Synergy
With a tri-stage impedance selector and varied impedance values for each PO, the ZMF Headphones Aegis has a very flexible output system. More so with the additional split voltage 4.4mm PO which gives it a more IEM-friendly nature than many competing tube amplifiers.
IEM Pairings
I paired the Aegis with four IEMs to hear how deft it is at handling various sensitive gear via its 4.4mm output.
This included the sensitive Vision Ears VE10 and Noble Audio’s Ronin to more demanding alternatives including the planar Campfire Audio Supermoon and the 80Ω rated Westone ES80, (custom version).
The resulting impressions were quite interesting. All four pairings exhibited zero waterfall hiss or tube pings. The Aegis’s 4.4mm output is super quiet, with excellent channel balancing at low volume levels.
With the right impedance setting you should not be getting diminished dynamic range from noise, it just isn’t a factor. However, the ‘right impedance setting’ is from a preference point of view.
Each IEM, save for the Ronin, sounds more boisterous or exuberant with the medium impedance setting. I say ‘save for the Ronin’ because it sounded smooth and cohesive on a low gain. With medium gain I felt the mids and highs had a somewhat stressed sound.
The VE10, the Supermoon, and the ES80 all sounded vibrant on the medium setting with the VE10 and the Supermoon sounding a bit smoother but also a touch flatter on the Aegis low impedance setting.
Again, this is a personal preference. The truest sound for the VE10 and Supermoon is low impedance but the lows from the medium impedance setting sounded more dynamic to my ear. Using high impedance is not recommended, the skew sucks the life out of the presentation of both of the IEMs.
The ES80 didn’t play out optimally on the Aegis high gain setting. It wasn’t as skewed as the VE10 and Supermoon, but it was not as vibrant or had as much sparkle in the highs as the medium setting.
Headphones Pairings
I tested 3 planar and one dynamic driver headphone and like the IEMs, the chosen PO and impedance value will greatly affect the performance.
Starting with the Meze Audio Empyrean II using the Aegis high impedance setting. This thickens the Empyrean II’s instrumental notes giving them a more saturated denser sound. Its bass depth and power are enhanced with a little more bloom but sounds slightly relaxed on the highs and not quite as articulate or as airy as the medium impedance setting.
Medium impedance is lighter bodied but not by much with more treble presence and wider channel separation. Spatial notes on extreme ends resonating stronger creating a more holographic soundstage and a slightly sweeter tonal quality.
The BOKEH will not drive well from the 4.4mm which has a fixed 2Ω output impedance rating and is only meant to be used on the low impedance setting with sensitive gear.
These headphones need the XLR output on a high impedance setting to sound deep and impactful. Anything below that gets progressively smaller and slightly softer sounding.
The Atrium is better sounding than the BOKEH on the Aegis with more texture and a juicier bass response. It is not as deep or as punchy, but rather more saturated and textured sounding.
Going high impedance and the XLR connection is ideal for the Atrium, everything setting below sounds lifeless and lacking in dynamic range.
Staying on high impedance the Caldera Open sounded spot on with more impact and better PRaT than the Cayin HA-300MK2 though not as airy and sparkling in the mids and highs. This pairing is a great example of what the Aegis can do with planar headphones.
Select Comparisons
The following comparisons were completed using a mix of the Holo Audio Spring 2 Wildism Edition DAC, an SMSL PL200 CD player with the Caldera and Atrium Open headphones from ZMF Headphones.
Cayin HA-300MK2
The Cayin HA-300MK2 is a second-generation SETA tube amplifier launched in 2022 and reviewed by us in the same year. It was also our 2022 Top Gear Award winner for Best Desktop Tube Amplifier.
Technical
Both are transformed coupled single-ended triode headphone amplifiers though the HA-300MK2 can dual as a power amp for speakers.
However, the HA-300MK2 is not a “cathode follower” meaning its gain is primarily in the voltage domain as opposed to the current domain. That is not to say it cannot handle sensitive gear, it can, but rather it is more suited to voltage demanding headphones.
And that is reflected in their respective tri-stage impedance selectors with the HA-300MK2 parameters up to 64Ω, 250Ω, and 600Ω, (balanced matched).
The Aegis parameters start at 5Ω up to a maximum of 85Ω but the precise value is different depending on the choice of output connection. The 6.35m output’s range is lower at 5Ω to 31Ω and the XLR going a bit higher at 11Ω to 85Ω.
The outpower power of the HA-300MK2 is nominally higher but when impedance matched they are quite similar in capability.
The Cayin can deliver a maximum of 6W from its XLR output for loads up to 600Ω but drops down to 2W for its low impedance stage value up to 64Ω which is very close to the Aegis 2W average across the board.
The other key difference is in their tube selection. The Aegis 6SL7 tubes are designed for ‘easy access’ rolling, tubes that won’t tax your wallet too much getting an assortment of options to test out.
The HA-300MK2 uses high-end Gold Lion Genelex PX300B power tubes and these go for around $200 for a matched pair. You can go a lot higher if you want in terms of 300B tube pricing making tube rolling for this amp more hardcore.
Design
Whilst I can recognize some crossover in their design aspects, the final finish of each looks very different.
Cayin had a hand in helping ZMF Headphones nail down the precise structure so there are some design languages I recognize being drawn from the Cayin box such as the rounded push button for power, the pillar structure and finish under the chassis, and to some extent the form factor of the housing.
Both are heavy courtesy of those big transformer boxes to the rear though the HA-300MK2 is split between amp and PSU at 20kg and 9kg whereas the Aegis is an all-in-one at just over 20kg.
Despite that, there is no way you could confuse these two heavyweights. The retro wood panel design of the Aegis is aesthetically warmer and more eye-catching though I acknowledge the superb engineering in the HA-300Mk2 which feels a little more premium with its reflective aluminum finish and tube guards.
Options are aplenty on both though the HA-300MK2 can act as a speaker amp so there are additional controls for that on the front panel.
Both have mechanical switching tri-stage impedance and output selectors to the front with XLR, 6.35mm, and 4.4mm outputs. The HA-300MK2 also has XLR inputs to the rear giving you a bit more input choice and a switch to control that choice on the front panel.
Performance
I started this comparison with the Caldera open version on the Aegis high impedance setting and a low impedance setting on the HA-300MK2.
This type of headphone is where I feel the Aegis might have a bit of an edge. Not that the Aegis is outright better than the HA-300MK2. There are strengths in the Cayin amp that the Aegis cannot match but driving the Caldera with authority when impedance matched is not one of them.
It’s that low-end impact that is missing from the stock tube setup of the HA-300MK2. It has a nice punch, very spacious, more so than the Aegis in terms of channel separation and staging width.
However, the weight and density on the lows favor the Aegis and this is where the Caldera needs to be to get that authoritative performance I know it can deliver. That means ‘drive’. not in terms of ability to power it but rather enjoyable PRaT.
The Cayin delivers a holographic airy and height-extended experience with the Caldera but it’s the depth and timbral density through the mids and vocals that convince more with the Aegis.
Changing to the Atrium produces a different set of outcomes. This is where the Cayin should be bossing the Aegis around a bit and in truth, it is ahead in terms of space, air, and just generally creating a more defined and intricate soundstage that maximizes the Atrium’s entire acoustical space.
The Aegis still has that density and additional weight on the lows but it sounds a little more subdued, swapping the pristine treble sparkle and sweet timbre of the Cayin for a smoother, juicier set of mids and highs.
The Atrium is already a fairly relaxed set of headphones so it sounds more balanced for my preference with the Cayin though I am fairly sure the smoother weightier tone of the Aegis will win a few over.
Feliks Audio EUFORIA evo
The Feliks Audio EUFORIA evo is the third iteration of the original EUFORIA OTL desktop amplifier from 2017 with a 2nd gen 20th Anniversary Edition launched in 2020.
Technical
The EUFORIA evo is a single-ended pure OTL or output-transformerless headphone tube amplifier with pre-amp and crossfeed capability.
There are those that would consider an OTL design as a more pure way of delivering a tube amplifier’s performance with the lack of a transformer stage seen as potentially limiting the potential resolution, dynamics, and potential bass response of the amplifier.
The OTL design means it’s more of a voltage king than the Aegis and as such its output impedance is a low higher by default making it much more suited to high impedance headphones, perhaps more so than SETA amplifiers.
It does not have the same level of gain in the current domain as the Aegis meaning it is less capable of handling low impedance high current headphones. Clipping and distortion can occur with modern planars using the EUFORIA evo which is not the case with the Aegis.
The tube setup is also a bit different and like the HA-300MK2, the EUFORIA evo uses some higher-end or more expensive tubes to roll including a matching set of PsVane CV181 MK2 “Gold” drivers combined with a pair of 6N13S (NOS) power tubes.
The 6N13S tubes are easy enough to replace or roll costing about $30 a set. However, the PsVane CV181 MK2 “Gold” drivers can cost around $200 for a matched pair making it the pricier rolling experiment.
Both amps are XLR output capable though the EUFORIA evo has no impedance controls. You get up to 280mW of SE output power with 20 dB of gain into a 300Ω load which is a decent level of performance.
Design
The EUFORIA evo creates a very different visual to the Aegis design. It’s understated, compact, ‘cute’ if you will with a cedar brown exterior and a relatively lightweight chassis at 7kg.
The EUFORIA evo form factor is one of those classic compact desktop tube designs that should appeal to those with more limited but study desktop space whereas the heavier and wider Aegis really needs its own rack space and a sturdy one at that for its 20kg body.
Feliks have gone for a sandblasted aluminum panel finish with a split front plate and sweeping arcs over a large rotary resistive rather than a stepped Alps potentiometer. The only break in the EUFORIA evo color and design is the use of black for the pot wheel and a beautiful little silver logo emblem right in the top center.
It’s a darker vibe visually compared to the retro warm wood panel and glowing VU meters of the Aegis. I quite like both, they do not compete with others in terms of styling though the Aegis will likely catch your eye first from afar.
Some differences in functionality and I/O. The EUFORIA evo can operate as a pre-amp with a set of RCA outputs as well as RCA SE inputs.
There is no pre-amp output option on the AEGIS though it does offer that split voltage 4.4mm PO on the front panel suitable for IEM users which the evo doesn’t have.
Should the evo have a 4.4mm option? Debatable as it’s not my first choice for IEMs or less so than the Aegis but increasingly modern high-impedance headphones can ship with 4.4mm cables.
Performance
The EUFORIA evo pairs beautifully with the Atrium but creates a very different tonal quality to the Aegis.
The Feliks pairing brings home that OTL sound with this 300Ω beast. Combined with the already atmospheric quality of the Atrium it sounds smooth as butter, very deep and slightly languid in its pacing but with vocal texture to die for.
I would place the Aegis somewhere between the HA-300MK2 and the EUFORIA evo in terms of bass weight and warmth. It sounds a little more balanced tonally, with more treble energy, and a cleaner set of mids though still with good weight on the lows.
Arguably, the Aegis is a punchier amplifier compared to the sub-bass bias of the EUFORIA evo and might sound more articulate and quicker-paced with a stronger percussion presence using the Atrium.
The weakness of the EUFORIA evo is driving planars, and that’s fairly evident with the Caldera when you start pushing up the dial to get the additional volume required to drive it.
You will start to notice at high volume levels some distortion on dynamic peaks on recordings and higher pitching vocals. It can get a little rough the more demanding the headphone is. Switching to more efficient planars such as the Audeze LCD-5 the distortion becomes more noticeable and not an ideal pairing.
On the Aegis, the Caldera and the LCD-5 playback without any distortion issues, making it the choice of these two amplifiers for planar headphones.
My Verdict
The ZMF Headphones Aegis easily hits the excellent sticker for tube amplifiers we have covered for 2024. It has a beautifully smooth but weighty tone, awesome gear flexibility including IEMs, and looks the ‘ZMF business” as only a ZMF piece of gear can.
This stunning amplifier is going to slot right beside the HA-300MK2 and EUFORIA evo as a bit of a ‘trinity’ of reference tube amplifiers I will consider using for review work in 2025. Heck, just for pure listening pleasure I am going to be warming up those ‘lil’ tubes quite a lot.
For planar users, this is a good one to try with popular headphones such as the Caldera, Audeze, or Meze models, to name but a few in the soon-to-heat-up audio trade show season in Q1 2025. There is very little I attached to this amplifier that did not have a pleasing outcome.
ZMF Headphones Aegis Technical Specifications
- Input impedance: 20kΩ
- Output Impedance Range: 1/4″ Out: Low: 5Ω, Med: 11Ω, High: 31Ω. XLR Out: Low: 11Ω Med: 28Ω High: 85Ω
- Power: Average of 2 Watts, 1/4″ and XLR 1W to 2.5W, calculated based on headphones from 8 to 300Ω.
- Frequency response: -3dB from 11Hz – 33kHz
- THD+N at 1mW: < 0.05%
- Tube Types: – Rectifier – 5V / 2A or 3A types; GZ34/5AR4, 5V4/GZ32, 5R4, 274B. 5Y3, 5U4G
- Inputs – pair 6SL7
- Outputs – pair power pentodes; 6V6, 6L6, EL34, EL37, KT66, KT77, KT88, 6550.
