REVIEW: HEGEL HD25 DAC

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by Marc Rushton

24th March, 2014

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REVIEW: HEGEL HD25 DAC

The HD25 from Norwegian AV manufacturer Hegel, is the brand’s flagship Digital-to-Analogue Convertor (DAC), or ‘Digital Hub’ in their words.

Developing their first DAC in 1994, two years before even releasing their own CD player, Hegel has enjoyed great success as a highly respected brand in the hi-fi world.

The Hegel philosophy, at least in my interpretation, is “more for less”. By that, I mean that Hegel believes in refining their design and circuitry to extract the absolute best performance, rather than opting for using exotic (and expensive) components and materials, in a run-of-the-mill circuit design and architecture.

“With Hegel's patented technology we are able to get better sound quality through regular "off-the-shelf" components, than our competitors can with esoteric and expensive components.”

This is a win for the consumer. Sure you can buy what could be perceived as higher grade products, but the resulting overall performance may not necessarily be any greater, for a higher outlay.

The Hegel HD25 enters the DAC or ‘digital hub’ market at a higher end price of $3,995 RRP. In comparison to the majority of DACs on the market this is considered a premium price, but let’s keep in mind there are numerous DACs from other brands at two and three times the price, and more.

The RRP of a product is dictated by a company’s investment in research and development for a particular product, the market demand, manufacturing costs, and of course the resulting performance. In this regard, I feel the Hegel HD25 carries a premium price, but backs it up with performance. But I'm getting ahead of myself.

So when the news broke of Hegel’s new flagship, forums lit up with comments, in particular regarding the HD25 aesthetics. Sadly, the released photos didn’t do the product justice, and with the lack of accompanying feature list and specs, a lot of assumptions were made.

Hegel HD 25 Angle

The HD25 measures a compact 210mm W x 60mm H x 260mm D and weighs in at only 3kgs. With a bead-blasted aluminium black faceplate and a painted steel case, it is easy to understand why, until you see a unit in the flesh, its aesthetics could have been prematurely criticised. The truth is it’s a solid, well-constructed unit, which looks quite at home amongst other high end components in your hi-fi rack of choice.

With minimalist design in mind, the faceplate is actually quite high-tech. Input selection, of which there are four (2 x Coax S/PDIF, USB, Toslink S/PDIF), is selected by double-tapping the faceplate. At first read of the manual this seemed like more of a novelty “because we can” feature, but after living with the HD25 for some time it becomes quite a likeable feature. Keep tapping to scroll through the inputs, without having to read fine print or fumble a dial or button in the dark.

The credit card sized remote control, will likely find its way to the deep canyons of your favourite listening chair (along with a heap of coins and your best guitar pick).  Personally, I would have liked to see an aluminium remote resembling the swish design and thought that went into the state of the art faceplate.

The market seems to be entering a new era for DACs, and we can see where Hegel is coming from with their reference to ‘Digital Hubs’. We’re seeing second and third generation DACs appearing in the market now, and the HD25 has a few features in its repertoire above and beyond those of many of today’s traditional DACs.

The HD25 has a built-in pre-amplifier and with the aforementioned remote control and multiple input source selection, the HD25 could quite easily become the heart of any hi-fi system. This could negate the need for a dedicated pre-amplifier in many cases.

There are three methods of synchronising a DAC over USB; Synchronous, Asynchronous and Adaptive.  To offer a little insight, Synchronous works via a real-time stream and is therefore avoided in DACs due to high levels of jitter.

Asynchronous is governed by a fixed speed clock in the DAC, with a feedback loop regulating the amount of data sent by the source. Adaptive mode is more flexible in that the speed of the clock in the DAC adapts to the amount of data sent by the source.

Hegel HD25 Internal

Debate exists amongst audiophiles and designers over the two, but Hegel engineers believe Adaptive sounds best, opting for that mode with the HD25.

One notable design feature of the HD25 is the power supply. I’m not a big fan of wall based or external power transformers - it’s not so much about the component that they are connected to, but I’m always more concerned about the noise they inject back through the AC circuit to other devices that are connected.

Opening the covers on the HD25 reveals a beefy power supply with a large toroidal transformer, and 30,000µF of capacitance. Combined with silicon-germanium transistors, you can’t help but remember the Hegel philosophy of simple design mated with excellent implementation.

“These components add extremely low levels of noise, resulting in unsurpassed levels of resolution and a more natural and pleasant sound.”

Hegel’s HD25 makes use of a 32bit/192 kHz multilevel sigma-delta DAC, which will support up to 24bit/192 kHz high-resolution material. The HD25 features a selector on the rear (A/B) relating to the USB digital input. Shipping from the factory in position ‘A’ (24/96), the theory is that the HD25 is ready to go out of the box. If you’re wanting the 24/192 facility (B), then according to the manual you will need to install drivers (if using a computer source).

Hegel HD25This caused me to have some reservations. I don’t use a computer source, per-say. Would it be possible to achieve 24/192 USB resolution without a computer source?

You see the HD25 arrived at just the right time. My audio journey had seen me recently heading down a digital streaming path, determined to achieve at least CD, or better than CD playback sound quality, from 16bit/44kHz and higher resolution material. The end result of this journey is very loosely described here, but ultimately, I can reveal the HD25 played an instrumental role, if not vital, in the final result.

One interesting feature I found was the ability to switch between two different digital filters (or ‘methods of timing’). From the remote, there is a selection between ‘F1’ and ‘F2’. I did notice an audible difference but it was certainly quite subtle. Probing Hegel’s technical team further didn’t result in any more information on what is taking place. In the end, I selected F1 or ‘normal’, as it just felt right.

Jumping in I flicked the switch to (B), being the higher resolution setting (24/192), made the connections and hoped for the best. At that time I was utilising a Squeezebox Touch (SBT) from Logitech, which most readers in the streaming world would know requires some custom firmware and kernels to play files of higher resolution than 24/96, namely Triode’s ‘Enhanced Digital Out’ or EDO, from USB and S/PDIF.

Initially, I was unsuccessful, unable to get a sync between the SBT and the HD25. After some configuration tweaks and an alternative kernel, I was up and running. My previous concerns about drivers with a non-traditional PC source were unnecessary it seemed.

All FLAC resolutions were supported, indicated by a little known feature of the HD25 that Hegel’s support team was nice enough to tell me. Press and hold the ‘Input’ button of the remote control and the resolution of the current material is briefly displayed. I’m not entirely sure why this isn’t promoted, or better yet, the option given to cycle the resolution on the display at all times. That would be an appreciated feature.

I’ve had a number of DACs through my system in the journey I mentioned (Burson Audio, Beresford, Bel Canto, to name a few), each with their nuances, and while my almost immediate response to the Hegel HD25 was very positive, I had not yet achieved that CD quality sound in A/B tests that I was seeking.

The HD25 had already revealed more than other DACs in my system, and at this point I was quite sure I had reached the limit of potential the Squeezebox Touch could offer, and therefore shifted to a Wandboard based source (outlined in my overview link above).

Hegel HD25 Rear

I find that it can be difficult to describe what is being heard, in universally understood terms, when writing about comparisons of digital audio playback. Perhaps most obvious is compression, grain and dryness, aside from more common, subjective terminology. Or at least, they were the issues I was confronted with most prominently in my comparisons up to this point.

With my new source configured with ease I was straight back into my listening tests.

Hegel’s HD25 ticks all the boxes. Soundstage cues are all present; width, height, depth, multi-layered 3D stage etc, perhaps governed more by other components in the system. But more subjectively, ‘musicality’, being predominantly what I had been lacking in previous digital streaming components, had arrived with the HD25. Any remnants of compression, grain and a ‘digital’ dryness had disappeared.

Hegel HD25 Resolution Display

I discovered the HD25 had unlocked the Wandboard’s full potential, but to be sure I had to compare against some of the previous DAC’s I had used in this setup. Changing between DACs confirmed my feeling that the HD25 is a ‘true DAC’, in that there is little to no colouration of sound and the output is true to the source. This transparency is, in my opinion, an important criterion for pre-amplifiers and DACs.

My digital streaming solution was complete, at least for now. The Hegel HD25 had become a vital component in the chain.

With consideration given to features and performance, the Hegel HD25 is a well-designed, dependable DAC that will reveal the full resolution of your sources, without any bottlenecks or colouration.  With added features such as a built-in preamp, digital filters and a swag of inputs, it would be just at home as the heart of an ultra high-end active speaker hi-fi system, as it would if used within a PC-based headphone solution.

Specifications (as advertised):

  • DAC resolution: 32bit / 192 kHz multilevel sigma-delta DAC
  • 0dBFS signal output: 2,5V RMS
  • Digital inputs: 1*USB soundcard, 2*coaxial and 1*optical S/PDIF
  • Line outputs: 1 pair of RCA unbalanced, 1 pair of XLR balanced
  • Frequency response: 0 Hz to 50 KHz
  • Phase response: Linear Phase Analogue filter
  • Noise floor: Typically -145 dB
  • Distortion: Typical 0,0006%
  • Power supply: Built-in toroidal transformer, 30,000 uF capacitors
  • Output impedance: 22 ohms unbalanced and 44 ohm balanced
  • Dimensions/weight: 6cm * 21cm * 26 cm (H*W*D), 3,5 Kg
  • Dimensions/weight US: 2.35" x 8.3" x 10.24" (HxBxD), weight 7 lbs

For more information visit Advance Audio.

Marc Rushton's avatar

Written by:

Marc Rushton

StereoNET's Founder & Publisher and still buried deep in the review room auditioning everything from docks to soundbars, amplifiers and headphones. Marc is also the founder of the annual International HiFi Show.

Posted in: Hi-Fi
Tags: hegel  hd25  dac  advance audio 

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