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COS D1 digital converter/preamplifier

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.

, COS D1 digital converter/preamplifier

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.


Those looking for a line level output from the D1 will find that the only way to achieve this is to set the volume control to maximum, illuminating all the lights underneath the control. Once you select an input you are left with a single small white LED that flashes if it’s not locked to a signal. Controversially the left and right channel in and outputs are inverted so that red is on top but even an experienced reviewer can figure out stuff like that given time! It comes with a set of impressive looking spike feet that screw onto the base but I have never been keen on the sound of spikes on glass shelves (as found on my Townshend Seismic stand) so left them off and used soft pucks of the large and rubbery variety. The resulting sound had remarkable delicacy and finesse. For example, ‘La Cancion Sophia’ is one of the quieter pieces from Corea, Clarke, and White’s Forever [Concorde Records] and the COS revealed just how low its noise floor is by unveiling oodles of fine detail at the quieter end of the spectrum, with strong imaging from the piano, bowed double bass, and cymbals, with the latter exhibiting greater reverb than you usually hear.

This was followed by Barenboim’s take on the Vivace of the ‘7th Symphony’ [Beethoven for All, Symphony No. 7 in A, Op. 92, 24/96, Decca]. Here the fine detail was equally well served, but the slow build up proved even more riveting. The weight of the plucked basses low down in the mix and the way that Barenboim delivers the tension and release of the piece shows that the COS can do dynamic range as well as low level detail. The two are of course facets of the same quality; the quieter a system is the more scope there is for dynamic expression. This also illuminates the fact that the COS does not indicate the sample rate of the incoming signal; I guess with high res, you are always using a streamed source of some form and such details should be available elsewhere, but it’s nice to have confirmation that it’s getting to the DAC.

I had a Bryston BD3 DAC on hand during the COS’s tenure and so made a few comparisons with a coaxial source. This revealed that the COS is a sweeter sounding, softer edged converter that gives away some ground in terms of the leading edge definition that makes detail more easily discerned. The Bryston also reproduces more of the acoustic scale of the recording. But these are chalk and cheese converters, the COS having a smoothness and finesse that those of a more romantic bent would likely prefer to the visceral clarity of the Bryston. It did make me wonder about the feet though (!), so big spikes were installed and the D1 sat upon small Bluehorizon damped receptors. This proved to be a better approach than the heavily damped pucks and injected a stronger sense of timing without undermining the subtlety of the DAC. Now it could do immediacy with greater effect and delivered more expansive soundstaging; in fact with better recordings there was acres of space and depth to enjoy.

, COS D1 digital converter/preamplifier

I also contrasted it with the Primare PRE60 reviewed elsewhere in this issue – a more likely competitor given its functionality and price. The PRE60 also upped the ante in terms of power and definition, adding stronger dynamics in the process when driven by a USB source. The COS on the other hand sounds more composed and more interested in savouring the moment than riding the leading edge. The sax on Herbie Hancock’s version of ‘Ain’t Necessarily So’ [Gershwin’s World, Herbie Hancock, Verve] has great tone; it positively oozes out into the room with excellent stereo solidity. The tempo is steady and seems very natural and when the next piece comes on Joni Mitchell’s voice is beautiful, full of expression and nuance, fully reflecting the nature of Mitchell’s sound on one of her last recordings.


As a preamplifier the D1 is pretty good, though it can be bettered; taking its output up to a Townshend Allegri with the volume maxed does increase resolution quite obviously, but it’s no slouch on its own. I tried both balanced and single ended connections albeit with different power amps and got a good result in both cases. With a balanced hook up to an ATC P1 Laura Marling’s ‘Friends’ [Once I Was An Eagle, Virgin] revealed what must be all of its layers; there are not that many instruments on it but more than you might think. Led Zeppelin’s ‘Immigrant Song’ [LZ III, Atlantic] is very compressed by comparison, but there’s no avoiding the power and drive that this DAC delivers when the signal warrants it.

The COS D1 is a beautiful piece of equipment; it has the sort of finish that puts it firmly in the pride of ownership camp and the fact that it combines two of the key functions necessary in a high end system is very useful. The electronic design is almost as unique as the physical one and a lot of thought has gone into achieving a particular sound rather than tweaking with the output stage. Its character is in the marmite category; you’ll either let it lie or love it, and those looking to get to the heart of their digital libraries could well be in the latter camp.


  • Type: Solid-state PCM digital-to-analogue converter/preamplifier.
  • Digital Inputs: Two Coaxial, two Toslink, and one buffered USB class 1.0 or 2.0.
  • Analogue Outputs: One stereo single-ended (via RCA jacks), one balanced (via XLR connectors). Both outputs have variable level operation.
  • DAC Resolution/Supported Digital Formats: All PCM up to 192KS/s with word lengths up to 24-bits.
  • Frequency Response: 20Hz–20kHz, ± 0.1dB
  • Distortion (THD + Noise): < 0.001%, –100dB, 20Hz–20kHz non weighted
  • Output Voltage (DAC): 2Vrms at maximum (unbalanced), 4Vrms at maximum (balanced).
  • User Interface: IR remote handset.
  • Dimensions (H×W×D): 100 × 415 × 280mm
  • Weight: 8.6kg
  • Price: £7,000

Manufacturer: COS Engineering

URL: www.cosengineering.com

UK Distributor: G-Point Audio

Tel: +44 (0)1435 86 55 40

URL: gpoint-audio.com

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