Burson Soloist 3X Performance


Headphoneus Supremus
A very powerful headamp performer
Pros: Extremely powerful headphone amplifier on both balanced and unbalanced outputs.
Three gain levels adjustable selector to accommodate all kind of headphones.
Three output plug types including the 4-pin one for headsets with microphone included.
Microphone pass-through for gamers and podcasters.
Integrated pre-amplifier with both balanced and unbalanced inputs.
High quality MUSES digital volume control resistance ladder circuit.
Cons: No unbalanced line-level outputs.
The torx L-key included for opening up the case wears out after couple of uses.
After recently Burson decided to change the look on their audio products there has been one product that was still left unchanged...well, till now! Yes, Soloist 3X Performance got it’s appearance on the market recently and, besides it’s new shiny polished look and the front LCD, it got the low-noise MCPS regulators inside and dedicated digital volume control. It’s also the first Soloist headamp that has a built-in audio preamplifier and hey...it has both balanced and unbalanced inputs that can be easily selected from the front menu.

This Soloist 3XP sample was sent to me by Burson so I can test it and write down this review, so many thanks to Burson team for this. The package is as expected: double package and thick foam in between, but there's also more foam inside the white box too.


Well packed Soloist 3XP

Like the Conductor 3 series, the aluminum "Cool case" design acts as a big heatsink for the big output-stage transistors and the power regulators. Besides its novel look & feel, the Soloist case also offers a very good shielding against any possible outside EMI/RFI interferences.

The “old” internal design has been completely "forgotten" and Burson swapped the big chunky transformer for the new MCPS regulators and a low-noise external power supply. They also installed eight big TO-220 transistors instead of four, like they did in their previous Soloist versions, so power got increased too. Gain has now a 3-stage digital selector, adjustable from the main menu, so another improvement over the 2-stage switch from their older model.

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Clean and nice design on both inside and outside

Internal amplifiers are powered via +/-20V rails coming from a couple of powerful MCPS regulators, so a total of 40V RMS is used to help out the output transistors to pump up the audio signal into the headphones. Quite a high voltage for a headphones amplifier, although this is not something new coming from Burson Audio, given the previously released Conductor 3X and Conductor 3 combos.

There are four dual opamps inside that are powered from dedicated +/-15.5V linear regulators, so if you’ll ever think of starting to roll opamps inside Soloist 3XP, then you have plenty of them on the market to roll. Two opamps are used at the input plugs and the other two at the pre-amp XLR outputs from the back. If willing to swap them, just don't forget to double check maximum operating voltage of the opamps you’re willing to install. Most opamps operates well up to +/-16V, including Burson V6 opamps, but some opamps are still having a max. recommended operating voltage of only +/-15V or even lower, to +/-12V, so double check opamp’s datasheet prior to installation inside the Soloist 3XP.


Soloist 3XP internal layout and design (photo copyright by Burson)

Under the hood we can see several transistors, the three MCPS power regulators, few black and silver ELNA electrolytic capacitors and several shiny ones from the new VZH-series of SMD aluminum capacitors from Lelon, the high-endurance and low-ESR ones, rated to last at least 5.000 hours at 105C (check out
http://www.lelon.com.tw/upload/guides/158200414292.pdf - pag. 102); well, under normal operating conditions (40-50C) these caps should last for several decades.

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Several low-ESR capacitors for minimizing ripple & noise

The relays used in Soloist 3XP are silent and are manufactured by Panasonic, model TQ2-5 ATQ209. There are ten such relays inside and they are used to switch between the inputs and output sources, but also to switch between the three gain settings and also to protect your headphones (power ON delay).

Like the Conductor 3X Reference, inside the Soloist 3XP there are four separated audio amplifiers: two of them are used to drive single-ended headphones (the non-inverted marked with + sign), while all four are operating when driving balanced headphones (both pairs of inverted and non-inverted are working together).


The four internal audio amplifiers

In the output stage we can see eight SMD transistors for each amplifier inside. These are SOT-89-3 case type transistors 2SA1213 (NY) / 2SC2873 (MY) that ensure sufficient voltage to "attack" the final transistors.

The big black transistors from the output stage are the same used in all Burson headphone amplifiers, the well-known Toshiba 2SC5171/2SA1930 complementary NPN/PNP transistors, having a max. power dissipation of 20W each!

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Drivers SMD transistors, DC-adjust variable resistors and low ESR capacitors (like V6 opamps)
Soloist's output stage design, very similar with the one seen inside the Conductor 3XR

Maximum voltage I was able to measure, coming out from the balanced XLR plug just before starting to clip, was 28V RMS @ 600 Ohms; that means 2 x 1.3W, so quite an extreme value.

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High gain setting - 28V RMS @ 600 Ohms coming from the 4-pin XLR plug

On the non-balanced jack output the voltage was cut in half to a bit over 14V RMS, under the same circumstances as above. Adding a 30 Ohms resistor I was able to measure a voltage higher than 21V RMS till starting to clip, meaning almost 2x15W of power!

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High gain setting - 21V RMS @ 30 Ohms coming from the 4-pin XLR plug.
Notice the rounded corners when approaching the clipping limit, similar with how a tube-based amplifiers usually does​

The well-known Neutrik XLR plugs can be seen on both front and back plates, ensuring a good electrical contact for the connected headphones.

The Texas Instruments boost regulators, which are part of the MCPS low-noise design, are followed by linear power regulators, to create clean and stable power rails for the electronics inside.

Soloist’s internal preamplifier is made around the Japanese high-end volume control chip MUSES 72320 that is "buffered" at both input and output by two couple of solid-state V6 Vivid dual opamps. The aduio signal will get unchanged from input to output, via the four opamps and the MUSES volume control chip.

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Soloist 3XP @2V RMS - I was able to measure a THD of 0.00095% with my Focusrite Solo 3, quite a good value

When used strictly as a pre-amp, the audio signal goes into a pair of V6 Vivid opamps, then into the MUSES 72320 volume controller, then it gets to the output pair of V6 Vivid opamps. This way, the connected external amplifier will benefit from the MUSES low noise and distortions, but also from the V6 Vivid sound signature.


MUSES 72320 - resistance ladder digital volume controller with -120 channel separation

The big orange SMD capacitors from top are for decoupling the input source from the MUSES chip, so the amplifier is AC-coupled. Some square-wave tests are a must here, just to check the speed of the amplifier, but also if there are errors or distortions.

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1KHz is plotted absolutely perfect
(red channel is from generator, while the blue channel is from Soloist)

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20Hz is plotted very well for an AC-coupled amplifier, probably because the input caps are having a large enough value
(red channel is from generator, while the blue channel is from Soloist)

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20KHz is plotted very well too, no signs of ripple or phase shift
(red channel is from generator, while the blue channel is from Soloist)​

Same MUSES chip is also used to control the volume of the headphones amplifier. Switching between pre-amplifier and headphone amplifier modes can be easily done from the LCD menu. You can not use Soloist 3XP as headamp and preamp at the same time; this is also a safety measure, to protect your hearing and headphones when feeding an external amplifier. However, when switching back from pre-amp to head-amp, don’t forget to adjust the gain and volume setting according to the headphones you connect!


LCD menu showing the volume level, the input source selected, the output source selected and the gain setting

The Low/Medium/High gain setting is also used for the pre-amplifier, not just for the head-amp, so the gain setting you choose will increase or decrease the output sound on both pre-amp and head-amp plugs. For the pre-amp feature I would recommend the High gain setting and the volume setting should not pass the 75 marking to not overload the external amplifier connected.


Inside the menu you can easily choose the input & output source and the desired gain setting

The powerful Soloist can easily drive up to three pairs of headphones at the same time, one connected to the balanced XLR plug and the other two connected to the 6.3mm and 3.5mm jacks. However, you should take care of the final impedance that results after connecting two or three pairs of headphones at once, because getting below 16 Ohms might not be recommended for the amplifier. Soloist 3XP can not adjust volume for each of the three headphones plugs, so same amount of power will be applied (actually double for the 4-pin XLR), so it might be challenging in getting the desired power for all the three headsets connected.

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From left to right: balanced 4-pin XLR, non-balanced 3-pin 6.3mm and 4-pin 3.5mm jacks (microphone headsets are supported)

The volume can be easily adjusted via the front-right rotary knob and the output level can be seen on the front LCD. Internally, there is no carbon potentiometer, but a resistance ladder circuit inside the MUSES 72320 chip that takes care of modifying the output volume with a very good precision, 120dB channel separation and minimum channel imbalance (unlike the older potentiometers that used to have a bad reputation when volume was approaching the minimum scale).

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On the right, the rotary knob for adjusting the volume, then follows the Settings menu button and the remote controller sensor

The Soloist design has V6 opamps DNA inside. I am referring to the eight SMD transistors from each internal amplifier and to the blue variable resistors (V6 has small white variable resistors inside) used to adjust the output DC-voltage. Try not to touch or adjust these blue resistors, as there will be no gain in the audio quality. These are not for adjusting the current bias into class-A! The current bias can not be adjusted, as it was already calculated and implemented correctly by the manufacturer.

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Similar design with the V6 solid-state operational amplifier

The output DC-voltage is already pre-adjusted by Burson to a minimal value. After a couple of minutes of warm-up, I was able to measure values between +/-1 mV and +/-5 mV of DC, so a respectable low value indeed. However, in case you intend to swap the default opamps inside, don’t forget to measure the DC on both jack and XLR plugs before connecting headphones and adjust the blue variable resistors ONLY if the DC is higher than +/-25 mV per channel (or wait more time to warm-up or swap back the opamps with the originals from Burson).

Given the very high amount of power and an output impedance pretty close to zero, Soloist 3XP will drive any dynamic or planar headphone connected, even the very hard to drive HE-5 and HE-6 from Hifiman.

I’ve also tested it with 127dB/V KZ AS10 and ZSX IEMs on the jack output and when Low-gain was used the sound was perfect and volume knob could be raised to 30-40 without getting worried of overpowering them. In a completely silent room, at night, a slight faint of hiss noise could be heard, but only if no music was playing and room was dead-silent. I had it compared side-by-side with Conductor 3XR and I found that the hiss noise on the Soloist 3XP is almost non-existent. With headphones having a lower sensitivity I couldn’t hear any hiss, no matter how hard I tried to.

Worth mentioning that the XLR plug is pushing twice the output power compared with the jack plugs, so the background noise will also get doubled too. However, the most sensitive “over the head” headphone I have is the AKG K550 with balanced cable and I’ve heard no background noise at all coming from them, when connected to the 4-pin XLR from Soloist 3XP, even if these cans are rated to about 115dB/V SPL (measured here).

I've tested this Soloist with LCD-2F, Hifiman HE-560, AKG K701, AKG K550, Audio Technica M30x and KZ IEMs and I had perfect match with each one of these cans. Finding the right gain setting was done starting from the Low gain, then switching to Medium or High gain if needed (only to HE-560 I could use the High gain, otherwise the Low or Mid were used). Half of the power is gradually delivered from 0 to about 85 reading on the LCD, then the boost comes up and unleashes the beast with the remaining power. That means that switching from a reading of 20 to a reading of 40 will not kill your ears, instead it will be a gentle logarithmic level increase.

Hifiman HE-560 (unbalanced & balanced), 100 dB/V:
- There are rather hard to drive planars, needing more current to be driven properly, unlike most of the dynamic headphones. Given the "oversized" output stage from inside the Soloist 3X, driving Hifiman planars was piece a cake and also an expected delight. The fast and powerful bass sounded clean, precise and even when cranking up the volume really high there was no sign of any distortion. The level of details was very good, like the rest of the Conductor 3 series devices, with a perfect channel separation and soundstage.

Fostex T50RP-mk3 (unbalanced), 103 dB/V:
- Like the above planars, bass was striking perfectly and sound was neutral and somehow warmish. I feel that I could listen for several hours without fatiguing my hearing, probably due to the low distortion amplifier inside or maybe due to the neutral but somehow warm sound the Soloist 3XP pushes into the headphones.

Beyerdynamic DT-880 600 Ohms (unbalanced & balanced), 96 dB/V:
- Most headamps will not drive them properly, due to the rather high voltage they need to be amped, but with the new Soloist this won't be a problem. They sounded right, brighter but with clear notes of bass and I was able to catch every little detail from the music. Of course, Low-gain setting is not for these cans, given their 600 Ohms impedance, so I needed to choose the Medium-gain when going balanced and even the High-gain when using the unbalanced cable (although it was fine with the Medium-gain too, but I want it to hear the Highest gain too).

Audeze LCD-2F (unbalanced & balanced), 105.5 dB/V:
- These are rather sensitive planars, so definitely not a problem in driving them with most headphones amplifiers, but they still need a decent amount of power to be properly driven. However, I was able to use both Low-gain and Mid-gain with these cans and listening to the music was a pleasure. It was a perfect match with the Soloist, on both XLR and jack outputs, and I totally recommend this amplifier for driving Audeze or Hifiman planars. I got an incredible amount of details and very fast and precise bass, without any signs of hiss.

AKG K550 (balanced & unbalanced), 117.8 db/V:
- These are neutral sounding headphones with a decent soundstage and very good bass reproduction and this is exactly how I perceived them with this new Soloist headamp. Given their high sensitivity I was expecting to hear a little bit of hiss coming out of the Soloist, but instead I got no background noise at all, not even when using the balanced 4-pin XLR plug. Of course, I've used the lowest gain setting to drive them and I never felt that volume should pass the 50 marking. These headphones sounded better than ever, despite their high sensitivity, so this is quite an accomplishment from Burson, given the extreme power rating Soloist 3XP has; I never thought such a powerful headamp could drive sensitive cans without hiss noise and without getting worried to not kill your ears while moving the volume knob.

AKG K701 (balanced & unbalanced), 102-104 db/V:
- Considered to be hard to drive dynamic cans, due to their below average sensitivity and the 62 Ohms impedance, I never felt the Soloist struggling in driving them at all. Instead, I've heard one of the most accurate bass ever coming out from K701, with a fast kick and a very detailed presentation. For some folks the increased soundstage of these headphones might be overwhelming, but for me is like a treat.

KZ ZSX (24 Ohms IEMs) & KZ AS10 (22 Ohms IEMs), about 127-130dB/V sensitivity:
- Really sensitive IEMs, so I only use them when I need to test for the background noise. I couldn't use them with Mid and High gain settings, due to the audible hiss, but also to protect my hearing, but when switching to Low-gain most of the hiss noise disappeared and only slight of it remained, but definitely not something to distract anyone. The hiss was barely heard and I was doing my critical listening inside a quiet bedroom at night. Comparing the Soloist side by side with the Conductor 3XR, given the darker background of the Soloist 3XP, I consider it a better match for sensitive headphones. Also, the KZ ZSX had an impeccable bass response, quite pleasant to find out that I could pair such sensitive IEMs with such a powerful headamp.

AudioTechnica ATH-M30X (unbalanced), 115 dB/V:
- I used these for monitoring only, connected to my Focusrite studio card, due their rather high sensitivity and accuracy of voice reproduction. Of course, no noise could be heard coming from the Soloist 3XP and both female and male voices were perfectly sounding.

In an A/B test done with Soloist 3XP Performance vs. Conductor 3X Reference I was unable to tell which one sounds different, no matter how much I struggled. Probably this was due to the very similar construction in both amplification stages and power supply as well. Worth mentioning that one C3XR from the below stack was having NJM5532D, while the other two devices were having V6 Vivid inside. I had also hard times in finding the C3XR with NJM5532D in a "blind" A/B test, so even with the cheap and good 5532 opamps these devices sound really good.


Stack of Soloist 3XP and two Conductor 3XR with NJM5532D and V6 Vivid opamps inside

Referring strictly at the headphones amplifiers, the only slight advantages the Soloist 3XP might have against the Conductor 3XR would be the lower background noise on both XLR and jack outputs, the simpler construction of the internal pre-amplifier, but also the 3-states gain adjust.

Soloist's warranty is 2 + 1 years, meaning that you get a default 2-years warranty and, if you register it online, then you will get an additional year of warranty. This is a good thing, especially that Burson claims and warranty department is very responsive.

Manufacturer link: https://www.bursonaudio.com/products/soloist-3x-performance/.
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I have the Soloist in my system for a week now driving my LCD-3 with my Cosmic cable silver cable with XLR & it is sublime. I previously had the Burson CV2 & the Soloist is a significant step up, just cannot stop listening, really shows what the LCD-3 is capable of when given this sort of power. I had auditioned the Chord Hugo TT2 which was fantastic but I prefer the Soloist/Qutest combination. Sacrifices a little of the TT,s DAC detail & insight but to my ears is more coherent overall. I rate the Soloist amp ahead of the TT's amp. Maybe the TT Dac with the Soloist would be even better but a step too far fro my budget.
Great write up. Now considering these for my Verite Closed. Damn you :dt880smile:
I have now had my amp a few weeks & it has improved further, I couldn't be happier, it does everything right, just sounds very natural with no obvious faults. familiar recordings sound significantly better, taking me right to the heart of the music. Completely addicted to it & allows me to forget I am wearing headphones, music just seems to exist around my head.