Linear Tube Audio MicroZOTL 2.0 Headphone Amp & Preamp Review 
Home Theater Preamplifiers Stereo Preamps
Written by Andre Marc   
Tuesday, 24 November 2015

Linear Tube Audio, formed in 2015, is based out of Washington DC, where they hand builds tube components in their workshop. The firm is headed up by Mark Schneider, a highly experienced product design specialist and engineer. Mark is very well spoken, polite, and is very passionate about his products. I contacted Mark about reviewing some gear and one in particular caught my attention, the MicroZOTL 2.0 tubed headphone amplifier and preamplifier, which sells for $1100.

Linear Tube Audio also offers the ZOTL10 and the ZOTL40, both power amplifiers based on ZOTL technology. ZOTL stands for “Zero hysteresis Transformer-Less”, a patented architecture invented by David Berning. Berning enjoys a loyal following and customer base with his ow line of impressive amplifiers that are not for the faint of wallet. They are audio works of art, visually, and state of the art, sonically.

In a nutshell, transformers are generally thought to be the major hinderance to amplifier performance, and eliminating them has been a longtime goal for engineers. OTL (Output Transformer-Less) amplifiers are designed and manufactured by more than a few companies, but according to Linear Tube Audio, ZOTL is a distinct and unique design, and a completely different take despite the common theme of having no transformer. I strongly recommend reading THIS PAGE on Linear’s website, which is extremely detailed and easy to understand.

Linear Audio says their are a number advantages to ZOTL design technology. These include, but are not limited to:
  • Drastically improved tube life due to lower current operation
  • No output transformer intermodulation distortion
  • No low frequency non-linearity
  • Improved bass due to flat, linear bass response to below 10hz
  • Low output impedance for easier speaker matching

The MicroZOTL 2.0, as the name might indicated is based on well reviewed product David Berning produced about fifteen years ago. Mark Schneider reconfigured and updated the original design to maximize performance with the goal of bringing it to a new level of refinement. Features include the following:
  • External power supply
  • Drive low efficiency planar headphones easily
  • Drive high efficiency speakers (89 db efficiency or higher) to adequate volume
  • Universal voltage power supply
  • 2 selectable inputs
  • Class A preamplifier output
  • Simulates the correct transformer turns ratio using impedance converter
  • Low impedance output easily matches wide range of headphones and speakers
  • Same technology & tone as more expensive Berning amplifiers
  • No heavy power or audio transformers
  • Optimized tube life expectancy of 10 - 20 years based on use
  • One year warranty

The MicroZOTL 2.0 is attractive,and beautifully made. My review sample came in black, but it is available in “midnight blue” as well. The top is transparent so all internal components and tubes are visible. There is a large volume knob and toggle switch to select between to line level inputs. Around back there are line outputs, and actual speaker binding posts. Extremely efficient speakers are required for the 1 watt per channel it outputs. I did not have speakers on hand that I could drive, so I used the MicroZOTL 2.0 as a preamplifier around 80% of the time, and to drive my Grado SR60 and RHA 750i headphones the other 20%.

For $1100, not only do you get a product with great build and appearance, but also loaded with high quality parts, including TUNG-SOL 12AT7 and 6NS7 vacuum tubes, locking headphone jack with silver contacts, silver-coated Teflon copper insulated wiring, Alps volume control, gold connectors throughout signal path, and premium metal film resistors.

http://www.avrev.com/images/stories/equippreamps/linear_tube_audio/linear_tube_audio_microzotl_2.0_top.jpg

Set Up

I used the MicroZOTL 2.0 across two systems, but mostly in my office system driving  both a CLONES Audio 25p, and an Onkyo M5000R power amp. Sources were a Sony TC 350 reel to reel and SOtM streamer and iFi DAC combo. Cabling was DH Labs, Stager, and Transparent. I connected the outboard power supply to unit via the supplied cable, and used a Mojo Audio power cord plugged into the power supply’s IEC receptacle. The whole system is plugged into an Audience power conditioner. Most of the listening was done with Magnepan MMG speakers.

I listened non critically while doing office work to let the unit settle in for a few days. When I finally did give the system my full attention, I was immediately taken with the MicroZOTL 2.0’s harmonic rightness, wide soundstage, and amazingly low noise floor. I was previously using a Tisbury Audio Mini Passive II volume control. The MicroZOTL 2.0 definitely provided more midrange bloom and liquidity, the things tube preamps are supposed to do. But it is also provided these things with no penalties. No soft bass, no tube hiss, and no chalky treble. What I heard was within the context of the system, near perfect top-to-bottom balance.

Listening

One by One, the 2007 debut of American singer/songwriter Robert Francis, is a modern folk rock masterpiece, and it sounded quite wonderful with the MicroZOTL 2.0 in the system. Acoustic guitar strings shimmered, cymbal strikes had nice bell like tones, and bass lines were easy to follow. It has been a while since I listened to this album and I am glad I selected it, as it provided a nice start to the review.

Next up was music with a bit more grit, the Japanese import CD of blues titan Little Walter’s Hate To See You Go. His gutsy harmonica playing and world weary voice were brought to life between the speakers with enough tube magic to satisfy, along with plenty of recorded detail. My favorite cut, “Blue And Lonesome”, had a nice analog feel, despite being and older Redbook digital release.



One of my favorite recent releases is Ryan Bingham’s Fear And Saturday Night, a rocking stew of folk, country, rock, and Americana. The album is well recorded and among Bingham’s best efforts. His gravelly voice make his incisive lyrics come alive, and the sympathetic arrangements are well focuses. The MicroZOTL 2.0 provided excellent body to Bingham’s voice, which is front and center, and bass lines were round and full, with intertwined electric and acoustic guitar lines easy to follow. Having seen Bingham live, it was clear the MicroZOTL 2.0 was producing accurate tone and timbre, with excellent layering.

Listening with headphones produced the same impressions as above. There was plenty of drive, body, and the notion of being surrounded by the music. For some reason I found myself drawn to jazz and ambient recordings with the MicroZOTL 2.0 when used as a headphone amp. The absolutely stunning recording by the Andy Sheppard Quartet, Surrounded By Sea (96/24 FLAC) on the legendary ECM label, was intoxicating. His saxophones had body and bite, the way a live sax does, and the double bass and percussion, along with other interesting additions, were living, breathing entities.

I note to readers that I am not a headphone expert and I do most of my listening through speakers, but the sound of the MicroZOTL 2.0 with the Grado and RHA cans were a real revelation. The word intimacy comes to mind. This feeling may have been brought to the forefront due to the total lack of background noise and virtually seamless tonal balance.

Ergonomically, the MicroZOTL 2.0 was flawless. At the suggestion of Mark Schneider, I left it on 24/7, as the tube life is essentially endless. I thought the volume knob provided plenty of sweep and usable range. There is no remote control capability for the unit, and I did not miss it one bit, especially in the smaller system. I used to be a remote freak, but I no longer
feel they are necessary.

http://www.avrev.com/images/stories/equippreamps/linear_tube_audio/linear_tube_audio_microzotl_2.0_rear.jpg

Conclusion

I enjoyed every minute with the MicroZOTL 2.0 headphone and preamp. Yes, I used mostly as a preamplifier, and it was a wonderful match with all the power amplifiers I used it with. If a clean, clear window into the music, with just enough tube magic sprinkled on, is your bag, here you have it. This is a purist product with no remote control, built-in DAC, or wal wart power supply. I would not personally want it any other way. If you have similar priorities, I highly recommend an audition of the MicroZOTL 2.0.

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Specifications



Linear Tube Audio MicroZOTL 2.0 headphone/preamp: $1100
www.urbanhifi.com

Amplifier class: Push-pull Class A, no feedback
Sensitivity: 0.6V RMS for full output
Output impedance: (measured at 0.5A, 60 Hz) 2 ohms
Input impedance: 50k
Power output: with 4-ohm load: 1W, 1% THD, with 14-ohm load: 0.5W, 1% THD
Channel separation: (4-ohm loads) 46dB, 100Hz-10kHz, (14-ohm loads): 54 dB,
Size: 7 7/8 inches (19.7 cm) deep, 9 1/2 inches (24.1 cm) wide, 4 3/4 inches (12 cm) tall (including connectors)
Net weight: 5.35 lbs. (total amplifier and external power supply)
Finish: Aluminum case with lexan top
Tube complement per channel: 12AT7 input, phase splitter, 6SN7 p-p output


Review System 1


Server: Bryston BDP-2
DAC: iFI Micro iDSD w/ iFi Micro USB 3.0
Tape Deck: Revox A77
Server: Bryston BDP-2
Preamp: CIAudio PLC-1 MKII
Amplifier: Audio Research VS55, Simaudio 760A
Speaker:  Bryston Mini T
Cables: Stager Sound, Acoustic Zen, Element Cable, DH Labs, iFi
Accessories: Symposium Rollerblocks and Svelte Shelves, Shakti Stone, Bryston BIT-15, Salamander rack

Review System 2


Music Server: SOtM sMS-100 w/ Battery XPS,
DAC: iFi Micro iDSD w/i iFi Micro iUSB 3.0
Power Amplifier: CLONES Audio 25p, Onkyo M5000R
Tape Deck: Sony TC-350
Speaker: Harbeth Compact 7ES3, Magnepan MMG
Cables: Stager Sound, Transparent,  DH Labs
Accessories: Cable Pro Noisetrapper, Sound Anchors Stands, Audience aR6






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