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Emotiva XPA-2 Design Overview


XPA2-top.jpgThe XPA-2 is a traditional class A/B design whereas the RPA-1 and MPS-1 are multi-rail class G design schemes. Both are sound designs whereas the A/B’s tend to be a tad more linear at the expense of efficiency. Despite the fact that Class G designs have come a long way, virtually eliminating diode rectification issues thanks to the usage of Schottky diodes with lower forward voltage drops, Audiophiles still prefer traditional class A and class A/B designs. I can understand Emotiva’s move back to the class A/B design in this capacity and, as you will later discover in this review, they took care in squeezing out as much efficiency as possible while also ensuring the amplifier runs cool during large power emands.

Unlike past Emotiva amps which have traditionally been mono block constructions with independent power supplies for each channel, Emotiva instead employed one large central power supply for all channels. This design philosophy is carried through for all XPA series amps such as the 3 channel XPA-3 and 5 channel XPA-5. While the advantage of truly mono block designs often is superior channel to channel isolation, you can achieve very good, and often nearly equal results having a single centralized power supply but with one huge advantage - more headroom available to any single channel since each channel now has the ability to tap from one larger supply. This is the methodology I usually prefer as I am all about headroom in amplifiers.

Emotiva claims the XPA-2 has a total of 120,000uF of power supply capacitance. Even if all 12 of these 50V 15,000uF capacitors were wired in parallel, it would add up to 180,000uF, NOT 120,000uF so I am not sure where they got this figure from. What Emotiva isn’t telling you, is that these caps are NOT all wired in parallel like most amplifiers. They can’t be parallel connected because this amplifier is rated at 250wpc into 8 ohms requiring at least 71V caps to achieve this power rating. Instead, Emotiva is wiring them in a series-parallel combination so that the total effective power supply capacitance is ¼ what it would be if they were all wired in parallel, but provides a potential of 100V storage to drive the rail voltage up high enough to meet their power goal. Thus this amplifier really has an effective storage capacitance of 45,000uF, NOT 120,000uF which is still very adequate for this amplifier. According to their website, the power transformer is rated for 1.6kVA while their user manual states 1.2kVA. Considering the max power consumption is 1500 watts, I’d tend to think the 1.2kVA rating is the correct one yielding a power factor of around .8. This is quite a massive power supply for a multi-channel amp, let alone a 2 channel amp costing well under $1k. I’d call shenanigans on their specifications, but considering what this amplifier offers for the money, I’d instead chalk it up as typos on their website which they can now go back and review.

XPA-2caps.jpgA peek under the hood reveals why this amplifier is so heavy. It’s got a lot of metal, heatsink area that is. Coupled with 12 output devices per channel and the aforementioned power supply, this is a solid receipt for stable high power delivery. I was simply amazed by the construction quality and that it utilized such massive tapered heat sinking. This is not something you find in amps at double the price demonstrating Emotiva has really put together a fine wine on beer budget pricing.

If for some reason you can’t get enough juice to your speakers with this amp, it is also bridgeable. The XPA-2 is rated to 1kwatt when bridged into an 8 ohm load but the manual clearly states to NOT bridge this amp when driving 4 ohm speakers. For those power hungry nuts driving inefficient 4 ohm speakers, you may want to consider stepping up to a pair of XPA-1’s which are fully balanced and differential from input to output and have nearly 3 times the power reserve (10 x 12,000uF parallel topology) of an XPA-2. Note in most cases you’d probably be ok running this amp in bridged mode for a 4 ohm speaker, but I respect Emotiva offering a word of caution for those tempted to hook up even lower impedance speakers in this configuration mode.

Bridge Mode: This connection allows you to use two amplifier channels to output opposite phase signals generated from one input signal. When you bridge an amplifier, you effectively double the output voltage witch can yield up to 4 times the rated output power assuming the power supply can deliver that much current. This is a good idea for applications that require lots of power to reach high SPL’s but its important to note that each amplifier effectively sees ½ the rated impedance of the loudspeaker so if your speaker system is rated nominally at 4-ohms, be sure the amplifier is stable for two ohm loads before bridging it. Never bridge an amplifier that isn’t designed to do so!

About the only criticism I could make on the cosmetics of this amp are the cheesy LED power meters which I thought died away in the late 80s. Apparently Emotiva isn’t always up with the latest trends but at least they made them defeatable. Personally I’d love to see the LED meters replaced with big analog glass VU meters and have them charge an extra $100 for this feature.


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Recent Forum Posts:

flemingg posts on September 24, 2013 05:10
Contacted renting it right now.

Darkwing_duck posts on September 24, 2013 03:30
Irvrobinson, post: 857390
Just out of curiosity I read this review recently, since I'm in the amplifier market right now. The quote above fascinated me. Gene, do you believe that there are audible differences between well-designed amplifiers performing within their specifications?

Good question Im curious to know as well
Irvrobinson posts on January 13, 2012 15:29
No, the XPA-2 doesn’t treat my music with the kid gloves that my much more expensive $7k Denon POA-A1HDCI amplifier is able to do, but it shares many of its sonic virtues while also besting it in sheer output power.

Just out of curiosity I read this review recently, since I'm in the amplifier market right now. The quote above fascinated me. Gene, do you believe that there are audible differences between well-designed amplifiers performing within their specifications?
scott911 posts on March 20, 2010 17:00
I'd like to see an option of a plexi or lexon type replacement cover… a very nice interior design. It's nice to see that level of attention to detail and pride.
PaulF posts on May 16, 2009 16:48
Gene, I noticed you used the unbalanced inputs for your review. What would be the resultant noise floor if balanced inputs were used?

I agree that an input sensitivity switch would make sense, I see no value in reaching 100% amplifier output with the volume at 50% when using a decent pre/pro. In fact I would prefer the more precise control the volume would allow with a lower gain amp.
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