Linear Tube Audio or LTA, is an American company based in Takoma Park Maryland, a suburb of Washington DC. The company, which was founded in 2015 by engineer Mark Schneider, specializes in tube-based audio amplifiers employing David Berning’s patented ZOTL output-transformer-less amplifier designs. Most of LTA’s amplifiers are low-power offerings of 10 to 20 Watts per channel, and their biggest amps are a design providing about 50 Watts per channel.
LTA sells only direct-to-consumer and has no dealer network. Customers deal directly with the manufacturer.
The LTA Z10e
As far as this reviewer knows, the Z10e is a unique product in the annals of audio design. It’s a headphone amplifier designed for electrostatic headphones, but it will also drive magnetic headphones as well as a high efficiency pair of speakers! But more about these incredible capabilities later. The primary purpose of this tube-based device is to drive a pair of Stax or Stax “pro-bias” compatible Electrostatic headphones.
The Z10e Consists of two chassis. The larger one is the amplifier, and its dimensions are 12.75” (32.4cm) wide, X 14.5” (36.8cm) deep X 6.5” (16.5cm) high with a weight of 18 pounds (8.2 kg). The smaller unit, is the power supply, the dimensions of which are 4.75” (12cm) wide X 7.5” (19cm) deep X 4.25” (10.8cm) high and weighs 5 pounds (2.3kg). The two chassis are connected together using a supplied proprietary umbilical cord.
The Z10e’s front panel consists, from left-to-right an illuminated push button standby/operate button (the system power switch is on the power supply), a three position toggle switch to select between it’s three inputs (two unbalanced Cardas gold plated RCA jacks) and a pair of two-way XLR/1/4-inch balanced input jacks). These are followed by a large, stepped volume control. To the right of the volume control is located another toggle switch which selects between speakers and headphones (about which, more, later). Below the switch is located the single Stax Professional 5 pin electrostatic headphone jack. Finally, on the extreme right, there is a large two-digit alpha/numeric LED display and directly below that are two normal 1.25-inch magnetic headphone jacks marked “Hi” and “Lo” respectively.
Again, from left-to-right, the rear panel consists of a 4-pin proprietary power supply input jack, and on the far right, top-to-bottom are two sets of unbalanced RCA jacks, followed on the extreme right by a pair of balanced two-way XLR plug female connectors, and below those are a set of four WBT 5-way binding posts for a stereo pair of speakers.
The Power Supply
The front panel of the separate power supply box (PS) has only one control and this is the power on/off switch and the power output port for the supplied umbilical cord. The rear panel contains the IEC power cord connector and a fuse holder.
After unpacking both of the two boxes in which the Z10e came packaged, I set the power supply box on the floor and set the main chassis on a small table next to my listening chair where my HiFiMan amp for my personal Jade 2 electrostatic headphones normally resides. I connected the included IEC power cord to the PS and the house mains and the umbilical cord between the two chassis. Next I connected the pair of balanced XLR cables from the balanced output of my Schiit Yggdrasil DAC which is located on my equipment rack across the room from my listening chair and is normally connected to my Jade 2s. I used balanced cables to connect the Z10e because I have to route my connection to the rest of my system around the periphery of my listening room. I turned on the main power on the PS box and switched the main chassis from standby to operate. Immediately, the LED display came alive with a marching banner that informed me that the unit was warming up. After an interval of a minute or so, the display changed to a two digit number reflecting the position of the volume control. Pushing the “input” switch on the front panel to its down position (of three possible settings) selects the balanced input. Making sure that that the speaker/headphone switch to the right of of the large volume knob, is set to “headphones” and reducing the volume control to a low number on the display, I plugged my Jade 2 headphones into the single electrostatic headphone jack to the right of the volume knob.
The volume control on the Z10e is a 100 step attenuator using discrete resistors that are relay-switched. The smallest step of the attenuator is 1/1000th of the total value and the amp employs Vishay Dale 1% precision resistors for accurate and repeatable volume settings.
The LTA Z10e Conforms to the Stax electrostatic headphone specification that Stax calls the “pro-bias” standard. This is a five-pin connector interface providing 580 volts of DC bias for the phones. This means that any electrostatic phone conforming to this standard can be used with this amplifier. This includes (but is not restricted to) Stax SR-007 MKII, SR-009 series, all of the Stax Lambda series, the HiFiMan Shangra-La and Shangra-La Jr phones and the Jade 2 phones, as well as the Mr. Speakers (now Dan Clark brand). There are a number of electrostatic headphones that are not compatible with this amp and these include the Koss ESP-950, the Monoprice electrostatic line, and the Sonore phones.
This amp also, uniquely, for an electrostatic headphone amp, has two ¼-inch standard phone jacks to accept normal magnetic headphones such as the HiFiMan planar magnetic line, the Audeze line, the Sennheiser HD-800 and HD-650, Sony’s line of magnetic headphones, etc. There are two jacks because one is designed for low efficiency phones and is labeled “Hi” for its output and can source phones that are seen as hard to drive with an output of approximately 2 Watts into a 50Ω load. This is ideal for phones like the HiFiMan Susvara which are notoriously difficult to drive. The other jack, marked “Lo” is designed for very high efficiency such as any with a rating of 93 dB or better such as the HiFiMan Ananda (93dB) and the Sony MDR-1AM2 (98dB).
We now come to what is possibly the most unusual aspect of the Z10e’s unique design. As shown earlier, this LTA electrostatic headphone amp has, on it’s rear panel, a left and right pair of high quality German-made WBT 5-way binding posts. These are there to supply 12 Watts of class-AB power, per channel (at 8Ω), to a pair of speakers! The heart of this amp is the Berning ZOTL output transformer-less stereo amplifier circuit sporting four EL84 (6BQ5) beam-power pentodes which can drive any speaker with an efficiency of 90dB/Watt at 1 meter or better. This means that depending on one’s speaker selection, this US$6,950 unit can serve as the heart of a complete stereo system. The unique design of this amplifier allows for a long tube life of about three times of normal tube amplifiers and generates about 1/3 of the heat output. When changing tubes, they do not need to be matched.
All front-panel functions of the Z10e are accessible using the enclosed Apple hand-held remote control. This includes standby/operate, input selection, volume, and selecting between headphones or speakers. In addition, the remote can be used to set a fixed output for any selected input (for home theater operation) or to choose any of 16 different brightness levels for the display as well as programming the display timeout for 10 seconds (normally, it’s on all the time). I was able to check this aspect of the Z10e’s performance because even though my review sample did not come with a user’s manual, I was able to find one on LTA’s web site. Hopefully, the retail version does come with a full set of printed instructions (my sample was S/N 009). I must say however, that putting aside, for the moment, the lack of a printed manual, that the Z10e is quite intuitive in its set-up and operation and can be easily configured by any seasoned audiophile.
As A Power Amplifier
Before discussing this unit as a headphone amp, I will describe its sonic attributes as a power amplifier for speakers.
I don’t have any speakers that can get by on 12 Watts per channel, but a good friend of mine owns a pair of Wilson Audio Cub 2 speakers which, with a published sensitivity of 94dB/Watt at one meter, and a recommended minimum power requirement of 10 Watts, falls within the guidelines for this amplifier. Moving the amp to his listening room, and connecting it to his Cub 2’s showed that even though rated at a mere 12 Watts, the Z10e produces a very big 12 Watts! The LTA amp will drive these speakers to ear-splitting volumes if desired, and at even very realistic listening levels, the Z10e produced an excellent, well controlled bottom end, a gorgeous, liquid midrange and silky highs. Distortion was audibly non-existent and the amp seemed to have plenty of headroom even on demanding orchestral music. My friend, who usually drives the Cub 2’s with a high-powered Spectral amp rated at 200 Watts/channel, was reluctant for us to return the LTA to my abode. It’s that good.
Magnetic Headphone Performance
I was anxious to try several pairs of magnetic ‘phones on this amp, to see how they fared. I started with a pair of HiFiMan Edition X, V.2. These phones have an efficiency of 103 dB and therefore are easily driven by a cell phone or iPod. I plugged them into the “LO” headphone jack and listened to Rozsa’s Violin Concerto with Jascha Heifetz and the Dallas Symphony via Tidal. I already knew that the Edition X V.2 phones were very good, and expected them to sound fine. What I wasn’t so sure about was whether or not 0.2 Watts could drive them adequately. I needn’t have worried. Heifetz’ Stradivarius was a sweet as a mother’s kiss and as smooth as a baby’s bottom. The phones played uncomfortably loud with the volume control at the midpoint. They would have played much louder, I had no doubt. I then switched to a pair of HiFiMan HE-560s. These phones have an efficiency of just 90 dB and I was interested in how the “LO” output phone jack would drive these. As long as I didn’t ask for more than an average amount of volume, setting the volume control to maximum could elicit a fair amount loudness, but when plugged into the “HI” output jack, the Hifi-Man phones would play as loud as anybody could possibly want. I then tried a pair of Sennheiser HD-800. With an impedance of 300 Ω, the Sennheisers are a somewhat difficult load as the power of the Z10e is rated 2 Watts at 50 Ω and ostensibly much less at 300Ω. But the LTA drove these excellent headphones as loudly as anyone could sanely wish. Sennheiser does not specify the HD-800’s efficiency, but the high impedance absolutely dictates that the “HI” output jack be used with them.
Electrostatic Headphone Performance
The raison d’etre for the LTA Z10e amplifier is primarily it’s ability to drive Stax Pro-bias spec’d electrostatic phones. I had at my disposal, a number of electrostatic headphones to try with this amplifier: my own HiFiMan Jade 2, Mr. Speakers (now called Dan Clark brand) “Voce”, and the Stax SR-009s.
One of the things I noticed is how different electrostatic phones can sound from one another. I understand why different magnetic phones sound different, they use a myriad of different technologies to achieve their sound as do magnetic speakers speakers. But I would think that since electrostatic phones all use the same basic driver design that they would all sound pretty similar, especially when driven by the same amplifier. All electrostatic phones consist of a micron-thin Mylar (or other plastic film) diaphragm all of which are sputtered with a molecule-thick coating of a conductive material, usually gold; and are stretched between two acoustically transparent stator screens where the audio is applied with a roughly 580 volt DC bias applied to the diaphragm. The housing cup for the diaphragm is large enough to surround the ear with a pad between the diaphragm and the wearer’s head and an open back with a protective screen over it to protect the transducer (and the user) from prying fingers (after all 580 DC volts is nothing to take for granted!). Boy was I wrong! All three of the headphones on hand sounded as different from one another as any other transducer. While I was surprised by the wide range of differences between each of these headphones, these differences did allow me to get a very good idea of the sound of the Z10e, especially when contrasted with the same phones through my Jade 2 amplifier.
The Z10e, though a tube amplifier is just as quiet on all the ‘phones as is my FET Jade 2 amp. I noticed no noise at any kind through either amp even when the volume is set at what would be an uncomfortably high level if any music were being played at the time, which there wasn’t (when conducting high level headphones tests, I always stuff my ear canals with in-ear hearing protection – just in case).
The things that I noticed that the Z10e imparted to all the phones is an expanded sense of space. Some headphones give a presentation that is more or less in-your-face (like the Stax SR-009s), while others present a more distant perspective. In all cases, the LTA presented a wide sound field that removed the music from inside one’s head (a classic headphone peccadillo) and spread it in front of the listener to a realistic width. I found this quite refreshing. The same headphones, on the Jade 2 “box” gave a presentation that was much narrower, and more of that feeling that the ensemble to which one is listening is mostly in one’s head; between the ears, with only a small portion of the music stretching beyond the ears into space. I have long since gotten used to that characteristic in headphones so, it doesn’t really bother me that much, but it was a bit of a revelation to hear another perspective from ‘phones with which I am otherwise familiar.
One expects that tubes would not have as tight of a control of the bass region of any transducer as does a solid state amplifier. All the ‘phones used in this review have bass response advertised to reach below 10 Hz (but none give limits in dBs). I remember reading something the late, great J. Gordon Holt wrote many years ago. He said that frequency response figures are meaningless without quoted limits. He went on to say that the tiny speaker from a six-transistor portable radio could be said to have a response of from DC to well above 20 KHz, but whether or not the speaker produced any sound at those speaker extremes was another matter and a tiny speaker such as those found in portable radios did not produce any sound below a couple of hundred Hertz! It’s a matter of being able to move a volume of air large enough to produce sound. In a headphone, the amount of air that needs to be moved is confined to the volume of the ear enclosing cup that is ostensibly sealed by the ear pads around one’s ear so that just the volume inside the ear cup and one’s ear canal has to be moved. Here, small transducers can produce satisfying amounts of low frequency material.
The Z10e produces oodles of clean, well controlled bass with no carryover and no boominess. I did a sweep of the amp with my audio oscillator app on my cell phone from 100 Hz to 20 Hz and while the audible bass fell off quickly below 35 Hz, on all the phones, my Hewlett Packard audio voltmeter, plugged into one of the ¼ inch headphone jacks showed that the amplifier was dead flat to 20 Hz! One thing about bass frequencies. They need a lot of room to propagate properly. For instance, a 20 Hz waveform requires 56 feet for one cycle from wave-crest to wave-crest! That means that even in the largest listening room, in spite of what one might have for speakers, or what the manufacturer claims for a speaker’s lower frequency limit, a 20 Hz waveform simply doesn’t have the room to form. Don’t believe it? Go to a cathedral, large church or concert hall that has a good pipe organ and listen to it. No matter how good your speakers are, you will never hear bass like that in your home and ditto with headphones – regardless of type or cost!
Moving up the frequency spectrum, the midrange of the Z10e is simply gorgeous. Here, the Stax SR-009s excels. With the LTA amp, the mids are liquid, smooth and articulate. In comparison, with the same phones the Jade 2 amp is slightly recessed, a bit more delineated, and somewhat rougher. With the Z10e, Julie Andrews’ voice is so real on the Columbia/Sony recording of the original cast recording of “Camelot” that it often sounds like she’s standing right next to you. This is most apparent with the Stax ‘phones, but is there to a lesser degree with the Jade 2 ‘phones, and not at all as realistic on the Voces.
Moving up to the treble region, great highs and fast high frequency transient response are the metier of electrostatic headphones. And here, all three phones were in their element and the Z10e delivered the goods. Many people believe that today’s planar magnetic phones now equal electrostatics in this area, but I have yet to hear it. I have a pair of HiFiMan Edition X V.2s and a pair of Anandas. And while they are very good, neither provide the extension or the “air” that a good pair of electrostatics can provide in the treble region. I have also recently had the pleasure of auditioning a pair of new Abyss AB-1266 isodynamic phones powered by Headamp’s GSX Mark II amplifier in balanced mode. These very expensive headphones sound great, but they lack the detail, cleanliness and effortless extension afforded by the Z10e when paired with the Stax SR-009s! This amp is so good in the highs, that I found myself listening to tracks with lots of percussion just to hear the realism of brushed cymbals, the staccato slam of hard sticks on drums, the attack of a xylophone or marimba, and the thump of bongos. The Z10e is very impressive, and while the Jade 2 amp is also very good at this, there is something extra about the presentation of the LTA amp that all others seem to miss.
The LTA Z10e is simply a remarkable component. It is sold primarily as a headphone amplifier for electrostatic phones, but is, in reality, so much more. If I were to offer any criticism at all, it would be that an amplifier advertised as being an electrostatic headphone amp, should have two electrostatic headphone ports and not just one. Most of this amp’s competition in this area from companies like Woo, Stax, HiFiMan, and Headamp. The Z10e can power all types of magnetic phones from a vintage pair of Koss Pro-4A all the way to a stratospheric priced pair of Abyss AB-1266 as well as phones designed for portable audio devices such as iPhones and iPods and equivalents. It also will drive a pair of efficient speakers with 12 Watts of output transformer-less power; play them loud and sound great doing it. If one chooses one’s speakers carefully, there is no reason why the LTA Z10e can’t form the heart of a state-of-the-art stereo system. With its two line-level single-ended inputs and it’s single pair of balanced inputs the Z10e is a complete integrated amplifier. The included Apple remote control allows one to select inputs, raise, lower the volume and change the left-to-right balance.
While, $6950 seems like a lot of money to spend on a fairly low power amplifier, there are certainly others which cost more, but few, if any have the versatility and sound quality afforded by this amplifier. Whether you use the LTA as the center of a fine stereo system, or just as an electrostatic headphone amplifier, There are few that can equal it in sheer performance. Impressive.
- Linear Tube Audio (LTA) Z10e Electrostatic Headphone Amp / Integrated Amp ($6,950)
- LTA Z10e Product Page
- LTA Z10e User Guide / Manual (372KB PDF)
- LTA Amp FAQs