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microZOTL Preamplifier

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We can only sell these products to customers in the USA.
All Linear Tube Audio products are hand made to order. Please contact us for lead time.

14 Day In-home audition/ return. Period begins when you receive the product. The return must be requested by the 14th day and must be in perfect - like new condition.

The ultimate expression of the microZOTL as a full-featured reference preamplifier and headphone amplifier.

After years of refining and testing the microZOTL circuit, LTA has created the microZOTL Preamplifier. This is the highest expression of the patented microZOTL technology as both preamp and headphone amp in a rack-friendly form factor.

The microZOTL Preamplifier has a beautiful new low-resonance aluminum chassis and offers reference-level sonics through upgraded internal components, shorter signal path, larger power supply, and a digital control system with LED display


This preamplifier renders the illusion of real music better then any other linestage I have had in-house for review.
— Terry London

mzpre3web.jpg

Tube tone + solid state detail

Traditional tube amps are known for their liquidity and linearity, but their “warmth” masks details and can sound thick. Solid state amplifiers give you that detail, but can be “clinical.” ZOTL amplifiers give you the best of both worlds: beautiful tube tone with the clarity of solid state(while being entirely tube-based.)

Sonic improvements at every level

New circuit board material, new volume control technology, upgrades in wire, capacitors, tubes, linear power supply. The microZOTL Preamplifier is the clearest, cleanest sounding microZOTL yet.


Yeah, it’s a really, really good preamp.
— Positive Feedback

Looks as good as it sounds

The low-resonance aluminum chassis of the microZOTL Preamplifier is designed and manufactured in Richmond, Virginia, by the award-winning industrial design crew atFern & Roby. Brass touch buttons, LED display, and machined aluminum front and rear panels exude quality.

Patented perfection

The microZOTL Preamplifier is based on David Berning’spatented ZOTL technology, the only advance in tube technology since the 1950’s. For a technology to be patented, it must be deemed “new, useful, and non-obvious.” We think that sums up our approach quite nicely.

Premium components = premium sound

If you use cheap, generic parts, guess what kind of sound you’ll get? That’s why we use only premium, name-brand components. Belleson regulators. Ohno OCC wiring. Vishay Dale resistors. Mundorf caps. Typically, these are names you’ll only hear in amps that cost $10k or more.


The MicroZOTL Preamplifier produced a spatial perspective that made my seven foot tall 21 driver speakers completely vanish in the largest and accurately layered soundstage that I have ever experienced in my listening room.
— Greg, Satisfied Customer

Made in the USA

Every LTA product is designed and built by hand in Takoma Park, Maryland, by a group of technicians who are also musicians, audiophiles, and music lovers. Some of whom have been with us since the company’s earliest days.

Quality assurance

The microZOTL Preamplifier is hand built by technicians with years of experience building the complex ZOTL circuits. All our products are backed by a 2-year warranty.


REVIEWS & TESTIMONIALS

Positive Feedback by Gary Beard

The Microzotl is a really good preamp. It is an open window of transparency; with fast transient performance, excellent drive, and a high level of dynamic swing. It has a quiet black background, lacks obvious coloration, and is coherent to the point of being dang near unflappable.

The MZ's Vishay Dale resistor stepped volume control is excellent. Noiseless, and transparent. Its taper is well set to give good control at the low end of the volume spectrum; and as such, the MZ excels at both high volume, and low volume listening.

Yeah, it's a really, really good preamp.

Home Theater Review by Terry London:

I still have a sense of being astounded at the level of improvement it renders in my system. The MicroZOTL Preamplifier has a beautiful chassis, great ergonomics, and a comprehensive set of input and outputs. Most importantly, this preamplifier provides rich organic timbres/colors, a sense of "aliveness" that I find in no other preamplifier, the smallest details easily heard, a spatial perspective that brings the musicians into your acoustic space, a sense of holographic imaging, and an effortless liquidity that lets the music spill into your room. I will be purchasing the MicroZOTL Preamplifier, which has surpassed my expectations, and it will be replacing its older sibling in my reference system.

Audiogon User Greg:

“I’m running the new preamp (S/N 005) with my XA30.8. The combination is flat out beautiful. I also have an MZ2 which worked well, but the new pre is just better in every way. Clarity, staging, dynamics (both micro and macro). Very liquid, fatigue free, but also dynamic and extended.

“. . . the beautiful chassis, the ergonomics, and that sound, rich organic timbres/colors, a sense of “aliveness” that I find in no other preamplifier, the smallest details easily heard, a spatial perspective that brings the musicians into your acoustic space, a sense of holographic imaging, and an effortless liquidity that lets the music “spill” into your room.

“. . . micro-details were clearer and were easier to hear all delivered with an overall liquidity and effortlessness that let the music flow into my room.

“. . . the MicroZOTL Preamplifier produced a spatial perspective that made my seven foot tall 21 driver speakers completely vanish in the largest and accurately layered soundstage that I have ever experienced in my listening room.”

Audiogon Review, by Terry London:

“Across every sonic attribute: timbres/color, image palpability/density, spatial qualities- air around players- tremendous soundstage depth/width/height, powerful overall dynamics, and deep extension with great low frequencies regarding tone/accuracy which gives a great foundation to the music.  All this and delivered with total liquidity and ease.  This preamplifier renders the illusion of real music better then any other linestage I have had in-house for review.”


SPECIFICATIONS

Printable Owners Manual: Click Here

Inputs: 4 Stereo RCA single ended inputs using high quality Cardas connectors; 1 XLR single ended input, with balanced input upgrade option with Lundahl transformers. Sealed, silver contact relays utilized in a short signal path. One additional Tape input.

Outputs: Headphone ¼” Phone jack, dual Cardas RCA single ended preamplifier outputs, and a Tape Monitor output utilizing Cardas RCAs (input level before volume control).

Amplifier class: Push-pull Class A, no feedback

Sensitivity: 0.6V RMS [full output]

Output impedance: (measured @ 0.5A, 60 Hz) 2 ohms for headphone outputs, 50 ohms for preamplifier outputs

Input impedance: 50k

Volume Control: Stepped attenuator constructed of 1025 steps of 50 ohms, with 100 positions selected to provide very fine resolution at the lowest volumes and a logarithmic control for higher volumes . Low noise, precision 1% Vishay Dale resistors and hermetically sealed silver contact relays are used for precise, isolated analog signal attenuation

Balance Control: 100% channel isolation using stored differences of volume values. Maximum balance differential is 16 steps

Power Supply: Linear supply user-switchable between 110/120 and 220/240 (100V linear supply available for Japan). Uses dual banks of organic poly ultra low ESR capacitors (4 times MZ2) and premium Nichicon electrolytic for over 100Kuf of output choke isolated storage. Oversize transformer secured with aluminum and brass mountings (no steel). Regulation is performed using low noise Belleson super regulators. Current transformer controls output protection circuit

Hum and noise:minimum 60mV RMS or 90dB below full output (20Hz-20kHz)

Power consumption from ac power source: approx. 50W

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, 100Hz-10kHz

Frequency response full power: (4-ohm load) +0, -1dB 10Hz-20kHz, (14-ohm load): +0, -1dB 5Hz-50kHz,

Voltage gain: (4-ohm load): 10.3dB, (14-ohm load): 12.4dB

Front Panel Control: Functions include volume, input select, headphone/speaker output select, all configuration menu selections, and amplifier power on-off. Capacitive brass touch buttons are utilized for menu control, input selection, tape monitor control and power on-off.

Remote Control: All functions, including Mute and the configuration menu, are available from the remote, except power on-off.  Uses an Apple TV remote.  The remote is registered to unit to limit control from unintended remotes. The Right-Left buttons can be configured as balance controls.

Auto-save Features: Volume level per input is automatically saved and the unit powers on using the stored volume levels. Balance and all other configuration menu selections are all saved as a global level across all inputs.

Display Controls: 16 levels of brightness and on-off selectable 7 second timeout

Home Theater Mode: an input can be selected from configuration menu to set one of the inputs to a high-volume level fixed input to allow surround sound device control the volume level

Front Panel Power Switch Override:power switch on front panel can be configured to be set to always on to allow external on-off control for device such as remote-controlled power conditioner

Tube complement: 2 premium hand selected 12AT7 input tubes, and two premium hand selected 12SN7 output tubes.  (6SN7s can be used with jumper settings) 12AU7s are often substituted for the 12AT7s to lower the gain if higher headphone output is not required.  

Size: 17 inches (43.2 cm) wide, 4.2 inches (10.7 cm) tall, 12.4 inches (31.5 cm) deep (including knob and connectors)

Net weight: 14 lbs. (6.35 kg.) Shipping weight: 22 lbs. (10 kg)


ZOTL TECHNOLOGY

ZOTL AMPLIFIERS - HOW DO THEY SOUND?

Many tube amplifiers have a sound described as "warm," "tubey," or "round".  This sound can be very nice to listen to. However, it is the output transformers that produce the "warmth" or the tone of the sound, and it is actually a type of distortion, though pleasant. The detail of the music can be lost in the "warmth." There is no doubt that many people love the warmth of what they think is the tube, but is actually the transformer.

The ZOTL amplifiers do not have the thicker, warm tone that many tube amplifiers have. They still have the liquidity and linearity of tubes, but without a transformer's tone.

ZOTL amplification achieves neutral accuracy without coloration. This achievement is supported both by listening and through measurement.

Switching immediately from other tube amplifiers (and solid-state amplifiers designed to be warmer) to a ZOTL amplifier can often feel like something has been lost. What is actually happening is more akin to adjusting the focus of a lens: an increase in clarity accompanies a reduction of haze. While haze can feel like "body" or "weight" that is no longer there, as you adjust to the ZOTL amplifier you realize you are hearing the more accurate weight and body of what you are listening to, and the consistency in performance over varying impedances will allow you to experience this accuracy throughout the frequency spectrum with many different speakers. 

ZOTL amplification's neutrality is also transparency. As source components increase in performance, ZOTL amps continue to reflect this, scaling up indefinitely.

DAVID BERNING - THE MIND BEHIND IT ALL

Considered to be one of the world’s foremost amplifier designers, David Berning is among the elite in his field.  A formally trained physicist, David’s unique perspective has invaluably colored every solution he’s designed for classic audio problems.  After 20 years of designing and manufacturing tube amplifiers, David Berning turned the technology on its ear when he invented ZOTL (Zero hysteresis Output Transformer-Less) architecture in 1996.

So radically different from anything around at the time, ZOTL was and still is considered the most significant improvement to tube amplifier technology since the 1960s.  Even out of production, Berning’s ZOTL amplifiers regularly collect accolades from the world’s top audio reviewers and publications.  His ZH-230 amplifier has received Absolute Sound Magazine’s "Editor’s Choice Award" every year since 2011. His Quadrature Z amplifier won HiFi+ magazine’s "Product of the Year" award in 2009.  His 211/845 ZOTL amplifier was introduced by Hi Fi One at the 2014 Munich High End Audio Show.  Timeless examples of Berning’s audio genius, the ZH-270 and EA-2101 are still highly sought after by audiophiles everywhere.

David Berning plays an integral role in the development of LTA’s offerings. Currently these include LTA's reconfiguration of his original microZOTL personal headphone amp, the ZOTL10, a mid-to-high efficiency power amp, and the ZOTL40, David's latest ZOTL amplifier designed for LTA, which is in essence the successor to his own, much lauded, ZH-230.

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 the solution: ZOTL.

First, the audio signals “ride” a carrier frequency, on which they are amplified by the tubes (it is not a hybrid amplification design), then the carrier is removed by the Impedance Converters and the remaining audio is delivered to the speaker, similar to how a radio station 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 Converteraccomplishes this match up. This super linear amplification process allows the amplifier to have a flat frequency response from 8hz to 50Khz, which is nearly 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 that the theoretically correct turns ratio for most tubes is typically 100 to 1 and even as high as 300 to 1. The ZOTL can use the impedance converter to effectively create the ideal 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 and accuracy of the sound.

OTHER OUTPUT-TRANSFORMERLESS (OTL) AMPLIFIERS

OTL (Output Transformer-Less) amplifiers manufactured by other companies are a completely different technology than ZOTL amplifiers.

ZOTL technology involves a linear amplification process using a carrier frequency as well as not having a traditional audio output transformer, instead using air-core Impedance Converters.  

Noted pioneer of amplifier technology, Julius Futterman, has inspired many different amplifier designs over the years.  Based on Futterman’s principles, other OTL amplifier designs incorporate two separate banks of parallel-connected tubes. The two banks are joined in series by connecting the effective cathode of one tube bank to the effective plate of the other tube bank, and driving the loudspeaker in a push-pull fashion directly from this junction point without a transformer. There are alternatives to Futterman’s principles that use low-impedance triodes, but the basic principles are the same - given a sufficient number of parallel-connected tubes in each bank, enough drive current can be obtained to drive the speaker.

The output impedance of other OTL amplifiers is nowhere near the actual speaker impedance.  In an OTL amplifier, a large amount of negative feedback is required to force the push and the pull to work together properly in order to provide sufficient damping for the speaker. Even with the lowest impedance triodes available, there is still a basic impedance mismatch between the tubes and the speaker in the OTL circuit. 

Traditional OTL technology requires a large number of power tubes which need to be driven hard to obtain the required output.  This results in drastically reduced reliability and tube life and generating lots of heat.  Fans or additional room air-conditioning may be required.  Power consumption is typically very high for OTL amplifiers, often exceeding one kilowatt for a stereo pair.

THE ZOTL ADVANTAGE:

  • Drastically improved tube life due to lower current operation

  • No output transformer intermodulation distortion

  • No low frequency non-linearity

  • Distortion by parasitic transformer elements of the audio signal no longer occurs

  • Improved bass due to flat, linear bass response to below 10hz

  • Removal of low frequency limit for bass response

  • Correct transformer turns ratio

  • Low output impedance for easier speaker matching

  • Having no load cannot damage amplifier

Further reading:

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