- Dec 21, 2009
REBIRTH OF A MAGIC HEADPHONE AMPLIFIER and its even better!
MICROZOTL 2: A spectacular rebirth of a magic tube headphone reference amplifieror “please send food and water, as im not getting up from the MZotl anytime soon”
note the MicroZotl2 will be referred to below as the MicroZotl2 or MZotl
About 15 years ago i was cruising the internet late at night, looking for new audio products
and gear that might feed my habit as a headphone fanatic. I came across an announcement
of a new patent that had been issued to one David Berning, an audio engineer specializing
in tube amplifier design. It was for a new device that used radio frequency wave technology
to bypass the distortion in the output phase of most tube amplifier designs.
I cant say i understood
exactly what he was doing (im not an audio engineer, just a hypercritical listener and
african djmbe drummer, music producer. Below i will post the current explanation of this
patented technology, which remains unrivaled! It was intriguing enough that i tracked down David
and asked him if i could obtain one of the minature version of his new amps (the headphone focused Micro Zotl( at
that time about an 800 $ device)
as opposed Zto the Zotl, which was a full size speaker driving reference amp, costing thousands The microZotl was putting out one
watt of power, but what a glorious one watt it was supposed to be!
David graciously agreed to make me one in blue (my nickname being drblue) and since then
my headphone test bench has used the original MicroZotl original design as the power source for driving
all the full size headphones i auditioned.
It was smooth, glorious sounding, and i never needed more than half the power to drive headphones.
It was lively, had great PRAT, and revealed details galore of the music. I was a happy camper.
and it was relatively affordable for such a break through new technology.
Years later (2014) with the headphone revival going in full blast on head-fi.org where i regularly
contribute observations and occasional reviews, i noticed there was no mention of this magic amp.
i queried a few of my headphone addict colleagues and they hadn’t heard of it. Was it time for a
revival? I couldnt find it for sale anywhere, so i tracked down David Berning and asked him about it.
He said it was out of production for years, but given possible new headphone fanaticism, he would
consider reviving it.
A few weeks later i was happily informed by David he was going to put the MicroZotl back into production
with Mark Schneider of urbanhifi.com and it would be available sometime soon. A few months later
Mark contacted me and let me know the new unit would be slightly redesigned with an external power
supply of 12 volts rather than the old internal power supply. Also there were new Russian tubes that
upgraded the unit from the old Chinese ones used in the original design. I asked him if i could review
and beta test the new design and recruit some other head-fi headphone afficiandos who were interested
in my enthusiasm for the original to comment on it. He agreed to that, and at the end of March i i received
a prototype with the final electronics design but not the final casing. Unfortunately the shippers had shook
the internal circuits to shreds, so i sent it back and waited again for a few weeks for a better packed prototype
to arrive in one piece. That new unit arrived about a month ago, and i have been in sonic heaven ever since.
The new MICROZOTL2 retains most of the original circuits of the first MicroZotl, with the exception of the
external power supply and upgraded tubes. It also has a preamp out built into the back control panel.
It is built a bit differently with a clear top instead of side clear
panel, allowing one to peer down into the magic circuits glowing with tube light. However, extensive
comparision of the sound of the old unit vs the new design has convinced me that the new design if a major
improvement to the sound quality of the design, and in fact takes it to a whole new level.
In short, the new design is a reference level amplifier that reveals the nusances of ALL the equipment in the
chain of sound, from source to digital processor, to cables, to headphones. It is an electron microscope
of sound amplification, which allows you to peer deeply into the structure of the music you are listening to
but most of all, has the capability of creating that GOOSEBUMP feeling that high end audio fanatics crtave.
Here is the description of the technology from the new manual of the Zotl2:
"In 1996 David Berning developed a new and technically advanced vacuum tube architecture designated as ZOTL. ZOTL stands for Zero-Hysteresis Output-Transformer-Less amplifiers. The ZOTL architecture eliminated the problematic sound quality issues that audio-output transformers caused.
Since ZOTL technology was introduced in 1996, the microZOTL amplifier has the lowest power output of all ZOTL amps so far. Hence the name.
Thes ZOTL amplifier uses radio frequency to change the voltage-current transfer characteristics of the output tube from its normal impedance plane to one suitable for driving a dynamic loudspeaker. The radio-frequency remapping is implemented using special high-frequency power-conversion techniques. The high-voltage, low-current tube impedance plane is remapped to the high-current speaker impedance plane through special transformers operating at a constant RF carrier frequency of 250kHz. Because the audio signal is riding on a carrier, it is not subject to parasitic elements of the transformer that would distort the audio signal. Unlike the conventional audio-output transformer, this impedance transformation operates on both the ac and dc components of the signal.
In the transformer-coupled amplifier, the turns ratio of the output transformer determines the impedance matching between the output tube(s) and the speaker. There are practical limits to how large this ratio can be made because of the parasitic elements of the windings, and it is difficult to make an output transformer with more than a 25:1 ratio.
With the ZOTL technology, the impedance matching is determined by the effective turns
ratio of the RF converter transformers. Without the parasitics to affect the audio, these
RF transformers can have much higher effective ratios, opening the door to using various
tubes under unusual operating conditions that cannot be implemented with output transformers.
In the microZOTL, the effective (plate to plate) turns ratio is 168 to 1, making it possible to
use a tube for output that is normally used for input or intermediate gain stages. The 6SN7 is respected for its linearity, but prospects for making a high-fidelity output transformer for this tube are dim indeed. With the high effective turns ratio in microZOTL, the 6SN7 works well, and a 2-ohm output impedance is achieved without using negative feedback."
Now im not just a headphone guy. My main system is the classic Apogee Divas with Krell reference HA100
amps, silver Audioquest wiring, etc etc. stuff that was ranked top of the heap in Stereophile years ago
and still stands up as realistic, musical and pure joy to listen to. The MIcrozotl2 adds a headphone
capability to myl listening options that is every bit as great as the main system capabilities with the right phones!
Since the new Zotl2 has burned in i choose headphone listening through it most of the time over systems
in my house costing way way more investment!
Times have changed and evolved of course. My main system was designed for vinyl, and vinyl is the main
source for me on it. my headphone test bench is designed for digital input, and i stream TIDAL CD files,
stored ALARC files and such. i havent gotten into high rez downloads, but i may later on with caveats.
My reference dac is a MOJO AUDIO NOS superdac designed by Benjamin Zweikel which has the most
natural digital sound i have ever heard, rivaling vinyl output, a 2500$ design (although i bought his prototype in
a heartbeat after hearing it I also use the new Denon DA dac with its breakthrough processing circuity
and Monsoon Audio Dacs.
My headphone collection ranges from Shure 1540s though Sennheiser 650s, woodie Audio Tecnica
W1000s full size phones, and the new HIfiman 400is, as well as about twenty other phones.
I did not test this new amp on iems yet and will leave that to another story in the future.
BOTTOM LINE: the new MicroZotl is so good (really really really) that i have found myself
marooned at my headphone test bench not wanting to get up for hours and hours, lost in the music
hearing audio nirvana. Caveats: its all very source dependent, you hear what comes down the
pipe, and much streamed stuff sounds thin and annoying. But with Tidal, most blues recordings
sound LIVE through the Microzotl 2, electro trance percussion stuff sounds like im in the middle
of one of my drum circles, and the audio realism is uncanny. this is all through the NOS Mojo Audio
Dac. with cheaper electronics, ie. ipad digital out to Denon DA the sound is still very very good,
and worth writing home about. but feed the MicroZotl state of the art top of the line sources
and it says YES SIR HAPPY TO PLEASE YOU and it responds like no other headphone amp
i have ever heard with breathtaking MUSICALITY. Here are the technical specs for the Zotl2:
Specifications (Typical Performance Values) • Sensitivity: 0.6V RMS for full output
• Output impedance (measured at 0.5A, 60 Hz): 2 ohms
• Input impedance: 50k
• 100V / 120V / 240V operation: Auto-switching
• Hum and noise: minimum 60μV RMS or 90dB below full output (20Hz-20kHz)
• Carrier: -50dB (250kHz)
• Power consumption from ac power source: 33W
• Power output with 4-ohm load: 1W, 1% THD
• Power output with 14-ohm load: 0.5W, 1% THD
• Channel separation (4-ohm loads): 46dB, 100Hz-10kHz
• Channel separation (14-ohm loads): 54 dB, 100Hz-10kHz
• Frequency response (4-ohm load): +0, -1dB 10Hz-20kHz, full power
• Frequency response (14-ohm load): +0, -1dB 5Hz-50kHz, full power
• Amplifier class: Push-pull Class A, no feedback
• Voltage gain (4-ohm load): 10.3dB
• Voltage gain (14-ohm load): 12.4dB
• Finish: Aluminum case with lexan cover
• Tube complement: two 12AT7s and two 6SN7s
Limited One-Year Warranty*
I just returned from producing my own music festival at my ranch, 3SidedWhole, in the desert outside of
Albuquerque and Santa Fe New Mexico. We built a professional stage, had a major sound system and
an experienced sound guy running and tuning the sound. We had flamenco/latin music, Reggae,experimental guitar
loops, Grateful Dead like jammin bands, and EDM for two nights. I sat about ten feet from the stage when
i wasnt up and moving with the music and it was glorious. The sound quality was pristine and live music
was wonderful! BUT…when i returned home and turned my headphone desk system with the Zotl2
running Tidal files i was transported to a higher level musically. Which is more real? depends…
but it was certainly more easy to sit my desk then the massive effort it took to organize and
produce a major live music festival with 16 speakers, yards of wiring and ten people involved in the
sound production. Live music is wonderful, AND it is a major accomplishiment to be able to have
the same or better musical excitement sitting at my desk listening through the Zotl2!
Some mp3 files jump out through it too. Beatles tunes from the album ONE popped out through it
to where i heard harmonies never experienced before. Chanting from new live recordings of
Kirtans from Jaya Lacksmi and Ananda made my head spin in sacred space. Blues were a special
treat. I just returned from a reference level Steve Earle concert a few days ago, and playing his
new great album Terrapin through the MicroXZotl and Tidal chain was like deja vu…..with the
lyrics somewhat clearer in fact.
Bottom Line 2: this amplifier is worth whatever David Berning and Mark Schneider want to charge for it.
at a but more than 1K$ it is a sonic miracle. its well built, adaptable to being a preamp or speaker amp
and a beautiful piece of audio art. and engineering. I used the original MicroZotl to drive
my Zu Audio Soul Superfly crossover less super speakers, and it it fine. this one will do better.
It blows away my solid state PS Audio reference headphone amp, shreds the sound of
Steve McCormack custom made headphone amp, trancends the old Krell headphone amp i used to
have and makes fe feel i reached the promised auido land. Some say that we headphone
fantatics at head-fi are on a quest for the holy grail. Well, you may now have your own holy grail of sound!
I have found it with the MicroZotl at the end of my aound chain through NOS Mojo Audio Dac,
and great ATH headphones or Sennheiser 650s. The Denon Music Maniac 600s
sing like they have been released from prison, with massive bass and lyrical mids.
The 400is, a planar electromagnetic
low impedence design, sound very flat and revealing, suitable for use in mastering. They also have a
clarity of detail and texture that is unrivaled by any other phone i own. I had the more expensive 560’s
on test tour, and the 400is, IMHO, blow them away. On the MicroZotl the 400is sing with
transparency and kindness to your ears at any volume.
The amp reveals the strengths of each of the
headphones used, which vary from design to design but each has its own muscical nirvana.My favorites
for listening so far on the Zotl are the AudioTechnica W1000s for lush musical bliss. It seems headphones
with a higher traditional resistance sound the best. The Denons, 400is, etc are designed for portable
systems with less power. While the MicroZotl handles them fine, it just powers the 650s and Audio Technica
with brute strength AND finesse and maximizes their sound quality.
You can use this amp in your sound experiments to reveal which components in your sound chain
need upgrading, it is scientific tool of the highest order in headphone research and discovery for
the afficiando or the developer. But Ive reached a rare point of satisfaction.When I hear on the headphones
what i heard live at live concerts or on the Apogee Divas, its more than good enough. Its nirvana.
The music is released and speaks for itself, the equipment disappears, and i stop listening to the gear
and dance in my seat and hear the emotional communication of the musicians. and isnt what that
what iits all about???
The preamp outputs work wondefully. Feeding my powered Fostex mini near field monitors on my
headphone desk (which also has a small sub in the system) the Zotl2 rocks the whole room with
clarity and power. A grammy award winning musician/producer friend of mine recently dropped by while i
was playing the near field monitors instead of the headphones and he smiled and said WOW three
times! Visitors who come in while im listening to phones through the Zotl2 are occasionally
abducted into a listening experience. Usually they have a hard time taking off the phones and
returning to the their visit or going back to work. Their eyes roll back in their head and they
start moving in place. i have to grab the phones back from them or they would keep listening
for hours. Yes, its that good!see Urbanhifi.com and lineartubeaudio.com for pictures of the Zotl2 and more information on its availabilty, choice of colors of the faceplate and more details.
THank you David Berning and Mark Schneider for unwrapping the fabric of sound to reveal
that musical triuth can be found at the end of the headphone path. I am truly awed.
If you are on a headphone quest that demands transparency of sound, power, dynamics and TOTL
performance of all the gear in your headphone chain you owe it to yourself to audition the Zotl2.
Its a landmark achievement in sound quality and performance that belies its price point. Its beautifully made
reliable and flexibe. Its use as a preamp is stunning. It could become your new best audio friend!
WARNING: despite my usual gonzo style of reviewing audio products, my comments above are NOT an exaggeration of how good this headphone amplifier/preamp is. This is new sonic territory. Hear it for yourself to find out what your headphones, and dacs are capable of and what is really in your music!!