- Written by Chris Groppi
- Published on 05 January 2009
Outwardly, the XPA-1 looks very similar to the XPA-2 stereo amplifier reviewed here at Secrets recently. The XPA-2 is a stereo amp with a single transformer and power supply, with a Class A/B output stage. The RPA-1 amp I reviewed is true dual mono Class H design, with two separate transformers and power supplies driving two amplifier modules in a single chassis. The XPA-1 is Class AB like the XPA-2, and looks similar inside. Rather than the two sides of the amp driving two independent channels, the XPA-1 uses the two "channels" of the amp to drive the hot and cold legs of the balanced input signal. The single ended input is copied, and the copy is inverted to feed the two sides of the amp. This is the ultimate expression of balanced drive, with two completely separate halves of the amp used to amplify the inverted and un-inverted legs of the input signal, and then recombined at the output. This completely cancels out any common mode noise that both halves of the input signal see in the amplifier. Bridging a stereo amplifier, as you can do with the XPA-2, does not offer the noise cancellation offered by a fully differential design.
The XPA-1 chassis is 5RU size, with a black anodized machined aluminum faceplate with clear anodized aluminum trim pieces. A single LED meter, doubling as a status indicator, spans the face. Both the meter and the status LEDs can be independently defeated via rear panel switches. The 1200VA toroidal transformer is mounted vertically in the front of the amp, just behind the front panel, making the amp a bit front heavy. The amp weighs 76 pounds, with a shipping weight of 90 pounds. Large, internally mounted heatsinks run along both sides of the amp inside the enclosure. The center of the amp sports over 130,000 μF of power supply capacitance. Unlike some "statement" amps by other manufacturers that are mostly empty inside, the XPA-1's chassis is absolutely crammed with components. The rear panel offers a mains toggle switch, 12V trigger inputs and pass-through, balanced XLR and RCA single ended input connectors, and a small toggle switch to select between them. An IEC input jack is present for AC input. The binding posts are in the same position as the XPA-2, but instead of serving as left and right, they serve as positive and negative and offer the possibility of bi-wiring. Ominous "Caution: Potentially Lethal Voltages Present During Operation" warnings are silk-screened in red next to each set of binding posts. Delivering its full rated power, over 60V are present at the terminals. Large, sturdy rubber bumpers are mounted next to each set of binding posts to prevent the amp from being pushed back into something to cause a short. This amp could serve as a high fidelity arc welder, so the extra margin of safety is welcome. A comprehensive set of fault protection circuitry helps to keep you from blowing things up with an incorrectly wired XPA-1.
In addition to all the features, the build quality of this amp is exceptional. No whining about the quality of Chinese made audio gear on this amp. It is as well assembled, and as well designed, as pretty much anything I've seen short of a Boulder 2050 (which costs as much as a new BMW, thank you). Board layout, solder joint quality, parts and materials quality needs no apologies. It isn't stuffed with ridiculously priced "audiophile" components, but everything is top quality for the real world.
As far as design and implementation go, I can't find much to fault with the XPA-1. One issue is that the positive and negative amp terminals are 13" apart. I had to send my Wireworld Eclipse speaker cable back to the manufacturer to have them re-terminated to reach the widely separated Emotiva terminals. If you order these amps, be sure your speaker cables can span a 13" terminal separation. Another weird thing was that the LED meters on the two amps did not seem to have the same sensitivity. I was testing a pair of prototype amps, so they could have been adjusted differently. This was a pretty irrelevant criticism though, as the meters are really just for show. Where the rubber meets the road is with the sound.