Hi all, Zombie-X here again with another review for the good boys and girls of Head-Fi.org. Up today I have the SPL Auditor, one of SPL's own high end headphone amplifiers that is intended for studio use. I've had this amp for about 6 months and it's quite impressive. Truly it's sound is high end. But you want to more, don't you?
I would love to give a big thanks to both Robert at Aphrodite Cu29, and all the employee's at Front End Audio for supplying the SPL Auditor as well as information and guidance. These guys are really helpful and have a lot of insight into the unit's. I'd also like to give a shout out to SPL for supplying me with more information as well as granting me the use of images in this thread.
During this review I will be comparing to my other amps: Audio-GD ROC, Woo Audio WA3+ (modded), and the Musical Fidelity X-CANV8P. Each amp will be compared quite extensively and will be tested with a wide variety of headphones. The Audio-GD ROC and SPL Auditor will utilize the XLR output from my Violectric DAC V800 while the WA3+ and X-CANV8P will be feed by the RCA Output from the DAC V800. The RCA output will be using Audioquest RCA splitters and the XLR output will be going through the SPL Auditor to the Audio-GD ROC.
SPL, or Sound Performance Lab, is a leading manufacturer of studio gear based out of Germany. All their equipment runs on their famous 120V technology. They manufacture lots a gear ranging from equalizers to headphone amps, even software plug-ins. All of their gear is high end and is for studio use, but does not seem to exhibit the typical studio sound, that being the music is dull, lifeless, and clinical. In fact from the gear I have tried their stuff is pretty natural sounding.
After getting this amp from Front End Audio, I noticed the size of the box itself. It's quite big actually! The amp is housed in a specially designed box, and you have to open it up a certain way. In my anxiousness I just used a razor blade and sliced the box open. The amp itself is quite big and despite it's size it's not that heavy at all. The finish of the amp is quite nice and the matte finish looking striking to say the least. The Alps potentiometer is buttery smooth and feels "right" when you turn it. All the jacks in the back are of high quality and use Neutrik parts, notably the XLR in puts and outputs. The power switch on the back is also nice and had a good click to it when you flip the unit on.
When turning the unit on, have the volume all the way down and make sure no headphones are plugged in. When powering down the unit be sure to lower the volume and disconnect the headphones before power down. Not doing so will result in no damage to the headphones or gear, but the amp will discharge residual voltages which will make the headphones "beep" a few times or until all the voltage has been discharged. Like I said this will not harm your gear at all but it's a nice precaution in doing so. I always do this.
The XLR outputs in the back are for a direct output, so a line level signal. They are independent from the volume control and are quite useful if you plan on daisy-chaining a couple amp or other equipment together. You can also use RCA cables on this amp but they will require the use of an adapter. Using the RCA cables with give you have the voltage of a normal XLR cable so the volume will have to e turned up more. I have tried it both ways and using RCA input will hinder this amp as it's designed for taking a balanced signal. I recommend a balanced DAC or other source if you plan on suing this amp.
You can also initiate a "Unity Gain" mode by turning the volume to 0. This will give you a non-attenuated signal, but you need another way of adjusting the volume earlier in the chain. Unity Gain mode will give you an unaltered signal and as such sounds a tad more full and slightly slower sound. It's a nice feature but is dependent on something else to adjust the volume before hand.
This amp in a few words is neutral, transparent, and faithful. There is nothing added or subtracted from the sound at all. No treble spikes or dips in the treble. The typical studio sound, as described earlier, is cold and analytical. Well you know what? If doesn't have any of those issues. It maybe ultra transparent and very neutral, but despite those it is quite natural sounding. Also there is a stigma that German gear tends to sound bright and thin and clearly this amp does not exhibit these issues at all. The amp will only sound colored if the source or DAC is colored. If your DAC is clinical, the amp will sound clinical. It really shows the flaws in anything higher in the chain. You can even hear if your other gear is not up to snuff. Quite a nice feat and in my opinion the amp should be the last thing in the chain to color the sound.
This amp has an output impedance of 9Ohms, and as such requires a headphone of 72Ohms or more. This is usually the case but not this time it seems. I have tried numerous IEM's and portable, low impedance headphones and they did perform nicely. One thing I have noticed is that the impedance mismatch causes the sound to become fuller sounding, but it's not bad in anyway. In fact I like how this amp sounds with my Shure SRH-440 (with SRH-840 ear pads). It gives the Shure more bass impact without sacraficing control. Typically the sound of a mismatch between amp impedance and output impedance makes the sound muddy but I ahve not heard this with this amp as of yet.
The amp itself is geared toward 600Ohm, which according to SPL, is the industry standard. As such the amp can output 1.7W into a 600Ohm load and can swing 120V. That's a huge voltage swing and this amp can drive the 600Ohm beyer dynamics quite well. The 600Ohm Premiums headphones are typically quite hard to amp as they needed a much higher than normal voltage to get loud and retain control. I'm glad to say this amp drives them all quite well, no that's an understatement. It drives them effortlessly and perfectly. The DT990 needing a bit more power than the DT880 in order to retain control over the bass, and this amp delivers. The bass remains tight and punchy without sounding muddy or bloated. In fact this amp may be the best $1,000 choice for the 600Ohm beyerdynamic models.
The K501 sound exceptional from this amp. As many know, the K501 is quite hard to drive well as it is lower sensitivity and higher impedance. Safe to say this amp gets them loud and then dome. The volume is only at a bit over 1/4 of the way up and the headphones are quite loud. It's not gain, but pure voltage that gets them there so fast. On my other amps the volume has to be almost half of the total volume the amps could do. The SPL Auditor really delivers the bass on this headphone as well. When properly amped the K501 has quite a bit of bass, and it deep, tight, and controlled. The whole sound opens up and the soundstage expands further.
The K400 is even harder to amp than the K501 and this amp does not disappoint at all. It drives the K400 effortlessly and without fuss. The K400 requires a bit more power than it's K501 sibling, but this amp handles it no problem. You immediately hear the bass is tight and punchy, the mids are detailed, and the treble is extended and grain free. The soundstage opens more, same as with the K501. When the K400 is underamped it can sound anemic in the bass but when amped it's quite generous. I've never heard a AKG headphone with this much bass, these easily have more bass than the K701, which is the bassiest of the current AKG audiophile headphone line.
TREBLE:
The treble on this amp is very well extended and never bright or strident. Completely grain free and smooth. The treble itself is quite clear and highly detailed. Out of my other amps this amp amp certainly has the most refined treble an is the most detailed treble. Extension is quite high and although you can't quite hear that high, you can tell it's extended.
MIDRANGE:
The midrange is this amps strong point no doubt. It's easily better than my other amps in this regard, and you don't even loose or sacrifice anything. The midrange itself is highly detailed and resolving. I can hear stuff in the mids that I have yet to hear before. Examples would be coughing in the background of tracks, light breathing, or someone else talking in the background. Guitar's are more, what's the word, distinct. You can clearly hear how complex some riffs are and even light tapping of the fret board is easily heard.
BASS:
Bass, bass, and bass. The amp has some of the deepest and most controlled bass I have yet to hear. It reaches really deep and grabs you by the throat. Remember this amp is neutral, but the bass is so pure and can sound visceral. The texture and ability of resolved complex bass passages of guitars is quite astounding to me. If your music is heavy on the bass, this amp will deliver it in gobs, but if light then it will give you light bass.
SOUNDSTAGE:
The soundstage is really good on this amp, yet again it has the biggest I have ever heard. Quite easily the most open of my headphone amps, though my ROC does come close. It's pretty three dimensional and has excellent depth, height, and width. Everything snaps into place when listening to music and sounds coherent and distinguishable.
VS. AUDIO-GD ROC:
The SPL trumps the ROC in almost every way. The ROC itself is a warmer sounding solid state amp that is toted as being a "wire with gain" amp by Audio-GD. For the most part they are right, but the amp is slightly warm with a slight emphasis on the mids and bass. The ROC falls short in terms of transparency and micro detail. With the Auditor, small details like light footsteps and faint breathing can be slightly masked. The amps itself is still quite good but is not as detailed and resolving as the Auditor. When comparing the two it's as if you are looking through a slightly tinted window with the ROC, but with the Auditor it is like the window is open. The bass on the ROC is deep and tight with a slight bump to it and a little "roundness" in it.
Another thing is how the ROC handles various loads. The ROC is optimized for 100-300Ohm loads from it's power output chart, but it does a better job with low impedance headphones such as IEM's. The ROC has better control of these headphones due to it's lower output impedance. The SPL Auditor has a 9Ohm output impedance and as such has a lower damping factor which makes it more suitable for higher impedance headphones of 80Ohms or more.
VS. WOO AUDIO WA3+ (MODDED):
These amps sound totally different. The SPL Auditor is dead neutral and transparent while the Woo Audio WA3+ is really warm and generally has a more lush and smeared sound. Smeared may be a bad word to use but what I mean is that the sound more or less blends together, aka smear. The WA3+ is very musical and warm, but it loses detail and extension on both ends due to the tubes. The tubes hinder the treble a bit and cause it to roll off. Even when using the neutral 7236 tube type the sound can still sound warm. It's just the nature of the amp. The amp also adds more bass to the mix and is a typical tube bass that sounds more rounded, aka full. The soundstage is still quite good but the ability to pin point stuff in the stage can be difficult as tubes blend the sound a bit. Besides that the soundstage is rather large.
The WA3+ is OTL by nature and that means it has a high output impedance. The OTL design will give you a higher voltage swing and the higher output impedance will make a good damping factor for high impedance headphones. The WA3+ does not do all that good with low impedance gear as the output impedance in the ballpark of over 60Ohms, and the amp can't manage much current output. The sound on low impedance headphones will sound mushy and bloated. In this case the SPL Auditor is a better choise, but still not ideal.
VS. MUSICAL FIDELITY X-CANV8P:
The X-CANV8P is one of the most versatile amps I have heard. It has an output impedance of less than 2Ohms, which means it can drive most headphone with a very linear sound. The sound of this amp is warm and musical, no doubt it's from the tubes inside. The amp is a hybrid design, in which the sound passes through the tubes and then goes through a solid state output buffer to the headphones. You get the tube sound and power of solid state. The amps also suffers from the tube smear as described above in the WA3+ description.
The amp also has a high damping factor and is good for low impedance gear. It fairs well with higher impedance headphone like the HD600 but falls flat with the 600Ohm DT880 and DT990. It sounds good with them but doesn't have enough voltage. With low impedance headphones this amp really shines. It can power all my IEM's really well and give the Shure SE215-K a boost in bass control and definition. The T1 also sounds nice on this amp but it doesn't sound that dynamic and more flat.
The soundstage is good but not great. When using the stock power supply it's only good at best. When using the Little Pinkie V3i PSU from Rock Grotto the soundstage becomes much bigger and precise. Still smaller than the SPL Auditors giant soundstage but still rather good.
The SPL Auditor is darned good amp for the price of $999. It has one short coming and that's the high output impedance and ability to properly drive low impedance headphones effectively. They don't sound bad, but it's not ideal to have that high of an output impedance for low impedance headphones. If you are in the market for a solid state amp that can drive your 600Ohm beyers effectively and without fuss, then this is the amp for you. It drives them all incredibly well, even perfectly I would say. It's easy for me to recommend this amp to anyone that has a 300Ohm-600Ohm headphone, especially if the 600Ohm headphone in question are DT770, DT880, or DT990.
