go to: Contents | On The Horizon | Feature | Disc Players | DACs | Music Servers & Accessories | Integrated Amps with USB DACs | Music Download Reviews | Buyer's Guide Equipment reviews DACs SPONSORED BY Click here to turn the page. 34 Digital Source Components www.theabsolutesound.com previous page NEXT page
go to: Contents | On The Horizon | Feature | Disc Players | DACs | Music Servers & Accessories | Integrated Amps with USB DACs | Music Download Reviews | Buyer's Guide EAR-Yoshino 192 DACute DAC Maximum Analog, Minimum Digital Dick Olsher When Tim de Paravicini set out to design the DACute, I’m fairly certain that he sought to maximize its analog footprint. After all, analog is his métier. In fact, he freely admits to trying to equate digital performance to good analog practice, the payoff being that smooth and soothing sonic sensation analog tape and vinyl provide so well. Take, for example, the DACute’s DAC chip, a Wolfson WM8741 multi-bit delta-sigma DAC. It’s a high-performance stereo DAC designed for audio applications. It supports PCM data-input word lengths from 16- to 32-bits and sampling rates up to 192kHz. The folks at Wolfson included a smorgasbord of features such as fine resolution of volume and soft-mute control, digital deemphasis, and a range of advanced digital filter responses. The digital filters include several selectable roll-off and performance characteristics. Tim’s approach was to minimize use of the internal digital filters. Because they cannot be totally bypassed, he set them for the highest frequency point and then implemented analog LC elliptic filters for 3dB down at a frequency of 40kHz. This is the sort of analog filter Tim has always used on analog tape recorders for bias and other ultrasonic-noise filtering. An LC elliptic filter is rather economic in terms of parts count for a given slope, but does produce a nonlinear phase response over its passband. In Tim’s view, the filters “are quite good as far as phase response is concerned over the audio band to about half an octave away from 3dB down, so up to 20kHz is more than good enough for me.” According to Tim, all these DACs by Burr-Brown, TI, Wolfson, or whomever produce significant high-frequency (HF) noise. Tim believes that it’s important to filter out HF hash lest these artifacts upset some amplifiers and tweeters. However, he still requires that response at 20kHz be within 0.1dB of the midband and frowns on the practice of rolling off the top end for so-called sweetness. The DACute uses a Cirrus SPDIF receiver and accepts up to 24/192 digital data from USB, coaxial SPDIF, and TosLink SPDIF inputs. After passing through the analog filters, the signal is fed to a line preamp stage that is configured like a single-ended amplifier. A 6922/ECC88 twin triode is used per channel. The two sections are cascaded with the second stage being transformer coupled. The output transformer incorporates two secondary windings, one of which provides unbalanced and the other balanced output. A tertiary winding provides some feedback. Maximum output is said to be 5V into 500 ohms with reasonable distortion figures. Tim says that he’s not interested in vanishingly low distortion levels at max output since “we hear best the stuff that goes on at lower levels, just where many digital systems fall down.” Dan Meinwald, the U.S. EAR distributor, sent along a pair of Philips JAN 7308 tubes, of which he is fond. And I have to agree; the Philips sounded gorgeous in this application and represents a big step up from the stock 6922. Needless to say, it didn’t take me long to make that call, and the Philips was used for the remainder of my listening tests. There’s not much to say about the motorized volume pot, except that I found the remote control a bit touchy to adjust and, as with other such volume controls, difficult to set to reproduce a particular volume setting. The presence of a volume control combined with an exceedingly low output impedance of under 60 ohms make it possible for this DAC to directly drive a power amp. However, should you desire to go through a preamp, simply set the volume control to about 2pm and let the preamp do the rest. Of course, one would expect some loss of immediacy when the signal is made to pass through two volume controls, and I can confirm that the most transparent soundstage to be had was with the DACute directly driving a power amp. The fact that the output stage is tube amplified and transformer coupled is quite significant. In my experience, a DAC or CD player’s output stage plays a major role in its overall sound quality. Quite frequently this boils down to the mitigating effects of tubes versus transistors. Call it heretical or even anachronistic, but in my view digital wants tubes—digital needs tubes. Tubes are the requisite “cavalry” to the rescue with a dose of textural warmth and liquidity. Even in the highest echelons of high-end audio, the presence of a solid-state output buffer or gain stage often makes for a double whammy—digital crispness aided and abetted by solid-state tonal-color blindness that makes toast out of musical textures. And it’s that sort of a sorry combination that has pushed many discerning listeners away from digital sources and back to vinyl and analog tape. I’ve been advocating for many years the insertion of tubes, as early as feasible, into a digital front end as a means of controlling digital nasties. And that’s exactly what Tim has done, and it’s also the basis for ModWright Instruments’ modification of the Sony XA-5400ES SACD player. At the heart of Dan Wright’s Truth Mod is a 6SN7-based output stage, which replaces the op-amp-infested stock analog stage. Not only that, but the tube stage is powered by an external high-voltage tube-rectified power supply. The Sony looks a bit odd with a couple of 6SN7 triodes sticking out of its top deck, but it has been a staple in my reference system for several years now. It really is that good. Naturally, I was curious to see how the DACute stacked up against my modified Sony. This comparison played out with the Sony acting as a transport for the EAR DAC, connected to one of its SPDIF inputs. Since both units are tube based I expected some common ground, especially when it came to imaging performance. And while that, indeed, was the case, the DACute outperformed the Sony/Truth Modification in several areas, at least in the context of a high-efficiency speaker being driven by the Triode TRX-M300 monoblocks. It 35 Digital Source Components www.theabsolutesound.com previous page NEXT page
Change language