Volume 5 No. 2
Another DAC Called Rega DAC
Rega's nomenclature might lack imagination, but Chris Bryant discovers that tis new DAC is a bit special.
Review By Chris Bryant

     I'm writing this on the day that digital music download sales passed £1billion in the UK. Even the most sceptical of us now have to accept that computers have some credibility as a music source, and even hardened audiophiles are being sucked into the unquestionably convenient medium of streaming music from them. Indeed, high resolution music files have the potential to offer some improvement over the long established 16-bit CD format.

However, computer based audio still has some way to go before it challenges the best CD players, and this is particularly true if the computer audio is transferred directly to a hi-fi system. Hi-fi companies have therefore been busily introducing new components, especially DACs (digital-to-analogue converters), in the quest to improve the transfer and hence the sound quality available from computer sources.

Rega might be one of Britain's better established and more successful hi-fi brands, but its roots in vinyl turntables and long term commitment to analogue techniques meant that it was also one of the last to embrace digital audio and introduce CD players. Once Rega had taken the plunge, its CD players proved very successful, and the company's new and unimaginatively named DAC is based on techniques developed for its recently introduced upmarket Isis CD player (Volume 3 Number 4).

A relatively affordable standalone unit priced at £500, the Rega DAC hits the currently hot and rapidly growing market sector of affordable DACs head on. Finished in satin silver or satin black, it has a sturdy case with substantial aluminium side extrusions, moulded plastic back and front, and steel top and bottom panels. Fit and finish is up to Rega's usual high standards.

Thanks in part to its Isis heritage, the digital to analogue converter circuitry is capable of playing 16/20/24-bit encoded material, with sampling rates from 32kHz to 192kHz. It has the input facilities to operate with all the usual digital sources that provide a two channel PCM digital audio signal: CD, DVD and Blu-ray players, plus PCs or other streaming devices (but no iPod dock is included). There are five inputs in total: two co-axial electrical and two TOSlink optical S/PDIF inputs, plus one isolated USB input. These may only be selected via the fascia buttons, as no remote control is included.

The unit is designed and engineered to perform way above its contemporaries, exploiting user selectable digital filters, separate parallel Wolfson WM8742 24-bit DACs using delta-sigma architecture, with buffered digital data inputs, and with discrete-transistor multiple-feedback analogue filters that use higher cut-off frequencies for the higher sampling rates. The output buffer is very similar to the one used in the Isis CD player. Efforts have been made to remove noise generated in any digital sources, including PCs.

Many DACs have sample rate converters to provide low-jitter asynchronous data, but Rega chooses to keep things simple by using synchronous clocking with the incoming data using a Phase Lock Loop to minimise jitter. The Wolfson DACs themselves are also claimed to have a high tolerance to clock jitter.

The interior is neatly laid out with a single double-sided PCB carrying all the important circuitry, while a separate front panel board supports all the switching and indicators. A decent sized multi-winding toroidal transformer feeds two diode bridges, followed by Nichicon FG power supply reservoir capacitors. Chip regulators are used, and while most of the circuitry has surface-mount components, some through-hole components are used where necessary. A separate power supply circuits used for the micro-controller to help reduce noise in the important digital and analogue stages, and numerous electrolytic caps are bypassed by polyester film types to help the high frequency performance. The on/off button operates a two pole mains switch and the fuse can be accessed on the rear panel. The analogue output is relay muted, and all the wired inputs use high frequency transformers to help isolate the unit from the outside world while preserving digital signal integrity. The mains input socket isn't the familiar flat-pin IEC type but a smaller round 3-pin (cloverleaf ) connector.

Three domed square silver buttons form a line on the front panel. One selects power on/off (confirmed by an illuminating Rega logo); another selects the digital filter setting; the third cycles through the five inputs. Fifteen little indicator lights provide relevant status feedback, confirming data lock, showing the incoming data sample rate, and which digital filter is selected.

The five selectable digital filter characteristics differ somewhat according to the sample rate of the incoming data, and are described in the accompanying Box. Trying to choose the best setting for each track is the sort of thing that can drive one a little mad. But they can also be very useful at times to balance a particular recording to taste.

 

DAC's Progress
Although the original hi-fi DACs (Digital to Analogue Converters) used ‘multi-bit' technology, which still has a high end following. But it's rarely encountered nowadays, and the vast majority of today's DACs use ‘low-bit' conversion technology. This offers exceptional measurements, beguiling the technocrat with its obvious technical ability, but subjectively it often still fails to excite those in search of musical perfection. The design of DAC chips has now progressed to provide a high 24-bit linearity, and it has become very easy to put together a few chips from the major silicon manufacturers and produce a digital audio product of exceptional technical competence. However, it still seems to take the specialist skills of a dedicated audio engineer to get the best sounds from them.

 

Lab Results
Time spent in the lab measuring only proved how linear the Wolfson DAC is, with no linearity error recorded down to below 100dB. The frequency response is very flat and is only -0.1dB at 10Hz into a 100 kohm load; it's just possible to see some filter ripple on some settings at high frequencies. Distortion alters little with frequency, measuring -85dB, which isn't as low anticipated given the specific linearity, but is very good nonetheless (likely contributed by the analogue stages). Channel separation is excellent: 100dB at 1kHz, falling slightly at the audio band extremes but still easily bettering -80dB. Channel balance is almost perfect at 0.016dB, and the intermodulation distortion at full level is a low -93dB. The signal-to-noise ratio is an excellent -107dB (A weighted), while the output was marginally high at 2.17 Volt. There was no DC offset.

 

Sound Quality
I'm not normally too fond of low-bit DACs but here I'm going to make an exception. I had been playing the Rega DAC with my computer as the source, through some desktop monitors, and when I replaced it with another, already recommended product, I was surprised how much I missed it. In every department it totally outclassed the cheaper replacement I had installed. Rega's DAC is just very likeable, free from any annoying vices and with no extra hard edges. However, it's by no means bland. It just gets on with making music enjoyable, and times quite well too in the context of my computer system. It was also very good for listening to talk radio as it seemed to make presenters' diction more intelligible.

In my reference system I found a little more to criticise. The high treble sounded slightly mechanical, and it had a little sibilant emphasis and hardness lower down the band. However, the soundstage is rather good, with fine focus, very good depth and excellent width. Timing is good too, in fact rather better than most DACs I have listened to over the last few years, and rhythms are well controlled. Not many can better it for musical integrity, and it creates a fine atmosphere.

Using a CD as the source, filter No3 seemed to be the best setting, making a very clean piano recording sound open and spacious. On filter No1 it sounded smooth but lacked some detail and dynamics, and the bass sounded a little slowed, even though it came over as powerful and well defined. Although some (admittedly rather more expensive) DACs have better spaciousness and transparency, the Rega is always delicate and detailed. I played with the filter settings on high-definition material to good effect and found my preference depended on the recording. Sometimes it can be difficult to hear differences, but changing to another track often results in better discrimination.

I had the same musical track in both 16-bit and 24-bit formats, and that increase in resolution was easily heard, the hi-res material sounding quicker with better nuances and cleaner highs. I could go on talking about the differences between the filter settings, but in themselves these do not define the quality advance that this Rega delivers against similarly priced opposition. If compared to the best high end products, the Rega DAC can be bettered in all areas of performance, but I can't recall hearing another under-£2000 DAC that can surpass it.

 

Conclusions
There is very little to dislike here. At £500, the Rega DAC is a class above the competition, and it can stand comparison with DACs costing several times its price. I gave it a score of 55 on high resolution material which makes it the best so far in this sector. It is strongly made with good components and should give years of trouble free music so it has to get a strong recommendation.

 

Digital Filter Types
For lower sample rates
(32/44.1/48kHz):
1 Linear phase half-band filter
2 Minimum phase soft-knee filter
3 Minimum phase half-band filter
4 Linear phase apodising filter
5 Minimum phase apodising filter

For medium & high sample rates (88.2/96 & 76.4/192kHz):
1 Linear phase soft-knee filter
2 Minimum phase soft-knee filter
3 Linear phase brickwall filter
4 Minimum phase apodising filter
5 Linear phase apodising filter

 

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