Solid State Power Amp Reviews

I am finding hard to grasp that it is almost 50 years since I first went to a hi-fi show. That show, held at London's Olympia exhibition center, was notable both for Yamaha's launch of a loudspeaker with a speaker diaphragm shaped like a human ear, and for being the first time I saw the drop-dead gorgeous Transcriptors Hydraulic Reference turntable, which was later featured in the film A Clockwork Orange. The most recent show I attended was AXPONA, held last April in the Chicago suburb of Schaumburg. There I saw no ear-shaped drive-units, but the final room I visited featured sound that the 1969 me could have only fantasized about (footnote 1). MartinLogan's Renaissance ESL 15A speakers, which we reviewed in January 2017, were being driven by Constellation source components and amplification, and I chatted with the latter company's Irv Gross about my reviewing a Constellation amplifier, which are made in the USA.

Gross suggested that he send me the new Centaur II 500 stereo amplifier from their Performance Series, which costs $55,000. I gulped at the price—Michael Fremer and Jason Victor Serinus hardly break a sweat reviewing amplifiers in this price range, but I'm made of cheaper stuff. But hey, nothing ventured, nothing gained.

The Performance Centaur II 500
Larry Greenhill reviewed Constellation's Inspiration Stereo 1.0 power amplifier in April 2018. The Inspiration Stereo costs $11,000, delivers 200Wpc into 8 ohms (23dBW), and on the surface looks very similar to the Performance Centaur II 500. Both are rectangular boxes of brushed aluminum with Constellation's distinctive perforated side panels concealing the heatsinks, and a long horizontal control bar on the front. I asked Irv Gross what the audiophile gets for five times the price. His primary answers were: more power—the amplifier I review here is specified as delivering 500Wpc into 8 ohms (27dBW), 1kWpc into 4 ohms (27dBW), or 1600Wpc into 2 ohms (26dBW)—and more weight. The Centaur II 500 weighs almost three times as much as the Inspiration Stereo: 150 vs 55 lb.

Like all Constellation amplifiers, the Centaur II 500 is based on the company's Balanced Bridged topology, which combines single-ended output modules, each of which uses eight N-channel MOSFETs to produce the desired output power. These modules nominally output 125W into 8 ohms; as each channel of the Centaur II 500, like the Centaur II, uses two modules, that suggests an output power of 250Wpc rather than the specified 500Wpc. (The Centaur II 500 is specified as offering 250Wpc into 8 ohms.)

That's where that back-breaking weight comes in: Squatting at the center of the chassis, behind the front panel, is a massive toroidal power transformer. The story goes that when Constellation's engineering team was working on upgrading the original Centaur amplifiers to the Centaur II models, they tried installing one of the higher-voltage transformers from Constellation's Reference Series Hercules II amplifier in a Centaur II Stereo chassis. The result—after upgrading the power-supply reservoir capacitors to ones with a high voltage rating, to cope with the higher rail voltages—was a stereo amplifier with the same 500W output power for each channel as a Centaur II monoblock.

Operation
On the rear panel of the Performance Centaur II 500, close to the corners, are four rectangular aluminum blocks; each of these conceals two fuses, one pair per output module. There are two pairs of heavy-duty Mundorf binding posts for hooking up the speaker cables. Two inset panels, one per channel and positioned one above the other, carry the input jacks. Each panel has two XLR jacks and an RCA jack, respectively labeled BAL (balanced), Direct, and RCA. A three-way toggle switch on the uppermost panel, which is for the left channel, allows you to select the input you wish to use for both channels. I used balanced connections (switch in the left position). The central switch position selects the Constellation Direct input, which bypasses the input voltage-gain module and should be used only with Constellation preamplifiers, which have their own voltage-gain module, rendering the one in the amplifier redundant.

After connecting the Centaur II 500 to the wall socket with its 20A IEC cable, you turn it on with the rear-panel Master power switch, which resets an internal circuit breaker. The LED in the center of the front panel glows red, indicating that the amplifier is in standby mode. Pressing the left side of the front-panel control bar for three seconds brings the amplifier out of standby—the LED flashes green, to indicate that the amplifier is warming up. A minute later, the LED glows steady blue: the amp is ready to play music.

The first time I followed this procedure, I got no sound. A quick glance at the manual informed me that a second switch on the upper input panel is used to mute or unmute the amplifier's output. Toggling this switch brought forth my music.

Sound Quality
From the first track I played with the Constellation amplifier driving the Wilson Alexia Series 2 speakers I reviewed in the July 2018 issue, I was impressed by the sweep of sound produced by the combination. In a Rachmaninoff mood, I'd cued up the reconstruction of the composer's Symphony 1 performed by the Concertgebouw Orchestra under Vladimir Ashkenazy (16-bit/44.1kHz FLAC ripped from CD, Decca 411 657-2). At the beginning of the final movement, Allegro con fuoco, when the big tune that follows the trumpet fanfare is propelled with blows on the bass drum, the Performance Centaur II 500 seemed to have no problem coping with the Wilsons' rather demanding impedance at low frequencies. And though this is a very early digital recording, the high frequencies were clean and clear.

And the stereo imaging—oh, the imaging! I was reminded of the very first high-end amplifier I bought, a Krell KSA-50, back in 1983—when, for the very first time, I could appreciate the ability of my system to throw a sonic picture in which acoustic objects were unambiguously and precisely positioned on a two-dimensional soundstage with width and depth. The image of the solo clarinet introducing the theme a minute after the start of the first movement was stable and suitably small compared with the size of the orchestral forces. The Wilson speakers, driven by the Constellation amplifier, were a transparent window on the acoustic of the Amsterdam hall where the recording was made.

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Footnote 1: Jason Victor Serinus and Jana Dagdagan shot a binaural video in this room; you can listen to the sound of this room for yourself (headphones recommended) here.