Linn Majik DS-I D/A integrated amplifier John Atkinson April 2011
Art Dudley reviewed the Linn Majik DS-I in the March issue and found that, when fed audio data over an Ethernet network, this D/A amplifier "presented a more open, nuanced, explicit, involving, and altogether natural musical experience than any USB-based digital source I've heard."
Strong words! But when I measured the DS-I before dropping it off at Art's place, I couldn't get it to recognize the music server on my home network, and therefore ended up doing all the digital-domain measurements using one of the Linn's optical S/PDIF inputs. After writing his review, Art shipped the review sample back to me, along with the router, Ethernet switch, and NAS drive that Linn's distributor had sent him.
Setting up a network to retest the DS-I via Ethernet was straightforward: plug the router, DS-I, and NAS drive into the switch and let the DS-I set itself upwhich it did without any problems. I then needed to transfer some of my test-signal WAV files to the NAS drive, which I did by hooking up my test-lab PC to the Linn network, then dragging and dropping the files on a new folder on the drive. Still, I then had to re-index the drive so that the new files would be recognized by a uPnP music player, in this case Songbird DS running on an iPod Touch.
To perform the measurements, I again used Stereophile's loan sample of the Audio Precision SYS2722 system (see the January 2008 "As We See It" and www.ap.com); I also used my Miller Audio Research Jitter Analyzer. As with the S/PDIF connection, the Ethernet input preserved absolute polarity and successfully locked to data with sample rates of up to 192kHz. Data representing a full-scale 1kHz tone gave a result at the DS-I's Line Out jacks of 1.92V, as had the S/PDIF input.
Fig.1 shows the FFT-derived spectra of the signal at the DS-I's Line Out, while it decoded 16-bit data (cyan, magenta traces) and 24-bit data (blue, red) representing a dithered tone at 90dBFS via the Ethernet connection. As before, the traces peak at exactly 90dB, suggesting minimal linearity error; and with 24-bit data, the noise floor was about 10dB lower than it was with 16-bit data. This implies a resolution of around 18 bits.
Fig.1 Linn Majik DS-I, FFT-derived 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).
In the measurements taken for Art's review, I'd found that the Linn's rejection of jitter via its S/PDIF input was dependent on the source component. Via the RME soundcard in one of my test-lab PCs, a TosLink connection gave 454 picoseconds peakpeak of word-clock jitter, as assessed by the Miller Analyzer housed in the same PC. This was due mostly to sidebands at the data-related frequencies of ±229 and ±689Hz. However, these sidebands disappeared when the same 16-bit data were fed via TosLink from the Audio Precision SYS2722 (fig.2) and the jitter level dropped below the threshold of the Miller Analyzer.
Fig.2 Linn Majik DS-I, high-resolution jitter spectrum of analog output signal, 11.025kHz at 6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz, 16-bit S/PDIF data via 15' TosLink from SYS2722. Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz (left channel blue, right red).
Repeating the measurement with the Ethernet connection gave an analog output spectrum that was very slightly noisier than with the TosLink-connected SYS2722 (fig.3), with the Miller Analyzer indicating jitter levels of 93ps pp (left) and 87ps pp (right). This is still superbly low, although very low-level sidebands are present at ±101, ±183, ±201, and ±400Hz. I have no idea from where these spuriae arise.
Fig.3 Linn Majik DS-I, high-resolution jitter spectrum of analog output signal, 11.025kHz at 6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz, 16-bit S/PDIF data via Ethernet from NAS. Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz (left channel blue, right red).
Basically, the measured performance of the Ethernet-connected Linn Majik DS-I is identical to that via S/PDIF. While there are small differences in the jitter rejection via the two digital connections, they are at the resolution limit of my test gear.John Atkinson