Note that we are now using Cardas speaker binding posts, not reflected in the photos above.

Reference. It’s that good. Plus a bit more…

Linear Tube Audio is proud to present the ZOTL40 Reference+ amplifier. A worthy flagship and the most refined manifestation of David Berning’s ZOTL design.

The latest iteration of LTA's EL34-based amplifier, the ZOTL40 Reference includes a new chassis, component improvements, and is supplied with EL34s that take this 50 watt-per-channel amp to a new level.

The ZOTL40 uses EL34 tubes, one of the best midrange tubes ever invented, so it has very solid midrange and authoritative punch.

Tube Options

KT77: The main differences between the Gold Lion KT77 and EL34 are in the bass response and midrange. The KT77 have a bit more grip and force in the low end. This is somewhat at the expense of the 'mid-range magic' that the best EL34s impart.

Ray SELECT EL34: The Ray SELECT EL34 have the closest characteristic sound to NOS EL34 that we've tried, only missing the last few percent of liquidity and realism. The Ray EL34 SELECT also seem to have a bit more sparkle. They seem to let a bit more detail through in the upper-midrange than the KT77.

Ray RESERVE EL34: The Ray RESERVE EL34 imparts a smoother, more refined presentation than the Select and may be favored when using detailed speakers or sources. They also impart a larger, more spacious soundstage. If rich tone, musicality, and ease of listening is your primary focus, the Ray RESERVE EL34 tubes are an excellent option.

Notes:

• When you purchase the Ray Reserve EL34 tube upgrade, they come in addition to the stock tubes.

• The Ray tubes upgrade is only available in the US. If you live outside of the US and order the tube upgrade, we will refund the tubes portion of your order minus a 5% service fee.

What’s New about the Reference+ Version

Two years after releasing the award-winning ZOTL40 Reference power amp, LTA is proud to announce the next generation of our flagship amp, the ZOTL40 Reference+.

After trying over two dozen component combinations, and countless hours of listening tests and comparisons, the new ZOTL40 Reference+ upgrade improves the tone and texture across all frequencies, and there is more detail and clarity around the performers.

These sonic upgrades are achieved through adding a massive 100,000µF of additional capacitor storage and changing resistors at key points in the audio path to high-end non-magnetic Audio Note Tantalums, each value specifically chosen for their location.

Reference+ Listening Notes from LTA’s Director of Sonic Quality

Yes, that is a real job title - some people have all the luck - and along with a cadre of test listeners, it’s their job to make sure the sound of the Reference+ upgrades keeps the LTA sound our customers love while raising the bar in the right areas.

Whether you are Sunday morning classical, late night jazz, or sweaty rock club listeners, everything comes out sounding sweet and immersive with the Reference+ version. There is tonal sheen, midrange elegance, and startling, controlled dynamics like never before. The Reference+ upgrades reveal more emotion in the music.

We’ve found that with the Reference+ update, listening fatigue is a footnote of the past, no matter the source. Even the most challenging torture tracks become immediately palatable and better yet, unskippable. When pushing to "live sound" decibels, instruments and vocals stay in place and simply get more vivid and real instead of breaking up or becoming shouty (suggesting the listener be more reasonable with the volume control.)

Whatever your preference, you'll find new appreciation for your all time favorites and fall in love with the latest new releases.

Upgrade your ZOTL40 MkII or ZOTL40 Reference power amp

Existing ZOTL40 power amp customers can upgrade their units via our ZOTL40 Reference+ Upgrade Program.

Reviews & Testimonials

Parttime Audiophile

There is more meat on the bone, but it doesn’t come at the cost of clarity or detail… You get plenty of imaging and soundstaging, but there’s more interplay within the space, more interaction between performers and individual sounds.

The Absolute Sound

"After experimenting with several analog front ends, there was no doubt in my mind that the ZOTL40 was a model of tonal neutrality, a rare happening amongst tube amplifiers. That’s not to say that it always sounded neutral. It basically took on the colorations of whatever I threw at it, much like a sonic chameleon. It never masked the character of any front-end component."

Positive Feedback

Staging is layered, dimensional, and expressive; with a noticeable ability to render a sonic presentation of venue / studio space. Bass is tangible, tonally accomplished, and powerfully deep. Treble is very good, with a complete lack of grit or glare. Midrange is delightfully musical, and realistic. Tone is uniformly excellent throughout the frequency spectrum. This amp plays any type of music with an unconstrained ease, and can be listened to for hours on end without fatigue. While the convincing three dimensional staging, and densely rendered imaging are fabulous, in my opinion, it is its flowing musicality that is the Z40's true star-turn.

Curated to be the best

Careful component auditioning with a broad range of available loudspeakers elevate the ZOTL40 Reference+ amp to deliver the best results possible in a wide range of systems.

The best tubes on the planet

EL34 tubes are rightly revered for their tight bass, velvet mids, and smooth highs that allow for hours of listening without fatigue. The ZOTL40 Reference+ ships with a matched quad of EL34 tubes.

Constant improvement

Listening is the only way to improve an audio product, which is why we take customer feedback so seriously. We have some of the most knowledgeable and discerning customers in the industry, and their input is a key part of our product development process. The ZOTL40 Reference+ amp is the kind of unbelievably good product that can only be achieved with careful development and experimentation over time.

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.)

Looks as good as it sounds

The low-resonance aluminum chassis of the ZOTL40 Reference is designed and manufactured in Richmond, Virginia, by the award-winning industrial design crew at Fern & Roby. Sturdy toggle switches and machined aluminum front and rear panels exude quality.

Patented perfection

The ZOTL40 Reference amplifier is based on David Berning’s patented 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. Vishay Dale resistors. Mundorf caps. Typically, these are names you’ll only hear in amps that cost $10k or more.

Never buy another set of tubes

Most tube amplifiers run through tubes every 1,000-2,000 hours. That sounds like a lot until you consider that we estimate tube life for our amps to be in the 10,000-20,000 hour range. Why? Because we use ⅓ the current through the tubes, which results in lower heat and dramatically longer tube life.

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 ZOTL40 Reference+ amplifier is hand built by technicians with years of experience building the complex ZOTL circuits. All our products are backed by a 2-year warranty and a 14-day in-home audition policy.

Speaker Recommendations

LTA amplifier owners have found great enjoyment using their amps with a variety of speakers outside of the below ranges. The below are guidelines, not rules.

Critical listening environments: 85db sensitivity and above

Smaller rooms / lower volume levels / non-critical listening: 80db sensitivity and above

If you have questions about your specific speakers, chances are someone we know has tried them. Don’t hesitate to reach out with questions about your specific setup. Also, don’t forget we have a 14-day no-questions-asked return policy.

Specifications

Inputs: One pair L & R Cardas RCA

Outputs: One set of stereo Cardas speaker binding posts

Sensitivity: 1.2V provides full output

Output impedance: 1.6 ohms

Input impedance: 50k

100V / 120V / 240V operation: Auto-switching

Hum and noise: 94dB below full output (measured between 8Hz-60kHz +0/-0.5dB)

Gain: 23db

Power output with 4-ohm load: up to 51W, 0.5% THD

Power output with 8-ohm load: up to 46W, 0.5% THD

Frequency response (8-ohm load): 8Hz to 50kHz, +0, -.5dB

Amplifier class: Push-pull Class AB

Net weight: 17 lbs

Dimensions: 17 inches (43 cm) wide, 5 inches (12.7 cm) tall, 13.875 inches (35.2 cm) deep

Finish: Aluminum case

Tube complement: two 12AX7s, two 12AU7s, & four EL-34s

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