This review page is supported in part by the sponsor

Transcription

6moons audio reviews: Tom Evans Audio Design Linear A
This review page is supported in part by the sponsor whose ad is displayed above
Reviewer: Jeff Day
Vinyl: Garrard 301 with Cain & Cain maple & walnut plinth, Denon 103 phono cartridge, Origin Live Silver
tonearm [on loan from Origin Live for the Garrard Project], SME 3012 vintage tonearm [on loan from Jonathan
Halpern of Tone Imports], Pete Riggle Audio VTAF (Vertical Tracking Angle on the Fly), Auditorium 23 moving coil
step-up transformer [on loan from Jonathan Halpern of Tone Imports], Tom Evans Audio Design Groove Plus phono
stage [in for review], Fi Yph phono stage, 47Laboratory Shigaraki phono stage [in for review], 47 Laboratory 4723
MC Bee phono cartridge [in for review], Tom Miccolis adjustable MC step-up transformer [in for review]
FM source: Vintage early 1960s Scott 370 FM vacuum tube tuner supported by Yamamoto ebony audio bases from
Venus HiFi, Magnum Dynalab ST-2 vertical omnidirectional FM antenna
Digital sources: Meridian 508.20 CD player used as a transport with the Audio Logic 2400 vacuum tube DAC
crunching numbers
Preamplifiers: Tom Evans Audio Design Vibe, Tom Evans Audio Design Vibe Series 7 with Pulse power supply [in
for review]
Integrated amplifiers: Almarro A205A EL84 SEP; Sonic Impact Class T
Amplifiers: Fi 2A3 single-ended triode monoblocks; Tom Evans Audio Design Linear A power amplifier [in for
review]
Speakers: Avantgarde Duo 2.0, Omega Super 3 & matching Skylan Stands
Cables: 47 Laboratory OTA cable kit [in for review]; Nirvana S-X interconnects between DAC and preamplifier,
Nirvana S-L interconnects between preamplifier and amplifiers, Nirvana S-L speaker cables between amplifiers and
speakers; a custom Nirvana wiring harness to connect the Duos midrange and tweeter horns and woofer module,
Nirvana Transmission Digital Interface [on loan]; Cardas Neutral Reference digital cable; Auditorium 23 speaker
cable [on loan from Jonathan Halpern of Tone Imports]
Stands: Atlantis Video Reference equipment rack, Billy Bags 2-shelf rack
Power line conditioning: none
Room size: 20' L x 17' W x 24' H
Review component retail: $8,500
http://www.6moons.com/audioreviews/tomevans/lineara.html (1 of 5)24-08-2006 13:55:56
The Innovators
I particularly enjoy learning and then writing about innovative audio designers who are passionate about music and bring
to our hobby new and invigorating design ideas that push the envelope of the audio arts by creating audio devices that
both sound great and play music extremely well.
Consider German audio innovator & craftsman Keith Aschenbrenner of Auditorium 23. His research into musical
realism during the early history of the single-ended triode (SET) movement in France and Germany resulted in his
introducing fellow German HiFi and music lovers to the musically irresistible combination of vinyl playback, SET
amplification and high-sensitivity loudspeakers. Keith's name has become synonymous with the brilliant Platine Verdier
turntables, the magnificent & historic Siemens Klangfilm loudspeakers, the Shindo Laboratories electronics as well as his
own innovative designs of loudspeakers, step-up transformers for vinyl playback and loudspeaker cables. And let me tell
you this: Keith isn't done yet. You can expect to hear more about Keith's works of art here at 6moons in the future. His
lifetime of contributions to our hobby has deservedly bestowed upon him the status of audio cultural icon. His admirers
call him the Tube Apostle of Germany for his trials, tribulations and ultimate success in bringing musical realism in HiFi to
the music lovers of Germany.
Then there is American audio artist/craftsman Don Garber and his now legendary 30, Watts Street store Fi that was once
upon a time in Soho/Manhattan. It would become the spark that started a fire that would burn through the American audio
landscape in the form of a single-ended triode amplifier revolution by offering the first American-made S.E.T. designs of
builders such as Noriyasu Komuro, JC Morrison, Gordon Rankin and Herb Reichert. Don's own unique & innovative ideas
about what sounded good & played music well manifested in his Fi creations such as the Fi 2A3 mono amplifiers and the
Yph phono stage that became legendary in the American audio underground and which I've had the privilege of writing
about for our readership.
Also consider Japanese audio genius Junji Kimura of 47 Laboratory whose innovative amplification designs utilizing
simple & short circuits based on operational amplifiers (op-amps for short) started a whole new audio movement. They
captured enthusiasts' imaginations with simplicity, reliability, superb sound and remarkable music-playing ability. JunjiSan's designs are a milestone in audio design that is as important as the single-ended triode revolution. Junji is an
original audio artist/innovator with op-amps and responsible for the emerging audio minimalist movement that employs his
principles of simplicity and short signal paths in amplifier designs using op-amps for output devices.
A New Star Rising
There's another innovator who has recently emerged to become recognized for his unique and innovative contributions:
Englishman Tom Evans. At this very moment, I have in my home the full complement of Tom's top of the line Tom Evans
Audio Design equipment: The Groove Plus phono stage; the Vibe preamplifier with optional Pulse power supply; and the
Linear A power amplifier, the subject of this review. Each one of these products is unique in concept & design compared
to anything else I am aware of. These Tom Evans designs are the real deal. They are true originals.
Not only that, when used in combination to drive my
Avantgarde Duos, they represent the most startling
advancement in the reproduction of music that I have
ever experienced in my home. When such a big
improvement occurs, it begs the question of whether this
is just a case of synergy between the components in my
reviewing system (plus a healthy dose of matching up
with my personal musical & HiFi tastes), or whether this
dramatic difference is some sort of baseline advancement
in the state-of-art. While I suspect the latter, I suppose
that ultimate judgment is something that only can be
decided over time by peer review consensus and in a
variety of system contexts - but consider me unduly
impressed.
Importantly, the change wrought by the suite of Tom Evans equipment is not merely an advancement in sound quality -though it is surely that -- but it also represents the most significant advancement in the reproduction of musical realism
that I have encountered short of sitting in with a band. Or in the words of my friend -- TAS reviewer & fellow moonie
Stephæn Harrell [system below with full complement of TEAD gear] -- after hearing the full suite of Tom Evans equipment
in his own system: "This isn't just HiFi; this is stupe-Fi-ing!" As we both were in our respective systems, you'll most likely
be stunned too when you hear the whole Tom Evans stack of gear playing the tunes.
I wish I could tell you that Tom's top-of-the-line equipment is affordably priced to be accessible to the audio everyman who
wants to employ the sensible & commendable concept of realsizing to the HiFi hobby - but it's not. The combination of
Groove Plus phono stage ($7000), Vibe Preamplifier ($4600), Pulse power supply ($4000) and Linear A amplifier ($8500)
is expensive. Unlike many expensive audio products, the Tom Evans gear is so good that I believe it to actually be worth
its asking price - and then some. Tom Evans Audio Design equipment is not yet particularly well known in the USA but if
what I'm experiencing is any indication, that's about to change, due to the efforts of new US importer Ed Sheftel.
Musician Ed Sheftel & Audio Omniscience
Before I segue into the Tom Evans story, let me take a moment to tell you about Ed Sheftel, Tom's US distributor. Ed is a
Northwestern University & Yale educated musician with a long and distinguished career as a professional musician. Ed is
a trumpet player with the distinction of being befriended & mentored as a youngster by none other than Louis Armstrong.
As Ed grew in years and stature as a musician, he and his Ed Sheftel Quartet were voted winners in the prestigious Notre
Dame Collegiate Jazz Festival for the "best small group" and "best trumpet" categories while in his senior year at
Northwestern University, he was praised by such notable judges as Quincy Jones and Billy Taylor. Ed's successes led
him to Yale University where he graduated with a Masters in music at which time he moved to Los Angeles. There Ed
landed the lead trumpet chair in the Los Angeles production of the controversial and wildly popular rock musical Hair,
which set records at the time as the longest running musical in Los Angeles history. Ed went on to perform in the equally
popular rock operas Tommy and Jesus Christ Superstar. Ed has played trumpet as a studio musician for television,
movies, recordings and musical theatrical gigs in Los Angeles for now over 25 years.
Ed is also that rare world-class musician
who became interested in HiFi. When Ed
heard the Tom Evans HiFi gear, he thought
it portrayed music in the most realistic way
he had ever encountered and in a way that
he thought no other equipment could match.
"Once I heard the realism of Tom's products
and experienced the excitement and passion
they were capable of, that was it! I was
supremely hooked!" Ed wanted to become
the US distributor after that first listen and
the rest is history. When he took over, he
decided to lower all US retail pricing by 10 to
14% while all the European companies were
raising their US prices by at least 20% to
compensate for the decreasing value of the
dollar in the world markets. In spite of this
ongoing exchange rate slide, Ed did
everything he could to offer Tom's designs to
the US market at the lowest possible price.
And while TEAD gear is still not inexpensive,
Ed opined that "the idea was to go contrary
to the High End flow and make these superb
audio products as affordable as possible." I
don't know about you but I like that attitude!
The Tom Evans Story
I've had a little trouble trying to figure out how to best tell the Tom Evans story simply because there is so much to tell. I'm
going to have to break it into several articles. I want to tell you about how Tom got started in audio; what his design
convictions and innovations are; describe the components in his product lines; do thorough reviews of each of the
components I have in for review; and then comment about the synergy of using these components together in my
personal system. That's a lot of ground to cover. For today, I'm going to handle a little introductory background on how
Tom got started in audio; some of his design philosophy; and finally review his new Linear A amplifier. In the next article,
I'll delve further into Tom's design innovations and philosophy, provide an overview of his present product line and review
the Vibe Series 7 preamplifier with the optional Pulse power supply. Finally, I'll wrap up with a third article that will review
the Groove Plus phono stage and discuss the rather remarkable synergy when using all these pieces together with my
Avantgarde Duos.
The Youthful Tom
Like many of us, Tom Evans got interested in music as a youngster by
being exposed to music in his parents' home. In Tom's case, that was
classical music but kids being kids, he soon discovered the popular
music of his time and place. Tom especially liked the space rock group
Hawkwind formed in 1969, which later went on to international fame
with albums like Hawkwind, In Search of Space and Doremi Fasol
Latido. These days, Tom enjoys listening to the music of the late Frank
Zappa, the 1960s psychedelic band Electric Prunes, blues-rockers Led
Zeppelin and Robert Plant's Mighty Rearranger.
Tom first became interested in HiFi at eleven when he began to wonder
how audio equipment created the illusion of live music. His first HiFi rig
consisted of an Acoustic Research XAU turntable, an NAD integrated
amplifier and Acoustic Research AR18 loudspeakers. Tom didn't care
for the sound of the NAD but since it had preamp outputs, he was able
to use a Leak Stereo 20 valve amplifier for a much more musically
satisfying combination. As Tom's interest in electronics grew in his late
teens, he developed a close relationship with disabled design engineer
John White who mentored him in the fine art of audio design. Tom
credits this relationship as forming the foundation for his present design
acumen. He continually quizzed John about the what, where, why and
how of everything to do with audio design and electronic equipment in
general and in the process discovered an important fact: "I'd learned a
strange thing about how little things change things in a big way."
http://www.6moons.com/audioreviews/tomevans/lineara_2.html (1 of 5)24-08-2006 13:54:52
The Education of an Audio Designer
Tom attended college and studied psychology but realized he was "more interested in learning how the ear and brain
worked in response to music" than he was in studying regular psychology. Tom's instructors nurtured his interests with
books on ear-brain phenomena but their student finally concluded that his interests did not lie with psychology so he
returned to his first love - working with electronics. Like a lot talented young scientists & engineers, Tom lent his
electronics skills to the defense community where he worked until the mid '80s. However, he never did forget his love of
audio electronics and music and eventually left defense work to pursue audio. The defense work turned out to be time
well spent. Hee was able to obtain permission for using some of the hi-tech government-developed parts in his design
work that was not available to other designers in the audio community.
Starting his design career in the mid '80s, Evans
developed an analog error correction circuit whose design
principles incorporated 6-layer printed circuit boards to
optimize the circuit used in the Finestra preamplifier Tom
designed for EC Audio. The Finestra is still recognized by
the audio underground as an excellent budget preamplifier
and phono stage. After that first foray into the world of
professional audio design, Tom founded -- you guessed it
-- Audio Design in 1989 and moved to the Welsh Valleys
where he designed the highly regarded Iso phono stage for
J.A. Michell Engineering in London. In 1992-3, Michell
Engineering again retained Tom's design skills for their
Argo preamplifier and Alecto power amplifiers [right].
In 1995, Tom formed Acoustic Precision with Patrick
Handscombe and together, they designed the FR1
loudspeaker and Eikos CD player. The plain looking and
terrific sounding $3000 Eikos was based on the humble
$650 Pioneer PD-904 CD player but Tom hot-rodded it to
an extraordinary degree with 10 of his first iterations of the
proprietary Lithos regulators, Elna Cerafine & Nichicon
Muse capacitors, a high performance output circuit and
Tom's favorite version of the Trichord clock (a highprecision oscillator module that replaced the player's stock
unit).
It was during the Eikos CD player project that Tom first started development of the Lithos range of regulators, an event
that would dramatically alter the performance envelope of his designs. Tom believed that the ultimate performance of his
designs was let down by the voltage regulators commercially available at the time. The best of them suffered voltage
noise equivalent to the output of a moving coil cartridge! Think about that for a moment: If you want to uncover all of the
information contained in very small audio signals, you need a big audio signal and vanishingly low noise to get the most
out of your music. If noise and signal are distributed evenly, a substantial amount of raw data is irretrievably lost. The very
slow transient response and recovery time of these noisy regulators further compounded the problem of signal
degradation. In response to the regulator problem, Tom began to develop his own high-performance high-speed
regulators. Dubbed Lithos, they would eventually provide the level of performance needed to begin his assault on the
state-of-art in audio amplification.
When all was said and done, Tom had developed a custom high performance regulator that consisted of a small printed
circuit board packed with surface mount devices (SMDs) that was a staggering 1000 times quieter, 53 times faster and
100,000 times more accurate than the best commercially available regulators used for audio applications. These Lithos
regulators provided huge advancements in speed and resolution that made for a much better sounding, more detailed and
life-like musical experience. That first Lithos D was a fixed 5V regulator.
Tom's work caught the attention of Pioneer GB who in 1995 signed him to a 5-year contract to develop a hot-rodded
budget system for the UK market. Evans designed the Pioneer Precision range of products that included a CD player,
tuner, integrated amp and cassette deck. Tom comments that the Precision designs had greatly enhanced performance.
"To this day, I have a lot of respect for Pioneer, their products and dedicated staff for their commitment to offer the budget
HiFi market place high-performance designs."
In 1998, one of Tom's UK dealers, Audio T in Reading, pestered him to design
an ultimate performance phono preamplifier. Tom took up the challenge and
developed the design now known as Groove. The first Groove contained Tom's
original Lithos A regulator with adjustable +/- voltage from the Eikos output
stage, which in 1999 would be fitted to the early Microgroove Plus phono
preamplifier. The Microgroove & Microgroove Plus phonostages were developed
as high-performance budget wonders to introduce Lithos hot-rod performance to
audio everymen.
In 2001, Tom continued development of the Lithos technology and produced versions 3, 4, and 5, also made available for
third-party OEM use. In mid-2001, Tom released the Vibe linestage, which received much critical acclaim from owners
and the HiFi press. In January of 2003, Tom released the Lithos 7 to replace the Lithos A regulator in the Groove &
Microgroove Plus phonostages and the Vibe preamplifier. Also in January of 2003, Tom debuted the Lithos 6, which he
refers to as "the big one". The Lithos 6 circuit is used in the Pulse power supply to "greatly enhance the performance of
the Vibe Lithos 7 preamplifiers." Later in the same year, Tom combined the Pulse power supply with the Groove phono
stage to form the Groove Plus with similar increases in performance. In October of 2003, Tom moved into larger premises
to satisfy the increasing demand for his products and to continue his design work and search for ultimate performance
from home audio electronics.
In January of 2004, Tom
started work on the singleended Class A Linear A 25wpc
stereo power amplifier with
Peter Chappell, an industrial
transformer designer who also
collaborates with Art Audio.
Tom finished the prototype of
the Linear A in May and sent
the first production model to
the Heathrow HiFi Show in
September. Demand for the
Linear A has kept it in weekly
production ever since. In April
of 2005, the Class A Linear B
55-watt fully differential
monoblock version -- another
combined effort by Tom Evans
and Peter Chappell -- was
finished and first units began to
ship to dealers and distributors
worldwide.
These days, Tom spends quite a lot of his time doing audio design for his company Tom Evans Audio Design, often
listening to music in his Welsh factory listening room until two or three in the morning. Wales is fittingly known as 'The
Land of Song'. Evans makes sure he gets a little time to unwind, down at his favorite pub over a few beers with his buddy
Ned who happens to be the lead guitarist for the Van Morrison Band.
The Linear A Power Amplifier
Tom quips that the Linear A has been "a lifetime in the making" and represents the best of what he has learned over the
years. You might even say that the Linear A has been two lifetimes in the making as it is the collaborative result of Tom
and Peter Chappell. "Take Peter and I who are both industrial design engineers with over 20 years of design experience
each. Mine is in the electronics industry, Peter's in the transformer sector. Both of us have worked for ministry of defense
suppliers in the UK. Put that experience together with our common interest in music and it's a given that we'd start
tinkering with our HiFi systems. We're of differing views on what's best from an engineering perspective but have agreed
to bow to each other in our respective areas of expertise and pool our knowledge for the best possible results."
The Linear A is an ultra-wide bandwidth stereo amplifier with a claimed flat response from 12Hz to 90KHz and
"vanishingly low levels of distortion". The Linear A is rated at 25.2wpc operating Class A, with output noise 150dB down at
700 microvolts! Note the distinction between microvolts (one millionth of a volt) and the millivolts rating (one thousandth of
a volt) of most amps. Microvolts are a thousand times less. Output impedance is 0.5 ohms, input sensitivity 0.7V.
The Name
Given the Linear A's
measurements, you'd
be forgiven for thinking
that its name is
derived from its
linearity over such an
extended bandwidth
and Class A operation.
The Linear A did not
receive its name for
that reason, however.
Its namesake is really
the Linear A language
of Minoan antiquity.
The Minoan civilization
existed circa 2000 to
1200 BCE and was
advanced artistically,
intellectually and in
their architectural
infrastructure. The
Minoans were known,
for example, for their stunning fresco artwork, their intelligent use of indoor plumbing and their development of the first
written language of Europe - Linear A.
Their original written language was based on hieroglyphics that communicated ideas as visual pictures of objects
engraved into clay, being more like what we might think of as story-telling artwork (early comic strips) rather than the
abstract languages of today. To convey more information and better articulate their ideas, the Minoans' hieroglyphic
writing system evolved over time to have more of a linear flow while introducing numbers to expand the analytical and
communicative ability of their language: Pictures, numbers, meanings, emotions. The connection is clear.
The Composite 10 Design
The Linear A amplifier is full of creative & innovative ideas that you might not fully appreciate from a quick perusal of its
specifications or a simple visual inspection. One of the more interesting aspects that ought to intrigue SET devotes is that
the Linear A is a single-ended, Class A, ultralinear device. Four single-ended EL84s per side are linked in parallel to
create a composite tube with characteristics that are "almost identical to the legendary Japanese 10 tube" according to
Evans. This composite approach to tube circuits reminds me of the Conrad-Johnson ART preamplifier and its
descendants but to my knowledge, nothing like it has yet been attempted with a power amplifier in quite this way. The
claim is that the Linear A amplifier measures as an almost perfect single-ended triode while delivering higher power
output and much more extended frequency extremes - along with the musical magic normally associated with SETS. [The
series-connected super-ultralinear KT88s of Audiopax too endeavor to 'clone' the perfect triode, in their instance a
combination of 2A3/300B THD behavior with the power output of a 211 or 845. - Ed.]
Tom explained that "the most complicated design problem we had was finding a tube that first and most importantly
sounded great, ideally was a triode, didn't run off lethal voltages and could be driven by an op-amp to produce over 20
watts of output power!" As many 6moons toob heads will recognize, that combination of traits doesn't exist in a single
tube. "We knew that we could, from both the op-amp & output transformer point of view, assemble a composite valve by
paralleling two or more tubes. What we needed was a tube that was both a pentode and a triode, had high gain and was
easy to drive and sounded wonderful .. oh blast deary me!"
What they chose was the much used and well-liked EL84 tube. "The data sheet shows it has an output power of 6 watts
but boy, it's also got 10% distortion! More importantly, it only requires 5 volts RMS to achieve this, well within the
capabilities of an op-amp. By using four EL84s, we can get 24 watts. If we use the suppressor grid (the other input
connection) and configure it in ultralinear, we get a small increase in power and a huge drop in distortion due to the more
linear tube characteristics giving us a pseudo triode."
The EL84 hasn't been on most peope's screen as one of the great tubes because it has been primarily used in entry-level
implementations because of its low cost. If you're lucky enough to have listened to the budget Almarro A205A SEP EL84
integrated amplifier, you know that the EL84 is one great tube. But what if the EL84 were implemented with the most
cutting-edge design possible? Then what would happen?
"Those of you versed in triode lore will blanch at our choice. However, one of the best-sounding triodes is the 10 tube and
its derivatives. Their problem is low power output, low gain, their input capacitance and highish anode impedance. I hear
you say that the 10's high anode impedance means it has high output impedance. Actually, its high anode impedance
means it's easier to drive and kinder on the output transformer. With any given transformer, change the tube it sees and it
changes the sound it produces. In one test, we compared a 10 with a 2A3, using the same single-ended output
transformer with a resonant frequency at 86kHz, its core gap adjusted for best inductance. The 2A3 achieved -1dB figures
of 18Hz to 12 kHz at 1-watt output. The 10 measured -1dB at 28 Hz to 20 kHz for the same output! Using our composite
EL84 as a "super 10 tube", we have effectively produced a triode from the transformer's perspective and one whose
electrical parameters nearly match a 10!"
Tom designed the Linear A to operate in Class A because he feels it offers the best sound quality, is on all the time so it
doesn't pulse the mains and doesn't stress the amplifier's parts like class B or D designs. Class A also works better with
differing power level demands and speaker impedances, an important consideration as you'll learn in a moment. Tom and
Peter also wanted a design that would produce 20 watts or more make it compatible with more speaker designs than
most SETs and would incorporate Tom's and Peter's favored topologies of op-amps with transformer-coupled valves.
Op-amp Input Drivers
If it wasn't innovative enough to use a composite single-ended tube approach, Tom and Peter went a step further to do
something that to the best of my knowledge has never been done before: They use op-amp technology to drive their
composite single-ended tube. Tom giggled, anticipating my reaction. "Look, they're using those new-fangled op-amps with
valves. Oh dear! Go back to the drawing board and better luck next time, boys! But hang on a minute. Op-amps and
valves used by themselves work well as you know. We have found through our research that using them together raises
the combination to a new level of performance that they can't match alone. Op-amp technology offers the strengths of low
distortion, compact topology, high gain and wide bandwidth but can't do large output voltage swings. On the other hand,
tube technology offers large output voltage swings and some tubes offer high gain - but as for the rest, they are
challenged. Combine the two devices and you get the best characteristics of both - if you do it right."
A major design goal for the Linear A was to react to the smallest changes of input voltage to maximize reproduction of the
subtlest details. "This is the reason I have always preferred op-amps. The tube and transformer act as one. The tube
amplifies the voltage and the transformer changes this voltage into a current. The EL84 has a current gain of 11 milliamps
per volt of input and a voltage gain of 32. Putting four in parallel, we get 44 milliamps per volt of input and the output
transformer converts the voltage gain of 32 into a current gain. Hence, the composite output stage converts 1 volt from
the op-amp driver stage to 1.72 amps for the loudspeaker. This gives 20 watts at 4 ohms and only requires the op-amp to
produce 3.88 volts. Couple this to the global feedback being enclosed in the feedback of the input op-amp and this makes
the input circuit a virtual high current gain op-amp."
The Power Supplies
Another innovative aspect of the Linear A is the use of two separate power supplies to power the input and output circuits.
"The power supply on conventional power amplifiers uses the same HT voltage to drive both the output stage and its
driver stage. Herein we faced a problem. We couldn't run our op-amps and tubes from the same voltage. Therefore we
built two separate power supply rails. One runs the Lithos board for the op-amp driver stage, the other provides a near
ripple-free supply to run the tubes. Rather than try and come up with a fancy regulator circuit to reduce the pulsing of the
mains from overstressed power supply diodes, we went for dual-mono 3-stage filtering using choke smoothing (two per
channel) to accomplish a >150dB ripple rejection from a 60Hz supply. This approach also has the benefit of eliminating
common mode distortion. This occurs because although you would assume that the output voltage of the device is
measured with reference to ground, the amplifier also produces signal between output and HT rail(s), the effect being that
the signal appears again in the next amplification stage via the HT to add distortion. In the Linear A, we've overcome this
ill and avoided hooking up the output devices to a common HT rail. We split the HT in half after the first choke filter, into a
further capacitor/choke/capacitor filter for each channel. The ultra low noise/distortion driver stage and active bias circuit
are powered by a Lithos 7 power supply variant."
The Amplifier/Speaker Interface
Tom believes that today's HiFi design culture has been looking at things "the wrong way 'round. First, HiFi requires a
source such as vinyl, CD, radio or tape. Then we need a whole heap of voltage & current gain to drive a loudspeaker or
two. After the signal leaves the source, the major factor determining a HiFi's ultimate sound quality is the amplifier &
speaker combination being used. Some might say, 'Aha! But don't all amplifiers sound the same? It's the speaker that
sounds different. You know: The boom & tizz, the sibilance & bass, man!'..."
Tom stresses that it's the interaction between amplifier & speaker that determines the sound as a whole. You have to
engineer with that in mind to extend the edge of the art in amplifier design. "There are more permutations of amplifier &
speaker combinations than you can count. To get an optimum match between most amplifiers and speakers, you have
less chance of success than winning the lottery. One of our design goals had to be that the Linear A would work equally
well in all those interaction situations to ensure consistently good sound for all of our customers. Keep in mind that the
laws of physics will apply to anything electrical and mechanical. We're faced with designing for an infinite variable of
customers with different room sizes, aesthetic tastes, budget, differing equipment and the often-overlooked fact of the
frailty of human hearing slowly fading from constant use. The end result is that the same system in different rooms and
with different ears will sound different for better or worse."
Tom uses the following analogy to illuminate loudspeaker/amplifier interactions: "The problem that most speakers pose
for an amplifier is that from an electrical standpoint, they are moving targets with respect to impedance versus frequency.
Imagine you're sitting at a piano. The furthest key to your left plays a 27Hz note, the furthest key to your right a 7000Hz
note. Loudspeakers try to mimic the sound of those two notes from a recording yet each note presents a different
electrical load to the amplifier due to the way loudspeakers are constructed. In the same way, a 40-watt light bulb
presents a different load to the mains than would a 100-watt bulb. Just as one light bulb emits more light, one note is
easier to drive from an amplifier's point of view."
"It's a widely held belief in the audio community that a high damping factor is all that's required to drive any speaker
impedance curve. Actually, the truth is that the damping factor merely stops the speaker from ringing or bouncing like a
spring once the music stops. As has been shown by Gilbert Briggs, founder of Wharfedale, the amplifier output
impedance only needs to be half the speaker's impedance to have this effect. I can hear you laughing and thinking we've
lost our marbles - but how come all amplifier manufacturers quote different power outputs into 4/8/16 ohms when the
magic low output impedance means it allegedly produces the same power irrespective of load? Worse even, transformercoupled tube amplifiers use multiple impedance taps. Look at any loudspeaker. Very few are ruler flat over their frequency
range and most look like the side view of a roller coaster fairground ride. A 32-ohm peak at bass resonance and
crossover point requires double the voltage of an 8-ohm load as does a 16-ohm peak against a nominal 4-ohm load.
Remember that amplifiers clip when supplying higher voltages and that all amplifiers have a falling power output into rising
impedance. As a result, the driver has a frequency response rolloff as the impedance rises.
The rising impedance with frequency, as seen by the amplifier, produces a benign inductive load. However, the
corresponding fall with frequency is capacitive and will cause the amplifier output devices to overheat. Because the Linear
A uses an output transformer and operates in Class A, it is immune to any of those ills usually associated with amplifiers.
Since the valves don't see the loudspeaker (only the transformer), and because they are on all the time, they don't draw
more current at higher power. However, the major advantage of the Linear A is that we have matched the transformer and
composite valve to produce over 20 watts between 5-10 ohms. The speaker output remains the same when its
impedance curve fluctuates anywhere between 5 and 10 ohms. The fall in power above 10 ohms is offset by the improved
output transformer efficiency. Since transformer losses are "current squared x winding resistance", the current
requirement falls off with rising impedance. In sonic terms, it means your loudspeaker presents a less peaky sound output
if you are using a Linear A."
The Chassis
The appearance of the Linear A's chassis has been somewhat controversial among the visitors I've had to my listening
room. As pal Pete put it: "It would probably be considered more attractive had not the toaster oven been invented first." I
was teasing Ed Sheftel about the toaster oven appearance after I had uncrated the amp. Ed quipped back that after I got
a chance to listen to it, its appearance would transform and I would begin to think of it as beautiful. It's true; I finally did get
used to the appearance and didn't think about it any further.
Tom explained that he tried to make the Linear A as unobtrusive as visually possible. While
a Class A amplifier is going to be sizeable, the Linear A matches the industry standard shelf
width. Tom believes most Linear As will spend their lives tucked invisibly out of the way on a
bottom shelf so appearance shouldn't be a big issue. For aesthetic sissies, the Linear A is
offered in a Special Edition (upgraded cosmetics, identical circuit - see left).
However, to focus on appearance is to miss the point completely as I now sheepishly acknowledge. Tom designed the
chassis very deliberately to perform important functions: to keep signal paths short and help isolate the circuitry from
vibration. The transformers are mounted directly below the circuitry to provide the shortest possible signal path. The circuit
boards are raised for decoupling. The chassis is designed to isolate active components by floating them in space on a
centered plane that is mechanically decoupled from the rest of the chassis. "One of my main design goals concerning the
chassis was to reduce the unwanted electromagnetic fields generated by putting a large mains transformer in a metal box.
This can effect the movement of electrons through circuits creating a negative audible effect."
Listening Impressions
Before we cover the results of my listening sessions, let me say a word about cables: The Linear A must be used with
shielded interconnects from the preamplifier. When I tried unshielded interconnects, the Linear A went completely
berserk, screeching like a banshee at the top of its lungs and scaring the living daylights out of me. I found Nirvana S-L
shielded interconnects to work well between the critical preamplifier and amplifier interface. I used unshielded 47 Labs
Cable Kit interconnects for all other duties to excellent effect. Speaker cables were either Keith Aschenbrenner's
Auditorium 23 cables or the 47 Labs Cable Kit cables.
Given that the amplifier is rated at 25 watts per channel, it's the most powerful amplifier I've had on my 103dB sensitive
Avantgarde Duos in a good long time. On the Duos, it sounds like a muscle amp. It brings them alive in ways nothing else
has yet. I suspect that the Linear A's extra power would also work great with excellent less-efficient speakers such as
Wilson Watt-Puppies or Quads, for example.
I listened to vinyl through my idler-wheel drive Garrard 301 Project turntable equipped with a Cain & Cain plinth, the new
$1100 47 Laboratory 4723 MC Bee phono cartridge and the Origin Live Silver tonearm. Phono amplification during the
Linear A listening sessions was either the Tom Evans Groove Plus or the combination of Fi Yph phono stage (I bought it
after the review so yeah, I really like it) and a stunning hand-made moving coil step-up transformer using vintage UTC
microphone transformers by NASA engineer Tom Miccolis. For digital listening, I used my customary Meridian 501.20 &
Audio Logic 2400 valve DAC combination.
Overall Impressions of the
Linear A
After I powered up the Linear A,
I noticed how quiet it was on my
highly sensitive Avantgarde
Duos. Even with my ear inches
away from the drivers, I could
only make out the faintest
amount of amplifier noise. I
listened to a lot of music over
the course of the review, both
digital and vinyl but mostly
vinyl. It's hard to resist the
superior resolution and
musicality of vinyl and becomes
almost mandatory as the
primary medium when
evaluating a cutting-edge
amplifier like the Linear A. I've
been on a buying spree lately of
the excellent Classic Records
remasters and enjoy Neil
Young's Greatest Hits; Graham
Nash's Songs for Beginners;
Crosby, Stills, Nash
& Young's Déjà Vu; Carole King's Tapestry; the Mercury Living Presence remaster of Balalaika Favorites; the Living
Stereo remasters of Clair de Lune, Rachmaninoff Rhapsody on a Theme of Paganini, and the Royal Ballet Gala
Performances; Lou Donaldson's Lou Takes Off; the 45rpm singles cuts of "Autumn Leaves" and Alison's "Uncle" off
Cannonball Adderley's Something Else; and the 20th Anniversary Commemorative 12" single of Bill Henderson's "Live at
the Times".
I also spun a few of my favorite Acoustic Sounds test pressings like Count Basie's Farmers
Market Barbeque, Curtis Counce's You Get More Bounce With Curtis Counce, Doc & Merle
Watson's Pickin' the Blues, Cookin' with the Miles Davis Quintet, Bill Evans Trio Waltz for
Debby, Gene Ammons' Soulful Moods of Gene Ammons, Chet Baker's Chet and the Tony
Bennett & Bill Evans album.
I knew that Tom Evans was a big Rock & Roll fan so one of the first albums was Englishman
Graham Nash's 1971 Songs for Beginners remastered by Classic Records on 200-gram
Quiex vinyl. This is a terrific-sounding rock album of great music by great musicians: Graham
Nash on vocals & acoustic guitar, Rita Coolidge on background vocals, Jerry Garcia on piano
and steel guitar, David Crosby on electric guitar - to name a few.
On the opener "Military Madness', the first thing I noticed was how well the pulsing of the beat
resonated through the music, making me want to tap my foot to keep time. In the wellestablished British tradition, the Linear A gets the beat right, vitally important for bringing
Rock & Roll to life. The dynamic rise and fall of strong and weak beats of the drums gives the
rhythm life and coupled with the bass drive, evokes a strong sense of exhilaration while
listening to the music. The percussion has plenty of startle factor due to the excellent dynamic
abilities of the Linear A. Kick drum gets a big lively feel with a tacit sense of air pulsing around
the drum head. Speaking of air, you can hear the interaction of vocals and instruments with
the air volume of the recording venue in a more tangible manner than I've heard before. The
vocals are natural and the harmonies grand. I couldn't help but reflect on how appropriate the
song's social commentary was for our own time with its message of tolerance, nonviolence,
the value of relationships and helping the poor. You really get a sense of the emotive impact
from the music through the Linear A. It makes the music sonically beautiful, emotionally hardhitting and philosophically thought provoking.
In the song "On Better Days", there is an impressive and startling crack of the drumsticks with
a rim shot off the snare drum. You get a definite sense of the air swooshing out of the hi-hat,
something I've never noticed before on this album prior to the Linear A. On "Wounded
Bird", the acoustic guitar sounds great. You not only get a sense of the individual strings but also of the body of the guitar
and the airspace within it, making the acoustic guitar sound very natural. Even with solo acoustic guitar, you can really
feel the sense of rhythmic flow the Linear A provides.
What did I learn while listening to Songs for Beginners? First off, this Tom Evans amp is a great rocker due to the way it
handles the beat to bring the rhythm alive. You can tell that Tom's been enjoying listening to Rock. There's something
else rockers will appreciate: the Linear A will play louder without your ears shutting down than any amplifier I am familiar
with. At levels where I'd normally be reaching for the volume control, I could listen along with no sense of stress or
discomfort. How the Linear A accomplishes this little feat I have no idea (perhaps ultra-low distortion and absence of
compression?), but it's very apparent and pleasurable. The Linear A is also very detailed and articulate so you get a real
sense of hearing all the detail on a recording. It does not sound etched or analytical at all, making detail recovery and
unraveling of fine nuances even more amazing. Acoustic instruments sound completely natural and organic as do vocals.
The Linear A's fine resolution of micro dynamics combined with its exceptional ability to reveal detail give a very real
sense of texture and feel to the music. Articulation at lower frequencies is phenomenal. I've never heard any other
amplifier in my listening room come close. The Linear A also gives an enormous sense of recorded space that infuses the
listening room with the air of the recording venue. There is a strong display of SET-like magic with well-defined and
illuminated images. The soundstage offers a good separation of images left to right & back to front. Image sizes are life
size and have a lot of presence. It's easy to hear all the different instruments contribute to the musical whole and it's easy
to pick out a particular instrument and follow it through the mix. The way the Linear A handles percussion is phenomenal.
Okay, so the Linear A rocks to beat of the band. But can it play something more complex and less beat-oriented like
classical music? To find out, I pulled out Classic Records' remaster of the Mercury Living Presence Balalaika Favorites
[SR90310] and cued it up on the big Garrard. Right off the bat, I was impressed with the amp's ability to both sound
slightly warm & dark while being able to retrieve more information off a record than any amplifier in my experience – an
intoxicating combination. The level of transparency and detail recovery coupled with the natural tonality of the Linear A
made for a captivating listening session. I could hear every little thing. The individual strings of domras, balalaikas and
goosli were resolved with great vividness and articulation. I also got a realistic sense of the sharpness of attack on the
individual strings and their decay. That I could hear this contribution both for individual strings as well as the strings of an
instrument or orchestra as a whole was really quite remarkable.
The perspective of the Linear A puts you up close to the musicians. With Balalaika, I felt like I was in the first row of the
hall, so immediate and live was the sound. Soundstaging too was superb. In width, the soundstage extended beyond the
outer edges of my speakers while depth wise, I could hear very very deep into the stage. The Linear A even produced the
height dimension of the soundstage very convincingly to render life-sized instruments in a big domed space.
Where the Linear A really excels beyond its peers is in its ability to recreate the sound space around the players and how
that relates to the sense of the hall ambiance itself. You can hear reverberation and decay of the instruments to an
extraordinary degree. Dynamic contrasts are another strength. I could easily track all the dynamic envelopes of individual
instruments and enjoy the dynamics of the softest and loudest sounds simultaneously with nothing lost. None of the fine
details were smeared, covered up or crowded out. Imaging as well was extraordinary. It wasn't simply in the relative
nearfield of the soundstage that instruments were easy to pinpoint. I could readily identify the exact location of an
instrument deep in the soundstage with rather remarkable palpability and focus.
So it's clear that the Linear A is a remarkable sounding amplifier. However, what makes it such a great amplifier is that it
not only sounds better than any amplifier in my experience but also plays music more convincingly. The Linear A reveals
the full drama of every cut on Balalaika by portraying the atmosphere, attitude and feeling of the musical performance. As
good as the sound was, I never once forgot that my focus was on listening to great music. No amplifier in my experience
recreates the feeling of a live performance like the Linear A does. It never failed to draw me into the music.
That's pretty much how it went with every album I played. Whether rock, classical, jazz or bluegrass, the Linear A proved
superior in every respect and by a rather large margin to any other amplifier I have experienced in my system. It excels at
audiophile sonic trickery while never letting it get in the way of the music. It opens a clearer & more detailed window onto
the music than anything in my experience, making everything else sound a little veiled and opaque by comparison. The
wonder of all this is that it can do that while still sounding warm and natural.
Summing up the Linear A
I have to congratulate Tom Evans on what is truly a remarkable achievement in amplifier
design. This chap is one of the true innovators of modern audio and marches to the beat of
his own drum. His Linear A sounds better and plays music better than any SET amplifier in
my experience - by a substantial margin. Coming from an SET devotee like me, I hope you
realize the high level of praise that represents.
The design of his Linear A is much more extraordinary than its plain appearance would
suggest, hiding as it does the composite 10 design with eight EL84s and op-amp drivers.
EL84s are cheap and easy to come by, quite unlike some of the exotic direct-heated triodes. And unlike many single-tube
triode amps, the Linear A is powerful enough to drive medium-efficient real-world loudspeakers.
How about downsides? The looks here aren't likely to incite passion in too many folks and shielded interconnects become
a must. Really, the only major downside of this amplifier is that at $8500, I can't afford one. I thought about loans, selling
one of my guitars, living without any creature comforts, munching on oatmeal and other crazy ideas. I finally came to my
senses but it was a struggle. If you can afford a Linear A and have reasonably sympathetic speakers to match its power, I
cannot imagine you being anything other than deliriously happy.
The Linear A is simply the finest amplifier I have encountered in all my years in audio but that's just the start of this story.
There's a lot more to talk about when it comes to Tom Evans' innovative products. Watch for upcoming reviews of the
Vibe preamplifier with the optional Pulse power supply and the Groove Plus phono stage.
Manufacturer's reply
Tom and I would like to overwhelmingly thank Jeff Day for his deeply researched, thoughtfully constructed and highly
insightful review of the Tom Evans Linear A Stereo Amplifier. Jeff articulately captures Tom's creative goals regarding the
development of the Linear A. This review is a "work of art."
Thanks.
Ed Sheftel, on behalf of Tom Evans Audio Design
PS. Of course, none of this could have been conceived without the gracious approval of Srajan for allowing us to submit
our Linear A, Vibe, Pulse and Groove+ for review. Thanks for your kind consideration on this matter. It is greatly
appreciated.
Manufacturer's website
US distributor's website

This review page is supported in part by the sponsor

Transcription

Similar documents

Step # 13 Open up TMPGEnc 4.0 Express and click on “Start a new

Bus Riders – visit to art collector Tom Böttiger

Rotary Club of Denver West | Golden, Colorado

Summer-Newsletter2014

24 News

Read the show blog

Parasound Halo JC 1 Monaural Amplifier

Article - SpindleTree Gardens

Contents - February 2002

CONTACT: [email protected] WEB: http://www.hm