- Written by Stephen Hornbrook
- Published on 04 February 2013
Introduction to the Burson Soloist Headphone Amplifier
Burson Audio hails to us from Australia, bringing its own design philosophy, "Less is More," to high-end headphone amplifiers. They gained notoriety with the successful HA-160 headphone amp, a pure class A design with an output of 250mW; which is enough power for most headphones, with the exception of a few top-tier power hungry beasts. To drive headphones such as the Audeze LCD3, or the HiFiMAN HE6, Burson has developed an amp which is capable of a more robust 4 Watts of output. The Soloist is part of the company's Musicians Series, a higher end line that also includes the Conductor which is essentially the Soloist plus an integrated DAC. The Soloist retails for $999, not a small chunk of change for even a full power amp, let alone a headphone amp. Is that asking too much or does the Burson Soloist deliver enough bang for the buck?
BURSON SOLOIST HEADPHONE AMPLIFIER SPECIFICATIONS
- Design: Headphone Amplifier
- Input Impedance: 36.5 kOhms
- MFR: 0 - 50kHz, ± 1 dB
- S/N: >96dB
- THD: <0.03% at 30 Ohms with 1W Output
- Channel Separation: >73dB
- Output Power: 4W at 16 Ohms
- Input Impedance: >8K Ohm @ 30 Ohm, 1W
- Output Impedance: <1 Ohm @ 30 Ohm, 1W
- Power Dissipation: >25W, Internal, Regulated Power Supply
- Inputs : 3 x Gold-plated RCA (line level input)
- Outputs: 1 x 1/4" Headphone Jack, 1 x Pair RCA
- Weight: 10 Pounds
- Color: Silver Anodized Aluminum
- Dimensions: 3.3" H x 7.2" W x 10" D
- MSRP: $999 USD
- SECRETS Tags: Burson, Headphones, Headphone Amplifier, Audio
Design and Setup of the Burson Soloist Headphone Amplifier
With the Soloist, Burson takes the "Less is More" philosophy to another level. They have reduced the component amount from 32 in the HA-160 down to 21. 21 individual components do the job that is normally done by a single integrated circuit such as the Texas Instruments NE5534 OpAmp which is made up of a whopping 53 components. An OpAmp is essentially a tiny mass-produced amp on a chip that takes the voltage difference from the input terminals and amplifies it via a single-ended output. There are many benefits to using OpAmps in a design, but first and foremost is cost and simplicity. You can get good performance out of a cheap OpAmp with little to no R&D costs. However, taking the quick and easy way out is often not the answer to better sound quality. Burson has spent many man-hours designing their Field Effect Transistor (FET) circuit for the Soloist in order to get the shortest (in terms of number of components) and cleanest path from source to output as possible. The benefits of spending the time and money on a discrete design reveal themselves in the sound quality produced by the Soloist. The fewer the components affecting the signal path results in higher fidelity and greater resolution of the source material.
The Soloist is essentially a solid aluminum box, albeit a beautiful one, with beveled edges and a brushed finish. A few tiny LEDs indicate power, input source and output level. The case is designed to act as a giant heat sink, dissipating heat away from the internal components without the need for ventilation or heat sink fins. During operation the unit never felt anything beyond warm to the touch. It has a nice heavy feel for its size, making you feel like you are getting something special for your dollar. On the front is the variable output stage selector that offers a low medium and high setting. For sensitive headphones or in-ear monitors, the lowest setting works great, but for headphones like the HiFiMAN HE6, stage 3 delivers the necessary output.
To increase fidelity, Burson employed a 24 stepped attenuator for volume control. The action on the volume knob was smooth while providing just the right amount of resistance and a satisfying "click". It is easily one of the nicest volume knobs I have come across. The only downside to this is that there is no remote control capability. Given I don't have a 20 foot cable on my headphones and usually sit right next to the amp, I would gladly go without a remote in favor of better sound quality. However, this does make its use as a pre-amp a bit more limited.
For connectivity, the Soloist has 3 gold-plated RCA inputs. You won't find any balanced inputs on this unit, but unless you are dealing with long cable runs, the benefits of balanced over unbalanced can be argued. The Soloist also has a set of pre-outs that enable it to be used as a pre-amp, a feature the HA-160 does not have.
Burson Soloist Headphone Amplifier In Use
One of the reasons the Soloist's development is the recent surge of demanding planar magnetic headphones. What better way to test it out than with the power hungry Audeze LCD3 and HiFiMAN HE6? I started out with the LCD3 and the first thing I noticed was dead silence, even with the volume knob cranked. The Soloist has a very low noise floor which makes for an intimate experience when it comes to quiet passages. When you take away that background hiss and hum another veil is lifted from in between your ears and the musician's performance. On the 2L SACD recording of Mozart's Violin Concerto in D Major, the Soloist was able to reveal all of the delicate detail of the stringed instruments without sounding systematic or overly precise like some solid states do. Acoustical music is organic and flows with infinite layers of sound which is why it can be so difficult to reproduce correctly. The Soloist embraced those characteristics and let them shine.
Having listened to John William's Sabrina score many times since its release back in 1995, it usually sounds distant and bottled up like a fly trying to escape a small glass jar. However, on the Burson Soloist via the HE-6 it sounded natural and full of life. The dynamic range of a CD is taken full advantage of when the orchestra picks up the melody midway. The Soloist had no strain at the peak levels, just fully engaging and robust music. The piano solos were more open and three dimensional than I have heard during previous listens. The bass clarinet notes had proper tone and body to lift the instrument into a space with realistic depth.
On Radiohead's OK Computer, the soloist gave the CD an almost analog like quality. Dynamic peaks were there, but without any strain to the ears. On the track "Exit Music" York's voice was larger than life and free of any murkiness I have commonly heard on systems. The resolution of the LCD3 headphones came through with the hauntingly real guitar strum via the Soloist.
As a tribute to the late, great Dave Brubeck, I finally picked up Analogue Productions 2 channel SACD remaster of Time Out. Listening to this great album via the Soloist and HE6 was exactly why I enjoy being an audiophile and hearing details in the recording that could not be heard on most other setups. I was able to feel the sound of the cymbals radiating out to the edge, like butter melting down a hot pancake. I heard no hint of compression in Paul Desmond's skillful alto sax as it filled the virtual stage of the headphones. Overall, the Burson Soloist was able to reproduce music with more life and body than most headphone setups.
Burson Soloist Headphone Amplifier On The Bench – By Chris Heinonen
The Burson Soloist has three levels of gain: High, Medium, and Low, depending on how hard your headphones are to drive. Low puts out a maximum of 2.75V, Medium puts out up to 5.5V, and High puts out 9.1V maximum. I did most of my testing at the medium level at 5V of output using AKG K701s as the load on the amplifier.
With a 1 kHz tone and 2V output, THD+N was only 0.01%. The 2nd and 3rd harmonics were both over 100dBV below the fundamental frequency. Moving this up to 5V drops that THD+N down to 0.002%.
With a 10 kHz tone, THD+N was 0.005% at 2V of output. Here the 2nd and 3rd harmonics are both almost 100dB below the fundamental respectively. I also tested this with High Gain instead of Medium Gain and the THD+N was the same, though the 3rd harmonic was higher than the 2nd harmonic, instead of being the opposite at medium gain.
Using 60 Hz and 7kHz IMD tones we see an IMD value of 0.03%, and there were no real sidebands, and the only harmonics visible were very slight at 2V. There was a single 2nd harmonic for the 7 kHz tone that is virtually invisible. When I pushed the output to maximum for medium gain, the IMD remained the same, though you can now see that harmonic at 14 kHz much better now.
Using 19 kHz and 20 kHz IMD tones, the 18 kHz and 21 kHz sidebands were close to 90 dbV below the fundamentals, allowing a good amount of headroom. There was no B-A peak aside from the low frequency noise visible in all the charts.
THD+N is a little higher in the deep bass area, but quickly falls to 0.0025% or so and stays there for the rest of the frequency spectrum. This matches up with what we saw on the 1 kHz and 10 kHz tests.
Aside from some noise in the lowest octaves, which was still around 75 dBV below the fundamentals, the Burson tested very well when used as a headphone amp.
Curiously, when used as a preamp, the RCA outputs put out the same voltage levels as the headphone jack. Talking to Burson, they've designed it this way to work well with a wide variety of amplifiers, so you can tailor the gain applied by the Burson to match your amplifier. Performance as a preamp was virtually identical to as a headphone amp, so I've not run the graphs as they are the same.
The only thing that concerns me with the Burson Soloist is the lower octave noise I saw. However this also showed up recently on a Blu-ray player I tested, so I believe there is some low-level noise in the power where I'm testing, that I can't avoid. Overall performance was very good, with plenty of power to drive any headphone and very good overall performance.
Conclusions about the Burson Soloist Headphone Amplifier
Unfortunately, I missed the boat with the Burson HA-160, but given the feedback it received, I knew I was in for a treat with the new Soloist. Its fit and finish are top notch; going above and beyond what you would normally see in a headphone amplifier. Its Variable Output Stage makes the Soloist a versatile amp as it allows for it to handle highly sensitive headphones as well as load-demanding planar magnetic cans. Even with the power hungry HiFiMAN HE6 the sound was dynamic, full, precise, and, most of all, musical. From its high-end build quality to its sinuous sound and low noise floor, the Burson Soloist delivers on all fronts and it easily fulfilled my expectations from a $999 headphone amp.