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GamuT M250i mono power amplifier

GamuT M250i mono power amplifier

In anticipation of my review of the GamuT RS3 loudspeaker in Hi-Fi+ issue 127, the GamuT team asked if I might consider driving the loudspeakers with a pair of their 250Wpc M250i monoblock amplifiers (priced at £8,658 each). Naturally, I was happy to oblige. Little did I realise at the time that the arrival of the M250i amps would force me to reassess my thinking on the profound, and in this case profoundly positive, impact that truly great amplifiers can have on the overall sound quality of one’s audio system.

While some claim, “all high-quality amps sound pretty much the same”, most Hi-Fi+ readers know that there are in fact clear-cut differences between amplifiers that can be heard by almost anyone willing to listen carefully and critically to his or her audio system. Even so, many of us also have a general notion of the probable magnitude of the sonic changes that amplifier substitutions are apt to make. Quite frankly, after installing the M250i amps in my system and giving them the GamuT-recommended half-hour of warm-up, my preconceived notions regarding the impact of amplifier swaps were immediately and completely upended (in a good way). I say this because the big GamuT amps dramatically took charge of my audio system and transformed it in delightful and somewhat unexpected ways.

Over the years, many of us have encountered (or perhaps even written) amplifier reviews that essentially declare that listeners face a dilemma. They can either choose lithe, agile, and nuanced amplifiers that, sadly, might have relatively limited power output capabilities, or they can select big, robust, and powerful amplifiers that are long on muscle, but potentially not very subtle or quick on their feet. What’s an audiophile to do, then? The Danish firm GamuT responds to this thorny topic with a suitably gnomic question: why not both? GamuT’s answer comes in the form of the M250i monoblocks.

The M250i is a very powerful, wide bandwidth (5Hz –100kHz) amplifier, capable of delivering a conservatively rated 250 watts into an 8 Ohm load, 500 watts into a 4 Ohm load, and a mind-bending 900 watts into a 2 Ohm load (actually, GamuT says the M250i is safe with loads ranging all the way down to 1.5 Ohms, which is the point at which GamuT, in its own words, draws “a line between what is a loudspeaker load, and what is a short circuit”). As you might expect, each amplifier sports a massive power supply complete with a huge toroidal transformer and beefy filter capacitors, which take up considerable space within the amp’s chassis. Internally, the amps use GamuT’s proprietary WormHole wires throughout.

 

But, to address the agility, nuance, and resolution side of the equation, GamuT has deliberately designed the circuit of the M250i to be as simple and direct as possible and to use—this is the really critical bit—as few amplification devices as possible. Thus, where most brawny amps use large numbers of beefy output transistors in banks, the M250i uses just two identical (not complementary), ultra high-capacity (NPN type) MOSFET output transistors—one per voltage rail—and that’s it; output stage completed.

Why did GamuT take the unorthodox approach of using identical NPN transistors to modulate both the positive and negative voltage supply rails of its amplifier, rather than follow the more common approach of using complementary sets of NPN/PNP transistors? The answer is that so-called complementary transistors are not, strictly speaking, truly complementary. GamuT says the inherent differences between PNP and NPN transistors inevitably “create phase smearing” and require use of compensatory resistors that, “reduce the output stage’s ability to control the speaker.” In contrast, GamuT’s M250i circuit topology “has the benefit that the difference between the two transistors (both of the exact same type) is 100 times smaller than it would be in a normal complementary based circuit.” The result, GamuT claims, “is an output section without crossover distortion, no emitter resistors, and very low distortion, consisting mainly of even-order harmonics.”

As you can imagine the two giant MOSFETs used in the M250i are no ordinary transistors. Benno Meldgaard, GamuT’s chief of design, observes that the huge and very costly MOSFETs used in the M250i do not come from the audio world at all, but rather are ‘industrial strength’ devices “normally used in big welding machines.” GamuT claims that each of these very special MOSFETs can handle “500 watts, and a peak current of 400 Amperes and 100 Amperes long-term,” meaning that just two of the devices are able to meet the amplifier’s hefty power output goals.

To further simplify the M250i circuit for critical listening applications, GamuT has given the amplifier two sets of outputs: one labelled ‘Normal’ and the other ‘Direct’. The Normal output incorporates a Zobel network designed to protect the amplifier from extremely low impedance and/or highly reactive loads. The Direct output, however, deliberately foregoes the Zobel network in the interest of even greater sonic clarity, purity, and immediacy. Meldgaard says that, “in 99% of all situations, the Direct Output can be used.” In our listening tests, we tried both outputs and found that, as claimed, the Direct output really does sound more open, airy, and transparent. Accordingly, we used the Direct output for all of our review listening.

As well as the PS Audio DirectStream DAC and YG Acoustics Carmel 2 loudspeaker system used in this extended feature, I also tried two other demanding (and revealing) loudspeaker systems: the Magnepan 3.7i planar magnetic panels, and GamuT’s own RS3 standmount monitors.

 

First, let’s observe the obvious; the M250i amps are well and truly powerful and have all the current drive capabilities any sane listener could want. As a result, the GamuT amps took the notably power-hungry Magnepan 3.7i’s to higher levels of performance than I had ever heard from them before (and I have heard them with a wide variety of amplifiers). Bass immediately seemed deeper, more articulate, and had greater impact, while dynamic capabilities all across the audio spectrum were markedly improved. The result was that, with the GamuTs in charge, the Magnepan 3.7i’s started to sound more than a little like their bigger brothers, the firm’s flagship 20.7 loudspeakers. To be sure, the 20.7 is still the better speaker, but the GamuTs helped Magnepan’s number two model close the gap considerably.

But what was impressive was not just the quantity of power on offer, but also the quality of the power. Some big amps are sadly a bit like competitive weightlifters: that is, massively strong, but not necessarily individuals you would want to see performing at the ballet. The M250i, on the other hand, is more like the equivalent of an imaginary, scaled-up version of Mikhail Baryshnikov in his prime. Suddenly, power and grace along with agility, expressiveness, and raw grunt come together in one remarkably capable package.

To hear what I mean by these comments, Mark O’Connor’s ‘Fanfare for the Common Man’ from the album of the same name [Sony Classical] makes a perfect illustration. The first four minutes of the composition are exactly what you might expect from an orchestral fanfare, complete with soaring and heroic brass section statements punctuated by deep, thunderously powerful tympani outbursts. The M250i’s take all of these things in their stride. But at about the four-minute mark the piece changes mood, emphasising softer, but quicker-paced passages featuring the voice of O’Connor’s solo violin. In an instant, the focus shifts from power to speed, subtlety, and nuance—a challenge that the big GamuTs answer with a deft, sure touch as well as cat-quick reflexes.

To further illustrate this point, try listening to Zhao Jia Zhen’s performance of ‘Three Refrains on the Yangquan Pass’ from Masterpieces of the Chinese Qin from the Tang Dynasty to Today [Rhymoi], as performed on a period-correct Song Dynasty Qin. The Qin is moderately large and typically seven-stringed fretless Chinese instrument, ancient in its origins, that is renowned for the many soulful and thought-provoking textures and moods its sound can evoke. It is, in short, an instrument that is all about subtlety and finesse all the time. The GamuT amps, playing through the YG Acoustics Carmel 2 speakers, met these demands with a performance that was delicate, perfectly paced, highly transparent, and heartbreakingly beautiful. On recording after recording, this pattern repeated itself, with the GamuT amps managing to sound big and powerful, yet small and agile, all at the same time.

 

GamuT’s M250i monoblock amps have proven revelatory for me. They are one of the very few amplifiers I have ever heard that can combine world-class power delivery and dynamic clout with all the subtlety, expressiveness, and pace that one could possible desire. Now if that’s not audio magic of the first rank, then I can’t imagine what else would be. Passionately recommended.

TECHNICAL SPECIFICATIONS

  • Type: Solid-state monoblock power amplifier
  • Analogue inputs: One single ended (via RCA jack), one balanced (via 3-pin XLR jack)
  • Analogue outputs: Two pairs of speaker taps (via 5-way binding posts): one Normal with Zobel network protection, one Direct without Zobel network features
  • Power output: 250 watts @ 8 Ohms, 500 watts a 4 Ohms, 900 watts at 2 Ohms, stable into loads as low as 1.5 Ohms
  • Bandwidth: 5Hz–100kHz
  • Signal to Noise Ratio: At least -100dB at full output (250 watts at 8 Ohms)
  • Dimensions (H×W×D): 164 × 431 × 470mm
  • Weight: 38kg/each
  • Price: £8,658/each, £17,308/pair
  • Manufacturer Information: GamuT A/S

URL: www.gamutaudio.com

UK Distributor: Sound Fowndations

Tel.: +44 (0) 118 9814238

URL: www.soundfowndations.co.uk

US Distributor: GamuT USA

Tel: +1 888-252-2499

Tags: FEATURED

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