Linear Tube Audio MicroZOTL Preamplifier

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Linear Tube Audio MicroZOTL Preamplifier

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Almost three years ago, I was stunned by the performance of the Linear Tube Audio MicroZOTL 2.0 preamplifier/headphone amplifier, used as a line stage, when it significantly out-performed my reference Concert Fidelity preamplifier on all sonic parameters. The Concert Fidelity, a hand-built piece from Japan that cost $24,000, had never been surpassed by any line stage I had auditioned for over five years in my system until the MicroZOTL 2.0 with an upgraded linear external power supply retailing for less than $2,000. Needless to say, the MicroZOTL 2.0 was selected as one of Home Theater Review's 2016 products of the year.

I have stayed in touch with Mark Schneider, CEO/engineer of Linear Tube Audio in Washington D.C., who recently shared that he was working on a full-sized single-chassis dedicated preamplifier that retails for $4,450 and promised to perform even on a higher level. The MicroZOTL Preamplifier is based on legendary audio designer David Berning's patented architecture known as ZOTL, which stands for Zero hysteresis Output Transformer-Less. Other companies have used OTL (Output Transformer-Less) designs to get rid of the possible bandwidth limiting and intermodulation that transformers often struggle with. However, Berning's patented architecture uses 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 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.

Mark and David are very close friends and worked together on the MicroZOTL Preamplifier. This three-year project led to numerous major internal upgrades.  These included high-grade ceramic circuit boards, Dale precision resistors, and OHNO wire used in the stepped volume attenuator, isolated Belleson Regulator and super low ESR poly-organic capacitors used in the power supply, and upgrades in all capacitors in the audio path. Linear Tube Audio contracted with the firm Fern & Roby to design/build the new full-size chassis, which is quite handsome in its appearance, constructed of slabs of aluminum with brass touch buttons. 

MicroZOTL_Preamplifier.jpg

The MicroZOTL Preamplifier I received for review was black, with the aforementioned brass touch buttons, weighing 14 pounds and having dimensions of 4.2 inches high by 17 inches wide by 12.4 inches deep. On the front of the preamplifier is the power button, headphone jack input, volume control, LEDs for input modes, brass buttons for different inputs, select/menu, and the digital front panel display out that displays volume along with left/right balance. There are sixteen levels of brightness for the panel display, along with an option that completely darkens it after you set the volume level.

Walnut_Amp_Stand_iso_with_MicroZOTL_Preamp.jpgAround back is where two sets of single-ended RCA outputs, five single-ended RCA inputs, one input pair of XLR, and IEC input and the main on/off power switch are located. The unit is shipped with excellent sounding NOS 12SN7s and 12AT7s, so there is no need to do tube-rolling to get the best performance out of this piece. If you have a collection of 6SN7s and want to use them, it's a very clear and easy procedure to remove two small internal jumpers, all of which is explained in the manual. I found the menu to set up all functions to be very easy and intuitive. You can use either the select menu button on the front panel or the supplied Apple remote to set up all functions of the preamplifier. Finally, the volume control is based on a 100 stepped attenuator, which makes getting to the "sweet spot" of every recording simple and easy because of the fine gradient of dB change with every step.

The Hookup
The Linear Tube Audio MicroZOTL Preamplifier was inserted into my reference system, replacing the MicroZOTL 2.0 Preamplifier/Headphone Amplifier. It's a stereo preamp, so installation wasn't all that complicated. Plug in analog inputs. Plug in analog outputs. Carefully install tubes without getting fingerprints on them. Pretty simple. 

The rest of my system's components are Jay's Audio CDT-2 MK2 CD transport, Lab 12 DAC1 SE, Pass Labs XA25 amplifier, Running Springs Dmitri power conditioner, MG Cable reference silver IC's and copper speaker wire, Audio Archon power cords, a Tomo rack designed by Krolo Design, and Tekton Design Ulfberht speakers mounted on Sistrum Apprentice Platforms.

Click over to Page Two for Performance, The Downside, Comparison & Competition, and Conclusion...


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HTR Product Rating for Linear Tube Audio MicroZOTL Preamplifier

Criteria Rating

Performance

5

Value

5

Overall

5

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