Linear Tube Audio Microzotl 2


There is no Dana, there is only ZOTL!
Reviewer for The Headphone List
Pros: Great PRAT, detail, air, soundstage, drives difficult headphones, tube benefits without the tube negatives
Cons: Not inexpensive

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I had heard of the Berning ZOTL electronics years back, in articles in the audiophile press, but hadn’t come across it. I had heard great things from some Head Fi’ers, notably DrBlueNewMexico about the MicroZOTL, so when the Mark Schneider, of Linear Tube Audio, gave me the opportunity to review it, I jumped at it.

I read the technical description of the Berning innovation for this amp (and a series of higher powered components for the regular stereo rack), but I'm not knowlegeable enough to explain (or quite understand them), but, from what I understand, in 1 sentence, output transfomerless amps remove distortions caused by the output transformer, but are difficult to keep stable and have inherent impedance problems, and ZOTL technology solves the OTL issues riding the signal on radio waves.

I'll quote from the Linear Tube Audio Site for more're welcome to explain it to me (thankfully, I don't have to understand it to appreciate the sound).

ZOTL – Resolving the Audio Output Transformer Issue

Audio amplifier design engineers have long sought to eliminate audio output transformers because of the restrictions they impose on amp performance. Leakage inductance and interwinding capacitance limit the high-frequency response of transformers while core saturation and magnetizing current limit their low-frequency response. Transformer-core hysteresis causes specific distortions of non-symmetric and transient waveforms that are characteristic of musical reproduction. Audio output transformers simply cannot achieve the correct turns ratios as they only max out at 25:1 due to saturation and hysteresis effects. This leaves much to be desired, which creates and issue that needs to be resolved. Enter ZOTL, the solution.

Zero hysteresis Transformer-Less (ZOTL) is a proprietary and patented architecture developed by David Berning and tweaked by Linear Tube Audio that achieves effective turns ratios of nearly 300:1 and resolves all issues involving audio output transformers by eliminating them entirely.


David Berning invented and patented the ZOTL after building tube amplifiers for 25 years. Known for the transparency, versatility, and reliability, Berning amplifiers are justifiably acclaimed works, as recognized by Absolute Sound, which has named the ZH-230 has been named as an “Editor's Choice” every year since 2011.

ZOTL amplifiers achieve such stunningly realistic sound because of their sophisticated and proprietary technology. First, the audio signals “ride” a carrier frequency, which amplifies them, then the carrier is removed and the remaining audio is delivered to the speaker, similar to how a radio staion and receiver work. This changes the impedance plane to match the impedance of the speaker, so the audio output transformer is no longer required to match the tube to the speaker. An impedance converter accomplishes this match up. This super linear amplification process allows the amplifier to have a flat frequency response from 8hz to 50Khz, which is near impossible with an output transformer.

However, the real advantage is in the transformer turns ratio. Output transformers are limited to a maximum of about 25 to 1 in turns ratio. This turns ratio does the matching between the tube output and the speaker. It turns out (sorry) that the theoretically correct turns ratio for most tubes is typically 100 to 1 and even as high as 300 to 1. Well, the ZOTL can use the impedance converter to provide the proper turns ratio. The microZOTL has a 300 to 1 ratio and the ZOTL40 has around a 150 to 1 ratio. This results in the detail iand accuracy of the sound.

So, hoping you all got that (there WILL be a quiz at the end...)

Let’s get to the review:

Music used in the review-all FLAC or WAV, usually from rips of CDs, or downloaded high resolution files.

Grateful Dead-Box of Rain (American Beauty 24/96 download)...because it’s an old Deadhead must.
All Time Low-Somewhere In Neverland (Don't Panic FLAC from CD)...because it's fun, and actually not a great recording, but I find good gear can pull bass (which is recorded muddily) and detail out of it. (and, it shows that I'm not a snob and can do punk-pop with the young 'uns)
Dave Douglas-Bridge to Nowhere (Time Travel ALAC from CD...great trumpeter/composer/bandleader, nicely recorded)
Elton John-Funeral For a Friend/Love Lies Bleeding (Goodbye Yellow Brick Road 40th Anniversary Edition, 24/96 download)
Lake Street Dive-Bad Self Portraits (Bad Self Portraits-14/44 FLAC)
Microscopic Septet-Hang It (Manhattan Moonrise, 16/44 FLAC CD rip...the funnest jazz group, played and recorded mostly in the 80's and 90's, recently reunited. This is a fine album, but Seven Men in Neckties (Best of the Microscopic Septet V1) and Surrealistic Swing (Best...V2) are essential and fun listening. Listen to Popadoc Jazz...)
Eagles-Hotel California (Hotel California 24/96 download)...all those guitars! All that detail! Those harmonies! That creepy lyric!
Henry Butler-Steve Bernstein and the Hot 9-Dixie Walker (16/44 WAV download included with the vinyl). (New Orleans jazz, R&B, fabulous singing and playing from this little big band, great sonics, INCLUDES WAV with the vinyl).
Laura Cantrell-I Can't Wait (No Way There From Here, 16/44 rip from CD, because she's too sweet to omit :bigsmile_face:
Fountains Of Wayne-Someone to Love (Traffic and Weather, 16/44 ALAC rip, because I love these guys, and at this point, couldn't stop)
Ella Fitzgerald/Louis Armstrong-They Can't Take That Away From Me (Ella and Louis, 24/96 High resolution download, because there is very little more sublime than these voices, singly and together. As a Mono, could focus on things other than soundstage. Plus, this was the album that, when I first got the ZOTL and the HE-1000, I played for my wife, and, for a short time, she thought I wasn't QUITE as crazy as she’d previously thought, MAYBE even worth it...NAH!).
Alvin Baptiste-Late (Late, 16/44 CD FLAC rip-Because I have to pull out artists and albums you don't know to show I'm hip)
Lorde-Royals (Heroine 24/96 download) (getting’ down with the commoners again)
Wayne Shorter-Witch Hunt (Speak No Evil, 24/96 FLAC download)

Gear used-mostly listened through my Hifiman HE-1000 (because I mostly listen through my HE-1000...what a revealing yet musical set of cans). I started with my Pono line out into the amp, then switched to my PC/JRiver/LH Labs 2G usb cable/Regen/Geek Out Special Edition. Hifiman has Norne Zoetic cable with various adapter cables (to use balanced into Pono, balanced, single ended). Used Zu and Audioquest (not too fancy) interconnect. For comparison (because what does it mean to say "bass is good", I have the Ray Samuels HR-2, previously my go to amp in approximately this range (lists for $875, a bit less than the ZOTL), for comparison.

Physically, the unit is attractive but not physically imposing. On the front panel, there is the power switch (lights up red to show the unit is powered), an input selector switch (allows 2 different sources via RCA connectors), volume pot in the center, and 3.5 mm headphone jack, which locks on connecting the headphones. The volume pot feels very secure, turns very smoothly, feels solidly built and secure (as does the rest of the amp). On the back, the 2 sets of RCA inputs, 2 sets of speaker posts, a preamp out, and an input for the power source. The power supply is a separate unit, with a detachable power cord and an umbilicus to the amp, said to be a high quality switching power supply. The sides and back are fenestrated metal for venting the heat, and the front is a thicker metal faceplate, with MicroZOTL written in the lower right corner. The top is clear plastic, allowing viewing of the internal electronics, and, especially, the glowing tubes. I'd say it is understated but attractive.

Let me tell you a bit about me. I'm in the audiophile game since the mid 80's, but the headphone world the past few years. Having a family meant I wasn't blasting the living room stereo when I wanted, too late, kids needed to go to bed, needed to do homework, couldn't stand what I wanted to listen to, etc. Jumping into the headphone world got me back to listening to music much more, like I did for many years when I was younger. I tend to hear differences in components, including cables, amps, etc, though the differences tend to be most prominent in transducers (speakers, turntables), more subtle in the stuff in between. I also tend to be more subdued in my responses, things tend not to be "the best ever", but, "good", "somewhat better", "OK"; when I pull out hyperbole, I'm really excited about something. The act of describing differences in something like an amp, by its nature, does tend to accentuate and emphasize the differences, making things seem more different than they really are. I try to get the differences noted, and the magnitude of them in perspective, but, again, focusing on the differences by its nature tends to highlight them. I also find it hard to describe the sound in isolation; the word "open" or "tight" or "textured" begs a "compared to what?", so I spent much time in this review going back and forth between the ZOTL and the nearest competitor I had on hand, the Ray Samuels HR-2. a solid state amp that sells for $875. I haven't had any multi-kilobuck amps at Chez Doctorjazz, so I can't say how they compare.

In trying to crystallize my impressions about the sonics, I referred to my notes, taken listening to all the above tracks, and a few words keep jumping out at me: open, wide, detailed, silent, textured. Now, let me say at the outset, this is a big step up in sound from the $100 dollar portable amps or built in phone amps one uses, but, getting into a similar price/quality range, the differences are more subtle, as I previously noted, and much less than different headphones/speakers have/ But, while I didn't test myself, I’m sure I could tell the RSA and ZOTL apart blinded.

Highs: These shimmer, allowing details of cymbals to be clearly heard, the different textures that come with different touches on a ride cymbal. Also allows for the very wide, open soundstage, that seems to go out indefinitely in width and depth. Listen to Herman Jackson's drums on Alvin Baptiste's "Late" hear the snap of the stick hitting the cymbal, the different tonalities depending on where and how on the cymbal it is hit, and the continued trailing of the sound which is distinctly a decaying cymbal, not a whoosh of indistinct white noise these can sometimes be. All Time Low's "Somewhere In Neverland", cymbals, which are a congealed hiss on lesser systems, are clear, distinct, sharp, sound like cymbals should. In comparison to my Ray Samuels HR-2, the highs are both more pronounced and less edgy, smoother, cymbal details and open space benefiting from this ZOTL strength.

Mids:, detailed, get the nuances of voices and instruments WITHOUT being overly syrupy or thick. Ella and Louis singing "They Can't Take That Away From Me" has to be one of the most sublime experiences one can have in music...when Ella hands to vocal to Louis, and he enters with his scat "Ba Ba Dee Boop De Doot Dee Doot" it is a moment for the ages, and sounds just marvelous through the ZOTL/HEK. His trumpet, Baptiste's clarinet, Dave Douglas' horn, Elton John's distinct pipes, Fountain Of Wayne's lead and harmony vocals are spot on...right there with you. Tone is rich and nuanced, instruments have a 3D roundness that makes it seem more real.

Bass-deep, forceful, tuneful, PRAT, bass and drums have bite, depth, body. I like to use All Time Low's "Somewhere In Neverland" for bass for the opposite reason most use tracks...this is really not well recorded, think they were looking for a "wall of sound" type sound, and things just congeal, arpeggios are smeared, bass is muddy and 1 note (my teen daughter, who loves this band, has no idea what a bass guitar does as a result). I find better gear helps me hear what the band actually laid down in the studio. It's pretty close between the RSA and the ZOTL, but the bass has a bit more definition, edge, note definition out of the ZOTL. Lorde's "Royals" was also pretty close, slight edge in depth and definition to the ZOTL, but almost too close to call. The Microscopic Septet's "Hang It" ends on a riff based on Hendrix's "Hey Joe" bass line. Through the RSA there is a smidgen of more impact, but through the ZOTL the bass has more impact, sounds more like a real bass in space (that should be NASA's next project...) Which leads me to...

Soundstage/detailing/overall presentation: Here is where the ZOTL shines. The soundstage is wide and deep, open, sounds like a real space. The RSA is closed in by comparison (again, by comparison, I never sat around when that was my primary amp saying, "man, does this sound closed in..."). The difference is not subtle, though. The ZOTL is open, clear, clean, like a solid state amp BUT removes a solid state haze you didn't realize was there until you hear music without it. Instruments and open space sounds more real, more THERE. In some ways, the RSA is more like a tube amp than the has a nice layer that does add some richness to the tone, but at the expense of a (small) bit of detail, and a (larger) amount of the sound of a real space. Detailing on the ZOTL is very precise, but without too much of an edge that would make it unreal. The microdetails are there, but they don't thrust themselves at you in a way that detracts from the main event. There is a good amount of "air" around instruments. I put on my hi rez download of Wayne Shorter's classic, "Witch Hunt", at first it wasn't clear to me which was better, but as I went back and forth, the wider stage of the Zotl, the lack of any haze in the "performance space", making for a realistic blackness, not just a lack of notes but the sound of open space, along with a slight increase of detail in texture of the sax and trumpet, and a certain "rightness" pulled me over to the ZOTL side.

I could've easily stopped at this point, but I was having fun listening to good music with the HE-1000 and the ZOTL/RSA amps, taking notes, generally being an incredible geek. So, to take things up a notch, I decided I would go to the best source I have in the house-Linn LP12 turntable (Ittok arm, Lyra Delos cartridge, Pro-Ject Tube Box @ phono preamp, sitting on Machina Dynamica Nimbus isolation table.
I pulled out some vinyl (and pulled, and pulled, and pulled some more...)

Lake Street Dive-Bad Self Portraits (from the same album, because I have it both ways, for comparison, and I like this Brooklyn Band)
Cecil Taylor-Jumpin' Pumpkins (?Mosaic Box, because it is different from what I played up to now, from a master of the free jazz movement, and another sign of my ultimate cool and eclectic taste)
Eagles-Hotel California (Hotel California, again because I had both...interestingly, the vinyl, a non descript pressing, was NOT as good sounding to me as the hi rez download)
Neil Young-Heart of Gold (Harvest-ORS Neil Young Archives 4 reissue, because he's an audiophile)
Schubert Symphony #9 (London Blueback CS6061, classic, 60's recordings, audiophile hit list) (to bring some class to da joint,,,)
Cheap Trick-I Want You To Want Me (In Color, Epic 34884, because I love this song)
Thad Jones/Mel Lewis Orchestra (The Complete Solid State Recordings of the Thad Jones/Mel Lewis Orchestra, Mosaic MQ7-151, a live recording by a fabulous big band, in the venerable Village Vangurad)

Well, the differences are similar to what I noted listening to digital, though, on good vinyl, the differences between amps widened. I particularly noted this on the Thad Jones/Mel Lewis Mosaic, the Cecil Taylor Mosaic, and the London Blueback, where the ZOTL was able to pull a bit away from the HR-2. On the Cecil Taylor, the stage collapses quite noticeably, and that "solid state haze" is there with the HR-2, absent with the ZOTL, with a cleaner, see through "live-ness" to the sound. Neil Young has more of an up-front perspective on the RSA, again, flatter, narrower stage, and Neil truly sounds like he's there, clear, sharp (but not edgy). The RSA again dulls the sound some (relative to the ZOTL, I reiterate). The London Blueback through the ZOTL has richer string tones, horns and winds have some meat on them, layering is exemplary, and, again, going to the RSA narrows and shortens the depth of the stage, and puts that "haze" between the listener and the music. You can really appreciate why this era is considered a Golden Age for analog recording. The live set on the Thad Jones/Mel Lewis Mosaic has a "you are there: quality with the ZOTL (great solos by Garnet Brown on trombone and Joe Farrel on tenor sax), and the ZOTL again shines, sections are punchy, separate lines can be separated out, and the instrumental timbre shines through, along with that toe tapping rhythm.
Again, the HR-2 is actually a fine sounding amp…didn’t appreciate the Hifiman HE-560 or the Sennheiser 650 until I heard them out of the RSA amp. But, the ZOTL definitely shows more of what the music is made of. The openness, lack of electronic overlay, open, wide stage, 3D layering of instruments and fleshing out of the individual instruments and voices, getting textures right without artificial sweetener, make it just great to listen to. It does have speaker taps for driving very efficient speakers, but I didn’t have any on hand to use to evaluate this. And, did I mention that the ZOTL and the HE-1000 are a terrific match? They both seem to do the same things right to my ears. I had initially planned to use some other headphones in the evaluation as well, but couldn’t bear to pull off the HEK.
So, while this is certainly not an inexpensive amp, I believe it does deliver good value, being a really fine sounding headphone amp in an attractive package. If you’re in the market for an amp in this price range or higher, I’d recommend trying out the ZOTL2.
(don't seem to be able to control the rating bars at the top-I wanted to have them extend ALMOST to the end for every category, only hedging because I haven't heard the kilobuck headphone amps out there...)
Very excellent and thorough review Doctorjazz!  Thanks for systematically exploring what the Zotl2 is capable of through your fine gear!  You have a very experienced ear and a great array of tunes used for the exploration, and you  do  appreciate the magic of Zotl2!  As a musician and high end audio enthusiast, your observations are valuable to the audio community in deep ways! Thanks again for your keen auditory observations and realistic conclusions.  Your enthusiasm is clearly based on your experience, careful listening and thorough evaluation. bought the review sample, that speaks miles....  Hope you continue to enjoy the Zotl2 magic in the music!  cheers, drbluenewmexico.
It should be noted that a number of audiophiles are reporting that replacing the stock Zotl2 power supply with a Mojo-Audio Joule power supplies very significantly increases the excellence of the Zotl 2.  that has also been my experience, improving the textures of the notes, the soundstage expanding and the dynamics improving even more.  worth investigating if you get a Zotl2!.
Been wondering about the improvements with an LPS, hopefully someone will have one at the Meet this Saturday and I'll be able to check it out. It does, of course, bring the cost of the amp to about $2k...


100+ Head-Fier
Pros: Stellar dynamics, free of harmonic grit, superb for planar or like design headphones (and speakers!)
Cons: case is flimsy, microdetail that much more expensive amps can provide is not there, looses chest thumpng bass
Microzotl 2 Review
The Microzotl 2  is an updated version of the original Microzotl, created by David Berning over a decade ago. Berning amps do not use heavy transformers, rely on a unique RF
scheme for signal amplification. This newer version is manufactured and sold under license by Linear Tube Audio ( ). It uses a complement of
(2) 12AT7 and (2) 6SN7GTB tubes , the stock tubes are sourced from Tungsol. Two switch selectable inputs are supported, pre amp out, and speaker connections for high efficiency
speakers that can be driven with 1 watt. A peculiarity of the design is that you should avoid having both pre out and headphones connected at same time as this may drive both outputs
in parallel, causing a reduction in power to the headphones. The retail price is $1100.

The Microzotl is special for  its price point. If you have tube equipment, chances are you love it for its mid-range soulfulness but have a closet of tubes you have experimented with trying to get the most out of it. Seems transformers, big capacitors, and tubes all interact with varying success in audio transparency as you go up and down the audible spectrum. Tube amps are often characterized as slow
on transients and compressed sounding compared to solid state gear. Pre amp tubes in a traditional tube amp can have wide variations in how each affects mid range sound. The Microzotl 2 doesn't
use big caps and transformers so those interactions are reduced..
Speed and freedom from distortion are the hallmarks of the Microzotl 2; listen to it on loud passages and you become aware of how other tube amps  blenderize instruments and collapse dynamics. And if you are used to a traditional tube amplifier you may at first question if you like this amp... its not the warm wool sweater of sound you are used to.  It is the sound of a tube amplifier but its one where the  mid range is fast,  no added coloration, almost a paradox. This is a wonderful match for moderately efficient orthodynamics in the Hifiman  and Audeze lines as these headphones introduce very little harmonic distortion, love this with the Hifiman HE-400 I own and  when auditioned with the Audeze LCD-2's. With a dynamic headphone like Grado SR-225 I found the harmonic distortion of the headphone driver canceled out a lot of the musical enjoyment, just couldn't hear all the amp was capable of doing.
And unlike the Music hall 25.2 and ifi Micro  headphone amps I own with pre out, the Microzotl2 can be taken seriously as a pre amp solution; sounds wonderful feeding Magnepan 1.7 speakers. It does show its heritage at that point as a headphone amp; big bass drum slaps you but doesn't pound you in the chest.
There is a good thread on this amp if interested; I make no claims that this amp is the right choice for everyone. But if like me you gravitate to planars, electrostatics and orthodynamic speaker
solutions, you owe yourself a listen to this amp.  Hopefully posting this will get more head fi-ers to give it a listen
I wonder if anyone has yet compared it head to head with the Ray Samuels Emmeline II Raptor?
I'm thinking I might finally sell my Hafler 101 the ethos of this guy's stuff.
Might wait until the dac/version arrives (you can try one out on me! Tho' I'm in UK)
Great review for a great amp. I've had mine for 4 years now going strong. Absolutely in love.