Exile Audio X600.4
Disclaimer: This review is strictly "my opinion", and should be taken as such. Any information provided should be considered yourself, as I am not a "professional reviewer", and am also not an "expert" on amplifier design. Also, I am not paid or compensated in any way (other than getting to play with the product in question for a short period of time) by the manufacturer of this product, so don't expect any portion of my review to be "sugar coated".
I would like to thank Ben Vollmer for purchasing this amp, and allowing others to test and play with it.
As with my other reviews, I will break this down into a few parts. The first of which is cosmetic build. This will entail fit and finish, and what I think of the overall look of the product. The next section will be dedicated to the electrical design, and will include my evaluation of the amplifier circuitry and parts. The last section is performance, where I will measure different aspects of the amp with the equipment I have at hand, and finally listen to it myself for a subjective opinion.
Cosmetics:
Having seen photos of this amp on the Exile web site (www.exilecaraudio.com), I first assumed it was made mostly of plastic. I could not have been farther from the truth. The ONLY item on the amp which is plastic, aside from the speaker and power terminals, is the LED holder on top. Every other part is aluminum, or steel. Many parts are castings, and some are extrusions.
As you can see on the bottom of the amplifier, it is made in China. That is quite common to see these days, so it does not count against the amp to me, especially since all engineering on it is claimed to have been done in the USA.
Then ends of the amp are solid cast aluminum, as are the badges on the top and bottom. These items are very heavy, and well made. I am confident one could easily beat someone to death with an aluminum end. Each part is nicely cast and fits to the amplifier flawlessly. The parts are held in from the bottom with self tapping Allen screws. I suppose one could also paint these for a custom install, but that would be a total waste in my opinion, as the aluminum really looks beautiful with its satin chrome finish.
Because of the layers that make up the amp, many options are available to alter how it looks. Some options are shown below.
I am a big fan of exposing the circuit board, and this amp allows you to do it with a reasonably high level of taste.
Many parts make up the chassis, the following show most of them...
The model number of the amplifier is nicely displayed on on of the aluminum ends.
The terminals are laid out nicely on the ends. All text is easy to read, and located conveniently. The terminals used are setscrew type. This is quite an improvement over cheaper barrier strip types. I also like how these are on an angle, instead of being a simple block. The angle allows the cables to come right out of the block, and then disappear into a hole in your amp rack. This should make for a clean look.
Two 25A blade fuses are installed on the power/speaker end of the amp. I think this is a nice touch on amplifiers. It tends to save them (unless fools install bigger ones), and it is easy to reach.
The controls on the amp are equally nice. The RCA jacks are off the shelf parts, but are nice enough.
This amp has no 2/4 input selection switch. If you want to drive the front and rear with a single set of RCAs, you need to use "Y" cables. This is a bummer, but is not the end of the world.
The overall look of the amp is a bit extreme for me, but it could grow on me. I am most interested in the ability to expose the circuit board through the metal mesh on top. The quality of the chassis parts, and the way they fit together is the best I have ever seen on any amplifier, with the only thing close being Zapco.
I cannot stress enough how nicely the parts fit together. Typically castings never fit nice, unless the tooling was really done perfectly. Well, in the case of this amp, the tooling was done very well, and the parts show it.
Electrical Build:
After seeing the attention to detail put into the chassis of the amplifier, and all its many metal parts, I was excited to check out the functional aspects of the product. Well, before I go any further, I need to put this into perspective. This amplifier is only a $300 to $350 entry level amp. After seeing the extensive effort put into the amplifier's chassis, there is really not a lot of budget left over for the board, and parts. This does not mean the amp will be sub par, it just means it will perform like a $300 to $350 amp, and not a $500 to $700 amp.
Right away I noticed tons of short metal jumpers all over the board.
As it turns out, this amp has only a one sided board! All soldering, and all connections are on the back side of it. This is the first amplifier I have seen built like this. I have heard that many entry level amps are going this route but have yet to see one in person. To make the amp's appearance better, Exile has painted on fake circuits on the top layer. This gives the illusion the amp is a double sided board when it is not. This is a nice cosmetic touch when looking at the amp's board through the screen top, or open top.
Some of you may wonder why I even care. Well, a double layer board has many advantages. First, it allows you to run more traces where you want to (instead of where you HAVE to), so you can make signals run shorter and less noisy paths. Next, any hole in a double sided board is plated with metal all the way through it. When you solder a component in, it has many times more solder holding it in place. Next, with a double sided board, you don't need all the little jumpers, so you have less connections. Less connections (soldered connections that is), the more reliable the product will be. I question the long term reliability of this amp, but that is likely just my paranoia. AudioControl and Phoenix Gold have built signal processors like this for years, and they last just fine.
Next, as far as I can tell, the board is not made of fiberglass. Fiberglass is an industry standard for high quality products. This amp seems to have some sort of fiberboard, or phenolic material used. The strength of the material seems to be fine, it just does not have a "quality" feel to me. I have seen similar materials used in older amps (Kenwood, Pioneer, etc), and they seem to last just fine, so I am likely being picky.
This amp uses clips to mount all its heat producing devices to the heatsink. I really hate clips. I spent about an hour just removing one. I am sure there is some sort of trick to it, but I don't know the trick, and I still think clips are a bad way to go. I would much prefer a clamping method like what is used on countless other amps out there. Clips are also a real budget move. They are cheap, and require minimal labor to install.
Exile informed me the clips are easy to remove and insert with a special tool. Well, I think I want to buy one of those tools! I have seen clips on high end amps out there (Arc comes to mind), but I still don't like them, and prefer clamps.
For input capacitance this amp has a pair of 2,200uF capacitors. This is far less than what I would like to see. At least 4 would be the bare minimum for this amp.
For rail capacitors, two 2,200uF 35v caps are used per rail. Again, this is the bare minimum one would want to use for a design like this, but considering the products retail price, it is on par.
Each channel uses a pair of TO-3P output devices. This is the minimum, but due to the potential of these devices, this is not all that bad. According to the Exile website, these devices are BJTs, not MOSFETs. This is very good news. BJTs are a more expensive way to go (far more parts needed), and BJTs are more linear for audio use. I could not remove the damn clips, to verify what exact devices they are. Maybe someday if I have a clip tool, and one of these amps, I will pull them off.
The transformer used is a nice one, with a ring on the bottom which it is glued to. This should keep it from making any noise, and also makes it more reliably mounted. In a recent review I read meant to discredit Exile, the actual size of the transformer core was questioned. Well, core size is not really relevant, unless you are talking extreme differences. So long as the core is the proper material, and dimensions for flux flow are designed properly, a small one can perform as well as a larger one.
I managed to remove the clip over a pair of power supply MOSFETs, and snapped a photo. They are very common TO-220 devices, which many companies use.
The issue is there are only four of them. Even though this is an entry level amp, six MOSFETs would have been nice to see.
This amp does have some nice points to it electrically. The preamp section is nicely organized, and large buss bars are used throughout the amplifier. All crossover controls are of the detented variety, and that is a BIG plus in my book. This amp uses 18db/octave slope crossovers. I would have preferred to see either 12db/octave, or 24db/octave due to less phase related issues, but for this price point, 18db is a great choice, and should keep some people from blowing their coax to pieces.
The input section looks a bit "cheesy". I am not a fan of ceramic disc capacitors, and this amp has plenty. I don't know if they are in the signal path or not, as I could not remove the device clips so I could pull the whole circuit board and get a look at the underside.
Even though the board, and the parts used were a letdown compared to the solid chassis construction, this still says nothing about the amp's performance. Hopefully in the next section, the amplifier can prove itself.
Performance:
Whenever I test an amp, the first thing I do is find out what its max unclipped output voltage is. This shows me the maximum theoretical power the amplifier is capable of. I drug out my oscilloscope, and a CD player with some test tones, and measured 17.2V per channel prior to clipping. Using basic math, that works out to 74W a channel. Not too bad for a 75W rated amp, and clearly in line with the products price point.
There is a catch though...
My power supply is 14V. Not 12.6V, and not 14.4V. It is my understanding this amp is unregulated (if I am wrong, someone let me know). This would mean that even less output voltage would exist when using the amp with the car off. Now the amp is not even meeting its ratings. Next, nearly every amp out there experiences a drop in output voltage, when loaded. Overbuilt amps with many output devices don't have this problem, and also double their power into lower loads. In the case of this amp, it has only a pair of output devices per channel, and only four MOSFETs in the power supply. I am confident when all channels are loaded with real world loads, and working in a car playing real world music (not test tones), the amplifier's output voltage will drop even further. Now, this is just a assumption based on my previous experiences. It is possible the amp will sustain its output, but I do not have the equipment to verify that. My assumptions here are based on all the testing of top of the line amps I have done in the past. I would have to test some other entry level amplifier to see if they follow this trend. My guess is they would.
In the same review I read meant to discredit Exile, crossover distortion was mentioned. I am not talking about distortion from the crossover in the amp, I am referring to the point where the transistors "hand off" the load. This can be seen on an oscilloscope, and would occur near where the signal crosses the "x" axis. Class B amplifiers have this issue (feedback can eliminate that however), and Class A/B was specifically developed to combat this problem. Well, I saw no signs of crossover distortion on my oscilloscope when I looked for it. It is very possible the problem was there, but my scope is quite old, and has a wide trace drawn by the electron gun. If it were there, I would likely not see it.
I ran frequency response plots of the amp to verify how flat it is. The results are shown below.
As you can see, the amp is quite flat (at least as flat as any other amp I have tested). The crossover also performs to spec (maybe a wee bit off), and will serve its purpose well.
I spent a considerable amount of time listening to the amp. Nothing jumped out at me as particularly great, or particularly bad. Usually when I hook up an amp, I will notice if something it wrong right away. I can't place WHAT is wrong, but just that something it wrong. For instance, when I listen to a Rockford amp, the output is far less stereo, and has no spatial presence to it. I have no clue why this is, just that I can hear something is off. This is totally subjective though, so others will likely hear things differently. Well, this amp seemed to sound just fine to me. I would also like to comment that the bass response seemed forceful, and accurate. Typically RF amps exhibit this, and the other amps I have tested (PG, Zapco, a few others) are somewhat lacking on the bass end. It was welcoming to hear good clean bass off this amp.
As far as sound quality is concerned, I feel you more than get your $300 worth out of this amp.
I would also like to mention heat. This amp has a TON of aluminum in its chassis. I was far from warm after a lot of use. In a car, on a hot summer day, I would expect it to get quite hot, but still functional, and still dissipating a lot of its heat.
Final Thoughts:
The first question I would ask myself is "would I buy this"? Well, currently, I am not in the market for an entry level amp, so no I would not personally buy it. However, I would recommend this to anyone I know looking for an entry level amp.
As stupid as this may sound, if it were sold WITHOUT a circuit board, I still think it would be one hell of a deal at $300 just for the chassis parts you get. Exile could probably sell these chassis for $200 and sell them like hot cakes for Exile users to stick other stuff in (EQs, Crossovers, DSPs, etc). The quality of the parts used in the chassis alone justify the amp.
Well, for $300, you get a killer chassis, AND a circuit board that plays music. This is almost like finding a prize in the cereal box.
After reviewing this amp, although I am not real impressed with the overall package, I am very excited to see what the future has in store. If Exile took the exact same chassis, changed the color of the parts (maybe all black), then stuck in a real impressive high end board with parts to match, boosted the price accordingly, and sold it as a step up line, I think it might be enough to get me to switch over. This would also be an easy project for Exile, as the amp currently has enough thermal mass to sustain a far more powerful design, and the cosmetic options would allow the user to display their work of art.