Devialet D-Premier D/A integrated amplifier Measurements

Sidebar 3: Measurements

I measured the Devialet D-Premier with Stereophile's loan sample of the top-of-the-line Audio Precision SYS2722 system (see www.ap.com and the January 2008 "As We See It"); for some tests, I also used my vintage Audio Precision System One Dual Domain. I measured the later, black-finish sample, serial no.00965, the mirror-finish no.00061 having been sent off for photography. Before testing an amplifier with a conventional class-B or -AB output stage, I precondition it by running it at one-third power for an hour, which thermally stresses the amplifier to the maximum extent. In theory, this test is irrelevant with the Devialet, but I did so anyway. At the end of the hour, the left side of the top panel was hot to the touch, at 131.4°F (55.3°C), the right side a little cooler, at 114.3°F (45.8°C). It might be efficient at converting wall current into speaker-driving power, but the D-Premier still runs hot. As Devialet warns in the D-Premier's manual, the amplifier needs to be well ventilated.

I didn't test the phono input's performance, as I didn't use it during my auditioning for this review. The phono stage's sound and measured performance will be covered in a Follow-Up.

The rotary volume control on the Devialet's remote control covers a range of "–97.5dB" to "+30.0dB" in accurate 0.5dB steps. With the control set to "+30.0," the voltage gain into 8 ohms for an analog source and a line input was a high 52.3dB. At "0.0dB," the gain, of course, was 22.3dB. The analog inputs preserved absolute polarity (ie, were non-inverting), and the analog input impedance was moderately low, at 14k ohms at low and middle frequencies, dropping slightly at 20kHz to 12.5k ohms.

Devialet specifies the D-Premier's output impedance as <0.001 ohm. I measured 0.04 ohm at all audio frequencies, but thus includes the impedance of the 6' of speaker cable I used for the test. But the fact that the D-Premier has an extraordinarily low output impedance can be seen in fig.1, where the voltage drop as the load changes from 8 to 4 ohms, and the variation in response with our standard simulated loudspeaker, are each less than 0.1dB. Even with a 2 ohm load (green trace), the level drops by less than 0.2dB in the audioband. With the D-Premier in its standard configuration, pressing the middle bottom button on the remote rolls off the low frequencies by 3dB at 20Hz (not shown).

Fig.1 was taken with the A/D converter that digitizes the analog inputs set to the default of 96kHz sampling. As a result, the response can be seen to drop like a stone above 40kHz, and a 10kHz squarewave has the distinctively rounded shape that is due to the absence of all harmonics above the third (fig.2). The 1kHz squarewave (not shown) has the usual time-symmetrical ringing visible preceding the start of each change in level (not shown).

Fig.1 Devialet D-Premier, analog frequency response with volume control at "0.0" at 2.83V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green), simulated loudspeaker (gray) (0.25dB/vertical div.).

Fig.2 Devialet D-Premier, small-signal 10kHz squarewave into 8 ohms with A/D converter on analog inputs set to 96kHz sampling.

Channel separation via the analog inputs was excellent, at >100dB in both directions below 2.5kHz (not shown). The D-Premier is specified as having a superb signal/noise ratio of 130dB, but without conditions or reference level given. My standard test with an integrated amplifier is to short-circuit the input but set the volume control to its maximum, which is very much the worst-case condition (some have called it unrealistic). With its very high gain, the D-Premier is put at a disadvantage under these conditions. I measured the wideband, unweighted S/N, ref. 1W into 8 ohms, to be a fairly low 47.1dB in the left channel and 48.5dB in the right. Restricting the measurement bandwidth to the audioband improved these figures to 51.6 and 52.3dB, respectively, while switching in an A-weighting filter gave further improvement, to 54.9 and 55.2dB. Reducing the level of the volume control will improve these ratios, of course, and fig.3 shows the low-frequency spectrum of the D-Premier's output while it reproduced a 1kHz tone at 100W into 8 ohms with the volume control set to "0.0dB." The noise floor is a little higher in the left channel than in the right, and rises by 10dB as the frequency decreases. The only other thing to note in this graph is the presence of a power-supply–related tone at 120Hz, but at –110dB ref. the level of the 1kHz tone, this is inconsequential.

Fig.3 Devialet D-Premier, spectrum of 1kHz sinewave, DC–1kHz, at 100W into 8 ohms (linear frequency scale).

The Devialet is specified as having a maximum output power of 240Wpc into, I understand, 6 ohms (22dBW). Fig.4 shows how the THD+noise percentage changes with output power into 8 ohms.1 The downward slope of the trace below the "knee" indicates that what distortion is present is actually buried in the noise floor. We define clipping as the power when the THD reaches 1%; fig.4 shows that the D-Premier was putting out 180Wpc into 8 ohms (22.55dBW) at 1% THD. Fig.5 shows the behavior into 4 ohms. The trace is similar in shape to that into 8 ohms, except that, very unusually, it slopes backward above the "knee," which occurs at 245.8Wpc into 4 ohms (20.9dBW). What is happening is that, with sustained drive at very high power, either the power supply starts to collapse or the DSP protection starts to operate, both reducing the power delivery. Because of this behavior, I didn't test the maximum power into 2 ohms.

Fig.4 Devialet D-Premier, distortion (%) vs 1kHz continuous output power into 8 ohms.

Fig.5 Devialet D-Premier, distortion (%) vs 1kHz continuous output power into 4 ohms.

I plotted how the output power changes with frequency at a level, 20V, equivalent to 50W into 8 ohms and 100W into 4 ohms, where the power supply would remain stiff. The results are shown in fig.6. Below 10kHz, the measurement is dominated by noise; above that frequency, and unlike a conventional class-D amplifier, there is almost no rise in THD. However, I haven't shown the behavior into 2 ohms as, again, the power-supply voltage would start to decrease after a few seconds' operation at 20V.

Fig.6 Devialet D-Premier, THD+N (%) vs frequency at 20V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta).

The lower trace in fig.7, taken at a level just below the discontinuity in fig.4, confirms that actual distortion in the D-Premier's output is buried beneath the noise. However, FFT analysis reveals there to be harmonics present at high powers, albeit at a very low level (fig.8). The two highest in level, the second and third harmonics, lie at –106dB (0.0005%) and –104dB (0.0006%), respectively, with all other harmonics lying at or below –110dB (0.0003%). Conventional class-D amplifiers tend to perform poorly when fed high-frequency intermodulation. By contrast, the D-Premier, given a mix of 19 and 20kHz tones at a peak level of 20W into 4 ohms (the highest level the amplifier would deliver with this signal without the power supply collapsing), performed well on this test (fig.9). The 1kHz difference tone lay at almost –110dB, and the higher-order intermodulation products were all below –90dB (0.003%).

Fig.7 Devialet D-Premier, 1kHz waveform at 150W into 8 ohms (top), 0.0022% THD+N; distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.8 Devialet D-Premier, spectrum of 1kHz sinewave, DC–10kHz, at 100W into 4 ohms (left channel blue, right red; linear frequency scale).

Fig.9 Devialet D-Premier, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 20W peak into 4 ohms (left channel blue, right red; linear frequency scale).

Turning to the D-Premier's digital inputs, I measured its performance at the speaker outputs, as that is how I used the amplifier. With the volume control set to "0.0dB," a full-scale 1kHz tone resulted in a level of 30.79V into 8 ohms, equivalent to a power of 118.5Wpc, just under 2dB below clipping into this load. This suggests that, with digital inputs, the volume control should be kept below "+1.5dB." The digital inputs were again non-inverting. Although the S/PDIF and AES/EBU inputs locked on to datastreams with sample rates from 32 to 192kHz, including 88.2 and 176.4kHz, the "AIR WiFi input was restricted to 96kHz and below.

Fig.10 shows the D-Premier's frequency response for its digital inputs with data sampled at 44.1, 96, and 192kHz. Unusually, the 192kHz rate gives only a slight increase in bandwidth compared with 96kHz. Digital channel separation (not shown) was similar to that for analog inputs. To remain consistent with the measurements of DAC resolution I have performed since 1989, I used a swept-bandpass technique to generate the traces in fig.11, which represent a dithered tone at –90dBFS with 16- and 24-bit data. Repeating the analysis with a modern FFT technique gave a similar picture (fig.12), confirming that the only power-supply–related spuriae present was a small amount of 120Hz, at –110dB. The increase in bit depth from 16 to 24 with both these graphs dropped the noise floor by around 12dB, implying a resolution of 18 bits or so, which is good, if not quite up to the standard set by the best-measuring standalone processors, such as the Bricasti M1, MSB Diamond DAC IV, NAD M51, or Weiss DAC202.

Fig.10 Devialet D-Premier, digital frequency response at –12dBFS into 8 ohms with volume control set to "0.0" and data sampled at: 44.1kHz (left channel blue, right gray), 96kHz (left cyan, right magenta), 192kHz (left green, right red) (0.25dB/vertical div.).

Fig.11 Devialet D-Premier, 1?3-octave spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS, with: 16-bit S/PDIF data (top), 24-bit data (bottom) (right channel dashed).

Fig.12 Devialet D-Premier, FFT-derived spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS, with: 16-bit S/PDIF data (left channel cyan, right magenta), 24-bit data (left blue, right red).

There is some peculiar scalloping of the noise floor visible with 24-bit data in the right channel in fig.12 (red trace). I am not sure what this means. Repeating the analysis with 16- and 24-bit data over WiFi using the D-Premier's AIR input and the Devialet iTunes streamer gave an anomalous result (fig.13). With 16-bit data, the 1kHz tone lay at the correct –90dBFS in the left channel (cyan trace), the noise floor lay at the correct level, and no harmonics were visible. However, the right channel's noise floor (magenta trace) lay about 5dB higher in level. Even more peculiarly, sending 24-bit data gave only a slight lowering of the noise floor in the left channel (blue trace), but a raising of the floor in the right channel (red). I tried rebooting the D-Premier by unplugging it from the wall and then powering it back up, but this did not restore proper operation with 24-bit data. This was with v.1.4.0 of Devialet's AIR client; I imagine it is something that can be fixed in a future software or firmware release.

Fig.13 Devialet D-Premier, FFT-derived spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS, with: 16-bit AIR data (left channel cyan, right magenta), 24-bit data (left blue, right red).

With S/PDIF and AES/EBU data, the D-Premier's reproduction of an undithered sinewave at exactly –90.31dBFS was essentially perfect (fig.14), with undithered 24-bit data giving a well-defined sinewave (fig.15).

Fig.14 Devialet D-Premier, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit S/PDIF data (left channel blue, right red).

Fig.15 Devialet D-Premier, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit S/PDIF data (left channel blue, right red).

Feeding the D-Premier a 24-bit version of the 44.1kHz Miller-Dunn J-Test via one of the TosLink inputs gave the spectrum shown in fig.16. No data-related jitter components are visible. However, a pair of sidebands around the 11.025kHz tone at ±120Hz can be seen. Although these lie below –120dBFS (0.0001%) and are presumably irrelevant to sound quality, they perhaps result from some power-supply interference at the DAC's voltage-reference pin. Repeating the test with Devialet AIR WiFi data gave rise to the same 120Hz sidebands (fig.17), but now some broadening of the central peak can be seen. And as with fig.13, the left channel's noise floor (blue trace) is not much lower than the 16-bit floor, while the right channel's floor is significantly higher in level (red). I suspect that this loss of resolution via WiFi is the reason I ended up preferring using a standalone USB-S/PDIF converter for the bulk of my auditioning of the D-Premier.

Fig.16 Devialet D-Premier, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit data via TosLink from AP SYS2722 (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

Fig.17 Devialet D-Premier, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit data via AIR from Mac mini (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

Other than its slightly anomalous behavior via WiFi, the Devialet D-Premier's measured performance is a testament to what can be obtained with switching-amplifier technology. However, sustained high-power operation into speakers with an impedance of 4 ohms or below is best avoided.— John Atkinson



Footnote 1: Because the D-Premier's output stage includes a class-D element, I performed all the distortion measurements using Audio Precision's AUX-0025 high-power, passive low-pass filter between the amplifier's output and the SYS-2722's input. But this really didn't appear to be necessary; unlike with the class-D amplifiers we reviewed in December, I could detect no ultrasonic switching noise in the D-Premier's output.—John Atkinson
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COMMENTS
mphatic1's picture

John,

 

In your opinion, how does the Devialet's pre-amp/DAC section stack up against the Classe CP-800?  I ask this because they both appear to be cut from the same cloth so to speak; beautifully styled, apparent 18 bit resolution, switching amp/power supply, highly configurable, and relatively future proof.  And, when you start to add power amps to the CP-800, you get up around Devialet money anyway.

 

Regards,

Brad

JadenKrosis's picture

"the most extraordinary product I have reviewed for Stereophile."

Considering the very long list of other very extraordinary products you`ve had your hands on, this says alot!

rumnyc's picture

but in the end went with a slightly more conventional setup.

for exactly the same price as a D-Premier, I went with a Linn Akurate DSM and Mcintosh MC452 amp. I couldn't compare them back to back but I like the below features from the Linn:

4 HDMI input instead of 1 (yes I could have used an outboard HDMI switcher).

Ethernet input and DLNA server compatible (AIR feature was not yet released)

And the Mcintosh had way more headroom than the D Premier's amp.

My speakers are B&W 802 Diamond.

stgomes's picture

 

After some very good 1st impressions on sound quality driving "conventional" speakers (impedance curve not bellow 2-3 Ohm) I was curious to audition the D-Premier with my Martin Logan Summit X speakers. Sound quality is very good, until I pumped up the volume. At about 85db, the protection LED on the front panel starts blinking and the amp starts to mute.

I have reported this problem to Devialet and they say it should not happen, but my dealer had the same experience with other D-Premier units driving other Martin Logan models (Montis, Spire, CLX).

My guess is that this amp technology is simply not designed to drive impedance loads like the ones present in Martin Logan speakers, which drop bellow 1 Ohm in the high frequencies.

Looking forward to your comments.

John Atkinson's picture

Quote:
My guess is that this amp technology is simply not designed to drive impedance loads like the ones present in Martin Logan speakers, which drop bellow 1 Ohm in the high frequencies.

That's what I expect, too.

John Atkinson

Editor, Stereophile

BradleyP's picture

Notice that with the new SAM technology, two Martin Logan speakers have been matched to the Devialet--the Theos and the Electromotion. Now, I am wondering about Maggies. If Devialet can both drive and tame those big bass panels, then that would be even more amazing.

jlesnick's picture

Hey John.

Thanks for this great review. How do you feel the Devialet (and its new iteration) would stack up to a Pass X250.5/Classe Cp-800 combo?

Cheers,

Jon

John Atkinson's picture
jlesnicj wrote:
Thanks for this great review.

You're welcome.

jlesnicj wrote:
How do you feel the Devialet (and its new iteration) would stack up to a Pass X250.5/Classe Cp-800 combo?

I haven't heard the XA20.5 but the Pass XA60.5s have been my go-to amplifiers for the past year. The beauty of the Devialet is that it is just one box, with a digital section up there with the Classe. A review of one of the less-expensive Devialets is in progress.

John Atkinson
Editor, Stereophile

bapcha's picture

JA/Other reviewers:

You guys are a prime example of promoters of peddlers of snake oil. If an Airport (Mac) or a Ayre CD player feeds data to a D/A you claim to hear a difference. How can you - when the data is exactly the same?

Let's take Boulder - I like the look of their products, but how would a volume knob - polished seven times and clear-coated - improve sound quality? It is a bloody waste of money.

Cheers,
Bapcha (yes, I am a marketer who can see through your ____)

John Atkinson's picture
bapcha wrote:
You guys are a prime example of promoters of peddlers of snake oil.

Good morning to you, too.

bapcha wrote:
If an Airport (Mac) or a Ayre CD player feeds data to a D/A you claim to hear a difference. How can you - when the data is exactly the same?

Yes, the data may be the same, but the timing of when those data are presented to the D/A chip is also important. Variations in that timing are called "jitter" and result in distortion in the reconstructed analog signal. The right data at the wrong time is equivalent to the wrong data. There are several articles on this subject reprinted in our free on-line archives.

bapcha wrote:
Let's take Boulder - I like the look of their products, but how would a volume knob - polished seven times and clear-coated - improve sound quality?

No-one has said that it does.

John Atkinson
Editor, Stereophile

bapcha's picture

I will keep the conversation very respectful. I am a chip designer with ten plus years designing analog and digital chips and, and ten more marketing them and SSDs. Four issued patents (primary author). Most chips now have PLLs. After it locks, it does not matter if the jitter is 5 pico seconds or 50 pico seconds, the data can be PERFECTLY reconstructed (or the designer will lose his job, and chip cannot be sold).

You claim to hear differences in jitter between 5ps and 50ps - when the data is PERFECTLY reconstructed post-jitter.

YES - you can hear a difference in ANALOG products. If a DAC has a DIFFERENT analog output, it will sound different from a cheaper one with a not so well designed output.

Also, FYI, it is easier to match currents on chips without trying too hard (it is called a common-centroid layout where transistors are laid our perfectly symmetrically (x and y axes). It is not too hard to make chip-based output stages that sound better than discrete (but it is cost-prohibitive). I own Bryston/Ayre stuff with properly designed circuits, and sincerely believe it is impossible to do better (note the word impossible).

I have collected serial data from a $10K Boulder DAC and a $1000 Bryston Dac. I gave up after 10 GigaBytes. The data was exactly the same. So, 24x oversampling = 4x oversampling = 2x oversampling (I know that you know the Nyquist-Shannon theorem). It is a fool's game after one gets past the Bryston/Ayre A* (not the K*) price point.

Word length matters. Sampling rate does not. If it does, then I have a TV that shows pictures in X-ray.

Even James Tanner of Bryston has admitted that the differences between their BP10/17/26/SP3/SP2 analog stages are identical or have minuscule (inaudible) differences.

Bottom-line: Looks like I am half way agreeing with you and half-way disagreeing with you.

Sincerely yours,
Bapcha

John Atkinson's picture
bapcha wrote:
I am a chip designer with ten plus years designing analog and digital chips and, and ten more marketing them and SSDs. Four issued patents (primary author). Most chips now have PLLs. After it locks, it does not matter if the jitter is 5 pico seconds or 50 pico seconds, the data can be PERFECTLY reconstructed (or the designer will lose his job, and chip cannot be sold).

An impressive resume. So with respect, I am puzzled that when you refer to phase-locked loops (PLLs), you don't seem aware that a PLL circuit has a corner frequency, below which it increasingly fails to eliminate jitter in the incoming datastream. You can see the effects of this problem in the various digital products that I test for for Stereophile. Some are very effective at eliminating the effects of datastream jitter; others are wide-open to timing variations in the data presented to the DAC.

bapcha wrote:
You claim to hear differences in jitter between 5ps and 50ps . . .

We have made no such claim, any more than we have claimed, as you accused us in your earlier comment, that the finish of the volume control on a Boulder preamplifier affects sound quality.

John Atkinson
Editor, Stereophile

bapcha's picture

Thanks for your kind and timely responses.

Bottom-line: JA - we all have our biases. Bottom-line is the you run the best publication for reviews of music reproduction electronics. Today, a Cisco router can transmit ALL of the data from the Library of Congress from point to point - in about four seconds. Yet - there is room for endless back and forth for a trivial range of frequencies. Let's call it 0 Hz to 100KHz. When we have mastered 10s of gigahertz, we should be able to do this trivial range in frequencies easily, cheaply, perfectly, every single time - and yet we don't. My take is that it is due to the EMOTIONAL component of this trivial data "band" if you may.

I wish you and your magazine the best. (I know Robert Greene rather well. He is a colleague of my uncle's at UCLA math)

John Atkinson's picture
bapcha wrote:
Bottom-line is the you run the best publication for reviews of music reproduction electronics.

Thank you.

bapcha wrote:
Today, a Cisco router can transmit ALL of the data from the Library of Congress from point to point - in about four seconds. Yet - there is room for endless back and forth for a trivial range of frequencies. Let's call it 0 Hz to 100KHz. When we have mastered 10s of gigahertz, we should be able to do this trivial range in frequencies easily, cheaply, perfectly, every single time - and yet we don't.

That the transmission of digital data without errors is a given. But it is when those data are used to reconstruct an analog signal that problems in implementation arise.

bapcha wrote:
I wish you and your magazine the best. (I know Robert Greene rather well. He is a colleague of my uncle's at UCLA math)

Thank you. But I am wondering if you are confusing Stereophile with The Absolute Sound. Robert Greene writes for TAS, and has never contributed to Stereophile.

John Atkinson
Editor, Stereophile

bapcha's picture

Nice guy anyway. Took him a long time to switch to digital, and solid state.....

Sincerely,
Bapcha

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