Review: Behringer A500 power amp

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.

Features

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.

Sound quality

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.

Suitable uses 

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.

Verdict?

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.

Futher reading

The Audio Critic have a very good review of this amp which includes measurements.

Audio Critic Review 

Which active option is right for me?

Previously I discussed the varios active crossover options. But which one is right for you?

Budget

MiniDSP is easily the cheapest option where US $125 covers a simple 2 way stereo configuration. DCX is the next step up and as this unit often can be purchased second hand, it can be very affordable. Thuneau Allocator will typically cost most, although this is highly variable depending on sound card choices, so you have some control there. DEQX is the most expensive option.

How many channels?

MiniDSP allows 2 inputs and 4 outputs, but multiple cards can be used to cater for surround systems of more complex designs. One master volume pot can control a number of boards. Given the low cost, MiniDSP boards can also be used to extend the number of channels for any of the other options. DCX has 3 inputs and 6 outputs and that will cater to most projects. 1 x 6 way, 2 x 3 way, 3 x 2 way are covered. Allocator both allow 4 channel, although if multiple sound cards are used it's possible to obtain more channels in running multiple instances of Allocator Lite. DEQX provides 8 channels.

Phase correction?

Only DEQX and Thuneau provide phase correction.

Dynamic options

DCX has a number of dynamic options that are not supported in the other options. Dynamic EQ allows the EQ settings to change with level. This means you can compensate for the insensitivity of the ears to bass at lower levels, a very handy feature. It also has limiters so you can make the system "teenager proof." You can also effectively dynamic driver protection so that bass is limited at higher output - effectively a rumble filter that only comes on at a certain level.

Ability to make quick changes

DCX wins here. It's quick and easy to tweak settings. Suppose you wanted to adjust the bass level as a particular CD or movie was bass heavy or bass shy. It's quick and easy with DCX. MiniDSP requires a PC to make any changes. I can't comment on DEQX or Thuneau.

Aesthetics

DCX is a bit like a circus and it will annoy some. DEQX looks more hifi and with the other options you are in control.

Sound Quality

MiniDSP is a new option and I haven't tried it yet. I'm not making any assumptions here as price isn't always a good indicator of sound quality.

The sound quality of DCX is a matter for debate. It certainly won't be more transparent than DEQX, but will you actually notice a difference? There is no shortage of people who claim DCX damaged the sound quality of their system, but that could easily be explained as bias against a pro crossover which many assume to be "mid fi at best." I suggest that those who have concerns make up their own mind, ideally with some sort of blind comparison. There mere suggestion of poor sound quality is enough to sway many away from a potentially great value crossover. Don't be too easily put off. Allocator will be as good as the sound card you choose.

Balanced or unbalanced?

In most home audio systems it would be best to run unbalanced lines. Where noise rejection isn't required, balancing actually adds noise. This is acceptable in a pro application where noise pickup over 200m of cabling would be a disaster, but for home use it's rarely a requirement. In the rare situations where long runs are needed, DCX is handy. You might put a concealed audio rack some distance away where it's convenient. Otherwise, this is a black mark for DCX.

Do you want a PC in your sound system?

If so then Allocator is probably your choice. This is a good time to consider other benefits of having a PC in your sound system as a media server for audio and video playback and storage. You can save some money here and gain a lot of new features, but it all comes down to whether you like the idea of a PC in the sound system. Personal preference comes into play.

Budget Blu-ray Review - Soniq QBP301B

How good can a cheap Blu-ray player be? The answer might surprise you. In this case, very good.

Soniq is JB Hifi's "home brand." They are low cost value-oriented electronics products. I purchased this to replace a much more expensive Sony DVD player which cost about five times a much. I have a John Mayer music DVD that displayed as black and white on the Sony, but with the Soniq it actually has colour! I've also noticed less problems with scratched DVDs.

Picture and sound quality

No complaints here. I won't say too much in this area since I haven't performed any critical comparisons to other units, but I'll say this much - it's very capable in both areas.

Remote control

This is nearly always the weak point. The remote is obviously cheap. The layout isn't too bad, but there are a few annoying aspects. The response is a little sluggish - often resulting in pressing a button more than once. Also the volume control is very tedious to use. You can't hold it down but each press reduces the volume by 1%. So if the volume isn't close to correct, you often have to press the volume button 50 times.

Multi region

It's very handy to have a multi region player, both for Blu-ray and DVD. This means you can buy cheap discs from overseas, and often it's simple to convert a player to multiregion. At the time of writing (August 2010), no such hacks are available. This unit will only play local DVDs and Blu-ray discs. This may change, but there's a good chance this player will never support multi region. If that's an issue for you, keep looking.

Inputs and outputs

You will find everything you expect here except perhaps multi channel outputs. Those who want to set up a budget HT surround system without a receiver should keep looking. Optical and coax digital outputs are provided.

There is also support for a memory stick in a USB slot. That means you can view photos, captured video (TV etc). Compatibility isn't guaranteed, and external hard drivers may or may not work. This is unfortunate as one could use a PC digital TV tuner to record TV then play it back via the Blu-ray player. This works out as a very cheap PVR system.

Basic use

With Blu-ray discs, the unit starts up quite quickly, but one source of irritation is ejecting discs. After powering up, it takes quite a while to eject, and often starts playing the disc even after the eject button has been pressed. Another gripe is that it lacks memory. With the Sony, I could watch part of a movie, eject the disc and watch another then in a few days put the first disc back in. It would resume from where it last played. The Soniq remembers the position for a very short period. If you have an "intermission" in the middle of a movie, chances are the spot has already been lost. You end up having to pause rather than stop.

Conclusion

Overall it's a capable player. It looks decent and has no major issues or problems. While there are a few minor complaints, at the price it does all that you can expect.

What's wrong with HDMI?

Have you been told that HDMI is the ants pants and bees knees? That it's the modern solution for the digital revolution and therefore always better than analogue? If so it might come as a shock to hear that it's not actually perfect, but a flawed format that's been enthusiastically adopted without really thinking things through.

HDMI was designed to benefit content providers first and foremost. It's all about copy protection - making it difficult if not impossible to pirate HD content. Of course, in order to gain popularity, something new had to be offered, so the appeal comes from using one cable for both audio and video. Sadly, it's a poor format that falls short in a number of areas.

Problems with HDMI

The biggest problem with HDMI is that it is not suitable for the kind of runs that will often be required in a home theatre. About 5 - 7m is the limit and beyond that you can expect problems with reliability. HDMI uses twisted pairs rather than coax which is the much more sensible choice. Coax cable can be run over much longer lenghts without any problems and is much easier to install.

Blue Jeans Cable explain the problems in more detail >

The future is HDbaseT - read about this new format that is far more promising more >

Bi-amp modules

Recently I purchased some bi-amp modules from the SNA classifieds:



This is one module and includes 2 channels:

50w class AB
350w class D
Switch mode power supply.

Since I have two of these modules, they are enough for active 2 way speakers.



With a few inputs and outputs I have 4 channels of power amps.

Coming soon: active surrounds

Soon here is a stretchy term, meaning hopefully some time this year. I bought these to power some active surrounds. The 50w channels will be more than enough for the tweeters and they are class AB. This is a good thing as I don't believe Class D is suitable for treble. I do have some hesitations even for midrange use, although they will probably be good enough.

The design I have in mind will involve compression drivers in waveguides for the treble, and efficient 10" mids in a low profile wall hugging design.

Why active? It might seem like overkill, but when these modules came up at a very attractive price, they were hard to pass up. Active are easier to design and it was a good excuse to get a MiniDSP board which I intend to use - the cost is similar to that of a passive crossover and it could easily work out cheaper considering I can try different options without buying more parts.

So the plan is to obtain a box from a non-working amp and include the MiniDSP crossover along with the amp modules all in one.

The surrounds are shown here:

Active vs passive crossovers

I'll say it up front. All things considered, I think active crossovers are better. This is a big topic and it's quite complex, so for now I will cover what I consider some of the stand out issues. First, I'll start with an opposing view.

Why passive crossovers might be better

Some argue that passive crossover components are in general more sonically transparent in mid and high frequencies and that active crossovers should only be used for bi-amping so that large inductors on bass drivers can be avoided. This is a point of view that can't be easily proven as in comparing active vs passive, there will always be many variables. I don't see any way that you could isolate "sonic transparency." So this will remain an opinion untested.

An obvious advantage to passive crossovers is that only one amplifier is required. This allows spending to focus on just one amp and this might be seen as a cost saving.

I'm trying to be objective here, but I see this as the extent of the "passive is better" argument.

Why active crossovers are probably better

Control and flexibility
One of the most significant advantages is that an active crossover has much greater power and flexibility. We can easily use steep slopes and a range of EQ and DSP options to gain precise control over the result. We can get tweeters to cross lower and we have far more power to get the most out of the drivers. Cone breakup is far easier to control. Dipole roll-off can be compensated for. Bass drivers can be matched to their box with precise control. All of this means clearly audible improvements and much less compromise.

Active systems have far better dynamics. A passive system will often see clipping caused by power hungry bass drivers, resulting in distortion and a harsh sound coming through the tweeters. An active system avoids this as the tweeter will have it's own amp. Clipping caused by the bass drivers will probably not be audible where with the passive system it causes the system to sound strained and harsh.

Specialist amplifiers
Each amp becomes a specialist and can be chosen for a narrower bandwidth. No need to compromise. You might combine a powerful pro amp for the bass, with your favourite amp in the midrange, and a low powered tube for the tweeter.

Tube amps
Many make the mistake of compromising their speakers simply to use a valve amp that they prefer. With an active system this is not necessary. Drivers can be chosen for ultimate performance in their bandwidth and efficiency becomes less critical. Many efficient drivers have a lot of coloration and problems - that's a high price to pay to use the amp that you prefer. A 7w valve amp will drive any tweeter to very high output levels.

This post is scratching the surface, but some of the best articles I've seen on active are here:

http://sound.westhost.com/bi-amp.htm
http://sound.westhost.com/biamp-vs-passive.htm

How to get started in active

First, have a look at your options. Starting out on a budget, I suggest MiniDSP which involves some light duty DIY. With a few more features and no DIY electronics, many choose Behringer Ultradrive. A step up in performance and a big step up in price is DEQX.

More about active options in detail >

You will need a basic measurement setup >

This will include a mic and mic preamp.

You will then need to obtain software and measure driver acoustic response and work apply filters until you can measure a nice flat response, but your journey won't end there.

Golden ratio rooms for bass

Do golden ratios work for bass? I must admit I'm more than a little skeptical. Talk of golden ratios has always sounded like nonsense to me, the kind of thing that often turns out to be silly when you actually start measuring. I'll investigate this here with some simulations with the FRDC room simulator.

Here is a golden ratio room - 4.8 wide x 7.8m deep x 3m ceiling.


Image courtesy of Cardas Audio
This is just one implementation of Golden Ratios, but could be applied to rooms of different sizes.

Listening is in an equilateral triangle spaced 2.1m from the front wall and 1.3m from side walls. Speakers are 2.1m apart and listening position is the same distance direct from each speaker.




The result is suprisingly good. The bold line shows the bass transfer function of the mains. It is very good! If you actually got that out of a normal room, it would be something to dance around the room about like a nutter. It is flat +/- 5db! 15 - 20 db is more typical.

The purple line is a corner sub combined with the mains. On it's own, the sub is flatter, except for a nasty dip at 60 Hz. Using this setup as a starting point, an excellent result could be achieved easily with a little tuning.

Is it a fluke?

Let's find out what happens when we start breaking the golden rules ...

If we move the listening position back further away, the reponse gets progressively worse, until we see a broad dip centred at 50 Hz at 2m further away.



If we move sideways half a metre, the midbass imrpoves slightly but we see a nasty dip around 120 Hz.

If we move the speakers back but keep the same listening position, so that the speakers are 1m clear of the front wall, we get a narrow dip at 60 Hz.

If we make the room much wider, as if it were now a living room adjacent to a meals and kitchen area (10m), it's not so bad. Finally a change that we don't get punished for!

If you can't beat 'em, join 'em!

I'm surprised to admit that there appears to be something in these golden ratios!

Actual results will vary. The room simulated has a lot of damping and reflects either a lossy room, or one that is well treated for bass absorption.

So if you are building a room you plan to use for audio, and you were going to build a typical 5 x 7m room with 2.7m ceiling, consider this option. Change the dimensions a little, and set up the room a little differently than you might have. Try to stick to it as close as you can. It seems you can get away with changing some things and not others. The beauty of this option is that you can get to a good result very simply. In fact, most will be happy with a simple plug and play setup. A pair of stereo speakers placed as per the ratios with no EQ or special room treatment. All this assumes a lightly constructed room with no concrete or bricks in the enclosing space.

If this doesn't work for you then you will need to work a lot harder for good bass.

More reading

Cardas Audio - Golden Cuboid Listening Room Diagram
Cardas audio - Setting Up Speakers In A Rectangular Room>