More and more people are listening to music through headphones. Of course the iPod, iPhone and other MP3 devices have been a big factor, but today we're looking at the high end of the headphone market. Those who are looking for something better than MP3 quality, those looking for better sound than they can get from the headphone jack in their stereo or CD player, those looking for great sound from their computer or internet streaming device, those who in some cases are looking for the ultimate in HiFi – these are the potential buyers of the standalone headphone amplifier.
We have quite a mixed bag of headamps in this group test. The simplest is the Graham Slee Solo SRG-II, the latest in a long series of refinements of the original Solo design. A plain compact silver box with a volume control and source toggle, it should be placed at a distance from the dedicated PSU1 power supply. Over in the UK, Mr. Slee never sleeps. He has come up with an alternative design, the Solo Ultralinear (UL), which he now offers at a small premium. This version has been designed to offer the sound characteristics of a fine tube amp without actually using tubes to get there. He even offers a kit to upgrade earlier Solo amps to UL DE status. Both headamps offer a choice of two unbalanced inputs and are the only ones in this test with just a single headphone output, although you can drive two pairs comfortably with the aid of a splitter.
The least expensive component in this group is
the Musical Fidelity M1HPA but it has quite a few tricks up its sleeve,
including a Pure Class A design, a built in DAC and preamp outputs. It features
a very large volume control which dominates the front panel and allows finer
control of volume than the others in this test. It also offers two standard
headphone jacks. It has a very healthy output level and a low output impedance
that should allow it to mate well with a variety of headphones.
The Woo Audio WA22 is also a simple device, but it's built on a massive scale and offers two sets of balanced headphone outputs in addition to the regular ¼" jack socket. You can use them all at once if you like, although you cannot control the volume level separately for each output. It's a fully balanced tube powered Class A output transformer-coupled design. It features a 5AR4 rectifier tube, two 6SN7 driver tubes and two 6AS7 output tubes and weighs a massive 25 lbs. With the standard tubes it retails for $1900 but you can easily spend over $2500 if you specify upgraded tubes. You can select between balanced and unbalanced inputs on the rear panel, and between low and high impedance outputs on the front panel.
The newest component is the Bryston Audio BHA-1 and it offers the most flexibility of the bunch. It has the same three outputs on the front panel as the Woo Audio, but it also doubles as a preamp with balanced outputs on the rear panel paralleling the balanced headphone outputs up front. You get a front panel selector for balanced input, unbalanced input or mini-jack input and this is the only model here to offer a balance control. The BHA-1 has been a long time coming as Bryston tried out many different designs, soliciting user input along the way. As launched earlier this year and reviewed elsewhere, the BHA-1 did not have the preamp output, and I am very pleased to see this additional feature, since it works remarkably well as a fully balanced preamp. Internally the analog output derives from six Class A fully discreet operation amplifiers of Bryston's own design.
Sadly none of these units has a remote control.
Perhaps most users sit close by their preamp – I don't.
Let us take a closer look at the units in operation.
Slee Solo SRGII and Ultralinear Diamond Edition
The Woo Audio WA22 is the final amplifier in this
grouping. It is hand built using point to point wiring throughout, which is much
more expensive than printed circuit boards assembled by machine. It is based on
a true balanced topology and no semiconductors are used in the design.
Sadly it had to go back before the Bryston arrived, so I was not able to compare them side by side. I did listen to it next to all the other amps and it certainly is a contender in terms of sound quality, especially when used in balanced mode. As a tube amp you'd expect it to be on the warm side of neutral, but if this was the case it was only to a very slight degree. It lacks preamp outputs but otherwise it has similar features to the Bryston, and rates even higher in terms of maximum output, making it the best placed to fully drive the AKG K1000s.
But like the first version of the Solo
Ultralinear, it is not a good match for highly efficient phones like the
Ultimate Ears. The problem is not hiss this time, but hum. In fact hum was
present with all phones to a certain degree, more on the left channel than the
right. Despite all efforts to avoid grounding problems, I could never completely
eliminate it. It seemed to be independent of volume level. You could only just
hear it on inefficient phones like the HD800s where it was inaudible when music
was playing, but it intruded with the Ultimate Ears so that even though the
sound quality was clearly excellent, the hum for me was a distraction. Now your
mileage may vary and hum may never be a problem for you but I strongly recommend
you try the Woo Audio in your home system before committing. You can try
different tubes to suit your taste and your wallet and the good guys at Woo
Audio offer a great deal of advice on their website in this regard. This is the
only amp here which can be tweaked in this way. I did some tube rolling and
could easily hear the benefits of the upgrades which added a greater sense of
ease and intimacy to the already fine sound.
The Sennheiser HD800s are the only phones that I
can drive both balanced and unbalanced, and I am very grateful to George Cardas
for supplying his superb Clear headphone cables in both balanced and unbalanced
formats for use in these tests. Now that I've done the comparison I am convinced
that the balanced option is not just of theoretical benefit, even if it academic
for most listeners whose headphones may not offer a balanced cable option.
While most of my listening comparisons are
centered around the HD800, I also used Ultimate Ears UE10Pro and AKG K701 phones
on all the machines in this group test. The results are consistent all the way
through, so I will not detail them separately. Listening tests involved
recordings of the highest quality including Schubert's Death
& The Maiden Quartet by the Lindsays [CD RSB 403], "Alfie's Theme"
by Sonny Rollins [Impulse IMPD 224], "While My Guitar Gently Weeps" from the
Beatles Love Album [Capitol 094637981023], MA
on SA [Crystal Cables Sampler] and Bartok Concerto
for Orchestra conducted by ZoltanKoscis [HungarotonHSACD 32187].
Woo Audio offers a large range of tube based
headphone amps. This one sits around the middle and is optimized for full sized
relatively inefficient headphones. If you are driving more efficient headphones
you might consider the WA6.
The famous old AKG K1000 ear speakers have seen little use in recent years in my house, because they need the direct output of a power amp, and I haven't had a power amp with speaker switching since my old Perreaux Radiance died. The K1000 has a two piece cable, with a DIN connection mid length. This DIN connector allowed me to try it with the Bryston, as long as I sat within a short distance from the amp. The K1000 is very inefficient indeed and even the powerful Bryston could not drive it to high levels but within a civilized volume limit it performed very well indeed. The sound is definitely tipped up towards the high frequencies, but this fault cannot be laid at the foot of the Bryston. The combination is stunning in its clarity and may be ideal on those recordings that possess something of a dark balance. Finally James Tanner of Bryston lent me his personal pair of Grado PS1000 phones, with a single balanced connector like the AKG K1000. Once again the Bryston drove these phones very easily and the sound was enormously engaging. I felt these phones were editorializing the music to a certain extent, making it more colorful than through the Sennheisers, and this was confirmed by switching to my reference speakers, the YGCarmels. The Sennheisers sound quite similar to the Carmels, but the AKG have quite a different balance. In any event I could only try the Grados through the Bryston, so I can only use the experience to indicate whether the Bryston would make a good partner for them rather than to compare the Bryston to the other amps.
The Woo Audio also sounded best through its balanced outputs but showed less of an improvement when moving from unbalanced to balanced headphones than the Bryston. It still retains the smallest of leads over the Bryston with balanced phones due to superior instrumental color that enriches vocals, strings and wind instruments alike.
Musical Fidelity And Bryston As Preamps
sound quality, the Bryston does exceptionally well. This is especially truewith
a balanced input. It may in fact sound better than a Bryston standalone stereo
preamp since the discrete operational amplifiers used here are of a new
iteration developed for the new Bryston Surround processor. Bryston has found a
way to reduce the parts count and this is said to be responsible for greater
presence and lower noise. Of course the calibration of the volume control may be
a better match for power amps with lower or adjustable gain (Bryston power amps
have such a switch) and remote control would be very valuable here. Substituting
the costly EMM Labs Pre2 preamp quickly shows the sonic limitations of both
Musical Fidelity and Bryston headamps by opening up a wider and deeper
soundstage with increased density of musical information and openness at
frequency extremes. Nevertheless, the Bryston's quality is fully competitive
with stereo transistor preamps in the $1000 to $3000 range.
Few Words About Build Quality
Ultralinear Diamond Edition
Woo Audio WA22
Solo UL BHA-1
Specifications / Company Information
Slee Solo Ultralinear Diamond