[size=medium]DAC-Amp Battle: Apogee Mini-DAC vs. AQVOX USB 2 D/A MkII vs. April Music Stello DA100/HP100 vs. Meier Audio Corda Opera[/size]
[size=small]Fit and Finish / Build Quality:[/size]
As you can see, these are some very attractive and well built components. The Opera certainly has a louder and more overt style than the other two, which trend toward the sleek and functional angle. The brushed aluminum and curved edges of the Opera make it quickly catch the eye, more so in real life than you can tell from a picture. The Aqvox is better looking to me in its’ new black garb than the silver model I’d previously reviewed. The light lettering and numerous blue LED’s stand out much more from the black background. Those LED’s also make it a bit of a miniature constellation come nighttime. The Stello components have the most understated appearance, and look quite appealing as well with their thicker faceplates and straightforward style.
The Aqvox is surprisingly light, given its’ volume, whereas the Stellos are surprisingly heavy. All three feel very well put together, but the Opera has a few touches like engraved labeling and hidden screws that make it just an extra bit inspiring. The Aqvox has a somewhat matte finish to the top, which attracts dust quite a bit more than the other two.
The Stello units, I find, have the most pleasing tactility. They have the largest and easier to turn knobs, and the rotary switch to change digital inputs is a nice and convenient touch. The also have the best RCA connectors, which are longer and feel more robust than those of the Opera (second best) and Aqvox. The use of self-closing optical inputs is nice bonus (don’t you just hate losing those little plastic optical port covers?) Also, by using the XLR disconnect tab on the headphone jack, the Stello offers an easy place to push when withdrawing a headphone so that you needn’t get fingerprints on the face of the amp. My complaints about the Stellos are that they don’t have very nice feet (very short rubber bubbles) and the filter switch is in the back
The Opera is generally pleasing to use, but has a few issues here and there. The volume control is very smooth and the indentation to indicate the volume level is quite pleasing. However the input selector switch is a bit too close to the volume knob, so the latter can only be grabbed from certain angles. Also, having the digital input switch in the back is a bit inconvenient if you switch from coax to USB often (although I can understand why it was positioned there). I get the feeling that the RCA connectors might be a bit close together for use with some of the boutique super-size RCA cables, but I don’t have any to confirm this with. The dual Neutrik headphone jacks both grip the 1/4” jack very well, as do those on the Stello. The LED indicator for the digital input pulses on and off constantly if a digital source is not attached, which I think some who use the Opera as a headphone amp only might find annoying. The choice to use a muting relay in the DAC where most companies use a potentially sound-degrading muting transistor does result in a clicking sound (from the unit itself, not in the signal) whenever the digital input signal drops to zero (on the gaps in between CD tracks, for instance). While using headphones, I usually didn't even notice it, but it could be an issue when using speakers.
The Aqvox is a very well-functioned device with few highs or lows. The headphone jack does not grip quite as well as the other two, and the volume knob is a bit on the small side, although given the slender front panel, a larger one might look out of place. The RCA connectors are the smallest of the group and even my simple Neutrik Pro-Fi RCA’s eat them up quite easily. It’s somewhat irksome that it is the only piece of gear I’ve used in a while that has the power input on the left side (of the back panel) and I/O on the right. The best feature it offers is the LED display of the current input frequency, which makes it easy to troubleshoot computer rigs in particular.
The Apogee is certainly the most visually Spartan of the group, not surprising as it has the deepest roots in pro-audio. It sports a rather unusual magenta-on-silver scheme, which stands out, but doesn’t cross the line into garishness. Two sets of four LED’s each are used to indicate the working sample rate and input signal levels. These LED’s are quite bright, but not to the point of distraction. The knobs are nicely finished and adequately sized for the unit, but you have to love the homage to Spinal Tap in marking the maximum volume at “11.” Unlike the others, the Mini-DAC uses an external power brick to supply DC, which is quite small, unobtrusive, and not terribly warm. Due to its’ diminutive nature, the back panel connectors are tightly packed, but not to the extent that any become unusable. The optical port also has a self-closing cover, a nice touch that is always appreciated. There are no RCA outputs on the Apogee, so one must use adapters from the XLR or mini-jack (1/8”) to their RCA-equipped gear.
[size=small]Features and Options:[/size]
All the systems reviewed here have quite a different feature set, and share only three commonalities: one RCA coaxial digital SPIDF input, one USB digital input, and at least one headphone jack. The Stellos and Opera both have two sets of RCA analog inputs, the Aqvox and Apogee have none (i.e. the headphone amp can ONLY be used in conjunction with the DAC). The Apogee, Stellos, and Opera all have analog preamp outputs, the Aqvox does not (i.e. it requires a preamp for use with speakers).
The Aqvox and Stellos both have a set of RCA analog line-level outputs, the Opera does not (less than ideal for use with an external preamp), and the Apogee’s outputs can be set to fixed line-level via internal jumpers. The Stellos have two optical SPDIF inputs, the Aqvox and Apogee one, and the Opera none. The Apogee has dual AES/EBU XLR inputs, the Aqvox one, and the others none. The Aqvox is unique in possessing a microphone input with volume control for use with USB audio. It also offers a large range of controls for DAC functionality (like phase, upsampling, oversampling, etc.) whereas the Stellos can only switch upsampling on or off and the Opera offers no DAC tweaking capability. The Opera also exclusively has crossfeed and dual headphone jacks (wired by default for low/high impedance output, but can be changed to dual low impedance if special-ordered). The Apogee is the only unit whose headphone and preamp outputs can be turned on separately from each other (i.e. you don’t need to power down your speakers or power amp to listen to headphones).
The Stellos and Opera both offer a gain switch for the headphone and preamp outputs, the Apogee and Aqvox don’t. The Opera has a lower low gain setting, which gives more useable rotation on the potentiometer for low-level listening and/or the use of low-impedance, high-efficiency headphones. The Stello offers a higher high gain setting, which would allow it more range for use with low-output sources, high level listening, and/or low efficiency, high impedance headphones like the AKG K1000 or various 600ohm models.
The Aqvox’s single gain setting is well chosen, as it offers a good degree of rotation while still having quite a bit of volume, though loudness with the most inefficient headphones could be a problem. For example I can listen to a quite classical track with my DT531’s (250ohm, 94dB/mW, approx. 100dB/V) at the highest level and the volume is only slightly louder than I’d prefer. This does not bode well for users of less efficient cans like the K1000 (approx. 83dB/V), K240DF (90dB/V), DT770/880/990 600ohm (98dB/V), or folks who like to really crank it up (you know who you are). I measured 1.2V peak output from the headphone jack when playing a 1kHz sine wave at 0dBFS.
The Apogee’s single gain setting is higher than the Aqvox’s, and I have not been able to get near maximum output with any of my headphones. The maximum output I measured from it is 8.9V peak, which is more than all but a very few headphones can handle safely. However, the trade-off is that extremely efficient phones, like the Shure E500 have very little useable rotation on the volume knob. I generally listen at one to two levels above zero. Fortunately there is only channel imbalance very close to zero output, so it is not a major problem.
[size=small]Test System Components:[/size]
Transport: FLAC files from EAC played in foobar2000 with no DSP’s active, and ASIO output to RME Digi 96/8 PAD
Digital Cable: DIY Belden 1694a or 1800F with Canare RCA or Neutrik XLR
Interconnects: DIY Belden 1694a or 1800F with Neutrik RCA or XLR
DAC April Music Stello DA220
Headphone Amp: Headamp Balanced Gilmore Reference (“maxed-out”)
Headphones: Audio-Technica W5000 & W11JPN, Beyerdynamic DT990 2005, DT831 & DT531, UE Metro-Fi 2, Shure E500
Speakers: Event Project Studio 5 (biamplified monitors)
[size=small] Settings Used: [/size]
The Aqvox was primarily used with upsampling on, dithering on, pulse filter, phase normal, and oversampling at 32 (lowest setting, manufacturer recommended). The DA100 was used with upsampling on. The HP100 was used in low gain mode, both filters A and B were sampled. The Opera was used in low gain mode, sampled with crossfeed on and off, and I typically only used the low-impedance output jack, except with the DT831 (which is designed for use with a 120ohm jack).
[size=small]Reference Music:[/size]
See the music list from my previous DAC review.
[size=small]Disclaimer:[/size]
The thoughts posted here about the sound of these products are my own opinions, and I do not pretend for them to be fact, though if you take them as fact, you do so at your own risk. Furthermore, one must keep in their head at all times that this is a comparison of very good products, and though comments about one or the other might sound harsh to an individual within the context of this review, one must keep in mind the forest for the trees.
[size=small]Sound Quality:[/size]
A few notes before we plunge into the true meat of this review: The Apogee, Aqvox and Stellos had no hiss or hum even with highly efficient IEM’s, but the Opera does have a slight background noise when used with them. I’d say it’s at least 6-10dB quieter than the background noise of the iRiver iHP-120’s headphone jack, for those that have that as a reference. I didn’t find it to be an annoyance, but some with more efficient IEM’s than mine could plausibly. I could not hear this noise with any of my headphones, including the very efficient W5000. Also, the Opera had no noticeable turn-off or plug-in thump, whereas The Apogee has both, and the other two both have a noticeable turn-off thump. The Aqvox also has a fairly loud thump when headphones are plugged or unplugged.
AQVOX USB 2 D/A MkII:
The Aqvox sound has certainly evolved from its’ predecessor which I reviewed last year. Gone is the somewhat euphonic midrange flavor, replaced with a leaner, but more accurate presence. I felt that the forward midrange of the MkI imposed a bit of a limitation on the perception of soundstage depth, however this is also not the case with the MkII. Instruments have a bit better separation and air around them than I can recall experiencing with the MkI. The change in the midrange characteristics and soundstaging makes the MkII a bit more relaxed or laid-back sounding than the MkI.
The headphone amp of the Aqvox deepens the same flavor offered by the DAC. If the Aqvox used as a DAC alone offers a very slightly laid-back sound, when used as both source and amp is it noticeably more so. To be very clear, this is not a blanket-over-the-speakers or “Sennheiser veil” effect, but one that can tame a bit of the rough edge of a headphone like the DT990. Listening to very active or busy music with more aggressive headphones, one notices less of a fatiguing effect. Overall, it performs very well for a solid-state headphone amp, offering very good extension to both ends of the spectrum, and leaving no stones of detail unturned. The noise floor is the lowest of the group.
April Music Stello DA100/HP100:
After the opportunity to compare them over the course of months, I maintain the opinion that the Stello DA100 sounds identical to its’ larger sibling the DA220, when used unbalanced (as one would tend to expect from devices that share the same receiver, ASRC, and DAC chips, not to mention output and filter stage topologies). The sound is characterized by a slight bit of extra weight to the upper bass and lower midrange, a lively and inviting tone, and a nicely open soundstage. As I’ve said about the DA220, I’d put the DA100 on par with the Lavry DA10 for sound quality, the only real significant difference being the aforementioned slightly weightier sound.
The DA100’s complementary HP100 does well to keep up with the performance. Much like the Aqvox’s amp, it does what one would expect from a high-grade solid-state headphone amp: pass on the output of a fine source with minimal distortion. What makes the HP100 unique in this field is the filter switch. In the A position, the overall sound is a touch brighter than any of the other headphone amps, which is most noticeable with a brighter headphone to begin with (like the DT990). I can see how the Stello duo has wooed a number of HD650 aficionados, as filter A produces a sound that I could easily see giving some extra spark and life to the Senn’s somewhat dark upper end. In with filter B enabled the high end is somewhat rolled off, and the presentation becomes more laid-back as a result, in fact more laid back than the Aqvox’s amp. Again this is a position with better synergy with brighter headphones, and I’d imagine it would would well with Grados. While the filter system gives the listener the ability to tailor the sound to suit their specific headphones and/or speakers, my only major concern is that one position sounds brighter than neutral while the other is more rolled-off than neutral, which leaves no middle ground.
Meier Audio Corda Opera:
While the Meier Opera offers a more limited DAC than the others, in terms of features and options, the sound quality is certainly up to par. Overall I’d say the Opera’s DAC sounds more similar to the Stello than others, with only a touch more smoothness (but no less detail) to the high end than the former. This is a much better showing that I had expected from a device whose DAC is not as prominently featured as with the other two.
The headphone amp section of the Opera is what makes it really shine. Using a first of its’ kind variable voltage output third channel, the Opera takes headphones to a higher level of sound quality than typical 2-channel amps can offer, closer to what more expensive and complicated balanced amps can produce. The following is a quote from my initial review of the Opera in TTVJ’s Forum:
Quote:
Regarding the Opera’s crossfeed, it moves the soundstage out of the head and a bit forward, an effect noticeable to varying degrees with all headphones I used. Unlike a past version of the Meier crossfeed I’d used in the past, it doesn’t noticeably decrease bass impact. Overall I consider the crossfeed excellent as it both reduces fatigue and increases soundstage coherency/believability, with no noticeable degradation of sound quality.
Apogee Mini-DAC:
The Apogee shares quite a bit of parts selection with the Lavry DA10 I used to own, and not surprisingly it is fairly similar soundwise. Like the DA10, it is a closer sounding DAC to neutral than the other competitors here, lacking the smoothness of the Aqvox or Opera, or the warmth of the DA220. In this regard it is a bit tougher on bad recordings than the others, since the upper midrange can have a stronger bite if mixed too hot. The very lowest of bass has a stronger presence from the Apogee, an advantage for electronic music and movie sounds that take advantage of that lowest octave, not too mention the ol’ pipe organ. The other main difference I found with the Apogee is in the soundstage presentation, which while not noticeable forward or laid-back, deviated from the rest. The images it throws seem smaller, but with more space or “air” between each other. This makes instrument separation seem slightly better (although the detail level strikes me as being no higher).
The headphone amp does well to keep up with the performance of the DAC, but as would be expected is not quite perfect in that regard. The soundstage of the in-built amp is somewhat compressed in depth, not to the point of a flat, plane-like presentation of sound, but noticeably less than what a higher-class amp can reveal. Also, the headphone amp has a very slight softness to the sound, which somewhat counteracts the harder, more revealing sound of the DAC, as compared to the others in this review.
[size=small]Final Considerations:[/size]
All three competitors offer a high level of sound quality, albeit in different potential flavors. A decision on these or similarly performing products should be equally based on the size, features, and simply how well the product fits a given usage pattern/situation. Considering the sound quality these options offer, if one has the right features for a given user it is certainly worth the cost of entry, as it could represent both a source and amp upgrade. Of course the final price for these items will vary a bit depending on where the buyer lives, which could be enough to swing the decision in favor of one or the other depending on how taxes, shipping, currency conversion, etc. all work out.
AQVOX USB 2 D/A MkII: The Aqvox MkII is certainly an improvement over the model I reviewed a year ago. Between the new class-A headphone amp, bigger power supply and any other additional tweaks performed, it is both more versatile and more realistic sounding. The feature set makes me believe it would be best at home in a speaker system using a preamp or integrated amp with no headphone output (or a substandard one). The headphone amp of the MkII will satisfy all but the most demanding headphone audiophiles, and the line-level only outputs dictate the use of a preamp for a speaker system. The ability to use the microphone input for room correction is another benefit of the Aqvox to speaker users. And of course, the Aqvox is the only one of the three to feature balanced line output. Due to the somewhat laid-back nature of the sound from the headphone jack, those looking into it for a headphone system will likely find a better synergy with Grados than Sennheisers (unless of course you are going for additive synergy).
April Music Stello DA100/HP100: This pair is probably the most versatile of the group, and not only because they are two separate units. The tone control of the HP100 allows the user to tailor the sound to individual headphones or speakers more precisely. The presence of both preamp and line-level outputs allow the pair to be used with or without an external preamp for a speaker system. Their modest dimensions also make them the most versatile for fitting into a given space. The only potential gripe regarding sound quality is what I perceive as the lack of a neutral filter setting, however so long as one filter or the other suits the headphones in question, it’s not really a problem. The filter A setting is certainly better for waking up relatively dark headphones, more so than any other competitor here.
Meier Audio Corda Opera: For headphone listening the Opera is certainly a level above the others thanks to innovative features like balanced ground and crossfeed. The Opera can extra a higher level of performance from almost any headphone than one is accustomed to from typical single-ended solid-state headphone amps. If one is reading this review solely with headphone listening in mind, the Opera gets my highest recommendation, so long as one can live with the more limited input/output options. Due to the lack of line-level outputs, the Opera is somewhat limiting as the source for a speaker system, as it must also act as the preamp. If one wants to flavor their speaker system differently with a preamp, they’d be stuck daisy-chaining it from the Opera’s preamp. It offers a novel look and sound quality, one just needs to be acquainted and comfortable with its’ limitations.
Apogee Mini-DAC: The Mini-DAC is a unique product in the field, packing a truckload of capability into a very small chassis, which can even double as a portable listening device with an appropriate battery. It’s relatively neutral sound lets it team well with a wide array of downstream gear and headphones. It also has a price advantage over these competitors, particularly if one opts for the non-USB version, which can be had for ~$700 NEW. But the USB version has the best USB support I’ve used on a DAC, as it includes custom drivers that enable ASIO input. The question of the Mini-DAC is whether one will be satisfied with the compact size and Spartan looks, which are undoubtedly plusses for some and minuses for others. If the pro-audio features, transportability, or neutral sound fit the requirements, the Mini-DAC is certainly a good bargain, even if it is not the Mt. Everest of the field.
[size=small]A Cumulative Ranking:[/size]
This is how I rank ALL the relevant DAC/Amp combo units I've owned or seriously auditioned in the last couple of years, on sound quality alone (i.e. not including price, build quality, looks, options, features, etc.), when using both the DAC and built-in headphone amp, because I figured this question would pop up sooner or later:
1) Meier Audio Corda Opera
2) Stello DA100 / HP100
3) Aqvox USB 2 D/A MkII / Apogee Mini-DAC
4) Lavry DA10
5) Benchmark DAC1 (not the newest version FWIW)
This second rating is meant to describe the units when used as a DAC alone, based again solely on sound quality. It includes several DAC’s that I’ve not owned or auditioned at home, but have auditioned extensively:
1a) Stello DA220 / Aqvox MkII / Lavry DA10 / Apogee Mini-DAC / CI Audio VDA2
1b) Stello DA100
1c) Meier Opera
2) Aqvox MkI
3) Benchmark DAC1 (older version)
4) Bel Canto DAC2
The explanation of the ranking is as follows. All the units under the heading "1x," I believe offer similar levels of sound quality (albeit with differing flavors). However, being that the first tier has balanced output, they have the potential to be used in a better sounding SYSTEM than the following two. The Opera is further differentiated for its' lack of a true line output.
If one isn't going to have a balanced rig, the DA100 is the best sound for the money of the group, for use as a DAC only. A used DA10, DAC1, or Mini-DAC can do well in this regard depending on the price. I think it would be a bit silly to buy the Opera and not use the headphone amp, as to significantly better it, one would need a balanced or tubed amp, depending on preferences. So my picks as a DAC only would be limited to the 1a&1b levels, 1a only if balanced output is needed.
[size=small]Acknowledgements:[/size]
I’d like to take the time to thank Todd at TTVJ for allowing me the opportunity to audition the Corda Opera, and likewise Norman at Aqvox.
[size=small]Fit and Finish / Build Quality:[/size]
As you can see, these are some very attractive and well built components. The Opera certainly has a louder and more overt style than the other two, which trend toward the sleek and functional angle. The brushed aluminum and curved edges of the Opera make it quickly catch the eye, more so in real life than you can tell from a picture. The Aqvox is better looking to me in its’ new black garb than the silver model I’d previously reviewed. The light lettering and numerous blue LED’s stand out much more from the black background. Those LED’s also make it a bit of a miniature constellation come nighttime. The Stello components have the most understated appearance, and look quite appealing as well with their thicker faceplates and straightforward style.
The Aqvox is surprisingly light, given its’ volume, whereas the Stellos are surprisingly heavy. All three feel very well put together, but the Opera has a few touches like engraved labeling and hidden screws that make it just an extra bit inspiring. The Aqvox has a somewhat matte finish to the top, which attracts dust quite a bit more than the other two.
The Stello units, I find, have the most pleasing tactility. They have the largest and easier to turn knobs, and the rotary switch to change digital inputs is a nice and convenient touch. The also have the best RCA connectors, which are longer and feel more robust than those of the Opera (second best) and Aqvox. The use of self-closing optical inputs is nice bonus (don’t you just hate losing those little plastic optical port covers?) Also, by using the XLR disconnect tab on the headphone jack, the Stello offers an easy place to push when withdrawing a headphone so that you needn’t get fingerprints on the face of the amp. My complaints about the Stellos are that they don’t have very nice feet (very short rubber bubbles) and the filter switch is in the back
The Opera is generally pleasing to use, but has a few issues here and there. The volume control is very smooth and the indentation to indicate the volume level is quite pleasing. However the input selector switch is a bit too close to the volume knob, so the latter can only be grabbed from certain angles. Also, having the digital input switch in the back is a bit inconvenient if you switch from coax to USB often (although I can understand why it was positioned there). I get the feeling that the RCA connectors might be a bit close together for use with some of the boutique super-size RCA cables, but I don’t have any to confirm this with. The dual Neutrik headphone jacks both grip the 1/4” jack very well, as do those on the Stello. The LED indicator for the digital input pulses on and off constantly if a digital source is not attached, which I think some who use the Opera as a headphone amp only might find annoying. The choice to use a muting relay in the DAC where most companies use a potentially sound-degrading muting transistor does result in a clicking sound (from the unit itself, not in the signal) whenever the digital input signal drops to zero (on the gaps in between CD tracks, for instance). While using headphones, I usually didn't even notice it, but it could be an issue when using speakers.
The Aqvox is a very well-functioned device with few highs or lows. The headphone jack does not grip quite as well as the other two, and the volume knob is a bit on the small side, although given the slender front panel, a larger one might look out of place. The RCA connectors are the smallest of the group and even my simple Neutrik Pro-Fi RCA’s eat them up quite easily. It’s somewhat irksome that it is the only piece of gear I’ve used in a while that has the power input on the left side (of the back panel) and I/O on the right. The best feature it offers is the LED display of the current input frequency, which makes it easy to troubleshoot computer rigs in particular.
The Apogee is certainly the most visually Spartan of the group, not surprising as it has the deepest roots in pro-audio. It sports a rather unusual magenta-on-silver scheme, which stands out, but doesn’t cross the line into garishness. Two sets of four LED’s each are used to indicate the working sample rate and input signal levels. These LED’s are quite bright, but not to the point of distraction. The knobs are nicely finished and adequately sized for the unit, but you have to love the homage to Spinal Tap in marking the maximum volume at “11.” Unlike the others, the Mini-DAC uses an external power brick to supply DC, which is quite small, unobtrusive, and not terribly warm. Due to its’ diminutive nature, the back panel connectors are tightly packed, but not to the extent that any become unusable. The optical port also has a self-closing cover, a nice touch that is always appreciated. There are no RCA outputs on the Apogee, so one must use adapters from the XLR or mini-jack (1/8”) to their RCA-equipped gear.
[size=small]Features and Options:[/size]
All the systems reviewed here have quite a different feature set, and share only three commonalities: one RCA coaxial digital SPIDF input, one USB digital input, and at least one headphone jack. The Stellos and Opera both have two sets of RCA analog inputs, the Aqvox and Apogee have none (i.e. the headphone amp can ONLY be used in conjunction with the DAC). The Apogee, Stellos, and Opera all have analog preamp outputs, the Aqvox does not (i.e. it requires a preamp for use with speakers).
The Aqvox and Stellos both have a set of RCA analog line-level outputs, the Opera does not (less than ideal for use with an external preamp), and the Apogee’s outputs can be set to fixed line-level via internal jumpers. The Stellos have two optical SPDIF inputs, the Aqvox and Apogee one, and the Opera none. The Apogee has dual AES/EBU XLR inputs, the Aqvox one, and the others none. The Aqvox is unique in possessing a microphone input with volume control for use with USB audio. It also offers a large range of controls for DAC functionality (like phase, upsampling, oversampling, etc.) whereas the Stellos can only switch upsampling on or off and the Opera offers no DAC tweaking capability. The Opera also exclusively has crossfeed and dual headphone jacks (wired by default for low/high impedance output, but can be changed to dual low impedance if special-ordered). The Apogee is the only unit whose headphone and preamp outputs can be turned on separately from each other (i.e. you don’t need to power down your speakers or power amp to listen to headphones).
The Stellos and Opera both offer a gain switch for the headphone and preamp outputs, the Apogee and Aqvox don’t. The Opera has a lower low gain setting, which gives more useable rotation on the potentiometer for low-level listening and/or the use of low-impedance, high-efficiency headphones. The Stello offers a higher high gain setting, which would allow it more range for use with low-output sources, high level listening, and/or low efficiency, high impedance headphones like the AKG K1000 or various 600ohm models.
The Aqvox’s single gain setting is well chosen, as it offers a good degree of rotation while still having quite a bit of volume, though loudness with the most inefficient headphones could be a problem. For example I can listen to a quite classical track with my DT531’s (250ohm, 94dB/mW, approx. 100dB/V) at the highest level and the volume is only slightly louder than I’d prefer. This does not bode well for users of less efficient cans like the K1000 (approx. 83dB/V), K240DF (90dB/V), DT770/880/990 600ohm (98dB/V), or folks who like to really crank it up (you know who you are). I measured 1.2V peak output from the headphone jack when playing a 1kHz sine wave at 0dBFS.
The Apogee’s single gain setting is higher than the Aqvox’s, and I have not been able to get near maximum output with any of my headphones. The maximum output I measured from it is 8.9V peak, which is more than all but a very few headphones can handle safely. However, the trade-off is that extremely efficient phones, like the Shure E500 have very little useable rotation on the volume knob. I generally listen at one to two levels above zero. Fortunately there is only channel imbalance very close to zero output, so it is not a major problem.
[size=small]Test System Components:[/size]
Transport: FLAC files from EAC played in foobar2000 with no DSP’s active, and ASIO output to RME Digi 96/8 PAD
Digital Cable: DIY Belden 1694a or 1800F with Canare RCA or Neutrik XLR
Interconnects: DIY Belden 1694a or 1800F with Neutrik RCA or XLR
DAC April Music Stello DA220
Headphone Amp: Headamp Balanced Gilmore Reference (“maxed-out”)
Headphones: Audio-Technica W5000 & W11JPN, Beyerdynamic DT990 2005, DT831 & DT531, UE Metro-Fi 2, Shure E500
Speakers: Event Project Studio 5 (biamplified monitors)
[size=small] Settings Used: [/size]
The Aqvox was primarily used with upsampling on, dithering on, pulse filter, phase normal, and oversampling at 32 (lowest setting, manufacturer recommended). The DA100 was used with upsampling on. The HP100 was used in low gain mode, both filters A and B were sampled. The Opera was used in low gain mode, sampled with crossfeed on and off, and I typically only used the low-impedance output jack, except with the DT831 (which is designed for use with a 120ohm jack).
[size=small]Reference Music:[/size]
See the music list from my previous DAC review.
[size=small]Disclaimer:[/size]
The thoughts posted here about the sound of these products are my own opinions, and I do not pretend for them to be fact, though if you take them as fact, you do so at your own risk. Furthermore, one must keep in their head at all times that this is a comparison of very good products, and though comments about one or the other might sound harsh to an individual within the context of this review, one must keep in mind the forest for the trees.
[size=small]Sound Quality:[/size]
A few notes before we plunge into the true meat of this review: The Apogee, Aqvox and Stellos had no hiss or hum even with highly efficient IEM’s, but the Opera does have a slight background noise when used with them. I’d say it’s at least 6-10dB quieter than the background noise of the iRiver iHP-120’s headphone jack, for those that have that as a reference. I didn’t find it to be an annoyance, but some with more efficient IEM’s than mine could plausibly. I could not hear this noise with any of my headphones, including the very efficient W5000. Also, the Opera had no noticeable turn-off or plug-in thump, whereas The Apogee has both, and the other two both have a noticeable turn-off thump. The Aqvox also has a fairly loud thump when headphones are plugged or unplugged.
AQVOX USB 2 D/A MkII:
The Aqvox sound has certainly evolved from its’ predecessor which I reviewed last year. Gone is the somewhat euphonic midrange flavor, replaced with a leaner, but more accurate presence. I felt that the forward midrange of the MkI imposed a bit of a limitation on the perception of soundstage depth, however this is also not the case with the MkII. Instruments have a bit better separation and air around them than I can recall experiencing with the MkI. The change in the midrange characteristics and soundstaging makes the MkII a bit more relaxed or laid-back sounding than the MkI.
The headphone amp of the Aqvox deepens the same flavor offered by the DAC. If the Aqvox used as a DAC alone offers a very slightly laid-back sound, when used as both source and amp is it noticeably more so. To be very clear, this is not a blanket-over-the-speakers or “Sennheiser veil” effect, but one that can tame a bit of the rough edge of a headphone like the DT990. Listening to very active or busy music with more aggressive headphones, one notices less of a fatiguing effect. Overall, it performs very well for a solid-state headphone amp, offering very good extension to both ends of the spectrum, and leaving no stones of detail unturned. The noise floor is the lowest of the group.
April Music Stello DA100/HP100:
After the opportunity to compare them over the course of months, I maintain the opinion that the Stello DA100 sounds identical to its’ larger sibling the DA220, when used unbalanced (as one would tend to expect from devices that share the same receiver, ASRC, and DAC chips, not to mention output and filter stage topologies). The sound is characterized by a slight bit of extra weight to the upper bass and lower midrange, a lively and inviting tone, and a nicely open soundstage. As I’ve said about the DA220, I’d put the DA100 on par with the Lavry DA10 for sound quality, the only real significant difference being the aforementioned slightly weightier sound.
The DA100’s complementary HP100 does well to keep up with the performance. Much like the Aqvox’s amp, it does what one would expect from a high-grade solid-state headphone amp: pass on the output of a fine source with minimal distortion. What makes the HP100 unique in this field is the filter switch. In the A position, the overall sound is a touch brighter than any of the other headphone amps, which is most noticeable with a brighter headphone to begin with (like the DT990). I can see how the Stello duo has wooed a number of HD650 aficionados, as filter A produces a sound that I could easily see giving some extra spark and life to the Senn’s somewhat dark upper end. In with filter B enabled the high end is somewhat rolled off, and the presentation becomes more laid-back as a result, in fact more laid back than the Aqvox’s amp. Again this is a position with better synergy with brighter headphones, and I’d imagine it would would well with Grados. While the filter system gives the listener the ability to tailor the sound to suit their specific headphones and/or speakers, my only major concern is that one position sounds brighter than neutral while the other is more rolled-off than neutral, which leaves no middle ground.
Meier Audio Corda Opera:
While the Meier Opera offers a more limited DAC than the others, in terms of features and options, the sound quality is certainly up to par. Overall I’d say the Opera’s DAC sounds more similar to the Stello than others, with only a touch more smoothness (but no less detail) to the high end than the former. This is a much better showing that I had expected from a device whose DAC is not as prominently featured as with the other two.
The headphone amp section of the Opera is what makes it really shine. Using a first of its’ kind variable voltage output third channel, the Opera takes headphones to a higher level of sound quality than typical 2-channel amps can offer, closer to what more expensive and complicated balanced amps can produce. The following is a quote from my initial review of the Opera in TTVJ’s Forum:
Quote:
| Originally Posted by Iron_Dreamer By comparison to my Headamp Balanced Gilmore amplifier driving the W5000 in balanced mode, the Opera driving them single-ended showed noticeable improvement over the Gilmore single-ended, and was much closer in overall enjoyment to it balanced. Bass impact is one noticeable area in which the W5000 improves when balanced, and the Opera was able to nearly match the Balanced Gilmore in this regard. The difference was very small, but palpable, an attempt to quantify it would probably be that the two were only 5-10% different. The Opera also opened up the soundstage of the W5000 much they way the Balanced Gilmore does. Here the difference between the two was solely in soundstage depth, where the Opera sounded a bit flatter. This difference was more significant that that of the bass, perhaps in the 20% region. Overall, this is a great showing for the Opera, considering the physical differences of a balanced and unbalanced rig. The traits of increased bass impact and a more open soundstage (as compared to a normal unbalanced headphone amp) were present on every headphone I used with the Opera. In all other areas, the Opera is a top performer, in that the frequency spectrum is presented in a very even and detailed way with no noticeable anomalies. |
Regarding the Opera’s crossfeed, it moves the soundstage out of the head and a bit forward, an effect noticeable to varying degrees with all headphones I used. Unlike a past version of the Meier crossfeed I’d used in the past, it doesn’t noticeably decrease bass impact. Overall I consider the crossfeed excellent as it both reduces fatigue and increases soundstage coherency/believability, with no noticeable degradation of sound quality.
Apogee Mini-DAC:
The Apogee shares quite a bit of parts selection with the Lavry DA10 I used to own, and not surprisingly it is fairly similar soundwise. Like the DA10, it is a closer sounding DAC to neutral than the other competitors here, lacking the smoothness of the Aqvox or Opera, or the warmth of the DA220. In this regard it is a bit tougher on bad recordings than the others, since the upper midrange can have a stronger bite if mixed too hot. The very lowest of bass has a stronger presence from the Apogee, an advantage for electronic music and movie sounds that take advantage of that lowest octave, not too mention the ol’ pipe organ. The other main difference I found with the Apogee is in the soundstage presentation, which while not noticeable forward or laid-back, deviated from the rest. The images it throws seem smaller, but with more space or “air” between each other. This makes instrument separation seem slightly better (although the detail level strikes me as being no higher).
The headphone amp does well to keep up with the performance of the DAC, but as would be expected is not quite perfect in that regard. The soundstage of the in-built amp is somewhat compressed in depth, not to the point of a flat, plane-like presentation of sound, but noticeably less than what a higher-class amp can reveal. Also, the headphone amp has a very slight softness to the sound, which somewhat counteracts the harder, more revealing sound of the DAC, as compared to the others in this review.
[size=small]Final Considerations:[/size]
All three competitors offer a high level of sound quality, albeit in different potential flavors. A decision on these or similarly performing products should be equally based on the size, features, and simply how well the product fits a given usage pattern/situation. Considering the sound quality these options offer, if one has the right features for a given user it is certainly worth the cost of entry, as it could represent both a source and amp upgrade. Of course the final price for these items will vary a bit depending on where the buyer lives, which could be enough to swing the decision in favor of one or the other depending on how taxes, shipping, currency conversion, etc. all work out.
AQVOX USB 2 D/A MkII: The Aqvox MkII is certainly an improvement over the model I reviewed a year ago. Between the new class-A headphone amp, bigger power supply and any other additional tweaks performed, it is both more versatile and more realistic sounding. The feature set makes me believe it would be best at home in a speaker system using a preamp or integrated amp with no headphone output (or a substandard one). The headphone amp of the MkII will satisfy all but the most demanding headphone audiophiles, and the line-level only outputs dictate the use of a preamp for a speaker system. The ability to use the microphone input for room correction is another benefit of the Aqvox to speaker users. And of course, the Aqvox is the only one of the three to feature balanced line output. Due to the somewhat laid-back nature of the sound from the headphone jack, those looking into it for a headphone system will likely find a better synergy with Grados than Sennheisers (unless of course you are going for additive synergy).
April Music Stello DA100/HP100: This pair is probably the most versatile of the group, and not only because they are two separate units. The tone control of the HP100 allows the user to tailor the sound to individual headphones or speakers more precisely. The presence of both preamp and line-level outputs allow the pair to be used with or without an external preamp for a speaker system. Their modest dimensions also make them the most versatile for fitting into a given space. The only potential gripe regarding sound quality is what I perceive as the lack of a neutral filter setting, however so long as one filter or the other suits the headphones in question, it’s not really a problem. The filter A setting is certainly better for waking up relatively dark headphones, more so than any other competitor here.
Meier Audio Corda Opera: For headphone listening the Opera is certainly a level above the others thanks to innovative features like balanced ground and crossfeed. The Opera can extra a higher level of performance from almost any headphone than one is accustomed to from typical single-ended solid-state headphone amps. If one is reading this review solely with headphone listening in mind, the Opera gets my highest recommendation, so long as one can live with the more limited input/output options. Due to the lack of line-level outputs, the Opera is somewhat limiting as the source for a speaker system, as it must also act as the preamp. If one wants to flavor their speaker system differently with a preamp, they’d be stuck daisy-chaining it from the Opera’s preamp. It offers a novel look and sound quality, one just needs to be acquainted and comfortable with its’ limitations.
Apogee Mini-DAC: The Mini-DAC is a unique product in the field, packing a truckload of capability into a very small chassis, which can even double as a portable listening device with an appropriate battery. It’s relatively neutral sound lets it team well with a wide array of downstream gear and headphones. It also has a price advantage over these competitors, particularly if one opts for the non-USB version, which can be had for ~$700 NEW. But the USB version has the best USB support I’ve used on a DAC, as it includes custom drivers that enable ASIO input. The question of the Mini-DAC is whether one will be satisfied with the compact size and Spartan looks, which are undoubtedly plusses for some and minuses for others. If the pro-audio features, transportability, or neutral sound fit the requirements, the Mini-DAC is certainly a good bargain, even if it is not the Mt. Everest of the field.
[size=small]A Cumulative Ranking:[/size]
This is how I rank ALL the relevant DAC/Amp combo units I've owned or seriously auditioned in the last couple of years, on sound quality alone (i.e. not including price, build quality, looks, options, features, etc.), when using both the DAC and built-in headphone amp, because I figured this question would pop up sooner or later:
1) Meier Audio Corda Opera
2) Stello DA100 / HP100
3) Aqvox USB 2 D/A MkII / Apogee Mini-DAC
4) Lavry DA10
5) Benchmark DAC1 (not the newest version FWIW)
This second rating is meant to describe the units when used as a DAC alone, based again solely on sound quality. It includes several DAC’s that I’ve not owned or auditioned at home, but have auditioned extensively:
1a) Stello DA220 / Aqvox MkII / Lavry DA10 / Apogee Mini-DAC / CI Audio VDA2
1b) Stello DA100
1c) Meier Opera
2) Aqvox MkI
3) Benchmark DAC1 (older version)
4) Bel Canto DAC2
The explanation of the ranking is as follows. All the units under the heading "1x," I believe offer similar levels of sound quality (albeit with differing flavors). However, being that the first tier has balanced output, they have the potential to be used in a better sounding SYSTEM than the following two. The Opera is further differentiated for its' lack of a true line output.
If one isn't going to have a balanced rig, the DA100 is the best sound for the money of the group, for use as a DAC only. A used DA10, DAC1, or Mini-DAC can do well in this regard depending on the price. I think it would be a bit silly to buy the Opera and not use the headphone amp, as to significantly better it, one would need a balanced or tubed amp, depending on preferences. So my picks as a DAC only would be limited to the 1a&1b levels, 1a only if balanced output is needed.
[size=small]Acknowledgements:[/size]
I’d like to take the time to thank Todd at TTVJ for allowing me the opportunity to audition the Corda Opera, and likewise Norman at Aqvox.
