In this feature, Marcus reviews the ZMF Headphones Aegis, a transformer-coupled balanced desktop tube amplifier with up to 2.5W of output power. It is priced at $3499.99.
Disclaimer: This sample was sent to me in exchange for my honest opinion. Headfonics is an independent website with no affiliate links or status. I thank ZMF Headphones for this opportunity.
You can click here to learn more about the ZMF Headphones products I have previously covered on Headfonics.
Note, that this article follows our latest scoring guidelines which you can read in more detail here.
The second ZMF Headphones amplifier released in 2024 is technically a collaboration with ‘L0rdGwyn’ (Keenan McKnight) of Head-fi fame with a refined version of his open-source 2022 DIY tube amplifier called the Aegis.
Priced at $3499.99, it sits at the top of the in-house ZMF Headphones amplifier lineup, which currently consists of the solid-state HOMAGE and their third-party Cayin line-up.
Although this is their debut collaborative product launch, Zach and Keenan have known each other for over a decade, so my only surprise is that it has taken this long for these two to lock heads and put something with both of their names on it out in the market.
In summary, the Aegis is a beautiful-looking desktop transformer-coupled vacuum tube amplifier with a very “ZMF” wood-themed front façade and a warm and deep yet very spacious sound signature that works a treat for headphones of varying impedance levels.
Intriguingly, the Aegis also uses a ‘cathode follower’ current gain-designed topology meaning it should provide an excellent platform for low impedance planar headphones, a traditional weak spot for OTL amplifiers.
How does this Aegis stack up against known behemoths such as Cayin’s SETA-based HA-300 MK2 and the OTL-designed Feliks Audio EUFORIA evo? I find out in my full review below.
Features
Current Gain
The ZMF Headphones Aegis is a medium-sized desktop vacuum tube amplifier with a transformer-coupled topology combined with a “cathode follower” design.
So, you get all the ‘yummy goodness’ of a tube amplifier’s sound signature combined with a typical high gain capability from its transformer-coupled design. However, instead of the gain levels residing in the voltage domain, the tubes are used to provide current gain.
That means a low output impedance level with a good current drive that is suitable for plenty of modern planar headphones as well as an array of voltage demanding headphones.
The Aegis has a tri-stage impedance output selector going from its lowest at 5Ω output impedance to 85Ω at its highest.
That value range is further tweaked depending on the PO socket with the 6.35m output starting at 5Ω and finishing at 31Ω and the XLR going a bit higher starting at 11Ω and finishing at a maximum of 85Ω.
You get plenty of flexibility for the likes of the BOKEH, Atrium and Focal’s Utopia 2022 but you can add IEMs to the compatibility list without any impedance skew concerns which is an exception in tube amplification.
Ideally, you want to be using the 4.4mm PO which has a voltage divider to reduce any potential noise for sensitive gear such as IEMs.
Combined with up to 2.5W of output power capability that should also mean the Aegis will drive headphones such as ZMF’s TOTL Caldera Open and Closed-back planar variants.
Tubes
Tubes? There are some indeed though nothing as magnificent as a set of 300B tubes. The strength here is flexibility with a very wide range of options plucked from the 6SL7 high mu triode vacuum tube series.
In this case, the Aegis comes with two JJ 6SL7 input tubes, 2 JJ EL34 driver tubes, and a Sovtek 5AR4 tube rectifier, known for its good build and durability.
ZMF has handily inserted a picture of the Aegis with a wide range of rollable options to suit most preferences. For this review and sound impressions, we will stick with the default configuration.
Design
Yet another stellar retro design from ZMF. To be honest, this is how I always imagined a tube amplifier should look like as a kid.
And I guess to some extent this is how I view the Aegis with its retro-styled VU meters inserted into a sumptuous premium kiln-dried hardwood front panel and topped off with beautifully CNC cut walnut knob in the middle, a similarly finished power button, and a grooved brass fastener at the base.
Even the weighty transformer boxes on the rear have a splash of ‘cool’ discarding regulation plain black and using instead complementary and very tasteful gold & ebony brushed overlay. From afar it’s almost like a set of marble blocks on top of a wooden cabinet. The TLDR is memorable.
To add to the aura of authenticity the Aegis uses some mightily large switches for impedance and output control on the front panel. These are beefy which I like. They feel like they will last a while and you are unlikely to miss them due to their size.
If there is one thing I think is missing it’s a removable tube cage for the US version, (one comes with the EU version). It does not add to the aesthetics but for safety and protection for you and your tubes during regular use.
Thankfully, the only time you have to give the Aegis the ‘reach around’ is for cable changing since everything else is on the front panel.
I/O & Controls
Which nicely segues into the controls of the Aegis which is not that complex on the rear panel. Just a pair of dual RCA analog inputs on the left side giving away its single-ended input design and the power plug on the right channel
All the controls are on the front panel including the output and tri-stage impedance selector switches as well as the resistance-based ALPS potentiometer in the middle.
The aviation-inspired dual VU are real VU and a bit more finely detailed than the one used inside the cheaper solid-state Homage amplifier. If you look very closely you will also see they are branded with ZMF’s logo on the bottom right side.
Like the Homage version, the dual VU presents a relaxing orange glow when turned on though there is no option to turn them off during playback.
The Aegis is loaded with 3 PO including 6.35mm, XLR, and 4.4mm with power differing slightly depending on the chosen output.
ZMF has calculated an average of 2 Watts on the 6.35mm output with XLR ranging from 1W up to 2.5W depending on the load up to a benchmarked maximum of 300Ω
Sound Impressions
The following sound impressions were completed using the Holo Audio Spring 2 Wildism Edition DAC as my main source with ZMF’s Atrium and Caldera Open as my main headphones with the Vision Ears VE10 and CA’s Supermoon for IEM testing.
Summary
The Aegis is probably one of the most flexible tube amplifiers I have tested in recent years. It will deliver excellent, weighty, smooth, and assured performance from a wide assortment of gear.
If you have sensitive IEMs or very low-impedance gear, its surprisingly black background and excellent low-volume channel matching from its 4.4mm output have you covered.
If you have a few higher-impedance dynamic driver headphones, such as the BOKEH, then no worries. It still sounds deep and punchy, as it should. Also, the 300Ω Atrium open puts in a very good performance with a juicy, heavily textured low-end and excellent staging capability.
The ace up its sleeve is planar or current demanding headphones. Here, the Aegis outcompetes the HA-300MK2 and the OTL Feliks EUFORIA evo with headphones such as the Caldera.
This is a set of planar headphones that need to sound authoritative on the lows, it should deliver good PRaT and clarity at the same time.
The Aegis can deliver that with a firm and punchier response and enhanced energy compared to the atmospheric swirl of the HA-300MK2, an amplifier whose stock tubes and stronger voltage bias endow the Caldera with a politer tone.
Unlike the EUFORIA evo, the Aegis will not distort at high volume with planars either. Everything sounds resolutely under control and natural sounding without distortion using the stock tube configuration.
Coloration
The Aegis delivers a natural to smooth response, produced with a satisfying reproduction of the fundamental frequency when required. Those headphones with a good bass performance will not sound underwhelming.
The sound signature with the stock tube configuration sits somewhere in between the airy and hyper-spacious holographic sound of the HA-300MK2 and the ‘chocolatey girth’ from the darker tuning of the EUFORIA evo.
What that means is a slight diminution in the highs compared to the HA-300MK2 but more treble sparkle and headroom than the EUFORIA evo. And on the other side of the coin, the Aegis has more weight and punch than the Cayin but less sub-bass bias compared to the Feliks.
Impedance selection will produce varying degrees of vibrancy in your chosen gear and here is where a bit of personal preference came into play for me.
For example, the sensitive Vision Ears VE10 on the 4.4mm output should really be on a low impedance setting but I found the performance somewhat subdued for my tastes. A very smooth performance but lacking in vibrancy compared to the peppier medium impedance setting.
Once you go up to medium impedance the VE10 sounds much more dynamic to my ears with that low-end dynamic driver firming up and producing a lot more impact.
The highs also sounded enhanced which in turn upped the level of contrast through the mids. Overall, better clarity and more immediate sound.
My personal recommendation is play around with the impedance value selector and see what satisfies you the most. Some gear will sound more dynamic on different values as was the case here with my gear.
Staging & Dynamics
I would describe the Aegis soundstage as reasonably wide and slightly relaxed on the highs but with excellent depth, and more importantly great control on those lows.
This is not just a wall of syrupy fulsomeness on the lows, it sounds deep but relatively well-controlled, with the right impedance value selected on headphones such as the Caldera Open and Empyrean II.
Mids are immediate also with vocal presence a bit more front and center than traditional SETA or OTL amplifiers. Instrumental presence through the mids and highs sound noticeably lifted on the Aegis compared to more chilled and romantic tunings such as the EUFORIA evo.
I would say though that it is not quite as well extended or holographic sounding as the HA-300MK2 with its sock tubes. It is a little firmer and ‘fleshier’ down the center image but just slightly softened on the extreme edges and highs compared to the sparkler and excellent headroom of the Cayin.
If you find the dynamics a little flat or the staging a bit narrow, I recommend changing those impedance values, they make a big difference with almost any Aegis pairing.
Click on page 2 below for my recommended pairings and selected comparisons.
