ZMF Pendant - Tube Headphone Amplifier - Review

Review written by Ian Dunmore (@Torq)

Introduction

When you think ZMF, you tend to think “headphones” - whether that’s Zach Mehrbach’s all-proprietary line of artisanal-quality, wooden-cupped, dynamic-driver masterpieces, like the recent Vérité or Auteur - or their original planar models based on a modified Fostex T50RP platform. But that’s not all that is on offer from ZMF - as in addition to their headphones, upgrade cables and a wide variety of pads (compatible with other headphone brands too), they also have their own dedicated headphone amplifier - the “Pendant”.

The Pendant is a pure-tube implementation featuring a high-power, transformer-coupled design capable of driving almost any headphone that you care to throw at it. It has been developed in collaboration with ampsandsound, a well-regarded designer and manufacturer of tube-based headphone and speaker amplifiers.

The unit used for review here was on kind loan from ZMF and has subsequently been sent to the next eager reviewer for their listening and auditioning.

The core gear chain/equipment used in this review can be found here, and the music I use in my reviews and evaluations is listed here.

Specifications

• Single Ended Ultra Linear tube amp
• 8 ohm (low-z) and 300 ohm (high-z) outputs
• Dual RCA inputs
• Pre-amp outs via RCA
• EL 84/6BQ5 Driver tubes, 12ax7, 12at7, and 12au7 input tube options, EL 81/6CA4 Rectifier
• Transformer coupled design
• 3 Watts @ 8 ohms and 2.5 Watts @ 300 ohms
• Choke-filtered PSU for dead-quiet sound reproduction
• ALPS volume pot

Features & Options

The Pendant has two headphone outputs, each of different output impedance (OI) referred to as “Low Z” (8 ohms, with up to 3W of power available) and “High Z” (300 ohms, with 2.5W of power on tap), respectively. This aids with matching the output and damping capability of the amplifier with your headphones. As a general rule, you’ll want lower impedance dynamic headphones (150 ohms and below) connected to the Low Z output to minimize frequency response shift, though this is not a requirement.

Options come in the form of a “Vintage/NOS” upgraded tube set ($200) - the specific tubes for which may vary, as well as the option for a custom-wood chassis ($300). The standard chassis for the pendant is black, matching the unit’s top-plate, and as shown below - and it’s quite a fetching finish. For me, given the excellent woods and finishes that ZMF is so well known for in its headphones, I would personally opt for one of the custom woods.

The Pendant is equipped with a pre-out connection, so can be employed either with external power-amplification, or active speakers, for integration into a 2-channel non-headphone setup.

Finally, there are dual, switchable, high-quality RCA-inputs (since this is a fully single-ended design), allowing the connection of two sources and easy selection between them.

Build

The Pendant is a very solid feeling, desktop-sized, unit, without being excessively heavy. The finish is, as with every ZMF product I’ve had my hands on, extremely appealing and of very high quality. There were no creaks, groans or rattles, nothing was loose, sockets were firm, switches positive and the volume pot is buttery smooth.

Inserting and removing tubes, which many tube-amp owners do a fair amount of, especially early on when rolling tubes to find which types/versions they like best, did not result in any perceptible movement in the tube sockets. And the fit was firm and consistent, without being so tight that it would cause concerns for damaging tubes when removing them.

The unit follows the familiar “ampsandsound” plate-on-chassis construction (an approach also used by other tube-focused companies such as Bottlehead and Decware, among others), with transformers, connections/sockets, controls and, most importantly, the tubes all mounted on the top of the main plate, with point-to-point construction for the internal components hidden underneath). This yields a very appealing aesthetic - most tube-amp fans like to see the glow as much as possible - and they are prominently on display here, while also facilitating super-easy access to the tubes.

Due to the top-mounted IEC power-inlet, you may want to consider a power-cord with a 90-degree angled head, but this is a matter of appearance rather than function. The unit was perfectly stable, with no movement at all, even with my heavy, big-gauge, solid-billet power cables in use (not used for listening as part of the review itself).

It is worth noting that the top plate on this unit differs in its tube labels from more recent models, which show the more commonly used references for the tubes used.

Sound

Tube amplifiers, especially pure-tube designs, are often assumed to be “warm”, “gooey”, “laid back” and/or “highly colored” sounding by those that don’t have experience with them; though there are certainly some models which would meet one or all of those descriptions.

The ZMF Pendant is not one of them.

Instead, equipped with the stock tube complement, it is punchy, dynamic and quick, with excellent resolution, while maintaining many other desirable traits of tube amplification - such as holographic presentation, expansive staging, solid tonal weight, lucid mids and silky-smooth highs, without the “drag” of an exaggerated, overly warm or tubby, bottom-end nor imposing a “laid back” sense to the delivery.

At the same time, the Pendant responds well to tube-rolling - which lets you tailor the sound in a variety of ways, depending on your personal preferences … something I’ll come back to in the “Tubes & Tube Rolling” section. But for now, I will stick with the stock tube complement - as that is how the main section of this review was conducted.

In More Detail …

Tone is effectively neutral with the included JJ Electronics tubes, though you can push it towards either warmer or brighter signatures with different input and power tubes. There’s no apparent emphasis here, from either output, with appropriately matched headphones. Instruments present naturally, from their lowest registers to their highest, even with the significant range of instruments like the Piano.

Timbre is accurately reflective of the natural sound of the instruments in question, with excellent, even visceral, texture, appropriate body/weight, and preserves the natural damping or reverberation of the piece in question. Instruments that bite, will do so convincingly here, be that the discordant overtones of brass being thrashed, or the initial pluck of a harp or guitar string. While more even/less-stressed, play, on less aggressive instruments, remains pure and smooth.

It’s even possible to discern variations in the timbre as it changes, subtly, with grip and position during longer pieces that have the performer repeatedly mount and unmount their instrument between passages. This is typically the preserve of more exotic amplifier designs - often those relying on much more expensive tubes, so it is particularly impressive to hear this on the Pendant.

Bass delivery is taught, fast and punchy with excellent articulation and sit-up-and-take-notice slam-capability. This is in stark contrast to many tube amplifiers that achieve their “bass presence” by being wooly, loose or bloated. You do need to pay attention to the impedance of your headphones to get the best of the Pendant here - once you start to stray shy of about 80 ohms on your headphones (on the Lo-Z output), bass-quantity will increase at the cost of some control.

The mid-range is pure magic, with proper tonal weight, oodles of detail, so-good-you-can-feel-it rendition of texture, and entirely lucid … even liquid … rendering. With the stock tubes it does not stray into editorialization with that I would call “lush” mids - though you can certainly take it there with alternate tubes if that’s your bag. I have a soft-spot for “lush” mids … which is why I tend to gravitate towards 300B-based tube amplifiers, but that “lushness”, while seductive, is not especially accurate - and accuracy is the side of the fence the Pendant walks with its normal tube complement.

Treble is silky-smooth, completely natural and detail-rich, with absolutely no sibilance, harshness or unwanted tension to it whatsoever. Blaring trumpets and horns bite and glare appropriately, without exaggeration. Cymbals crash and ring, without exaggerated splashiness, and sound like the brass they are with no hints of steeliness.

Dynamic delivery is extremely powerful, with an effortless sense to even the most significant shifts from pianississimo to fortississimo, the abrupt sonic impact of cannon-fire, or Germanic-operatic crescendo. Staccato shifts to and from silence to max-level replay, leave the Pendant completely unfazed. Impact is high. This is a shock-and-awe experience even compared to some of the most dynamic tube-hybrid designs and rivaling more expensive solid-state performers. Ample power-reserves allow unrelenting power and slam, even with demanding cans, and at no point in my listening was there even a suggestion that the Pendant was not “keeping up”. Even with low-impedance planar-cans, a common weakness for (relatively) high-OI amplifiers, the sense of effortless and limitless power reserves was preserved.

This macro-dynamic prowess does not come at the expense of nuance or subtlety, however. Even with the stock tubes, as used here, the emotive, granular, micro-changes in volume, help convey vocal emotion, instrumental stress/texture, and general passion and energy in a piece - at a level not commonly heard in any amplifier. It is not uncommon for tube amplifiers to lose-out here, especially with inexpensive tubes, but ZMF/ampsandsound’s little wonder fully preserves these details and nuances, capturing the most subtle tremolo or vibrato, and the end-result is an enormously engaging and emotionally involving musical rendering.

Commonly, inexpensive-to-mid-tier tube-amplifiers can lack somewhat in speed and transient performance. Indeed, it is not uncommon to find tube-hybrid designs stealing the show here. This is not the case with the Pendant. It is extremely quick. Transients are fast, sharp, with no audible overshoot. String-plucks are immediate and precise. Percussion strikes are, well, striking. The black/white transitions of synthesized/electronic “instruments” are stark yet bold … the best aspects of tubes and solid-state.

Stage presentation is expansive, something often found with good tube amplifiers, with venues rendered in a manner in which their ambience - the low-level echoes, reverberation and even the sense of the air in the space - is both palpable and portray and appropriate sense of scale. One of my favorite tracks for getting a feel for this, due to its simple origins and acoustic nature, is “Mining for Gold” (Cowboy Junkies, “The Trinity Session”). It is not an exaggerated presentation, the stage doesn’t seem larger than life, but is more vivid in how it is delivered such that it becomes a bigger part of the musical whole.

Imaging-wise, elements rendered within this space are holographic in their dimensionality, placement and stability within the audio image. Something easily heard with a track I’ve more recently added to those I’ve previously when assessing imaging, to has been Holly Cole’s “Train Song” (Temptation) - where depth and lateral placement are both precise and easily discerned - rather more easily so with the Pendant than with most solid-state amplification that plays in the same price tier.

Noise

While tubes have an impact on the noise level with pure-tube amplifiers, the Pendant was extremely quiet. Via either the Lo-Z or Hi-Z outputs, and using the Vérité as the test headphone, no noise/hum/hiss was apparent in any normal listening scenario, even during silent passages/pauses in the music with the volume cranked up as far I would normally dare listen.

If you turn the amplifier up to its full volume, with no music playing, then you may, depending on your tubes, hear some very low-levelnoise, but that represents a playback level that with actual music would fry your headphones, not to mention your ears, in very short order.

In short, this is just not a concern here unless you have noisy tubes (and those will be noisy in any amplifier).

Headphone Pairing

The Pendant will drive pretty much anything you want to throw at it, with ample power. When it comes to pure-tube amplifiers, there is a bit more to matching headphones and amplifiers than raw power. Tube amplifiers tend to have higher output impedance (OI or “Z”) than solid-state or tube-hybrid designs and that can lead to underdamped bass or shifts in frequency response with low-impedance headphones.

Pairings

While I found the Pendant to be more than capable with a wide variety of headphones, of varying nominal impedances, I felt it was at its best with headphones of 80-100 ohms impedance or higher (from the Lo-Z output). Above that, while somewhat more compelling, the differences become rather small. Though I will say that running higher impedance headphones from the Hi-Z output was my favorite way to listen with the Pendant.

I also generally preferred it with dynamic-driver units - though this is likely because I only own one high-impedance planar can and typically prefer dynamic headphones anyway.

Synergistic Matches

These headphones represent the best pairings from my collection, all of which were absolutely captivating listens via the Pendant, with my general preference here being the Hi-Z output. All exhibited excellent detail, control, speed and precision down into the lowest registers.

• Audeze LCD-4 (Lo-Z)
• LB-Acoustics MySphere 3.2 (Hi or Lo-Z)
• Sennheiser HD650, HD800S, HD820 (Hi-Z)
• ZMF Aeolus, Eikon and Vérité (Hi-Z)

I did some cursory testing with other higher-impedance headphones (>=150 ohms), with similar results. Some of the more bass-happy cans in that realm faired a bit better from the Low-Z output, but that’s why you have both options.

Excellent

These units also gave an excellent account of themselves, though tended to favor the Lo-Z output overall. Even so, I would definitely give them a whirl on the Hi-Z output both for reference and to account for different tastes.

• Focal Utopia (Lo-Z)
• Sennheiser HD58X, HD660S (Lo-Z)

The Utopia was quite interesting here … a little lift in the low-end and a particularly smooth treble delivery from the Pendant actually results in very good synergy, and addresses the most common complaints about Focal’s flagship, but strictly speaking its a bit of a diversion from their natural tuning.

Preference-Driven

Here there was either some low-end tonal shift apparent when driven off the Pendant, or the bass region began to exhibit some bloom or became a little looser-sounding. Listeners that go all-in on bass-quantity will likely find this rather agreeable, where bass-heads that are more about precision and speed down into the sub-bass may find things to be a bit too much.

• Abyss AB-1266 Phi TC (Lo-Z)
• Focal Stellia (Lo-Z)
• Meze Empyrean (Lo-Z)
• Rosson Audio Design - RAD-0 (Lo-Z)

The Stellia was the least impacted here, despite its very low (35 ohm) impedance, with the bass level coming up noticeably but still maintaining good control. The three planar models felt a little less controlled in the low-end for my personal tastes (though still a fair bit better than most high-OI tube amps with such cans), with the Empyrean being somewhat bloated. Though the impact and scale of deep bass notes, be it big organ pipes or synthesized bass was quite impressive with the Abyss.

Tubes & Tube Rolling

The sound of pure tube amps, like the Pendant, are affected to a much greater degree by the tubes they are using than tube-hybrid designs. Where tube changes in a tube-hybrid design tend to be very subtle, with a true tube amplifier they can significantly alter the overall character of the amplifier (for better, or worse). And the more aspects of the design that are tube-based, the more potential there is for changes when tube-rolling.

The Pendant uses three different types of tube - one for rectification in the power supply (EZ81 or 6CA4), one dual-triode (12AX7/ECC83S/7025), 12AT7/ECC81/6201, and 12AY7/ECC82) signal tube for pre-amplification and two pentodes (EL84/6BQ5) for the power stage, giving it more potential for tube-based tweaking than most amplifiers in its class.

The stock set of tubes that comes with the ZMF Pendant (at the time this review is being written) come from “JJ Electronics”, and comprise a pair of EL84s, an ECC83S and an EZ81 - and these were used for the primary review/listening sessions. In addition to providing excellent sound, and a solid base-reference point, they’re also a very nice aesthetic match with the black/red color scheme of the Pendant, and exhibit quite visible glow even in daylight usage.

Tubes I selected here are more about covering the range of sound/changes they can bring about with the Pendant, based on tubes I have available (and am familiar with) - there are many more options, at many price points.

Prices, where available, are PER TUBE and approximate (and may/may not included balancing/matching sections/tubes) and links should not be taken as an endorsement of the vendor - they were simply either the best price or only vendor with stock I could find at the time of writing.

Input/Signal Tubes (12AU7/ECC82, 12AT7/ECC81, 12AX7/ECC83)

In general, I found that changing input/signal tubes has the biggest overall impact on the sound here. This is not always the case - with my big SET amplifiers it is usually the power-tubes that make the biggest difference.

Mullard 12AT7WA/CV4202 NOS - ~$50

Medium gain, so you’ll have more range on the volume dial than stock.

A little warmer than the included tube, with a hint of added liquidity in the mid-range, and an extremely polite treble, but perhaps at the cost of some low-level resolution. Some added tonal weight/richness, but still quick and punchy. Generally leans towards the more classical “tube” presentation without robbing the Pendant of its clarity, tone or resolution. A hair less slam than the other tubes mentioned here, but a little more low-end presence offsets that nicely.

Mullard “10M” ECC83 “BVA” (Master Series, D-Getter) - Circa 1950, old Mullard “shield” logo

This was my favorite input/signal tube in the Pendant, and resulted in the biggest and most appealing audible change, relative to stock, of any tube I tried.

These can be very hard to come by, especially if you’re after NOS (as opposed to used). A good, strong measuring, used tube can run $100-$150, and a NOS tube with closely matched sections can easily be more than double that.

This is a higher gain tube, with a Mu of 100 (same rating as the stock JJ Electronics tube).

This little guy took an already excellent amplifier up to the next level, building on its strengths and adding some mid-range lushness, without losing any resolution/detail/clarity. Bass hits/slams a bit harder here too, which wasn’t lacking to start with. Treble takes on a hint of sweetness and adds a little shimmer/sparkle while maintaining its extension, air and space.

If you want the Pendant to retain its technical chops, but nudge it to sounding more like a stereotypical tube amplifier, without the undesirable effects sometimes associated with those, then as far as I am concerned, this is the tube you want.

Telefunken ECC83/12AX7 Smooth Plate/Long Plate NOS ~$395

Hard to get, expensive, but the most resolving and fastest-sounding tube I tried in the Pendant, with higher gain as per the stock tube.

Low level details are clear and more easily discerned, be it background noises in the recording, more nuanced instrumental textures, and micro-dynamics are more vivid and present. Top end has excellent extension and a very airy and open delivery (particularly noticeable with the Vérité Closed). Stage takes on a slightly larger-than-life sense, but imaging precision is even stronger and the holographic sense to the image, something that is generally a strength of this amplifier anyway, is even more apparent.

Tonal changes were not very apparent here, with most of the deltas being heard as improved technicalities and I did not find any shift toward, nor away from, the Pendant’s innate signature - that of a resolving, neutral, fast amplifier.

Power Tubes (EL84/6BQ5)

Tubes in the power-stage of the Pendant affect the overall sound a little less, in general, than the input tubes, and rather more than the rectifier tube, but still contribute a significant amount to the overall renderinr of the amplifier.

Tung-Sol 7189/EL84 (Re-Issue/Current Production) ~$30

Neutral tone and serious kick. Macro-dynamics are front-and-center here. Effortless delivery, even with huge dynamic excursions. Staccato electronica or major orchestral “drama” pieces exemplify the Tung-Sol’s contribution to the ZMF amplifier’s delivery. Quick, punchy and addictive for fans of especially high BPM, “percussion”-laden, pieces.

Extremely good noise performance, low susceptibility to physical (microphonic) or radiated (RM/EM) interference, yields a coal-black background (and the Pendant already has excellent “black-ground”).

Easy choice as a first upgrade from the stock power-tube, especially well suited to planar cans.

General Electric EL84/6B5Q NOS - ~$55

Somewhat richer and more luscious, particularly in the mid-range, than the stock tubes and, indeed, the Tung-Sols mentioned above. Not quite as punchy as the Tung-Sol, but tonally sweeter and with a little more overall body. A little-less low-end grip than the stock or Tung-Sol tubes, but the slight increase in bass-level is pleasantly rendered and doesn’t stray into excess nor bloat.

Not the best mix for already-bass-exuberant planar-cans, and with ZMF’s headphones you’ll probably want to be running on leaner-sounding pads (e.g. the Vérité pads, or some of the suede variants), but a rich, engaging and seductive option. And something that no tube-swap in a tube-hybrid amplifier will begin to approach.

Mullard EL84/6B5Q (First Gen, Circa 1950) White Label, Square Getter NOS - ~$100-$200

Lush mid-tones, punchy and articulate low-end, sweet, sweet top-end, rich with detail and imbued with a little harmonic glow/richness. Expansive stage, with rock-solid imaging. Highly resolving. Excellent macro and micro-dynamics. Only tube I’d consider as an alternative, right now, would be a similar-era Amperex “Bugle Boy” with D-getter and the treble-clef logo, but those are rarer and more expensive.

Perhaps the best expression of how malleable the sound of a pure-tube amplifier can be, and the best I’ve heard with the ZMF Pendant, but not so far ahead of the more readily available GE tube mentioned that I would stress over it.

Rectifier Tubes (EZ81/6CA4)

These are listed last because, while important - as they impact power quality for the entire amplifier, they demonstrated the smallest level of audible change in the signature and performance of the amplifier.

Amperex 6CA4/EZ81 “Bugle Boy” (Dutch Production) - ~$40

The “Bugle Boy” tubes are well regarded, and this particular tube adds a bit more kick to the already stout and solid bottom-end of the Pendant. It is not as prettily-glowy as the stock JJ Electronics tube, with a denser plate construction, but in exchange for the loss of orangey-ness, percussion hits a little harder (if not faster) and with Vérité Closed, Eikon or LCD-4 is impressively visceral.

Might be the “sweet spot” upgrade if all you want is a bit more “classically tube-like bass” reproduction, though technically it is perhaps not quite as taught sounding as the stock tube.

Mullard EZ81 NOS Blackburn, UK - Philips Miniwatt Circa 1965) - ~$75

Hits hard and fast, with excellent macro-dynamic impact. A little sub-bass bloom. Slight increase in tonal weight overall. Wetter; or at least “moister” presentation. Similar speed to the stock tube, with better control and a hair faster than the stock or Amperex tubes. No notable tonal shift. Quantitative bass-heads might enjoy this the most.

Was most agreeable with lower-impedance planar cans (which are not the ZMF amplifier’s best match, otherwise). Low EMI/RFI susceptibility. Probably wouldn’t buy one specifically to pair with the Pendant - the Amperex was overall more enjoyable for me, for less, and the Telefunken (made by Mullard anyway) was technically superior across the board.

Telefunken 6CA4/EZ81 NOS Mullard Production, Blackburn UK - ~$150

This tube demonstrated almost no susceptibility to airborne EM/RF contamination and yielded the lowest noise floor (all tubes used in these comparisons were noiseless in normal listening situations, but this performed the best when, for example, playing digital silence and then cranking the volume to maximum).

Overall presentation was the most articulate and smooth, especially when faced with music with massive dynamic swings. Low-level details and micro-dynamic elements were consistently more easily discerned (Leonard Cohen’s voice had more nuance and detail in its “gravel”; Mile’s Davis trumpet had more appropriately aggressive bite and glare).

Low-end slam was harder hitting, particularly with the LCD-4, and bass articulation, with big dynamic bass swings or extreme sub-bass content (e.g. Trentemøller’s “Chameleon”), was faster, more deft and better controlled.

Small-Tube Quirks

Small signal and power tubes sometimes exhibit audible sensitivity to common in-home sources of EMI/RFI. This is, in part, due to their smaller metal elements being closer to the ideal antenna length for the emissions of things like WiFi and cellphone signals. Some specific tubes, even with a given family, can be more, or less, sensitive than others.

As a result, it is possible that some tube combinations with the Pendant will require the unit be placed away from WiFi routers, especially high-power models. Cell phones, also, can cause chatter and/or “helicopter chop” sounds if place to close to the unit when running certain tubes.

Summary

I thoroughly enjoyed my time with the ZMF Pendant - in fact that’s an understatement … I loved listening with it — and my time with which passed all-too-quickly; I found myself not wanting to give it up when it was time to let someone else get their ears on it. I have missed it progressively more since it departed.

The Pendant does an excellent job of delivering the best aspects of tube-based listening, and indeed the “tube amp experience”, including the ability to usefully affect its sound with different tubes, while leaning more towards accurate, rather than heavily editorialized, rendering.

I would describe the Pendant as being “how you build a pure-tube amplifier, when you want to get the best out of tubes, without ignoring technical competence”.

That’s in contrast to a large number of other tube amplifiers, which seem to be tuned to deliver a sound that is closer to “what people that haven’t spent real time with pure-tube amplifiers think tube amps will sound like” (typically overly laid-back, warm/gooey and/or rolled-off).

As such, this is a real breath of fresh air compared to many of its immediate counterparts.

In common with most pure-tube designs, the Pendant does fair best with higher-impedance headphones (80-100 ohms and up, with my favorite pairings being 300 ohms), though the bias here is not nearly as pronounced as with many other such units, and is minimized further with transformer taps yielding both low and high output impedance.

Ultimately, ZMF’s Pendant offers fantastic performance, extremely engaging and compelling reproduction, serious power and, of course, the “full tube experience” wrapped up in one of the most practically-sized (and priced - even down to the tubes being relatively inexpensive), quality tube-amplifiers I’ve had the pleasure of listening with.

If you’re coming from a solid-state background, the Pendant is a rare treat - true high-end tube amplifier performance at solid-state pricing. And if you’re a current denizen of tube-hybrid world, ZMF’s amplifier will deftly demonstrate how lucid and technically capable a pure-tube amplifier can be, while simultaneously dazzling with its tube-rolled-adaptability - far beyond anything you’ll experience with hybrid designs.

I h