COS D1 digital converter/preamplifier

Solid-state preamplifiers,
Digital-to-analog converters
COS Engineering D1
COS D1 digital converter/preamplifier

If one were to judge this particular book by its cover it would not be hard to come to the conclusion that an awful lot of effort and expense had gone into the casework and perhaps that’s all there is to it. The COS D1 does have a spectacular chassis, but thankfully a lot of effort appears to have gone into its circuitry as well. Machined from solid aluminium, the D1 chassis has but the one control; however, as its the sexiest knob on the audio planet we can forgive its minimalism. Especially as the rotary protruding from the top gives lets you access everything this DAC/preamplifier can do.

COS is a young Taiwanese company and the D1, its first product, was launched two years ago; a second, apparently more affordable design, looks like it will be released soon. COS stands for ‘connoisseur of sound’ and the D1 specification suggests that the people behind it do know more than most about audio electronics, for example they have devised a custom algorithm for upsampling incoming data to 24-bit at either 176.4kHz or 192kHz using integer multiples at 32-bit precision. This is an effort to avoid a conventional IIR filter which they consider likely to “contaminate phase”. Its digital inputs have a one second buffer prior to conversion, and COS claims sub-picosecond jitter precision from their re-clocking circuitry. There is no mention of high PCM sample rates or DSD in the literature, but under scrutiny it seems that the D1 is good for DSD up to 128 and PCM up to 384kHz via the USB input: the S/PDIF inputs cater for DSD 64 and up to 192kHz, although where you’d get either from is open to debate.

A dual transformer-based power supply is used to feed analogue and digital sections discretely: the D1 has both types of input so it can be used as a preamplifier in the full sense, if one balanced and one single-ended analogue input is enough. And COS means fully balanced: the whole device operates that way because the company is keen to keep noise at bay. The DAC chips themselves are stereo devices running in mono to produce that balanced output, “manually tuned” to achieve distortion figures 6dB below spec.

Alongside the balanced and SE in- and outputs for analogue are four S/PDIF connections and a USB input, the latter fully asynchronous as you’d expect and able to operate in switchable Class 1 or 2 mode. There’s another switch on the back marked BUF, which indicates the buffer mentioned above: it’s best left on unless you are trying to synch pictures and sound in an AV seting. Build quality on the outside is very high indeed: if this were the creation of an established European or North American brand the price would be considerably higher for reason of fit and finish alone. The remote handset is equally attractive and hewn from the same material; it offers volume and input control as well as mute and standby, which does not apper as an option on the front panel. The only drawbacks of this DAC/pre’s minimalist appearance is that you have to remember which input light corresponds to which source, and a complete lack of a headphone output, whch seems odd for a 2016 device.

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