July 2020

LTA MZ3 Vacuum Tube Stereo Preamplifier
Anyone who loves solid-state amplifiers should go listen to an MZ3.
Review By Sam Rosen Of Positive Feedback

  For those who have read my other reviews on Positive Feedback, one thing that is probably apparent, is my love of tubes. I find that tubes bring a sense of space and realism that is rare in solid state amplifiers. Now tubes are not perfect, they have their drawbacks. For example, if you are using a transformer coupled amplifier, you have to deal with the coloration that the output transformer adds to the sound. Similarly, if your tube amp is of the OTL variety (Output Transformer-less) headphone / speaker matching becomes incredibly important, and power will likely be more limited. However, the results from an OTL amplifier can be really magical, and when I read about what Linear Tube Audio was doing with David Berning's ZOTL technology I knew I had to hear one of their amplifiers.

After getting in touch with Nicholas from Linear Tube Audio (LTA), he was nice enough to send me a MZ3 for review. I have been using it over the past two and a half months with a variety of headphones, and to cut to the chase, it is an exceptional amplifier. It is also an incredibly capable preamp. We will get to this later in the review, but if you want to skip to the end, the MZ3 is well worth owning.

Let's Talk About David Berning's ZOTL Technology
Tube amplifiers come in two top level forms: with output transformers or without output transforms (OTL). At a high level the output transformer provides a way to convert the large voltage swings of tubes into current. This is useful for driving speakers and headphones, and as a way to match impedance. The transformers also protect the tubes, acting as a middle man between the tubes and the speakers / headphones.

As most audiophiles know, anything that sits in the middle of a circuit will likely impart its own sound, and the output transformer is not different. Transformers may limit the overall bandwidth of the amplifier, resulting in more shallow or less impactful bass, or possibly rolled off highs. Now, a well-designed amplifier will not exhibit these issues, or if they do, the impact will be minimal. But in a perfect world, most designers would agree that an amplifier without an output transformer will have a more pure sound than one with. The issue though is OTL amplifiers have their own drawbacks, traditionally lower overall power, lots of heat, and the need to carefully match the impedance of the speaker or headphone to the amplifier.

This is where David Berning's ZOTL technology comes in. It is considered by many to be the most significant improvement in tube amplifier technology since the 1960s. ZOTL stands for Zero Hysteresis Output Transformer-Less, it's the architecture that underlies all amplifiers made by LTA, which exclusively licenses the technology for David Berning. The architecture uses a carrier frequency and air-core impedance converters to effectively get all the benefits of an OTL design (purity, clarity, and no output transformer), without all of the major drawbacks (large number of tubes, extreme heat generation, and the need to carefully match the headphone / speakers to the amplifier). The result is amplifiers that are extremely linear, with a flat frequency response from 8Hz to 50kHz, that can be matched with pretty much any modern mildly efficient headphone. They also tend to be more transparent than their transformer coupled peers. Also ZOTL based amplifiers push tubes far less hard, which LTA claims results in tube life that could be well over 10 years. In operation, it is clear the tubes run less hot than my other amplifiers.

At the end of the day, what matters most is how the amplifier sounds. So let's dive in and talk about the listening experience.

The Review System
I set the MZ3 up on its own little system, with the following attributes:

· Streamer/Server: Pro-Ject Streambox S2 Ultra, Home Built Roon Core

· DAC: Chord Hugo 2

· Amp: LTA MZ3

· Headphones: LSA HP-1, Hifiman HE1000SE, Focal Stellia

· Power: 4 amp balanced power conditioner

· Cabling: Wywires Platinum Interconnects

Features, Un-Boxing, and First Impressions
Saying the MZ3 is packed full of features would be an understatement. It is a reference headphone amplifier, reference preamplifier, and even a speaker amplifier. It provides three single ended inputs and two single ended outputs. To support its use as both a preamp and an integrated amplifier it has a remote control that controls inputs, volume, and additional features such as assignable home theater bypass and balance controls.

Volume control is handled by relays providing perfect channel matching with 100 positions. Increasing or decreasing the volume results in a solid thunk as the volume changes, which is oddly satisfying. Remote control duties are handled by an included silver Apple remote, the same used on the first few generations of Apple TVs. I keep seeing these first generation Apple remotes used, and I am quite happy about it. These remotes work well, are well designed, fit well in the hand, and I am always happy to see companies use them instead of shipping a cheap feeling plastic remote with their products.

The MZ3 is a stunning device, thanks to LTA's partnership with the design company Fern & Roby. The case work is some of the best I have seen, regardless of price point. The fit and finish of the metal chassis is flawless, the buttons and switches have a satisfying tactile feel, and the volume knob feels great in the hand. To see the volume level, the MZ3 has a white LED dot display to show the volume level, as well as other menu options. The volume control looks great, works well, and is easy to read from across the room.

The MZ3 is quite light, thanks to the lack of output transformers, it is relatively small at 10" x 4.75" x 8.5" and could fit very easily on a desk. Looking at the top, there are four cutouts for the four tubes that allow the MZ3 to operate. The MZ3 takes two 12SN7 acting as power tubes via jumpers, and it can also accept 6SN7 tubes. While the jumpers are nice, the 6SN7 is quite expensive, where the 12SN7 is more or less identical but much cheaper. The preamplifier section of this amplifier runs two 12AT7 tubes, and can also take 12AU7 tubes if the user desires less gain. The units ship with NOS tubes that are broken-in at the factory.

The last thing to talk about is the Linear Power Supply; similar to the MZ3, it is built like a tank, and quite handsome. It uses a four pin XLR cable to connect the MZ3 to the Linear Power Supply,  which feels secure, and the cable itself is well built. Now to be clear, the Linear Power Supply is not small at 12.25" x 5.25" x 4.25" so it is important to plan out where you will put it if space is limited.

I provided a lot of detail above, but to summarize, the MZ3 is one of the best built pieces of equipment I have had in my system in a long time. It reminds me of the fit and finish that AURALiC's G2 product line has, which is the biggest compliment I can give to any piece of HiFi equipment. In operation, the unit always responded to button presses and remote commands, and for the most part was intuitive and a joy to operate.

So How Does it Sound?
In this section we will talk about how the MZ3 sounds using its headphone output, with volume controlled by the MZ3, and the Chord Hugo 2's volume set to line level.

In general the MZ3s sound can be summarized as fast, tonally rich, and accurate. Don't worry I will explain what I mean by this, but the result is addicting and really quite lovely to listen to no matter the genre of music I throw at it.

When I think of tube amplifiers, most of the time, I think of transformer coupled tube amplifiers, like the amps and sound Bigger Ben. While I think the Bigger Ben is incredibly fast, it has nothing on the MZ3. The MZ3 sounds much more like a high end solid state amplifier when it comes to speed. Everything seems immediate and effortless, in a way that I only ever experience with a solid state amplifier. However, it retains the tonal richness that I expect when I listen to tubes. In my experience solid state amplifiers, while fast, can sometimes sound thin or dry, but the MZ3 maintains the richer and weightier sound that I expect from a traditional tube amplifier without sacrificing speed. To be honest it is a strange phenomenon, and can make someone question if they cannot simply have it all (speed of solid state, harmonic / tonal richness of tubes)?

For example, listening to "Sad Forever" by LAUV, which can be a bit of a grating experience with solid state amplifiers, was a true joy on the MZ3. The vocals sounded clean, without being peaky, and the lower bass line was awesome, with the bass being reproduced with the texture and detail that I would only expect from a solid state amplifier.

Changing to one of my favorite test tracks Melody Gardot's "Mira," the sound stage was both wide and deep. The thing that stood out to me was the detail that I was getting from the bass player. I could both hear and feel his fingers hitting the chords. While these details were present on my reference amplifier, I found the MZ3 revealed this detail more naturally, I didn't have to listen for it, it was simply there.

It took time for me to come to this conclusion, but the sound from the MZ3 was almost light. Now don't read into this as thin, but instead more like skimming the fat off the top of chili as it cooks.  What I mean by this is that it supplies the richness that you expect with tubes, but without the extra warmth and weight. This results in much more detail, and an overall cleaner experience. I found myself listening at much lower volume levels then I traditionally do, simply because I found no need to increase the volume.

The above is not necessarily perfect, and does have some drawbacks. For example, I personally like a warmer, and heavier presentation (which explains my love for single ended triode amplifiers), and recordings that are thinner, or have been treated to a hotter mastering process, can be less enjoyable on the MZ3. But this also means the MZ3 is more transparent. I also find that while bass detail is absolutely present on the MZ3, the impact of the bass is a little lighter. This last point comes down to taste though, I like impact, and am willing to sacrifice a bit of clarity on the bass to get the impact. However, if you are someone who likes ultimate bass clarity, the MZ3 has one of the most clean and detailed bass presentations I have ever heard, second only to a custom built Darling headphone amplifier that has a retail price of about 20% more than the MZ3, and far less versatility.

Headphone Compatibility / Matching
The MZ3 is not too picky when it comes to headphone matching. However, you need to make sure the headphone is not too power hungry. From my testing and experimentation I would guess anything above 90dB/mW efficiency will probably pair quite well.

The MZ3, in my testing, had no issue whatsoever powering my Focal Utopia and Focal Stellia (both 104dB/mW efficient), and was even able to remain silent at 100% volume, which in and of itself is an incredible achievement. It had no issues powering the HiFiMAN HE1000SE (96dB/mW), nor did it have an issue power the LSA HP-1 (104dB/mW). Not surprisingly though, the same cannot be said for driving the HiFiMAN Susvara (83dB/mW). This was expected, but did show that the MZ3 can run out of steam. To be clear, with all headphones except the Susvara, the volume knob never went past 15 out of 100.

The issue I have seen in the past is that some headphone amplifiers simply sound best with high efficiency headphones, however, they are not quiet enough to provide a black background for those headphones. I am very happy to say that the MZ3 provided a pitch black background for all of my headphones. I found the higher the efficiency of the headphone, the better the MZ3 got, and while I did not have one on hand, I would imagine a Grado PS1000e would have sounded wonderful on this amplifier based on my memory of that headphone.

Using The MZ3 As A Preamplifier
The MZ3 and the larger MICROZOTL preamplifier use the same circuit. Other than the single chassis and the extra inputs / features, the MICROZOTL preamplifier and the MZ3 perform pretty much identically according to LTA. So how does the MZ3 perform as a preamplifier?

The MZ3 is one of the best preamplifiers that I have ever had in my system. The reason for this is that it imparts its sound signature on the downstream equipment. Its detail retrieval, immediacy, and drive is transferred to the power amplifier, and the speakers that connect to it. Using it with my Anthony Gallo 3.1s and the Emotiva XPA-1L mono-blocks produced a smooth, detailed, and clean sound. To be clear, these speakers and amps were never lacking in these areas, but the MZ3 really brought out that last bit of detail and tonal accuracy that the system was missing.

Similarly, connecting the MZ3 into my headphone power amplifiers (amps and sound Bigger Ben) resulted in many of the positive attributes that I enjoyed about the MZ3 getting mixed and combined with the strengths of the Bigger Ben. Unfortunately, this combo resulted in too much gain, or else I don't think the MZ3 would be leaving my system at the end of this review.

As a preamp the MZ3 will be at the top of my list when I build my next two channel system. Currently, my plan calls for higher efficiency speakers (98dB/mW and up), the MZ3, and a SET amp. Based on my experience with the MZ3 this combination will be reference level and I look forward to the day I get to put the pieces together.

Are There Any Cons?
I spent a lot of time thinking about this section as I prepared to write this review. The MZ3 is a nearly perfect device when looked at in a vacuum. When you look at its versatility, the fact that it is a headphone amp, integrated, and a reference preamp makes its value proposition remarkable, however, you actually have to use all of the functionality to make the numbers work.

At $3700 the MZ3 is simply not cheap. It is easily one of the best headphone amplifiers I have ever heard, but for many in the headphone hobby $3700 on the amplifier is a lot of money. If you will also use the speaker binding posts or the preamplifier functionality, the price, in my mind, is no longer an issue. Honestly $3700 for a preamplifier that performs as well as an MZ3 is a bargain, but if you plan on just using the MZ3 as a headphone amplifier, you need to make sure you have a DAC and a pair of headphones of similar quality to ensure you can enjoy all of the benefits of the MZ3. If you do, the MZ3 is worth every penny.

Concluding Thoughts
Reading that David Berning's ZOTL technology was the biggest advancement since the 1960s for tube audio caused me to have high expectations for the MZ3. I can safely say the MZ3 hit or exceeded every single one of my expectations. The unit itself is built like a tank, looks incredible, feels great to operate, and more importantly sounds incredible during operation.

Anyone who loves solid-state amplifiers should go listen to an MZ3. My guess is they will be forced to re-examine their preconceived notions of what a tube amplifier is capable of. Similarly, for the group like me that loves SET amps, but would like a bit more speed or a bit more linearity, ZOTL technology is the solution that you might not have known existed.

I am sad to send the MZ3 back, if I did not already have a headphone amplifier in my system geared to high efficiency headphones it would not be leaving. Similarly, if I could justify keeping it in my office system I would in a heartbeat. What I do know is that LTA will join the short list of audio companies that I recommend without a second thought to my friends and family. I cannot wait to have a system to test out there power amplifiers with, and I hope to own an LTA amplifier in the future.

Be careful, if you audition one of these, make sure you have the money set aside to purchase it, because you likely will. Thank you Nicholas and the MZ3 team for allowing me to review the MZ3, it was a true pleasure.

Check Out Positive Feedback
See many great reviews by Positive Feedback at this link.

Specifications
LTA MZ3 Preamplifier
Retail: $3700

Manufacturer
Linear Tube Audio (LTA)
Website: www.LinearTubeAudio.com