Tip #75: Electrocompaniet AW180 Monoblock Power Amplifier
Reviewed by Dick Olsher
Matti Otala may not be a household name, but in the early 1970s he created quite a buzz in audio circles by focusing attention on Transient Intermodulation Distortion (TIM) in transistor amplifiers. That proved to be the catalyst for Electrocompaniet’s development and successful launch of a TIM-free 25-Watt solid-state amplifier in the mid 70s. Rather unceremoniously named “The 2 Channel Audio Power Amplifier,” it nonetheless literally redefined transistor sound. Riding the wave of their Otala series, Electrocompaniet established a significant international presence, which was re-energized in 2004 when Mikal Dreggevik, a savvy entrepreneur, purchased it outright. Mikal cares about music and aims to adhere to Electrocompaniet’s avowed goal of the closest approach to the original sound; hence, their slogan: “Closing the gap to the master.” In what is a refreshing change from the paradigm of “designed in the West and built in the East,” production takes place near Stavanger, Norway, combining operations with Westcontrol, a sister company and an avionics defense contractor engaged in development, prototyping and manufacturing of electronic components.
The AW180 is a Class AB push-pull amplifier, certainly a rational choice for any high-power amplifier able to sink 650 W into a 2-Ohm load. The output stage uses bipolar power transistors and is biased such that the first 7W are Class A. Design wise, the AW180 is half of an AW600 Nemo monoblock, which consists of two AW180 amps bridged together. Its styling is modern rather than traditional, featuring a thick Perspex front panel, no handles, and a top-mounted power indicator. The power switch is located on the back panel together with the input and output connectors. Only a balanced XLR input connector is provided. However, using an XLR to RCA adapter the AW180 can be made compatible with single-ended preamplifiers. Don’t bother with mass market adapters, I highly recommend the Cardas Audio adapter (XLR male/RCA female) with the rhodium over silver plating. Ergonomically speaking, the biggest annoyance involves the binding posts, two pairs bunched together making it difficult to finger tighten connections. Why not use Cardas binding posts in a product of this stature? In my estimation, these are the best sounding posts in the business, or as a minimum, deploy hex-shaped posts that can be tightened with a nut driver. The busy back panel includes a balanced connection to an additional amplifier for bi-amping.
TIM is often taken as an indictment of negative feedback (NFB); nothing could be further from the truth. The culprit is excessive feedback (say greater than 40 dB) which can cause transient overshoots and clipping due to insufficient slew rates. NFB reduces the input sensitivity of the amplifier and is typically expressed as the ratio by which gain is reduced. For example, if the gain of a voltage amplification stage (without NFB) is 100 and feedback from the output terminal reduces the effective gain to 5, that’s a ratio of 20 or 40 dB of NFB. The problem with NFB is that it isn’t always precisely 180-degree out of phase relative to the input signal. Application of feedback over a loop that includes several gain stages (global feedback) is risky due to phase shifts with increasing frequency, potentially giving rise to high-frequency instability and oscillation. However, the answer is not to throw NFB out the window. It is an essential design tool for linearizing a gain stage and thus minimizing harmonic distortion. I dare say that the mythic notion of a “straight wire with gain” would be impossible without judicious application of NFB. Electrocompaniet’s research has shown that local feedback applied around individual amplification stages is sonically preferable to global feedback. Hence, no global feedback is applied to the AW180’s first gain block, which uses FETs at the input and bipolar transistors the rest of the way.
It was also Matti Otala who first called attention to the real-world peak current demands of conventional multiway loudspeakers. Say the nominal impedance of your loudspeaker is 8 Ohm. Otala’s simulations showed that for several hundred microsecond bursts it was possible for such a speaker to draw almost seven times more current than expected. In other words, for short periods of time the speaker could approximate nearly a 1 Ohm load due to “the simultaneous parallel excitation of several drivers of multiway system, by the summation of cancellation currents originating from the energy stored in the mechanical and electrical reactances of the circuit, and by impedance transformation effects in the crossover network.” Later work by Benjamin indicated only a factor of two increase in current draw from such effects, but the fact remains that your speakers may be greater current hogs than you realize. Therefore, current delivery into low impedance loads is an important design consideration, which I’m happy to report was not overlooked by Electrocompaniet. The AW180’s maximum peak current delivery is in excess of 100 amps, and that goes a long ways toward explaining its superlative performance with the Analysis Audio Omega loudspeakers. As you might expect, the power supply of each monoblock incorporates a massive 650 VA toroidal transformer and a 60,000 micro farad capacitor reservoir bypassed with polycarbonate and polypropylene capacitors.
In my view, an important amplifier design goal should be minimal load interaction. And that can only be achieved through a high damping factor, implying a low source impedance. The AW180 sports a source impedance of 0.008 Ohm! That translates to a damping factor of 1,000 relative to an 8-Ohm load and guarantees good behavior even when driving difficult loads. The MartinLogan Summit X is a case in point. The impedance of its stat panel is capacitive in nature and decreases with increasing frequency, reaching a minimum of 0.8 Ohm at 20 kHz. That makes the Summit a prime candidate for amplifier-speaker interaction, especially when you consider that the average tube amp exhibits a source impedance of around 1 Ohm. Several tube amps rolled off the Summit’s highs dramatically. One amp in particular managed a whopping -10dB at 20 kHz. The AW180, on the other hand, was unperturbed by such a load.
My first impression was in the context of the DALI Helicon 400 Mk.2 loudspeaker, a moderately sensitive 4-Ohm nominal load. Although the Helicon can be driven fairly well by a 50 wpc tube amp, the AW180 demonstrated that more power is a good thing in this context. My notes are pretty explicit: what a monster of an amp! It allowed the Helicon to glide effortlessly from soft to loud. Its exceptional transient speed relative to that of a typical transformer-coupled tube amplifier was most welcome. Speed of attack coupled with deliciously resolved transient decay resulted in the impression of exceptional clarity - no fuzz or veiling to speak of. There was plenty of low-level detail being retrieved, and in particular, treble nuances were nicely resolved. Harmonic textures were smooth and grain free. Bass lines exhibited iron-fisted control. Check out Mari Boine’s Radiant Warmth CD (Antilles 314-533-520-2). The lead track, which interestingly enough was recorded and mixed at Rainbow Studio in Oslo, features ferocious drum accompaniment. The end result with the AW180 in the system could only be described as visceral impact – magnum force!
As with any inherently neutral amplifier, it was impossible to divorce the AW180’s sonic performance from that of the associated preamplifier. It let the preamp do the talking, or should I say, the editorializing. I experimented with several tube preamps. That in itself should come as no surprise since I had been advocating the use of tubes ahead of solid-state power amps for many years. The reason, to paraphrase Pablo Picasso, is that solid-state preamps are useless; they give you details instead of feelings. The flavor of each tube preamp shone through. With the Mystère CA21 line preamplifier, outfitted with 7AF7 Loktals, the presentation tilted a bit towards the romantic. Harmonic colors were more vivid, image outlines more palpable, lower midrange warmth left intact, and most importantly, the music flowed with greater emotional intensity. Enter YS Audio’s Audio Experience A2-SE balanced preamplifier. The presentation could now be characterized as rhythmic, fast, clean, and pure. The A2-SE, however, did not fatten up the lower midrange and lacked the Mystère’s textural density. It should be noted that the A2-SE sounded far better feeding the AW180 from its balanced versus its single-ended outputs. The best match for the AW180 in terms of harmonic textures, timbre authenticity, and a wide dynamic palette turned out to be the Air Tight ATC-2. This particular line preamp has been in house for many years but has only recently been tweaked by rolling in a pair of Mullard box anode CV4003/12AU7 triodes. Rounding out the tube complement is a 5751 Sylvania gold pin.
My plan all along was to mate the AW180 with the Analysis Audio Omega planar magnetic/ribbon loudspeaker for a definitive assessment. Its preference, or should I say appetite, for high current drive is a well known fact. This therefore would appear to be a perfect setting for a high-power amplifier to strut its stuff. And I had already evaluated several amplifiers in this context, including the Spectron Musician III Mk.2 Class D monoblocks rated at 800 watts per channel into 4 Ohm. In addition, I was most curious about a head-on competition with the far more expensive Lamm Audio M1.2 Reference monoblocks. The game was afoot! It became clear that relative to the M1.2, the AW180’s color temperature was a bit lower. It sounded a bit cooler, and in addition, textures were not quite as smooth. But when it came to scaling the dynamic range from soft to very loud, the AW180 was king. Macrodynamics were absolutely riveting. While the M1.2 did well revving up from soft to loud, it couldn’t keep up with the AW180 – it just did not have that last gear. The AW180 laid out a powerful orchestral foundation with a thunderous low end. Romantic classical music never sound so convincing. The soundstage was exceptionally solid with excellent image focus. Factoring in its textural purity, low distortion signature, and transient clarity, the inevitable conclusion was that the AW180 had vanquished all previous contenders. I suspect that similar loads, e.g., Magnepan, would also benefit from being partnered with the AW180.
With the AW180 you firmly cross the Rubicon into muscle amp territory. An American automotive analogy would be a sleek, racy, Corvette. Think mind-blowing dynamic headroom. But this is no ordinary muscle amp. Its sound is also pure, fast, always in control, and it is able to deal with current-hungry real world loads. Planar magnetic aficionados need look no further. Keep in mind that the AW180 will sink or swim based on the associated preamp. It needs a dose of tube warmth. Once you cater to its needs, rest assured that its performance is more than competitive with far more expensive gear. I suspect that this is one amp I’ll be unable to walk away from. Highly recommended!
Power Output: 180 W into 8 Ohm; 350 W into 4 Ohm; 650 W into 2 Ohm
Output Impedance: (20 Hz - 20 kHz) < 0.008 ohm
Input Impedance: XLR (balanced) 110 kOhm
Input sensitivity for rated output: 1 V
Max. peak current: > 100 A
THD (measured at 1 kHz half power, 8 W): < 0.001 %
Noise: (measured with both inputs shorted) 90 µV (400 Hz - 30 kHz); 100 µV (10 Hz - 30 kHz)
Power consumption: (no load or signal) 115 W
Dimensions: 215mm(W) x 288mm(H) x 470mm(D)
Weight: 48.4 lbs.
Price: $4,800 ea.
97 Linden Street
Oakland, CA 94607
Voice: 510-291-1222; Sales & Order: (323) 363-5171