The evolution of amplifier design, wrongly called “digital” (it would be more accurate to speak of switch-mode power supplies and Class D), has been revolutionizing the professional audio market for a couple of years now. We are used to judging power amps by their weight (back when heavy toroidal transformers were an unmistakable sign of solid current delivery), but the landscape is changing radically, betting on quality and setting aside concerns like handling, weight and whether or not they carry that kind of transformer. Both developments (the switch-mode supply and Class D amplification) have been known for many, many years. In the case of the switch-mode supply, it is enough to note its presence in just about every personal computer ever made. As for Class D amplification, it has been (and still is) dominating the telecommunications market, since it allowed high-frequency signals to be broadcast with less power consumption and less space. But it was not until a Class D amp could be designed to work with low frequencies (20 Hz is a clear example) that it arrived on our market.
From a practical standpoint, today’s sound engineer appreciates two really important things about these power amps. First, their weight, reduced by as much as three quarters with almost no loss of the technical performance of other designs. And if weight is not excuse enough, ask the truck driver (who is responsible for keeping the load within legal weight limits) or the tech who hauls all the gear from the truck to the stage.

But there is another important point, which is power consumption. Interestingly, this electronic design is far more efficient; in other words, it delivers the same output power (or amps, if you prefer) while drawing much less. This comes from its efficiency, much higher than Class AB (let alone Class A), which carries over into other practical benefits. Higher efficiency means that for every watt we take from the mains we get “almost” 1 W of output power. When efficiency is lower, we may get perhaps 0.6 W, or even less, and if we stay true to Einstein’s maxim (“energy is neither created nor destroyed, only transformed”), we will understand that the remaining 0.4 W (sometimes even more) has to turn into some other kind of energy, which in our case is usually heat.

By doing away with heavy, cumbersome toroidal transformers and achieving higher efficiency (that is, running cooler), it is not only possible to use switch-mode supplies (also lighter and more efficient) but also to build much more compact chassis, sometimes without needing fans for forced-air cooling.

E45, a switch-mode design
Our guest in these pages is one of the latest creations from MC2 Audio Ltd. The company has more than 10 years of history designing high-performance amplifiers for the professional market. Led by Ferry Clarke and Ian McCarthy, it enjoys a good reputation among industry professionals, thanks in part to products that offer a good balance of quality and price. The story of this brand with the curious name begins in 1994 at the AES convention held that year in Amsterdam, where its first two products, the MC450 and MC650, were introduced and drew great reviews from professionals and the trade press.

The E Series (to which the E45 we are about to analyze belongs) was first presented at the Pro Light & Sound show in March 2003. It was already distinguished by its distinctive front panel, and two models arrived: the E25 (1,250 W per channel into 4 ohms) and the E15 (750 W into 4 ohms). A year later, at the same show, the E45 came out, standing out at first for its 2,250 W into 4 ohms in a chassis just 2U tall. It is still the latest addition to the E Series catalog and, even back then, it drew enormous interest from users.

The E Series comprises a family of designs aimed at the touring live sound market, combining quality sound with the solid performance of the MC and T Series without being as heavy, while keeping the characteristics that have made MC2 a renowned company.

Our guest, as I mentioned, can deliver up to 2,250 W per channel into 4-ohm loads, reaching 6,400 W in bridge mode into 4 ohms. It stands out not for that electric-blue aluminum front panel (quite seductive, or so it seems to me) but for packing that much power into a chassis just 2U tall and weighing only 11 kg. Its overall dimensions are 88 x 482 x 428 mm. The manufacturer highlights the capacity of the power supply (switch-mode, of course), which can deliver power peaks without that “flabby bass,” keeping distortion low at all times and always operating within a controlled safe area. The secret, they say, is a sophisticated “intelligent” limiter that accompanies all of the circuitry.

In terms of connectivity, this MC2 is well equipped. On the rear panel we find only balanced XLR audio inputs for the line signal (and outputs, so it can feed other amps), which points to its professional orientation. The power outputs are made only through Neutrik connectors. The different attenuation (pad) levels are selected with two switches, allowing the signal to be reduced by 2, 4 or 6 dB. Another switch converts this two-channel amp into a bridged one, with its own separate output, also on a Neutrik connector. The power cord is hardwired, rather than using the usual and more practical IEC connector.

On the front we find two level pots and some LED indicators; I criticize the fact that the signal LED only reports the signal “going out,” not the signal coming in. It would be nice if it showed whether signal is arriving or not without having to turn up the volume.

The technical data the manufacturer offers aim very high for an amp at this level. Besides the stated power ratings, both its THD (below 0.008%) and its damping factor (below 400) could convince anyone “blind.” It even claims a frequency response of 20 Hz to 20,000 Hz with variations of only +/- 0.5 dB. What better way than to try it out and enjoy it.

Putting it to the test
For the tests I used unprocessed JBL SRX cabinets and, to judge the sound of the E45, I compared it with another amp that I use regularly, the Crown Macro-Tech 3600. For the reader’s information, the 3600 is a professional amp that delivers 1,500 W per channel into 4 ohms, that is, 700 W less under the same conditions than our guest, although the price difference is slightly larger.

In any case, this comparison lets me offer a more objective opinion and confirm, off the cuff, that when the price is lower the quality is lower, too. With the chosen cabinets (2 x 15"), it was clear from the first moment that there are still switch-mode designs whose low-pass filter needs to be improved, which is imperative when you know the amplification topology being used. In a direct comparison, the Crown runs rings around the E45 in almost every respect. First in current delivery, where the Crown wins by a noticeable margin. But also in audio reproduction. The E45 does not achieve excellent high-frequency reproduction, with everything above roughly 12,000 Hz noticeably lost. That leads the engineer to boost that band (for example, drum cymbals, especially the hi-hat) and spoil the musical production a bit. The same happens in the midrange, where there is a noticeable dip around 400-700 Hz, right where some voices need more presence and punch. Honestly, I don’t know how the manufacturer can claim a frequency response as flat as the one it specifies.
In the low end there is no comparison either, although its behavior is fairly linear. On the other hand, it does offer very good attack speed.

If I had not compared it with a reference model like the one I chose, I would probably have talked about a lack of “brightness” and punch in the midrange, though without the harshness mentioned above.

Conclusions
If weight, space and more or less decent performance matter a lot, the E45 can certainly be a good choice. But next to higher-quality products (with fewer features on paper), it would come off a bit bruised. Even so, given its potential with low frequencies, the E45 could be, for example, an excellent option for powering subwoofers or low-mid cabinets in active systems. Although the power rating may be lower than advertised across the whole audible spectrum, its fast attack makes this model a precise partner in that role. But let nobody be left with a bitter taste, because the Macro-Techs I compared it with are a true reference, and it is only logical that, head to head, they come out ahead most of the time. The E45 is a good amp that very efficiently combines light weight, performance and a certain linearity. The engineer will have to work a little harder, and that’s it.