Many HTR readers have emailed me, asking about the possibility of reviewing a tube-based preamplifier that would retail for no more than $2,000 yet compete with more expensive preamplifiers. I've read a lot of very positive statements in different chat rooms regarding the unbelievable performance of Linear Tube Audio's MicroZOTL2.0 preamplifier/headphone amplifier, which retails for $1,695. So I contacted Mark Schneider, owner/engineer of Linear Tube Audio, located in Washington DC, to see if he was interested in having me review the product. Mark was very supportive in making this review happen; as soon as he had an available MicroZOTL2.0, he shipped it to me. This became one of the most remarkable experiences I've ever had in my years of listening to and reviewing stereo equipment, and it simply started with trying to find an inexpensive tube-based line stage that would offer great "bang for the buck" for our readers.
Mark started Linear Tube Audio because he became friends with the legendary audio designer David Berning, who gave permission for Mark (under Berning's supervision) to manufacture drastically lower-priced, high-quality versions of his headphone amplifier/line stage and amplifiers. These products are based on Berning's patented architecture known as ZOTL, which stands for ZERO Hysteresis Output Transformer-Less. In general, most engineers would agree that transformers can be a major hindrance to both preamplifier and amplifier performance because of bandwidth limiting, which produces intermodulation distortion. Many companies produce OTL (Output Transformer-Less) amplifiers and preamplifiers; however, Berning's OTL design has unique aspects that the other designs lack.
One special aspect of the ZOTL strategy is to use a superimposed carrier signal for the music signal at 250 kHz, which is then extracted through an RF-converter transformer to obtain the high current and low impedance required by loudspeakers. This simply means that, unlike a normal audio transformer operating over the total audio bandwidth, the RF-converter transformer operates at a single frequency, allowing a very pure signal with zero global feedback.
The MicroZOTL2.0 consists of two black-colored enclosures (you can also get them in midnight blue). The first is a large, robust, separate power supply (internally, it has Organic-polymer capacitors, a medical-grade EMI filter, and a low-noise toroidal transformer), which measures 4.25 inches high by 3.25 inches wide by 12 inches deep and weighs 12 pounds. The second is the headphone amp/preamplifier, which measures 4.75 inches high by 9.5 inches wide by 7 inches deep and weighs 5.35 pounds. The top of the MicroZOTL2.0 is built out of Plexiglas, allowing you to see the glow of the internal tubes. The quality of the internal parts is at a high level (an Alps volume control and silver-coated and Teflon-insulated copper wiring), and the overall build quality demonstrates excellent craftsmanship.
On the front plate is a toggle switch for changing between the two inputs, along with the on/off button for the volume control and the headphone output. On back, you'll find the input for the power cord from the external power supply, a single-ended preamp out, two single-ended inputs, and speaker wire connections (the MicroZOTL2.0 can be used as an integrated amplifier). The ZOTL2.0 is shipped with Russian Tung-Sol reissue tubes that consist of a pair of 6SN7 power tubes and 12AT7 input tubes. The magical performance created by the MicroZOTL2.0 became apparent even while using the stock tubes. However, when I rolled in my pair of NOS Tung-Sol black glass, oval plate 1947 6SN7 along with a pair of NOS Gold Brand Sylvania 1957 12AT7, the performance went to an even higher level of performance across the board.
When I put the MicroZOTL2.0 in my reference system, in place of a $24,000 preamplifier, I was patently shocked with what effect it had over the performance of my system. In listening to John Coltrane's album Ballads (Impulse), what was immediately striking to me was the beauty of the timbres and tonality of his tenor saxophone. The MicroZOTL2.0 produced the best colors and tones of any preamplifier that I have ever had in my system. The timbres of the other instruments (such as the piano, acoustic bass, and drums) were the most life-like that I had ever heard from this disc.
As I listened to Rosemary Clooney's album Blue Rose/Duke Ellington and His Orchestra (Columbia/Legacy), another virtue of the MicroZOTL2.0's abilities was on display. Not only did it create the most accurately layered soundstage that I had ever heard in my system's overall spatial performance, it also rendered the most palpable three-dimensional imaging of each individual player on that stage. The MicroZOTL2.0 turned out to be the quietest preamplifier I have ever had in my system, which made it extremely easy to hear the micro-details because of the lack of any background noise.
Because the MicroZOTL2.0 is a tube-based line stage, I feared it could be lax regarding overall macro-dynamics, bass extension/power, and high-end extension. I tested these parameters with Steve Winwood's album Nine Lives (Columbia), which is a collection of blues-influenced rock and roll. This album is also very well recorded and contains great punch, deep bass, and high-frequency guitar riffs/solos that were all handled with aplomb by the MicroZOTL2.0. Not only did it drive the system with intense punch and pace, it did this with effortless liquidity that just let the music fill the room.
• The Linear Tube Audio MicroZOTL2.0 is hand-build in the U.S. and is based on the innovative patented design of David Berning.
• This preamplifier renders beautiful colors, timbres, and tonality of instruments when compared with other line stages.
• The MicroZOTL2.0 will compete with any other preamplifier, regardless of cost, in the areas of overall spatiality, image density, and three-dimensional imaging.
• Because of the way the MicroZOTL2.0 regulates both its power and input signal tubes, they will last for many years compared with other preamplifiers.
• The MicroZOTL2.0 has virtually no noise floor; therefore, micro-details are heard easily, and your system will have less background noise and grunge.
• The MicroZOTL2.0 produces taut, accurate, and extended bass frequencies that provide the underlying drive/pace to the music.
• The MicroZOTL2.0 lacks a theater-bypass option.
• It only accepts single-ended connections, not XLRs.
• The MicroZOTL2.0 only has two inputs and lacks a remote control.
(Linear Tube Audio will be coming out with a remote control option this summer.)
Comparison and Competition
Two preamplifiers in the price range of the MicroZOTL2.0 are the AVA FET VALVE CF, which retails for $1,899, and the Mystere ca21, which retails for $2,295. Neither preamplifier comes anywhere close to the performance of the MicroZOTL2.0. The AVA FET VALUE CF fell far short of the beautiful timbres/tonality and sounded "dry" compared with the liquidity of the MicroZOTL2.0. The Mystere ca21 did better in the area of tonality but was still far behind. When it came to overall dynamics and punch, the Mystere ca21 could not keep up with the MicroZOTL2.0.
As I stated at the beginning of this review, my experience with the Linear Tube Audio MicroZOTL2.0 headphone amp/preamplifier has been one of the most remarkable and surprising experiences I have ever had as a listener and reviewer. The MicroZOTL2.0 may be a very inexpensive, ordinary-looking, unpretentious headphone amplifier/preamplifier, but it's one of the best-sounding preamplifiers on the market. This was an amazing discovery, particularly when you consider the product's price. Because of its spatiality, three-dimensional imaging, lack of a noise floor, beautiful timbres and instrument colors, tremendously powerful taut bottom end, and overall dynamics, the MicroZOTL2.0 does not take a back seat to any preamplifier.
In my home reference system, the MicroZOTL2.0 was teamed up with Pass Labs XA-60.8 mono blocks, a Pass Labs X-250.8, a First Watt SIT 2, and First Watt F7. I wanted to make sure that the magic I was hearing was not just some synergy with these great amplifiers, all creations of Nelson Pass. So, I hit the road and tried the MicroZOTL2.0 in three different systems using excellent amps from Canary Audio and Magnus Audio. Each time, the same dramatic changes happened that I detailed in this review. After experiencing the effects of the MicroZOTL2.0, the owners of these other systems found it difficult to go back to their own preamplifiers because their systems sounded "washed out" and had more two-dimensional imaging compared with the MicroZOTL2.0.
Over the years, I have listened to and reviewed many excellent preamplifiers, both tube-based and solid state, from companies like VTL, CAT, Canary Audio, Raven Audio, Audio Research, Ayre, Woo Audio, Backert Labs, Mark Levinson, Luxman Audio, Lamm Audio, Purity Audio, Placette, Shindo, Esoteric, Simaudio, Boulder, and Concert Fidelity. The MicroZOTL2.0 is at least on the level of these fine preamplifiers, which are much more expensive. Without hyperbole, I believe the MicroZOTL2.0 might be a better performer than all of them. I will absolutely be purchasing the review sample to become my go-to preamplifier in my large reference system.