Update (March 2013): I posted previously that this amp had failed. However, it turns out that it was in fact the IEC power cord that failed, a rare problem and fortunately one that is easily solved. However, I do still hesitate to recommend this amp due to problems with one of the inputs. Since this is a popular page, I'm leaving it here but I'd suggest people consider Emotiva power amps.
Behringer A500 is one of the best value power amps on the market. I have used this amp in my active system for a number of years and find it's performance to be quite respectable.
Aesthetics and build quality
For many the looks will be a stumbling block to uncovering a bargain. The attenuators and face plate are plastic and do appear a little cheap. The lights on the front show the output level are a little more bright than many would like. With the lights down low for a movie they are over-bright and can't be dimmed.
The case seems sturdy enough and for the price there is nothing to complain about regarding it's quality.
Looking inside the box, you can see the power supply certainly does appear decent.
Both balanced and unbalanced inputs are provided, along with a choice between two different speaker cable outputs. Bridging is included for 8 ohm loads, but conventionally it is stable into 4 ohm loads and provides 230w into 4 ohms or 160w into 8 ohm loads, or 500w when bridged into 8. Clip indicators warn of over driving.
No muting relays
Unfortunately this amp does not provide muting relays. A conventional hifi amp provides relays which prevent thumps when the system is powered up or down. After switching on such an amp, there is a delay of about 5 seconds followed by a click. In those 5 seconds, the amp remains switched off. Other components up the chain might have thumps that could get through at this point and they can be irritating or even destructive. When powering down, muting relays disconnect the outputs before any thumps get through.
This is one corner I wish Behringer did not cut. Suitable relays cost about $10 each and while this might sound trivial, electronics at this price point eliminate everything they can.
In my blind test results post, I mentioned one test in which this amp was found comparable with much a more pricey amp. In keeping with that result, I have found it to be quite decent. Others have reported less than flattering results, but I always take these kinds of reviews with a pinch of salt. I use this amp in an active system driving only the midrange, so I can't comment too much on the top end or bass performance.
You won't find a long subjective description here with words like liquid midrange, shimmering highs and you definitely won't hear words like rhythm, pace and timing! But I will simply comment that the sound quality differences between this amp and one many times the price are far smaller than many audiophiles would have you believe.
Woofers gone mad
In 2010 I witnessed a system that used this amp to power some dipole sub drivers. I was watching the lights get very close to clipping as I was concerned the amp was running hard. Then something strange and disturbing happened that sent onlookers into a mad rush to shut down the system, including myself. The drivers were moving wildly at very high excursion, yet the music did not seem to demand this. They were moving as if playing sine waves or test tones. We shut the system down to avoid failure, then started scratching our heads about the cause. After some digging around and discussing the issues with two suitably qualified experts, I came across an answer that makes sense.
It was clear that the driver and amp got caught in a feedback loop, very similar to what occurs in PA setups. We all know the scenario - if the mic is in the direct line with the speakers, the mic picks up the sound from the speakers and tries to amplify it further, resulting in a loud high pitched noise. In this case, the drivers were acting as the microphone. Why doesn't that happen all the time? Normally the amplifier has a damping factor, which prevents this from happening. The situation is made worse by the use of high levels of global negative feedback, which is used to give a lower distortion figure.
Now there is one missing piece in the puzzle - why didn't the damping factor prevent the feedback loop, as would normally be the case? Some amps have their damping factor drop to zero when clipping occurs. It would appear that this is such an amp. Once a certain clipping threshold is passed, the damping factor protection is removed leaving the drivers vulnerable. Had the system been left on, say to break in the woofers, it's possible they could be fried.
Where not to use this amp
This amp should not be used for dipole woofers as it has been found to be unreliable as described above. It should also not be used with drivers that may be sensitive to damage resulting from power on/off transients. In particular it should not be used in an active system for the tweeters. I also don't recommend it for demanding high power applications or subwoofers. I would hesitate to use this amp for demanding speakers such as electrostatic speakers.
This amp would make an idea upgrade to the main channels of a home theatre system. Where you have pre outs on your AV receiver, you could use this for the mains. It's an ideal amp for most conventional stand mount or floorstanders. It's a good amp for a studio system, and for domestic 2 channel and multi channel systems.
Others have had apparently good results in using this amp to drive subs, so your experience may vary. I would not use this amp in that way - the Europower amps are in my view a much better choice.
Is it a giant killer? I can't say that it is comparable in all respects to many of the amps it will be compared to. No doubt many will consider it alongside more expensive options like Emotiva, NAD and Rotel. All of these products have advantages beyond the sound that make them still worth considering. However, at the price there are few other options and overall I'd call this amp a very attractive option for those who appreciate bang for buck.
The Audio Critic have a very good review of this amp which includes measurements.
Audio Critic Review