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ZOTL Technology

Do LTA amplifiers have good bass?

Yes.

Many of our customers describe the bass as “thunderous.” Steve Guttenberg of CNET described the bass of one of our products this way:

Bass depth and definition were well-ordered... There's no muddiness down there of the sort I get from a lot of tube amps.

From a technical perspective, ZOTL amps have a linear frequency response below 10hz.

To put that number into perspective, the lowest most full-range speakers go to is about 20hz, with most being closer to 28-32hz. Even REL, arguably the world’s top subwoofer manufacturer, their flagship subwoofer goes down to 14hz.

So, whatever is in the music, our amps will be able to deliver.


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Are ZOTL amplifiers different from other OTL amps?

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.

Why would you want to remove the output transformer from an amplifier?

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 Converter accomplishes 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.

How do ZOTL amplifiers 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 downside is 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.

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.

What are the advantages of ZOTL amplifiers?

Without getting too technical, here are the unique benefits of the patented ZOTL amplification technology.

Less distortion: Most amplifiers have output transformers. You don’t have to know what those are or even what they do, but what you need to know is that they introduce distortion into the audio signal. As the name suggests, distortion is generally bad. Our amps do not have traditional output transformers, so our amps have very low distortion.

More detail: Distortion also tends to cover up details in the music. Things like a performer taking a breath, the unique click of a weighted piano key, a background guitar lick, or a softly brushed cymbal or snare drum. With ZOTL amps, you hear all of these things.

Easy speaker matching: ZOTL amps work equally well with 2 ohm speakers, 4 ohm speakers, 8 ohm speaker, even 16 ohm speakers. This is because of the low output impedance of our amps, but we promised not to get too technical.

Less heat: If you’ve ever put your hand on–or even stood next to–a tube amp, you know they get very hot. Like, dangerously hot. ZOTL amps do not get as hot, because we send much less electrical current through the tubes. Bonus: pet-, kid-, and cooling-bill friendly!

Longer tube life: Heat kills tubes. Since tubes don’t get as hot in our amps, they last a lot longer than traditional tube amps. We’re talking the difference between 1,000-2000 hours in traditional amps vs 10,000 - 20,000 hours in LTA’s ZOTL amps. Bonus: you save money on tubes!

Better bass: Most amps go down to 20hz, which is right at the low end of the what humans can hear, but they start to degrade well above that. ZOTL amps have a flat (aka linear) frequency response all the way down to 8hz. This means more controlled, natural bass at the levels humans can hear.

Mono and/or Stereo: All LTA ZOTL power amplifiers (the ZOTL10 Mk II, Ultralinear, and ZOTL40 Reference) can be used in stereo mode (one amp for two speakers) or bridged to mono mode (two amps, two speakers) at the flip of a switch.

There are lots of interesting reasons why Linear Tube Audio’s ZOTL amplifiers offer unique benefits over traditional tube amps, like correct turns ratios and removal of distortion by parasitic transformer elements. If you want to dive into all the technical stuff, we invite you to explore more details about the ZOTL technology.


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Do LTA tube amps generate a lot of heat?

Linear Tube Audio amplifiers produce far less heat than traditional tube amplifiers.

The ZOTL technology allows us to run ⅓ the electrical current through the tubes than normal, which results in much cooler tube operation. You could leave your amp on for days and still comfortably place your hand on the top of an LTA amp (not the tubes themselves).

Heat kills, so this also extends the life of tubes, to somewhere in the 10,000 - 20,000 hour range. Ask any other amplifier manufacturer about tube life, and the answer will be 1,000-2,000 hours, tops.

The reduced heat also makes our amps more child- and pet-friendly.


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Are LTA amps hybrid tube + solid state amps?

No. Linear Tube Audio amps offer 100% tube-based amplification.

The confusion lies in some of the language often used to describe our amps.

Phrases like, “tube tone + solid state detail” and “all the magic of tubes and all the benefits of solid state.” Or, our favorite, as one of our customers once said: “the gap between the best of what solid state amplification has to offer and the best of what tube amplification has to offer just got blown up.”

While all these phrases are true, due to the unique nature of our ZOTL technology, we can see how people could get confused.


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