Amplifiers

(here are excerpts. click above if you would like to read full review)

PREFACE

– THE INELUCTABLE MYSTERY OF HIGH POWERED AMPLIFICATION

After more than two decades as an audiophile, I have a confession to make: There is a lot I don’t know about audio. Indeed, the area where I have devoted most of my energy and attention – high powered amplification – is where I find myself most often confronting important questions without obvious answers. So, let me come clean and highlight through this review some of the questions that perplex me, for the answers to them may well shape my buying decisions in years to come. First question, how much amplifier power do you need? One possible qualitative answer is sufficient power to ensure that your amplifier never clips. To be sure few audiophiles would feel good about sending clipped audio waveforms from their amplifiers to their speakers irrespective of whether you could discern the resulting distortion or not.

But while the qualitative answer has an inbuilt psychologically good ‘feel good’ factor about it – the quantitative answer required to underpin the ‘never clips’ proposition will flat out shock you. Assuming you own a pair of average sensitivity (circa 87dB) dynamic loudspeakers and assuming your choice of music is orchestral or heavy rock (which can peak for very short periods at 109dB or more) and assuming you sit about 3 meters from your loudspeakers the quantitative answer suggests you would want an amplifier rated at 500 Watts per channel.

Based on my own subjective experience with high powered integrated and power amplifiers such as the Abbingdon Music Research (AMR) AM-77; the Plinius Hiato; the GamuT DI-150; the Gryphon Diablo; the Bel Canto Ref 1000 MkII monoblocs; the Sanders Sound Systems ESL Stereo and the Jeff Rowland Design Group Continuum 500 (see references for reviews) the effortless and unobtrusiveness power delivery of big amps brings a sense of relaxed and uncongested grace to all sorts of recordings. There is no hardening as the amplitude increases, no collapse of soundstage or roll off of frequency extremes as the amplifier is presented with awkward loads or gasps for breath as it flat out lacks the extra oomph to reproduce the scale and attack of a bass drum. Well-designed big amps also have momentum, an unstoppable metronomic progression which underpins continuity to the music whilst still be able to respond quickly to transient changes. Done right the rise times on big grunts can be blindingly fast aiding transparency and moreover, one often observes very deep, extended, and powerful bass and a retained grace even during massive 109dB orchestral and rock peaks.

Conversely, I’ve found that if an amplifier is under-powered for your needs, you’ll never hear the system at its full potential. The sound will be constricted, dull, muddy and often fatiguing and you will notice a hardening of timbre and a dilution of dynamics as the amplifier strains and gives up as it runs out of power. Furthermore one frequently witnesses a tendency to homogenize individual instruments and their specific locations within the soundstage as an amplifier is being unduly taxed.

Please don’t get me wrong, I am not suggesting for one minute that “power outputs” are any reliable guide to the quality of an amplifier – but one observation I will boldly make up front is this; well-designed high power amplifiers typically possess one consistent ace up their sleeve and that ace comes in the form of large and heavy power supplies with high current capability which is demonstrated by their ability to increase output power into low impedances. Since it is current that ultimately drives the cones in your loudspeakers back in forth it is actually the amplifiers power supply design, not some lofty and frequently misrepresented wattage moniker, which underpins perceptions of sound quality. Since high current capability comes from massive power supplies and lots of output transistors, all of which are expensive items, well designed high powered amplifiers don’t come cheaply.

On first glance there is nothing on the outside of the Magtech to suggest that anything special lurks within. Indeed cosmetically the Magtech is quite unremarkable (even if pleasingly simple) and entirely lacks the butch machismo expected of muscle bound amplification. Many audiophiles like to have their equipment look as they expect it to sound and in this respect listeners really are in for a ‘Little Red Riding Hood’ experience.

Cosmetically the product is stylistically indistinguishable from the Sanders ESL amplifier and that visual continuity is actually reassuring given the performance that product exhibited a couple of years back when I borrowed a unit to review some large KingSound ESL speakers (see references) I had in residence at that time.

Compact at just 43cm wide, 40cm deep and 14cm tall the Magtech refreshingly presents no real estate challenge. The plain 3/8 inch aluminium front plate houses a blue backlit “Sanders” logo to indicate operation and the rear panel is adorned with RCA and XLR inputs, speaker outputs, fuse holders (one for each channel and one for the AC line) and an on/off switch. The XLR input connectors (pin 2 ‘hot’) are genuine Neutrik and they use professional metal sockets with locking devices. The RCA connectors are Cardas with Rhodium plating. The WBT speaker binding posts are thoughtfully placed at 45 degrees for ease of routing stiff speaker cables. The inch deep heat sinks along both sides of the chassis, which look oddly insufficient for the amplifiers power rating, mercifully lack sharp edges and are child safe. Closer inspection of the heat sinks however reveals there are no less than 53 fins, each with a surface area of 10 square inches. When you add up all this area, plus the area of the aluminium chassis, which also dissipates heat, the total heat sink area in the Magtech amplifier is nearly 10 square feet! As a result, the heat sinks are adequately designed to keep the amp cool. I dwell on this simply because I see lots of high-quality amplifiers out there with large heat sinks but using just a few big fins. While such heat sinks may look impressive, they are not very efficient and waste a lot of space.

While the Sanders ESL amplifier was designed from the ground up to drive electrostatic speakers, the Magtech, as the ‘Mag’ before the ‘tech’ clues, has been specifically designed to drive conventional magnetic speakers. Recalling the importance of a robust power supply, the Magtech is uniquely equipped with what Sanders refers to – rather un-uniquely – as a ‘regulated power supply’. Readers interested in details on this should read the white paper entitled “The Magtech Regulated Power Supply White Paper” hosted on the Sanders Sound Site. The crux of this reads that the Magtech is equipped with an extremely robust (stiff) power supply, which is capable of maintaining voltage even when the output transistors are demanding large amounts of current whereas unregulated power supplies (more typically found in amplifiers) simply can NOT maintain their voltage, even under only moderate load, and certainly not under high current conditions, leading to degraded sonics.

The power supply then underpins an impressive spec sheet. The Magtech will deliver 63.4 volts RMS to the speakers, which translates into 502 watts into an 8 ohm load. Further down the impedance scale the Magtech delivers 900 watts into a 4 ohm load and about 1600 watts into a 2 ohm load. What makes these spec’s all the more impressive is that the power ratings are for both channels driven at any audio frequency (20 Hz to 20 KHz) and with a THD level cited in the manual of just 0.01% at any power level below clipping. At 1 watt ("small signal"), the specification less honest manufacturers use to rate distortion, the THD is no more than 0.004% and typically 0.0024%. As the reader might imagine the output stage needed to drive these sorts of power levels is nothing short of colossal, comprising of OM NJL4281 and NJL4302 transistors in complementary pairs. Note that these are the new "Thermal Trak" type of transistor that has a temperature sensor built into the transistor junction. This makes it possible to instantaneously correct for the huge swings in bias current due to the problem of instantaneous junction heating caused by sudden, large, current flows. As a result, the amplifier is able to maintain a constant bias current at all times -- something that is not possible in conventional transistor output stages.

In sum the output stage is capable of handling about 7,000 watts of power, so the transistors are never being taxed and protective circuitry can be eliminated from the design. Since protective circuitry sounds harsh and generally awful when in operation, eliminating it is the key – in the designer’s opinion – to making amps sound superb. To deliver its power the Magtech employs of the use of a single 2200 VA transformer and medium sized capacitor bank. In an age when many amplifier manufacturers for reasons of cost savings are reducing transformer sizes and relying more on capacitance to supply the brief bursts of power required – the use of ‘heavy metal’ in the Magtech is both refreshing and commendable.

Megalomaniacs who feel that 900 watts (into 4 ohm loads) really isn’t enough juice to get their Magnapan or Apogee panels vibrating have the option of ordering the Magtech as a mono-bloc and in this guise 2000 watts is available. With these sorts of power levels the reader may be wondering whether the Magtech is Class D in operation. The answer is no. The Magtech is Class AB from the get-go since the designer believes nearly all Class A amps are under-powered and he sees no point in wasting power driving the amp into Class A or even high bias, Class AB operation as he prefers to bias as low as possible to conserve electricity and keep the amp cool.

Mentioning energy conservation and high powered conventionally biased amplification in the same sentence may seem ‘a bit rich’ to some so let me expand on this for a moment. The Magtech runs cool because its transistors have an extremely linear transconductance function and therefore do not require much bias to eliminate crossover distortion. Understand that most of the heat produced in a Class AB amp is produced by the bias current. The sole purpose of the bias current is to eliminate distortion. Through the use of the most modern and linear “Thermal Trak” transistors very little bias current is needed to eliminate all distortion and the amplifier as a result runs very cool. Impressively, the Magtech idles with each channel drawing only about 16 watts of power, so the total idle power used by the amp will be about 32 watts which is identical to my Bel Canto Class D 1000 Watt monoblocs. This means the Magtech amplifier can economically be continuously left on and indeed the designer recommends this.

 

SET UP

In setting up the Magtech there are a few things to observe and consider not all of which is covered in the operating manual.

The first is that the Magtech is a differential/complementary design which means that its frequency response is flat right down to DC. Typically in such designs there are no capacitors in the signal path that would block DC, so if you feed it a DC signal – and many preamps "leak" DC – it will amplify that signal and can easily burn up your woofers due to its high power. So, it is important to avoid DC offsets in your pre-amp when using the Magtech or indeed any other directly coupled amplifier. As a compromise Sanders employs the use of DC blocking capacitors in the unbalanced inputs of the Magtech since tube preamps are the worst offenders and most are unbalanced. The designer leaves the balanced inputs free of capacitors since those who use balanced equipment tend to be the most concerned about capacitors in the signal path. For the record Sanders Sound can easily omit the capacitors in both circuits, or add them to both circuits if a customer wishes. The customer simply needs to specify his desire at the time of his order and there is no additional charge either way.

The second is an injunction on the use of power conditioners. Sanders distaste of such products is consistent to that of other high powered amp manufacturers such as Krell, Bryston and Gryphon with the central concern being that power conditioners can seriously degrade performance. Most conditioners add series resistance in the power line and this will tend to limit the amount of current fed to the amp and when dealing with amplifiers that are as powerful as the Magtech, they need all the current they can get. So please plug the Magtech directly into the mains receptacle in the wall.

Finally, the manual notes “The Magtech Amplifier is designed to be left on continually”. One reason cited is stabilization of internal temperature which produces lowest distortion. Understand here that amplifiers are relatively massive devices and it therefore takes several hours for the heat produced by the bias current in the output transistors to completely soak through the entire unit and eventually stabilize an amplifier's chassis, heat-sink and internal temperatures. However, Sanders primary concern here is not temperature stabilization (important as that may be) but long-term reliability. Remember that Sanders amps come with a lifetime transferable warranty, so it is extremely important that they never fail. Turning a component on and off stresses it. Switches are damaged slightly each time you throw them. Doing so causes a small electric arc between their contacts, and this gradually destroys the contacts. The arcing is worse at turn-off, but an arc will also be present at turn-on. An even bigger problem is the big power supply capacitors. When the amp is off, these caps will discharge to zero volts. At turn on, they are then hit with high voltage (100 volts in the case of the Magtech). Since a large cap at zero volts is a dead short, a massive surge of electrons will flow into the cap when the amp is turned on. This high current flow causes a tiny amount of damage to the cap's plates and will lead to eventual failure if they are cycled enough times.

Remembering that a power amplifier is only going to sound as good as the equipment surrounding it the audition included the use of Lightspeed Attenuator (used at times in place of the Cary pre-amp) and three different loudspeakers; an average sensitivity reference bookshelf speaker (Raidho Acoustics C-1.0, 87dB), a medium sensitivity near full range floor-standing speaker (Nola Contender, 90dB) and a low Sensitivity electrostatic speaker (Kingsound ESL, approx. 80dB).

Furthermore, over the audition period the performance of the Magtech was subjectively referenced against two other high powered amplifiers, a Gryphon Diablo (Power Amp Mode) (Denmark, solid state, Class AB, 250 watt per channel, US$ 16,000) and a pair of Bel Canto Ref 1000 MkII mono blocs (USA, solid state, Class D, 500 watt per channel, US$ 5990 per pair). The scene now set, let’s discuss the sound!

THE SOUND

From the first disc the attributes of the Magtech are clear. The Magtech sounds solid, powerful and extremely dynamic. Bass is tight and firmly controlled, yet full bodied and rich, while the treble is airy but focused and clean. There is nothing sweet, mellifluous or euphonic about the way which the Magtech reproduces music, rather the Magtech appears to be a model of neutrality wearing clarity and dynamics very much on its sleeve.

Feed with demanding opening soundtrack to “The Pacific” (The Pacific, Music from the HBO Miniseries, Rhino Entertainment – 8122-79810-9) and compared to both the power amplifier section of the Gryphon Diablo and the high powered Bel Canto monoblocs the Magtech possessed a noticeably greater ability to follow the dynamic contours of the music. When compared to my 120 Watt Unison Research amplifier I was surprised more than once when climaxes in orchestral recordings I thought I knew well continued to grow and expand beyond the point where (on the Unico) they would have stopped. Further, this is an amplifier that loves pace picking up transient cues instantly, as if it is anticipating the music even before the DAC decodes it.

Continuing with last scale orchestral music, in The Snow Maiden (from Exotic Dances from the Opera, Reference Recordings, RR-71) it was possible to indulge in near concert hall volume levels without feeling that the amplifier was straining. The Magtech possessed purpose coupled with majestic grace as it relentlessly tracked the towering opening tuttis with a broad and deep soundstage adding to the sense of power and the orchestral sweep of the music. The timpani seemed bolder than I’ve earlier recalled the skins with more texture and air with other percussive instruments being sharper and more solid then reproduced by the comparator amplification.

And as good as the Magtech was with dynamic orchestral tracks nothing could have prepared me for the next act which was the reproduction of Olivia’s Ong’s live 2010 concert in Taipei. The anticipation of the crowd was palpable as was the cascade of drums that open the concert above the background noise of the restless crowd. Big, solid, real drums with visceral whacks you feel as the stick strikes the skin, with the resistance of the skin itself and incredible presence and transient impact which ordinarily places enormous strain on lower powered amplifiers here being treated and presented as no stress at all. The leading edge clarity on the drums combined with seemingly perfect decay is the best I’ve heard in my system to date. As the crashing cannonade gives way to the vocals the communication of the immediacy and pulse of the live performance added considerably to the belief that the event is happening a few meters from my listening chair! Another interesting observation during this recording was that the Magtech shone more light on the backing singers which appeared (comparatively) as dull and less defined with both the Bel Canto and Gryphon amplifiers.

The Magtech proved no slouch on complex studio albums either. Taking “The Power of Good-Bye” and “Frozen” both Orbit inspired masterpieces from Madonna’s GHV2 (Madonna, Greatest Hits Volume 2, Warner Music Group – 9362480002) as examples, the layered soundscapes are effortlessly reconstructed, sucking the listener into their complex texture and minutiae detail even whilst the underlying beat propels the tracks momentum with solid energy. These tracks play up a particular strength of the Magtech which is not just dredging awesome amounts of bass out of low efficiency speakers but demystifying complexity and thus allowing the listener to see into the recording as a representation of the event. These tracks also show the resolution of the Magtech to be quite simply ‘top draw’ and whilst I have frequently heard people scoff minutiae of detail as musically irrelevant – listening to the Magtech gives me cause to once again ponder whether these same people are simply making excuses for equipment that is incapable of reproducing them?

Staying with vocals for a while longer, a good test of vocal articulation can be found in Warnes “Some-where, somebody” (Jennifer Warnes, The Hunter, 24K Gold Special Edition, Sony BMG Music – GDC 8012-2) where a discrete blend of lead female singer, male accompaniment and instruments meld and can on many systems become confused. With this piece the Magtech did an outstanding job in ensuring that first, the lead voice maintains it position relative to the musical parts with the appropriate weighting and second, that the accompanying male vocal maintained clear articulation and his lines were not lost in the melee.

Music though is more than just sorting out priorities and rendering tracks intelligible, it is also about rhythmic organisation and making that out of the morass that comes from the surface of all too many discs these days. That’s not to suggest that the Magtech can transform a run of the mill recording into a masterpiece, but proving it is not just another ‘dumb metal jacket’ the Magtech can and indeed does manage to extract the musically important core from the mire. Case in point is ABC’s digitally re-mastered but still poorly recorded 1999 album, entitled Classic ABC (ABC, Classic ABC, Mercury Records – 546 804-2). This album serves as my bad recording reference, noisy and grainy 1980’s synth-pop at its worst, but it nonetheless sits on the top shelf of my CD rack because hits like “Look of Love”, “Poison Arrow” and “All of My Heart” are all defining musical moments of 80s nostalgia for me. It takes a well sorted audio system to extract the music from the compressed mayhem and the Magtech rose to the occasion by cutting straight to the heart of the recording and never letting go. Mercifully, the sort of insight the Magtech delivers is what’s there in the recording rather than pulling the recording apart and where the Magtech excels is in the area of momentum, it succeeds even in poor recordings in keeping things rhythmically taunt without becoming forward or bright.

Perhaps though the greatest challenge for any high powered amplifier is reproduction of the human voice at low volumes. In my experience low level listening is traditionally an Achilles’ heel to some behemoths with the sound all too often collapsing into the speakers. Not so with the Magtech. With Katie Melua’s “Haunted House” (Kate Melua, The House, Universal Records – B0014568-02) the Magtech excelled even at low listening levels by successfully creating the tracks suspense and brooding menace whilst not ignoring the litany of low amplitude micro-dynamics, tonal shifts and dynamic contrasts which create the contextual atmosphere.

CONCLUSION

To summarise, during the period of my evaluation there was nothing that caught the Magtech out. Even with different speaker designs and loads it seemed more than equal to every-thing. Tonally colourless, the Magtech performance is self-assured and immensely stable, driven by the kind of contained power that I’d normally associate with a steam roller. If a ‘but’ has to be inserted somewhere it is that readers bought up on the rounded warmth and intimacy of a classic valve power amp may find the Magtech somewhat academic and stark. The injunction here – as always – is that ‘know thyself’ is an essential pre-requisite for all audiophiles and whilst many philosophically claim to desire absolute neutrality in audio reproduction – it is a claim for some that lasts only as long as actually hearing it...

Perhaps the easiest question to answer was what the Magtech sounded like? The answer is “whatever it is connected to” and this observation rather underpins the synthesis that is how you assemble a system around the component in question that really determines the results. Careful selection of upstream components will be important and for what is worth I vastly preferred the Magtech when paired with a high quality valve 

Minimalist in the flesh the Magtech is not a trophy product and this will sit uncomfortably in a world of affluent hi-fi aficionados who can (and frequently do) proudly list a string of ever changing and ever more expensive ‘branded’ products that they have owned. Such owners seemingly treat hi-fi like a thoroughbred bloodline in the mistaken belief that brand and high price always translate to high performance. In a very sad sense, ‘high end’ has all too often become a price point rather than a performance benchmark and Sanders Sound Systems Magtech serves as a much needed reminder that audio priced at unconscionably high levels is not only unfair to consumers and damaging to the industry – but also completely unnecessary.

                                                                             Listening Room View

Designed then for musical appreciation rather than to impress your friends the fait accompli is this – it is like you haven’t got an amplifier in the system at all – it’s so neutral and ‘invisible’ sonically. Designed to maintain the integrity of recordings, the acoustic energy propagates so naturally that the mechanics of the reproduction cease to intrude. Moreover the lack of dynamic constraint and superb localisation of instruments and / or actors makes the whole reproduction of the experience much, much more convincing and in this regard the Magtech will tell you more about the music on your records and how it got there than any number of highly touted and priced alternatives. Those of us that work for a living have reason to rejoice, for the unflappable and unobtrusive Magtech stereo power amplifier serves to prove that simply spending more money on something (much) more expensive is even less of a satisfaction guarantee than it ever was.  Recommended.