:
https://www.stereophile.com/content/quad-ii-classic-integrated-amplifier
So have others:
https://www.hifinews.com/content/quad-ii-classic-integrated-%C2%A34500
http://www.hifiplus.com/articles/quad-ii-classic-integrated-amplifier-hi-fi-73/

While you're more than welcome to the QUAD, I'd prefer the Luxman LX-380.
https://www.speakershop.com/product/luxman-lx-380-vacuum-tube-integrated-amplifier-lx-380

tonykaz's picture

Geez, I've never owned any Luxman piece.

I've never had a Luxman in on trade.

I've never even known anyone that owns a Luxman

or

known anyone displeased with Luxman.

Hmm.

I just checked eBay to discover about 100 pieces of Luxman are selling per month from US owners, from the low $100s to about $3,000! Global eBay sales 150 Luxman pieces from about $100 ranging to $7,000!

There are plenty of eBay Luxman integrated Amps in the $3,000 range.

Hmmm, Luxman ( along with Sugden ) seems another Brand I've forgotten that I would like to own and enjoy.

Thanks for the reminder.

Tony in Venice

ps.. a Clean Luxman piece is "Obviously" resealable for 120% of purchase price, it's a Brand with Integrity.

Bogolu Haranath's picture

Artera Solus may be a better value for the money than several integrated amps selling under $3k, because it has a built-in CD player, hi-res DAC and multiple DAC filter options :-) .......

Bogolu Haranath's picture

I'm waiting for some one to come up with a name 'pleasant (sounding) filter' on their DAC :-) ........

Dr.Kamiya's picture

The narrow filters seems a bit too narrow. 44.1kHz files cut off at just 10kHz?

Bogolu Haranath's picture

There is a pending firmware update ........ See manufacturer's comments :-) .......

David Harper's picture

Except when the CD player eventually starts malfunctioning in some way (which most of them tend to do in my experience) I'm completely S.O.L. But then I guess I could just continue streaming.

count.de.monet's picture

He'd probably be so angry he'd jimmy slap that stupid integrated into the skip as they call it there over on that side of the pond. Where the fuck is the emoji button?

Hummer189's picture

Hi Herb,

I read in your review that you used Audirvana for you digital files, could you let me know what settings you use in Audirvana?

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