HIFICRITIC OCT | NOV | DEC 2014 1

HIFICRITICWWW.HIFICRITIC.COM ISSN 1759-7919

REVIEWED THIS ISSUE: SOUNDKAOS WAVE 40, GRAHAM AUDIO BBC LS5/9, DALI ZENSOR 1, NVA BALANCED MAINS UNIT, HENRY AUDIO USB DAC 128 MKII, NDS + 2X555PS, THRAX SPARTACUS, VALVE AUDIO DEVICES DAC-12 DSD, SONUS FABER OLYMPICA II, NEAT MOTIVE SX2, LEAK SANDWICH, VALVE AMPLIFICATION COMPANY SIGNATURE MK IIA, APPLE EARPOD, SENNHEISER HDVA 600, SENNHEISER HDVD 800, TRILOGY 933/900, VERTEX AQ HIREZ SOLFONN, PHILIPS FIDELIO X2, RUSSELL K RED 50

AUDIO REVIEW MAGAZINE £15 Vol8/No4 OCT - DEC 2014

KAOS RULESPaul Messenger tries out the extraordinary Soundkaos Wave 40, an Anglo-Swiss confection that redefines the full-range driver loudspeaker

MUSIC WITHOUT WIRES (OR STANDARDS)It’s getting easier to stream music wirelessly, but there’s no shortage of competing standards to confuse consumers, says Andrew Everard

I’M SPARTACUSThe Thrax Spartacus valve monoblock is the finest amplifier Chris Bryant has ever heard

NAIM NDS PLUS 2x 555PSMartin Colloms tries out Naim’s flagship NDS streamer/DAC with twin 555PS power supplies. Does streamed audio replay get any better than this?

REVIVING THE LS5/9With assistance from ex-Spendor Derek Hughes, Graham Audio has reincarnated the BBC LS5/9, a compact stand-mount with an illustrious monitoring pedigree

CHEAP BUT VERY CHEERFULDali’s Zensor 1 is probably the cheapest speaker HIFICRITIC has ever reviewed, It’s also rumoured to be a serious bargain. Paul Messenger checks out the rumour mill

SANDWICH ANYBODY?60 years on, Martin Colloms re-assesses Leak’s famous Sandwich loudspeaker, with surprising results

MUSIC & MORE

HFC_issue36 9.indd 1 13/12/14 14:47:38

22 HIFICRITIC OCT | NOV | DEC 2014

■ REVIEW

Spartacus RulesTHRAX’S VALVE-BASED MONOBLOCK POWER AMPLIFIER IS CALLED SPARTACUS, AND IT HAS REALLY GOT CHRIS BRYANT GOING

Two years ago I encountered an expensive Orpheus phono stage from a Bulgarian operation called Thrax (see HIFICRITIC Vol6

No4), and was somewhat surprised to find it was the best sounding amp of the type I’d thus far experienced. I’ve since been eagerly awaiting another product from the brand, and in September a pair of Spartacus monoblocks arrived. After unpacking, inserting the valves and connecting it to my system, it was left to settle down for a few minutes, but after only the first few bars of music it was obvious that it was something rather special and demanded to be heard. There is no secret to the performance of Thrax equipment: it’s clearly explained in the literature. A preferred technology is chosen, such as a simple short signal path with zero feedback. The best bits currently available are painstakingly selected and put together very carefully, while careful design then ensures everything continues to run with optimum operating parameters. Thrax describes its approach as ‘engineering overkill’ and isn’t prepared to stop development until it sounds just right. Add the elegantly understated styling and excellent build quality to create a component that at first sight appears anachronistic until its design is fully appreciated. Spartacus is a two stage, shunt regulated, monoblock power amplifier, using directly heated triodes and with a claimed output of up to 70W into 4 or 8ohms. Two rectifier choke input power supplies feed film reservoir capacitors, so there are no electrolytics to age and need replacing every few years, and sound quality should be improved too. Each stage has its own shunt regulators, each with a constant current feed. The input signal goes straight into a high quality transformer which leads into a driver stage that uses a single directly heated triode operating with grounded cathode and fixed bias. This is loaded with a special Japanese transformer that couples via independent windings into the grids of the output valves. The output stage uses a pair of directly heated triodes driving a costly Japanese permalloy-core transformer. Automatic biasing uses innovative thermal circuitry, and the heater filaments are powered by low noise voltage controlled current sources. Each amp weighs around 35kg, the casework made from different thickness aluminium panels

machined from solid aircraft grade billets, with a moondust type finish. Since there’s no cover underneath it’s possible to see the two large circular fans part concealing the mains transformer and choke that hang centrally from a mid-mounted dividing plate. This brings the centre of gravity down, so the smaller signal transformers can be mounted on the top panel while still maintaining stable equilibrium (and away from any mains transformer or choke flux leakage). The sensitive electronics are housed in another cavity below the valves. The case outside is totally clean, and looks like a solid block – and at 35kg it feels like one when moving it around. One small criticism is that the panels have sharp edges, and with no base it’s not the most comfortable lift. Our early sample had no valve guard, but I gather one is normally available (for EU safety standards). A large round silver ‘on’ button sits in the middle of a elegantly sculpted front panel. The front has only an on off switch: first a red LED flashes, turning to green three or four minutes when the amp is biased and ready for use. A built in timer tracks the valve operating time, a speaker impedance switch selects 4 or 8ohm operation, and another switch selects low, medium or high input gain. The output stage is a matched pair of costly 520D B3 directly heated triodes – a state of the art product based on the 300B tube but more efficient, with higher gain and better bass control. The input driver is a highly regarded PX25 triode with an SV811-10 used in the shunt regulator, two 6D22C rectifier valves and an SG13P glow discharge voltage reference. Costly Furutech Torque Guard speaker binding posts have pre-set torque settings to prevent over tightening. Inputs include one unbalanced RCA/phono socket and one balanced XLR with a illuminated switch for selection. The heart of the amplifier is the PX25 direct heated triode, which is a rather pessimistic mark of the lack of progress made over the years in the art of sound amplification. Originally a British design first introduced in 1932, it sounds beautiful but has limited power (only a few Watts), and it is still used by triode-enthusiastic audiophiles. The massive 520B output valves are a development of the famous Western Electric 300B which first appeared in 1938. The valve designs have therefore

HIFICRITIC OCT | NOV | DEC 2014 23

REVIEW ■

CHRIS BRYANT

been around for a few years, though the ones used in this design, sourced from Emission Labs, are thought to be the best currently available. A servo circuit keeps the anode current in both output valves constant, so they continue working perfectly as they age, and balance the DC component in the output transformer. Heater supplies come from a separate transformer winding, feeding a rectifier and capacitors; a matching voltage regulator and gyrator ensure a stable, low noise heater current. One key to formalising this design is the use of advanced modern magnetic materials and the latest transformer fabrication techniques, but attention to detail is also an important factor.

Lab ReportI thoroughly tested this object just in case some technical anomaly was fooling me about the sound, and managed to get 55W into 8ohms and 42W into 4ohms at 1kHz using the preferred 8ohm output tap. At 20kHz, 25W was measured for 8ohms and 32W into 4ohms, while it was less successful at 20Hz, producing only 11W for visual oscilloscope distortion into 8ohms,and I got no reliable figure for 4ohms at 20Hz. These figures are actually quite reasonable for a low feedback valve amplifier of this type, while the dominant midrange power output is particularly encouraging. The output impedance of 2.5ohms in the bass and midrange then rose slightly to 2.8ohms at 20kHz, which is much as expected, and may well introduce some audible change in timbre with some loudspeakers (potential purchasers please note). At 1W, midrange harmonic distortion is low at -68dB (roughly 0.03%), and HF intermodulation distortion was an equally encouraging -53dB (about 0.2%), and a very good signal-to-noise ratio was recorded 84dB (A-weighted at 1W). On ‘high gain’ the 168mV input sensitivity will suit a wide range of pre-amplifiers. Although the frequency response rises by almost 2dB at 20kHz, and below 200Hz falls to -1.8dB at 20Hz, it’s essentially flat through the important midrange region. This behaviour is not unusual with this type of amplifier, and I consider it has little impact on the listening experience. These amplifiers do get quite hot, consuming (and therefore radiating) about 400W each. Local cooling is down to a commendably quiet fan, and while such heat might be fine in winter, it can be a little too much for comfort on a warm summer day.

Sound QualityThe Spartacus is capable of more musically realistic reproduction than any commercial amplifier I’ve heard to date. The observation that it’s so sweet

and subtle, and produces such an exceptionally interesting sound is almost intoxicating. Everything you thought you knew well now sounds better, easier to listen to, and with less listening fatigue. Textures are lusher, the stage is more realistically portrayed, and every phrase has more meaning. Voices sound more natural and are substantially more articulate. It doesn’t matter whether it’s jazz, a string quartet, solo violin, massed orchestra, choral or modern synthesised pop and rock – all are rendered more enjoyable and exciting than I’ve been used to, and old recordings sound revived. Spartacus invariably seems able to extract more information from sources than was previously thought possible, and improving the source produces better sound quality. But the ability to extract more from what is fed into it also seems an almost unreal skill for a power amplifier. Its micro-dynamic reproduction is exceptional, and extra audible nuances are now a delightful experience. For example, backing vocals that were previously masked are now revealed. It has you going back to listen again and again, and leaves you wondering why the many other amplifiers I’ve experienced had managed to obscure so much information. Surprisingly and delightfully, midrange percussion has real power and natural dynamics, bringing greater realism to hi-fi reproduction. Percussion also sounds startlingly realistic in the upper bass. Focus is top class, with great stage depth, image stability and precision. The treble is detailed and coherent, with excellent ‘shimmer’ that’s as natural and complete as the silky smooth and very coherent midrange. True, the bass doesn’t have the thump and sheer power of the best transistor amplifiers, but it has

“The observation that it’s so sweet and subtle, and produces such an exceptionally interesting sound is almost intoxicating. Everything you thought you knew well now sounds better, easier to listen to, and with less listening fatigue”

24 HIFICRITIC OCT | NOV | DEC 2014

■ REVIEW

Thrax Spartacus Frequency Response 1W (Red) and Distortion (Green) 8 ohms load

plenty of detail and an impressive ability to reveal pitch and structure. Timing is not quite as up beat as the fastest solid state designs either, but it still has rhythm in spades due to the plentiful detail and wonderful dynamic contrasts. Its presentation is thoroughly beguiling and its musical phrasing just draws you in. It also has a wonderful start/stop quality, so the listener doesn’t have to guess exactly where a note starts and finishes. It simply explains just how each sound and nuance is carefully structured in great recordings, allowing real artistry to be revealed in the most unlikely places. All the recordings I tried, both new and old, digital and analogue, had their story retold, making it essential for me to try and re-visit my entire music collection, in order to discover exactly what had been previously left unexpressed. Trying the three gain settings, the highest gave a slightly looser sound: less incisive, but sweet and still clear, though not quite as beguiling. Low gain was tighter but not quite as interesting, sounding less rich and generous. The middle setting proved the best in my setup. Furthermore, the 4ohm speaker tap sounds less transparent than the 8ohm example, and not as dynamically interesting in either a gross or micro-dynamic way, whatever the actual speaker load. Piano doesn’t sound as natural, showing a

bit of extra ring at the top of the scale, and music doesn’t seem to flow in the same mellifluous way. It just sounds less immediate, losing some of the almost magical ability shown on the 8ohm tap and that middle gain setting. I tried various speakers, including Magico S5s and my own familiar full range 8ohm system, and this amplifier never failed to produce that extra fidelity. It even managed to enhance the entertainment quotient of TV sound, the Thrax simply improving the diction and intelligibility of everything I watched. It might not transform the indifferent TV sound quality that the BBC, for example, seems to think is good enough for its audience these days, but it makes the most of a bad situation. (I tried to watch one of the Proms broadcasts but the sound was so undynamic and bland I gave up after about five minutes. Yes I know I should have listened on Radio 3 but I really expected they would try to provide decent sound quality for what is, after all, a flagship music programme.)

ConclusionsI only had these amps for a limited period, but kept hold of them for as long as possible simply to revel in their amazing abilities, and even managed to get them back for a second visit to consolidate my early opinion. I don’t take the word amazing lightly in the context of hi-fi (or anything else for that matter), but Spartacus certainly had a startling effect on me. I certainly want a pair, but at £32,000/pair it’s not a purchase that can be taken lightly. Since these monoblocks are typically only capable of 50W, they may not go loud enough for owners of modern low efficiency speakers. But anybody who wants really convincing music in the home should either get hold of some live performers, or choose a compatible loudspeaker, sacrifice the ultimate in sound level, and try some Thrax gear. Certain even lower power purist triode amplifiers might conceivably sound even better in specific systems, but will never drive the wide range of loudspeakers as effectively as Spartacus. (An alternative might be to use a home cinema system for the loud stuff and set up a purist hi-fi system for exquisite personal musical experiences.) The Thrax Spartacus amplifier is not perfect – nothing is. It could be slightly more up beat and have better bass impact in the lower octaves, but the rest of the sound is so amazing, these small shortcomings can be easily forgiven. Scoring is difficult, but it has an array of attributes that are comparatively lacking in the others I’ve heard, so on balance 250 points seems appropriate, and I find it very easy to place it in the Audio Excellence class.

MC CommentsAfter a warm up, and playing through Magico S5s that were still running in, I was entranced by this power amplifer’s sheer musicality. Its outstandingly natural acoustic sounds, excellent resolution, great communication skills, and driving sense of performance, was very seductive. Familiar material was rendered in a more complete manner, and one instinctively knew that this sound was simply more correct. It somehow amalgamated many separate strands of known detail and quality into a superior whole. Musically it delivered more natural timbres, greater expression, and a deep, glowing soundstage, and the familiar limitations found with less stratospherically priced power amplifiers were clearly absent.

AUDIO EXCELLENCE

POWER AMPLFIER TEST RESULTSMake Thrax _________________________________________________Model Spartacus Ser. No. 312302_________________________________________________POWER OUTPUT 20Hz 1kHz 20kHz_________________________________________________Continuous 8 ohm 1channel 11 W 55 W 25 W_________________________________________________Continuous 4 ohm 1 channel W 42 W 32 W_________________________________________________Output impedance (ohms) 2.5 ohms 2.4 ohms 2.8 ohms_________________________________________________Distortion, THD inc. noise -38 dB -68 dB -55 dB_________________________________________________Frequency response -1.5 dB 0 dB 1.8 dB_________________________________________________Intermodulation Distortion 19.5kHz/20.5kHz 1:1 rated power, 8 ohms dB_________________________________________________Intermodulation Distortion 19.5kHz/20.5kHz 1:1 1W, 8 ohms -53 dB 22Hz – 22kHz_________________________________________________CCIR A weighted_________________________________________________Signal to noise ratio ref. 1W 8ohms 73 dB 85 dB 84 dB_________________________________________________Signal to noise ratio ref. rated power 91 dB 103 dB 102 db_________________________________________________DC offset Left 0 mV Right 0 mV _________________________________________________Input Data Socket Sensitivity Loading_________________________________________________Input single ended phono 168 mV ohms nF_________________________________________________Absolute Phase correct _________________________________________________Size WxHxD 210 mm 420 mm 440 mm_________________________________________________Price £32000.00