Music in the Round #35
Still, two characteristics remained that might be problematic for some listeners. First, the dullness of the upper midrange and lower treble, which I find common in many switching amps, was so reduced in the original Ref1000 monoblock power amp that it was a problem with only a few recordings and/or loudspeakers that shared a similar deficit. Second, all class-D amps seem to throw a lot of noise back into the AC line. I determined this by listening to FM with the Ref1000s plugged into wall sockets in the same room, but not connected to the system in any other way. Line filterseg, an Environmental Potentials EP-2450 on the amps, or American Power Conversion S15 on all source componentseliminated the noise, and proved that the problem was not airborne RFI but was in the AC lines themselves.
I didn't attend last October's Rocky Mountain Audio Fest, having already had my fill of Denver in September at the CEDIA Expo, but I read with interest that Bel Canto had introduced Mk.II versions of its Ref amps, to great acclaim. Having felt that the originals were just dandy, and a nearly ideal match for some speakers, I was intrigued to find out if "new and improved" might mean more than it does on a cereal box. Bel Canto sent me three Ref1000 Mk.IIs ($5990/pair)and I hung on to my review samples of the "Mk.Is" so that I could compare them side by sideor, as it turned out, stacked atop each other.
Externally, there is nothing to distinguish a Mk.II from an original Ref1000 except for the name printed on the rear panel. Connections and operation are identical. Selectable XLR and RCA input connectors share the rear panel with the AC input, a power switch, and those confounding but sturdy, EEC-conforming speaker posts. The front panel's single LED indicates when the amp is powered on.
Under the skin of these little bricks, however, the differences are significant. You can see this by comparing the Mk.II (see photo) with the picture of the original. In the original, there appears to be only the B&O 1000ASP ICEpower module with Bel Canto's added ferrite filters, high-quality connectors, and damping. The Mk.II has a new version of the B&O board, still with BC's tweaks, and accompanied by a more complex input board (the small one in the upper left) and a new power-supply board (at the right, with the two large capacitors). According to Bel Canto's John Stronczer, the new input board is "our own custom high-CMRR input stage," and the changes to the power supply are "to improve the raw DC supply fed to the switching power supplies on the ICE amp modules. The switching supply can be fed either 120VAC/240VAC or even 300VDC and works just fine. In prototyping we found +400 joules of energy storage, low noise rectification, and additional filtration on the raw DC supply made a big improvement, as did an input stage with higher CMRR/input impedance and lower output impedance to drive the amp modules."
The least difficult assessment to make was that the problems with AC line pollution were gone: the Ref1000 Mk.II didn't need to be isolated from the AC line with a filter. Connected to my system, with or without the Environmental Potentials filter, the three of them were dead silent when I held my ear to the loudspeaker driven by eachor, indeed, to the amps themselves. And the Ref1000's small size meant that, when I placed each 500W monoblock directly behind the B&W 802D speaker it was to drive, the amp was completely hidden. How's that for WAF?
Did the Mk.IIs sound better than the originals? I wasn't sure there was a big difference when I played them just out of their boxes, but chance helped prove otherwise. After only five or six hours of use, one Mk.II went silent and had to be sent back to Bel Canto for rehabilitative therapy. While the complete round-trip took less than a week (the problem was only a cranky rectifier), I took the easy route and used one of the original Ref1000s for the right channel while leaving the new Mk.IIs to drive the left and center speakers. It sounded just fine, as you might expect, but reinserting the fully recovered Mk.II into the system helped me hear the differences...and they were all in favor of the new guys.
First, although all Bel Canto amps have had tight, well-defined low ends, the Ref1000 Mk.II seemed to have more heft at the bottom without sacrificing clarity. Organ-pedal notes were obvious beneficiaries, but so were bass drumsthese instruments, though unpitched, convey very distinctive characteristics of their construction, use, and, more important, the acoustic in which they were recorded. Lower strings, whether plucked or bowed, enjoyed a similar transparency, a term I usually reserve for descriptions of treble instruments. These characteristics, and those described below, were instrumental in my enjoyment of Dmitri Kitayenko's traversal of Prokofiev's seven symphonies with the Cologne Gürzenich Orchestra (5 CDs, Phoenix Edition 135).