Sidebar 3: Measurements
When he reviewed Channel D's Lino C 2.0 phono preamplifier in his June 2019 Analog Corner column, Michael Fremer wrote, "My ears instantly accepted its combination of drop-dead, noise-free backgrounds and lack of obvious colorations or sonic personality." He concluded, "After a few months of listening, my initial enthusiasm and appreciation for the Lino C 2.0 continues." I had been impressed when I performed the measurements to accompany MF's review of Channel D's earlier Seta L phono preamplifier in August 2010 (so much so, in fact, that I purchased the review sample), so I asked for a sample of the Lino C 2.0 to measure.
Like the Seta L, the Lino C 2.0 is powered by a rechargeable battery. However, that's where the resemblance ends. Whereas the Seta L used conventional voltage-mode circuitry, the Lino operates in current mode, amplifying the output current generated by a moving-coil cartridge (footnote 1). Its input impedance is effectively a short circuit. I measured the Channel D Lino C 2.0 with my Audio Precision SYS2722 system (see the January 2008 "As We See It"), which is intended for use with voltage-mode devices. I therefore used the adaptor lead I had constructed to measure the Sutherland Little Loco phono preamplifier. I soldered a precision 10k ohm resistor in series with each of pins 2 and 3 of a male XLR plug, then soldered a 10 ohm resistor between those two pins. The Audio Precision's balanced output stage would thus see an appropriately high 20k ohm load, but the signal presented to the preamplifier would be typical of an MC cartridge. This setup attenuated the Audio Precision's signal level by 67dB, a 1kHz signal with a level of 1V resulting in 437µV at the preamplifier's input.
After performing preliminary testing with this cable, I continued the testing with a two-channel, balanced attenuator module supplied by Channel D's Rob Robinson. This performs the same function as my cable but offers adjustable attenuation; I set it to reduce the signal level by 66dB. It can also be adjusted to simulate different cartridge source impedances; I left it at the default setting of 6 ohms. The following measurements were made with the Channel D module but were no different than the ones I took with my own adaptor cable, other than being in stereo rather than mono.
The Lino was operated on battery power for the testing. The preamp preserved absolute polarity, and its output impedance was a low 73 ohms, balanced, and 10 ohms, unbalanced, from 20Hz to 20kHz.
Each channel of the Lino has DIP switches to increase the gain by 6dB or 12dB compared with a nominal value (footnote 2). (The switches are concealed by rubber covers on the Lino's bottom panel.) With the switches set to the medium position, "+6dB," I measured a gain at 1kHz of 69dB, which is a little on the high side for a moving-coil cartridge. Setting the switches to "0dB" reduced the gain by exactly 6dB; with them set to "+12dB," the gain was increased by 5.93dB compared with the medium-position gain.
The Lino featured superbly accurate RIAA equalization, the best I have measured (fig.1). This graph also reveals the extremely close channel matching. Channel separation was excellent—greater than 86dB in both directions above 1kHz (fig.2). The Lino's unweighted, wideband S/N ratio, measured with the input shunted with the 6 ohm resistor and with the medium gain setting, was a good 63.3dB (average of both channels), ref. 1kHz at 500µV. Restricting the measurement bandwidth to 22Hz–22kHz increased the ratio to a respectable 65dB, while switching an A-weighting filter into circuit increased it further, to 72.2dB.
Footnote 1: See Jim Austin's "As We See It" in the February 2020 issue. Footnote 2: Other DIP switches allow the RAA equalization to be disabled, to optimize the Lino for needle drops made with Channel D's Pure Vinyl app.
Fig.1 Channel D Lino C 2.0, response with RIAA correction into 100k ohms (left channel blue, right red) (0.5dB/vertical div.).
Fig.2 Channel D Lino C 2.0, medium gain, channel separation ref. 1kHz at 1mV input (R–L blue, L–R red, 20dB/vertical div.).
Spectral analysis of the Lino's low-frequency noise floor with the input shunted by the 6 ohm resistor (fig.3) revealed that random noise components were very low in level. (I had to hold the attenuator module well away from the analyzer's host computer in order to prevent the unshielded and relatively high-impedance module from picking up some interference at 60Hz and 180Hz from the PC's power supply.)
Fig.3 Channel D Lino C 2.0, medium gain, spectrum, DC–1kHz, of output ref. 500µV input with input shunted with a 6 ohm resistor (left channel blue, right red, linear frequency scale, 20dB/vertical div.).
The Channel D Lino C 2.0 offered vanishingly low distortion before the onset of clipping. Fig.4 shows the spectrum of the Lino's output with the input fed 1kHz at 1mV. No distortion harmonics can be seen above the noise floor! When I reduced the load impedance to the punishing 600 ohms, the third harmonic made an appearance, but this was at –87dB (0.004%). The Channel D also had extremely low levels of intermodulation distortion (fig.5). With its gain set to "0dB," the Lino's overload margin was a good 14.65dB across the band, though this margin decreased by 6dB for each 6dB increase in gain. I recommend Lino owners use the lowest gain setting that gives acceptable loudness with their favorite moving-coil cartridge.
Fig.4 Channel D Lino C 2.0, spectrum of 1kHz sinewave, DC–10kHz, into 100k ohms for 1mV input (left channel blue, right red, linear frequency scale).
Fig.5 Channel D Lino C 2.0, HF intermodulation spectrum, DC–30kHz, 19+20kHz into 100k ohms for 100mV peak input (left channel blue, right red, linear frequency scale).
Considering its superbly accurate RIAA equalization, low noise, and vanishingly low distortion, I am not surprised that Michael Fremer was impressed by the Lino C 2.0's sound quality.—John Atkinson
Footnote 1: See Jim Austin's "As We See It" in the February 2020 issue. Footnote 2: Other DIP switches allow the RAA equalization to be disabled, to optimize the Lino for needle drops made with Channel D's Pure Vinyl app.
