What's getting replaced
I have an Alesis RA-150 power amplifier that I used primarily for driving a good pair of studio monitor speakers. Unfortunately, it started developing some problems in the left channel. Sporadic and often only partial cut-outs made it a very frustrating problem. Finally, after sending through some white noise and carefully adjusting the level, I can now usually reproduce the problem quite quickly. Giving the unit a firm tap (never recommended!) usually demonstrates some sort of audible change in the output.
It's out of warranty (of course), so I took off the top cover to see if there were any visible problems or anything easily serviceable. There are a 2 cables (send & return) on each channel for the volume control. Both the cables and the pinned connection headers looked quite delicate. I tried swapping each assembly between channels to see if the problem would follow with the change, or remain as-is. Unfortunately, I wasn't able to reproduce the problem either way - until I had everything put back together and the case closed again!
I checked at a local music store to see if they happened to have anything used and/or cheap that would be a suitable replacement. They didn't. However, while talking to one of the staff, he mentioned that he had the same unit at home with the exact same problem, though he recalled it to be in the right channel. He's curious to take a look at mine to see if he can fix it (and then his, too). He promised not to charge me if he couldn't get it fixed, so I'll probably take him up on that soon.
Besides the unreliability, the RA-150 was a bit underpowered compared to my speakers, so a replacement seemed in order. If the RA-150 can be cheaply fixed, I can find some other uses for it.
A different music company in Wausau likes to speak about Behringer with some very poor ratings. One time, they even told me that Behringer was bought out by Radio Shack - a total lie, and one that I can't even find a rumor of on the Internet. (So instead, instead of thinking poorly about Behringer, I now avoid that music store.) In fact, I'm quite impressed with the German company, including a Eurorack MX 1604A compact mixer of theirs that's served me well for many years. (The 1604A is discontinued, but is only a slightly smaller version of the MX2004A.)
The A500 is marketed as a "Professional 500-Watt Reference-Class Studio Power Amplifier", and I feel the title fits well. Complete specs, photos, and other information can be found on Behringer's site. I also ran across a very detailed, informative review by Peter Aczel at The Audio Critic.
One thing that The Audio Critic incorrectly states is that the A500 doesn't support bannana connectors / banana plugs for output: "...the so-called professional output terminals accept only spade lugs or bare wires—no banana plugs". They really can't be blamed though - neither Behringer nor any of their seller's product pages really say anything about this. Additionally, out-of-box, the binding posts don't appear to have the holes at the back to accept a banana plug. However, after some careful looking, I found that they are simply filled with protective covers. Using a needle-nose pliers between the crevices on the binding post worked quite well to pull the covers out. While using the binding posts without the banana plugs definitely results in a more secure connection, using banana plugs can be quite a bit more convenient in some cases, especially for temporary use or testing.
While the Behringer A500 looks quite similar to my Alesis RA-150, the A500 does have 2 connectivity options that were lacking on the RA-150: XLR signal inputs and 1/4" speaker outputs. (Both have the RCA-style and 1/4" balanced/unbalanced signal inputs and binding post/banana plug outputs.) The one thing I noticed that the RA-150 seemed to handle slightly better was while powering up. The RA-150 would mute the output while power cycling either way, to avoid causing the speakers to pop. The A500 does the same while powering down, but while powering up there is a audible, low-frequency pop, but nothing dangerous or too obnoxious.
I purchased my Behringer A500 at less than $200 through Full Compass in Middleton, WI (Madison). Besides being a great company to work with, their relatively close location helps to save on shipping costs, and ground shipping means overnight.
Two other places I sometimes order through are Sweetwater Sound and American Musical Supply. In Fort Wayne, IN, Sweetwater is a bit farther away, but they have a very good service department. AMS is in Spicer, MN.
Alternatively, you can purchase this from Amazon, as shown to the left.