Auris Audio HA-2SF Review

Synergy

Efficiency

The HA-2SF is rated at 2w into a 32Ω load which is quite similar to the flagship Formula S from Xi Audio, double the output of the older HA-2SE as well as the 1W 32Ω Studio 6.

Bear in mind that this is an SE design with balanced connectors similar to the Formula S so you will get the same output profile for both the balanced and the 6.35mm outputs. All our compared amplifiers below are purely SE designs be it solid-state or tube.

There are definitely more powerful amplifiers out there right now if you need something heavyweight for your Susvara or Abyss headphones. The likes of the Little Dot LD H1 on paper offering up to 5W into a similar load and integrated solid-state DAC/Amp’s such as the Violectric V590‘s 6.4W into 50Ω load rating.

However, this is Auris Audio’s more powerful headphone amplifier to date and for a significant number of headphones, especially modern planars around 92-3dB SPL upwards, it should offer enough voltage and current control to sound nicely driven.

Certainly, I had zero issues with the Meze Empyrean, the Rosson Audio Design RAD-0, and the Audeze LCD-XC, all of which hang around the 98-100dB SPL marker. The HA-2SF also had no problems handling the light impedance but sluggish 92dB SPL-rated AEON 2 from Dan Clark Audio.

 

Pairings

The HA-2SF has had a proper reboot over the original HA-2SE in terms of perceived dynamic range as well as the power to do justice to most modern planar headphones and a good range of dynamic headphones also.

Darker Headphones

On top of that, the slightly cleaner timbre and the resulting sharper resolution from top to bottom pairs much better for me with darker headphones such as the Empyrean and the Pre-Fazor Audeze LCD-2, (now the Classic & Closed).

I actually found the Empyrean to be comparatively softer sounding with the original HA-2SE whereas with the HA-2SF there was much better headroom, improved depth, and power, as well as a more spacious midrange.

Vocals still sound forward with the Empyrean but the rest of the band is not pushed forward with them and competing for the same space. Imaging has vastly improved on the HA-2SF. 

Reference Headphones

Perhaps my favorite pairing was the Final Audio D8000 Pro for two reasons. The first was its generally transparent sound signature teasing out the tonal strengths of the HA-2SF and the second, the twists with the impedance selector.

Coming in at 60Ω, the low impedance selector on the HA-2SF will give you a very clean and spacious tone with neutral levels of body and a smooth treble delivery. I would consider it a lightish touch with more of a reference profile and a reasonably punchy mid-bass but not a huge amount of warmth or power. Dynamics are just ok but nothing special.

Push it to medium impedance you get an injection of welcome bass warmth, additional low-end power, and a stronger vocal presence. The D8000 Pro becomes a bit of a ‘swinger’ if that makes sense and a lot less dry.  Importantly, the treble still sounds energetic but with a bit more of a liquid tone to its attack allowing for a beautifully sweet-sounding midrange timbre.

Impedance Selector

Indeed, a lot more importance should be given to the impedance selector once you do go up to higher impedance headphones. It does make a qualitative difference to my ears and in some cases, it works very well indeed, perhaps better than some costlier amplifiers that do not have that same flexibility.

Another good example outside of the D8000 Pro is the pairing with the 80Ω 100dB SPL Solitaire P flagship headphones from T+A. On the low impedance, the Solitaire P sounds thin, lacking in low-end weight, and a bit top-heavy in terms of sonic bias. I can live with it but its staging is a bit shallow and lacking in essential PRaT.

The Solitaire P has a treble peak that needs to be matched carefully or countered correctly. You can do that by switching up to the HA-2SF median impedance setting which in turn injects a mid-bass to lower-mids bloom with some welcome warmth creeping into the midrange.

Suddenly, the treble sounds properly balanced, a little edge was taken off and a bit more weight on the bottom to counter the elevated highs. Now it sounds almost perfect to my ear.

On the flip side, the 32Ω Empyrean needs to stay on the low impedance selector to retain a dynamic and clear sound. Once you up to medium impedance it starts to sound too soft with a bit too much warmth and less clarity for my liking. 

Something similar also for the newly tuned Audeze LCD-XC which seems to lose a lot of bit of dynamic range and vocal focus using the medium impedance selector. The low-impedance setting sounds far more vivid and immersive with excellent vocal presence.

Select Comparisons

Auris Audio HA-2SE

€2070

The HA-2SE was launched back in 2017 and is Auris Audio’s most successful headphone amplifier to date. We also gave it the Top Gear Award for Best Desktop Tube Amp that same year so you know what our feelings were about it also.

Technical

Like the HA-2SF, the 2SE is a SET Class A bias desktop tube amplifier. However, it is purely for headphone output with no pre-amp capability which the HA-2SF has. The SE also does not have the new balanced connection input and outputs that the 2SF now has but both amps are still a single-ended design.

Although both amplifiers have a ‘4+1’ tube configuration the older HA-2SE used an entirely different family of tubes from the EL/PL95 series as the drivers and a single input Tung-Sol 12AU7W / 6189.

The HA-2SF uses four JJ Electronics ECC99 power tubes and a single input JJ Electronics ECC82 tube. The ECC82 is a 12AU7 medium gain pre-amplifying double triode design. Some tube fans might find the new configuration more flexible for rolling plus the difference in these stock tubes’ dynamic range and sonic signature quite easy to differentiate.

The output capability has also changed with the HA-2SF offering 2W into 32Ω load as opposed to 1W from the older SE version which should provide a bit more headroom for more demanding headphones.

That enhanced power also comes with a jump in dynamic range from the HA-2SF over the 2SE from >98dB to >100dB and an improvement in SNR by up to 5dB. There is also an overall drop in the HA-2SF’s THD performance by 2% to <1% via the SE output versus 3% from the HA-2SE’s output.

Design

We have gone into a lot of detail on this already on page 1 so we will just summarize here.

The HA-2SF is now a bit more streamlined with superior cylindrical flat rubber feet for a safer desktop grip, a glass shield instead of the older fixed wood and metal tube guard, more grandiose LED lighting complete with working VU meters.

The HA-2SF PSU is now an external linear power supply as opposed to the HA-2SE’s internal PSU. The weight remains the same and the optional remote control works with both units so there is some continuity there. 

In terms of I/O, there are some considerable changes. The HA-2SF has pre-amp capability so on the back you have a new set of dual-RCA SE pre-outs. The HA-2SF still has 3 inputs but instead of 3 dual-RCA SE from the HA-2SE, it has 2 dual-RCA SE and a single dual 3-pin balanced XLR inputs with an additional high/low gain switch.

Impedance selection has also changed with the HA-2SF offering a vaguer 32 to 600 Ω high, medium, and low impedance selector as opposed to the 4 ‘precise’ 50 to 600Ω options on the HA-2SE. 

All dials are now on the top panel of the HA-2SF as opposed to the front of the HA-2SE to allow for the Vu Meters as well as provide more space for the additional power button and balanced 4-pin XLR headphone socket.

Performance

If you are a photographer you might understand this brief description of the differences between the original and the new.

This is like working with two telephoto lenses of the same focal range but one has a variable aperture setting and the other a constant with better glass. They both capture a great shot in the center but the HA-2SE gets a little softer towards the edges and the HA-2SF stays tack sharp from edge to edge.

Translated into audio, the HA-2SE captures a beautiful classic but not overly warm tube timbre with an excellent black background for a device in this class. Imaging is more center-focused with a thicker lower midrange, a softer bass/treble delivery, and a liquid-like rich vocal timbre. 

The HA-2SF delivers something a bit more dynamic and to my ears also a bit more resolving from end to end. The tone is a shade more neutral in terms of body but still to the sweet side for instrumental and vocal timbre.

However, the transient response is quicker, the definition tighter and the imaging definitely more expansive so it delivers a more complex staging presence with better depth and more headroom using our test headphones, the Meze Empyrean.

From there the detail shines through a little bit more, aided by that cleaner treble and a slightly more accurate harmonic balance. Though you will still be hard-pressed to push out any unnatural sibilance from the HA-2SF, the delivery is now more vibrant than the HA-2SE.

Xi Audio Formula S

$3499

Technical

The Formula S took the top gear solid-state desktop amplifier of 2018 and still one of the best today unless you want to spend megabucks.

Both of these amplifiers have a Class A bias; however, the Formula S is a resistor-based single-ended headphone amplifier implementation whereas the HA-2SF is a tube SET headphone and pre-amp design.

Xi Audio has opted for a Class A full discreet BJT rather than a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) amplification. BJT stands for Bipolar Junction Transistor is primarily a current-controlled amp design and was picked for its specific tonal quality for the Formula S.

The HA-2SF uses four JJ Electronics ECC99 power tubes and a single input JJ Electronics ECC82 tube. Here also, the ECC82 was picked specifically for its own tonal qualities and plays a large role in what makes the HA-2SF unique sounding.

In terms of output power, the Formula S is capable of 2.1 watts into 46Ω which is quite close to the 2W 32Ω rating of the HA-2SF so you will find both should be able to work fine with similar headphones in terms of voltage. 

The quality of that output is not too far off in terms of THD with both offering under 1% though to get that measurement the loads seem to be different with the HA-2SF rated for 1W and the Formula S at 300mW. 

Where you might find a difference though is in the dynamic range with the HA-2SF rated at 100dB and the Formula S doing better with an additional 10dB at 110dB. The additional $1k has to go into something right?

Design

The polar opposites in terms of design. The Formula S has that classic hardcore amp aesthetic with integrated heatsinks, black and silver aluminum paneling, and a brushed silver metal front panel design. It’s cold, menacing, and a tank of an amp if you will.

The HA-2SE is softer, more organic, with that nuanced mix of wood grain panels, flushed vintage brown leather, and a discreet aluminum black panel finishing to the rear. The only nod to the industrial vibe of the Xi Audio creation is the accompanying linear PSU which is basically a big black aluminum box with 2 lights. 

The Formula S is the more compact of the two and probably a better space saver whereas the HA-2SE demands the top shelf with its tall toroidal black cylinder to the rear, and that light show seeping through the VU meters and under the tubes. It is nowhere near as robust but definitely a prettier-looking amplifier. 

I/O is a bit more comprehensive on the front of the Formula S with 4-pin, 6.35mm, and a dual 3 pin XLR which the HA-2SF does not have. To the rear, both have a gain switch, however, there is no pre-out on the Formula S and only a single set of dual RCA SE inputs. The HA-2SF is much better equipped with two dual-RCA inputs and a single set of 3-pin XLR connections. 

The Formula S does have an additional 7-pin power supply connector to link with its linear Powerman external PSU though it is entirely optional. The HA-2SF comes complete with its own linear PSU free of charge but not optional. 

Performance

This was a comparison where I feel the HA-2SF’s impedance selector played a vital role in teasing out something of a competitive edge over the excellent Formula S, at least in terms of headphone matching.

All things being equal, the Formula S has some classic solid-state traits with a bit more top-end presence and treble sparkle and an altogether snappier but more neutral sound. It was tuned specifically with Abyss headphones in mind so it is unsurprising that the timbre is a little to the cooler side but with some incredible articulation. 

Head-to-head with the Empyrean on the low impedance setting, the HA-2SF is a little more relaxed but weighted or warmer in tone with a longer decay. The Formula S sounds more energetic, cleaner, and slightly more spacious in its delivery with a wider staging quality. Switching to the higher impedance settings on the HA-2SF only seems to heighten a perceived comparative softness.

However, throwing in the 80Ω T+A Solitaire P flagship planar produced a remarkable turnaround on the medium impedance setting on the HA-2SF. It sounded almost perfect in terms of the desired instrumental and vocal body and excellent tonal smoothness. Even the perceived dynamic range took a swing upwards with something of a cork released with its performance.

The Formula S had no issues driving the Solitaire P but it sounded a bit thinner, drier, and less involving, like painting by numbers. The harmonic balance was accurate enough with excellent detail but this headphone comes to life with a slightly more weighted and richer sound which the medium impedance HA-2SF gives it.

Dropping it down to low impedance on the HA-2SF sucks the life out of the Solitaire P by the way but then again that is what having an impedance selector choice is there for.

ALO Audio Studio 6

$3999

The Studio 6 has been an office stalwart for a while now. This was a private purchase hence we did not review it but we have used it for reference purposes in quite a lot of reviews since then.

Technical

Like the HA-2SF, the Studio 6 is a SET single-ended headphone amplifier but unlike the Auris design, the Studio 6 has no pre-amp capability.

Instead, this is a pure headphone amplifier with no less than 4 individual SE 6.35mm outputs as opposed to 2 on the HA-2SF. On the rear, you have 3 dual RCA inputs like the old HA-2SE but no balanced connector, gain switch, or those SE pre-amp outputs.

The Studio 6 also does not have any impedance selection though it is set up to handle headphones ranging from 8 to 600-Ohms. In my opinion, the performance is at its best with higher loads.

The tube configuration is quite different also. The Studio 6 uses a wider range of more expensive stock tubes that includes an Electro Harmonix 6SN7, two Tung-Sol 6V6’s, two Raytheon OB2’s, and a single JJ GZ64.

This is a little more complex than the cheaper four JJ Electronics ECC99 and a single input JJ Electronics ECC82 tube inside the HA-2SF though some prefer the simplicity in the tube management for rolling.

Output power is a little lower on the Studio 6 at 1W into 32Ω with the HA-2SF double its capability at 2W into the same load. The SNR is also marginally better on the 2SF at >80dB compared to 78dB on the Studio 6 and perhaps the quieter of the two overall. 

Design

I would class both as offering a retro style of design but in a very different manner. The HA-2SF has a 70’s vibe to it, especially with the brown edition whereas the Studio 6 has more of a 50s feel with its aged aluminum rounded casing, greater weight, and copious honeycombed ventilation on the top panel. Almost a steampunk vibe to it.

The HA-2SF has a much softer organic aesthetic, with warm tube glows and even warmer LCD lights with everything lit up. It is smaller, lighter, and more blended in terms of that wood, leather, and aluminum casing. 

To the front, both have input selectors and Alps potentiometers though I find the HA-2SF pot a little more resistive and accurate. The current bias on the Studio 6 tends to run better towards the end of the run whereas the HA-2SF volume control release is much more even. 

One final observation is the 4-pin power connector on the rear of the Studio 6 which allows it to fully integrate with ALO Audio’s matching phono stage without needing an additional power cable. No pre-amp? Try turntables instead. 

Performance

The noticeable ‘aggression’ gap between the HA-2SE and the Studio 6 is reduced somewhat with the HA-2SF’s better dynamic range. Both have a lovely expansive soundstage and both sound a little more vivid than the HA-2SE as a result.

DAC’s can make a difference so both amps will have a slightly darker tone with something like the R2R Pegasus and a punchier cleaner sound with the Chord Qutest. But therein, the amps do have traits that balance that out or enhance the DAC characteristics. 

The core traits lay in a lighter sub-bass rumble on the Studio 6 but a punchier mid-bass as well as a more aggressive upper-mids/lower treble. The HA-2SF has some additional bass warmth and a more rounded tone to its instrumental and vocal timbre. The treble also sounds a little more liquid and smoother.

With the Empyrean I would go with the Studio 6 if the Pegasus is your DAC of choice as the ALO Audio SET amp is a little more forceful on the highs. That mix blends better with the Empyreans relaxed treble tuning so you get a bit more bite in percussion and a livelier vocal. 

With the HA-2SF, I find the balance to be more neutral and forgiving so if you prefer your vocals to be smoother then the match is very good. Otherwise, I would pick a brighter punchier DAC like the Qutest. 

Pairing with the Solitaire P did not work quite as well with the Studio 6 as it did with the HA-2SF. Again, it is down to that medium impedance switch which releases some nice mid-bass bloom to counter the Solitaire P’s energetic treble. The Studio 6 bass didn’t quite offer the same bloom when paired with the Solitaire P so it ended up sounding brighter.

Our Verdict

The Auris Audio HA-2SF is an upgrade in every sense of the word over the older HA-2SE. You get better output power, a palpable upgrade in dynamic range, enhanced resolution, and a sound signature that veers more to the natural and clean side than before.

Externally, any design is always one for the eye of the beholder but in terms of form factor, the lower profile will definitely improve rack-friendliness whilst still retaining that beautifully inviting retro-soft wood and tan finish. This amp is full of ‘yum’ aesthetically speaking, cannot deny that.

The LED light show will offer plenty of pop from the new Vu Meter display and under the tubes, though if possible a simple switch to turn various aspects off might appeal to those who like a more discreet system. Also, wouldn’t it have been something if those balanced ins and outs really did connect to a balanced amplification circuit?

Perhaps the cleverest aspect is something both the old and the new share and that is the impedance selector. I do wish more amps would offer this feature, it can make the difference between a sterile headphone performance and a very pleasurable listening experience. Smart stuff indeed!

Auris Audio HA-2SF Specifications

• Tubes ECC82 x 1 , ECC 99 x 4
• Amplifier Configuration Single Ended
• Input Sensitivity 1Vrms
• Power output: max 2 W
• Output Impedance 32Ω – 600Ω
• Analog Inputs 3 x Lines ( 2 x RCA / 1x XLR )
• Analog Outputs 1 x XLR / 6.3 mm Phono Jack

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