Volume 19, Issue 98
HP Reports
The VAC Renaissance
One-Forty Triode Amplifier
This is the first in a series of eight reports on
individual components that are the cutting edge of the audio art. Each
of the installments will be written by HP, each will lead off the review
section, and each hereafter (see the Contents page this time) will feature
color photography of the product. The eight reports will be spaced
over the next 18 months, and while the Editor has chosen some of the
components that will be featured, he has not selected all eight as of yet.
The Valve Amplification Company's 130-watt monoblock triode design,
entitled the Renaissance One-Forty, represents the most promising approach
to amplifier design in two decades. It invigorates what is,
perhaps, the oldest amplifier technology, that of the triode, with almost
every new strategy that has been learned in the past 50 years.
Of course, not all triode designs are alike. Many are what is
dubbed "single-ended," wherein (usually) a considerable amount
of the second harmonic, a musically consonant distortion, is generated.
Too much second harmonic, and there will be an "aura" of
overtones sitting apart from the instrument being voiced, an "aura"
that will sound almost phasey in its imaging imprecision. (There are
other effects as well.) Other designs are more or less variations
upon standard pentode technology that do not take full advantage of the
triode's sense of immediacy. Some designs even use feedback, which
itself throws a curtain - scrim may be the better word - over the
soundfield and, all other things being equal, creates a perspective that
becomes more distant as the feedback goes up, and an inherent "character"
or coloration that is pervasive through the frequency spectrum, sometimes
being manifest as a darkening.
Once you've heard a triode amplifier, properly functioning into a good
two-channel stereo system, you'll certain understand why such designs are
suddenly the rage, just as you'll understand their potential for getting
closer to the music. And you'll understand why triodes represent the
beginning of a new era in amplifier design, despite their seemingly
inherent limitations - low power, increased amounts of some very old and
most euphonic distortions, distortions that many of the modern
stereophonic era may never have heard from contemporary amplifier designs.
This is another way of saying that not all triode designs are the same,
and just because something says "triode" doesn't mean that
you'll be getting true "triode" or a device of any great
practicality. There will be, no doubt, a proliferation of triode
amplifiers and amps calling themselves triodes over the next few seasons,
and many of these will be attempts to create a true triode amplifier of
high power and acceptably low distortion products.
The Renaissance One-Forty represents, to my way of thinking, the first of
these once and future amplifiers. Its unique push-pull circuitry,
correctly applied, will cancel excessive second harmonic distortion.
Its capacity for self-biasing will make unequal tube wear no
problemski (a consummation devoutly to be desired). Its freedom from
any feedback will,
with most speakers, allow the ultimate in transparency.*
*[I realize that some do not think that a push-pull triode design is "pure"
triode, but I see no reason why push-pull technology, applied with wisdom
and care, is incompatible with pure triode operation. In the case of
the VAC, designer Kevin Hayes' approach to push-pull is decidedly
unconventional and is an attempt to get around some of its inherent
shortcomings. See his sidebar.]
VAC has been in business since 1988. Its first two products, the
triode PA-45a and 90a amps (which caught HP's attention during the summer
of 1992 and which he found most promising) were sweet, slightly euphonic
(especially in the midbass and upper midrange), and sadly underpowered.
But in terms of their transparency and within their tiny power
range and dynamic contrasts, both were ear-openers, which this writer did
not find very practicable given the current-hungry nature of most today's
speaker system (although Hayes allows both sounded exquisite on the Quad
electrostatic).
It was the Renaissance Seventy/Seventy, VAC's first second-generation
product, that proved to be such a revelation. Here we had a sense,
not that the listener was transposed into the concert hall, but rather
that the concert hall soundspace had been transposed into the home
listening room. The walls of our Music Rooms (3, and later, 2) seem
no longer
to provide the constructions and defining limitations they once did.
There was an immediacy to the sound that was so fresh, and so true
to the perception one has of the music itself, that I, far from being
intimately acquainted with possible triode distortions, at first wondered
if the glories of the Seventy/Seventy were, in part, the result of
distortions, particularly the musically consonant second harmonic. Before
I tell you that I know better now, at least in regard to the operation of
the current generation of VACs, let me say that I finally came to
see a kind of profundity in Daniel van Recklinghausen's
adage, to wit, if a component doesn't measure well, but sounds good, then
you're not measuring the right thing.
Once you think about it, how can it be otherwise? Even the presumed extra
consonance of a second harmonic won't fool the ear forever; it will, to
the contrary, prove more and more fatiguing over time because it
will impose a "sameness" to the sound, no matter what its
source, a sameness that will destroy the sense of "surprise"
(or, as Jon Valin would have it, "jump" in the music). One might
even take the quotation a step further and say that if it doesn't
measure well and sounds like music, then any such measurements aren't
worth much in determining the accuracy or truth of the amplifier's
performance. In writing the parts of the essay on amplifiers and the
sound of music [see Issues 90, 91, 94, and 96], and in two years worth of
listening to some of the best amps then extant (call this HP's pre-triode
era, if you will), I came to believe that it was the basic amplifier that
was the key to a musical sound and that the entire subject needed a
from-the-ground-up rethinking. I also hold the amps-sound-the-same
school responsible for much of the mischief that led to stagnation
in amp design. That mischief, in its mildest form, would have us
believe that amplifiers are the most nearly perfect part of the
reproducing chain, and perhaps less worthy of serious attention.
Hayes, interestingly enough, believes this: "We have to ask
ourselves, as designers, what the equipment really should be doing,
and to do that we have to return to the first principles of design. I
have this sense that a lot of people continue to ask the wrong questions:
"How do I get a piece of electronics that will give me 60 watts of
power, with such and such percentage of distortion, into such and such a
load?" Those are secondary issues. We have to back up and
look at the more fundamental questions: What should this particular device
be doing, or what should this stage be doing, how do we keep each step in
the process operating as purely as possible? You must rethink the
entire process [of amplification] from the very beginning."
At something shy of 70 watts per side, the Seventy/Seventy would often,
with speakers of (what passes for, today) moderate efficiency, go into
clipping. Partly this was because of its exceptionally wide dynamic swings
on musical material, swings that made it difficult to determine in advance
just how much any given program material might force clipping.
Partly, I'd suppose, this was also because the sound was, overall, so low
in the usual kinds of distortion and so musically immediate that one would
want to achieve a realistic sense of concert hall, if not rock stadium,
playback levels. The distortion, at clipping, was also particularly
disturbing. Bright, even a kind of "tearing" sound, as if
the sound were
being, somehow, chopped up and shredded. It also seemed to me that
there was, after a certain dynamic point, a kind of correlation between
level and brightness. And so, it was, with some anticipation, that I
awaited the arrival of the 140 watt monoblocks.
* * *
During the period in which these, the initial evaluations of the
Renaissance One-Forty were done, HP (with the able assistance of his
Hardware Editor, Scott Markwell) made continuous refinements to the main
reference system.
To be specific, we added the Townshend Audio Seismic Sinks, a brilliantly
effective floating platform, the VPI TNT Turntable - first with
Wheaton Triplanar IV Ultimate Arm and the Clearaudio Signature cartridge,
then the top-of-the-line Clearaudio Insider, whose mass requirements
prompted us to switch to the lower mass Graham arm (beginning with
Immedia's RPM-2 turntable and ending up, because of the next change, with
the latest version of the VPI TNT Series III turntable on a Bright Star
Big Rock sand-filled base). As I suggested, this became necessary
when we decided to install the Air Tangent 10B with the Insider for a more
nearly optimal mating of arm, cartridge and table. At the
pre-amplifying stage, we began with the Jadis JP-80MC, switched, for
testing purposes, to Stan Klyne's Model 7PX2.5 phono stage with the Melos
headphone amp acting as the line stage. Toward the end we used the
Audible IIIusions Modulus III, at first separately, and then with its
moving coil stage feeding into the Melos.
Some of our observations on these components will be found in
future editions of HP's Place; more to the point, certain other major
re-configurations of the reference system are yet to come in our
preparation for Issue 100 and a first-ever HP review of an entire system,
whose costs will exceed that of a mansion in many a heartland state.
(The speaker
system, the Genesis One, remains a constant as have the cables from
Transparent Audio. One thing we have learned, or at least I have learned
from these sessions, is that the Genesis is a much more neutral system
than I had at first imagined, thus the concluding part of my essay on it
will appear in Issue 100. We are, at this writing, on the verge of
substituting new cables into the system, as well as one or two new
preamplifiers or formidable advance repute.) Virtually all of the
listening to the VACs was with analogue sources, since they were, alone,
capable of supplying enough information and information
resolution to test the VACs' mettle. We did do a bit of CD
listening which prompted JWC, on hand for one of his rare visits and
an ardent CD promoter, to say, "Well, CD has a way to go, doesn't it?"
From me, no argument on this point. In fact, with this system,
it seemed that CD had even further to go than I thought after last year's
round of listening to digital-to-analogue converters.
With the VACs powering the system, and because of their signal resolving
abilities, we were not only able to hear each and every change occasioned
by the substitution of different components, but to hear them instantly
and in relation to whether they were truthful in the musical sense of
merely "hi-fi" or euphonically intriguing. In other words,
the VACs were less colored and thus more reflective of the truth than most
of the associated components we were using.
This experience certainly reinforced the new maxim that, in audio, every
associated component matters.
* * *
Those who have followed the amplifier essays will know that what I hoped,
in the writing of them, was to further expand this magazine's working
vocabulary for describing events observed during extensive and controlled
listening sessions. We
explored the new boundary or "edge" definition, continuousness,
and the elusive "gestalt" that makes music sound like music,
rather than reproduction through a stereo system and gestalt's Siamese
companion, "presence." We also tried to further illuminate
some working concepts, such as dynamic contrasts, texture or "grain",
character or pervasive colorations.
One aspect of reproduced sound we did not discuss was the trait that the
VACs make most evident - if that is, you listen carefully, and that is the
difference between "space" and "ambience," which are
not the same things. Several things occurred to highlight the
distinction. First off, in listening to the Classic LP series of
resuscitated Living Stereo recordings, we observed that there was a
loss of onstage ambience in the Classics that was clearly audible in the
original LSC series, and that true whether the hall was in Boston or
Chicago. At the same time, the acoustic of the hall itself was
much clearer on the new Classic LPS. Now, if anything, despite the
loss of onstage ambience, there was a decided gain in the replication of
the space on the stage, both in terms of its volume and its depth. Meanwhile,
Jonathan Valin, in reviewing a formidable $40,000 amp, found himself
vastly impressed with that amp's ability to reproduce ambient cues, and
decidedly unimpressed by the flatness of the images within the soundstage,
a failing I attribute to the shrinkage of the space on that stage.
Space and ambience are not the same things. And no amplifier that I
can readily think of will underscore this difference more markedly. With
the VACs, you can hear ambience both on stage and in the hall (if such are
present on the original recording), but you can also get an idea of
space involved, something akin to the volume of the space, but, I think
more than that, because of the dimensionality of both the space and the
images within that space. (If I had to point to a failing of nearly
all transistorized gear, it would be in the recreation of space in this
sense.)
I do not know whether this is the same thing as the VACs other first
effect, that of bringing the music, ambience, space, and dimensionality at
once, into the listening room to seemingly obliterate much of the
listening room's effect on the sound. But
once you put the VAC into the system, suddenly the music seems to be
there with you, not you transported to some miniature and distant "there",
through a glass darkly. What I do know is that the VAC does this
without sounding "forward" in the comin'-at-ya sense,
though it can with the right (or wrong) piece of equipment, e.g., the
Modulus III which jumps outward at you. Put a Klyne into the system,
and suddenly the sound becomes quite reserved, pure, and highly refined,
even delicate, in the top octave, but minus wide dynamics contrasts. If
you are to get the most out of a listening
session with this amplifier, please do not assume that what you are
hearing is the VAC; it probably will be a result of the VAC's resolution
of something ahead of itself in the component chain. (The Parnassus,
to my consternation, sounded quite grainy in the upper midrange and even a
mite congested. And this quality, once heard, became evident in
lower resolution systems, though, naturally, not to the same degree.)
The VACs, in either edition, are grain free. And they sound quite
vivid, but only, I think, in the way that the real thing does. It
isn't a matter of coloration, but rather of proximity. Drop in the
feedback, which is adjustable (via a switch on the amp's
chassis), and both the vividness and its transparency suffer, and the VAC
begins to sound much like conventional tubed amplifiers.
If you combine this "vividness" and presence with the dynamic "jump"
the VACs have - assuming your phono stage does not suppress "jump"
as the Klyne did to a disturbing degree - then you are likely to be, like
me, bowled over, and stay that way. Time and time again, I forgot to
take notes and just listened for the pleasure of it, a rarity for
someone who has spent so much time listening professionally that he
usually opts not to (with reproduced music anyway) during his off hours.
Over and over, I found myself experiencing what J. Gordon Holt (only
half-jokingly, I assume), calls the goosebump
factor, i.e., that degree of emotional involvement that, as Hayes himself
puts it, reminds you of the first time you hear reproduced music as a
child, "that old thrill" as he puts it of experiencing the music
afresh, the same thrill one always get in the presence of a living
orchestra. (This is not, sad to say, what I got from either the
Manley or Melos "triodes", although the Melos/Pristine
electrostatic combination did, with certain material, suggest some of
this, albeit without much in the way of correct ambience retrieval.)
The experiencing of these amplifiers can be nearly overwhelming, at least
for one used to reproduced sound that is both mechanical and/or more than
faintly "electronic" in character.
These qualities are entirely absent here, but I cannot, at this point,
pretend that I have taken the full measure of the 140s, especially on
their negatives. Their clipping characteristic sounds unlike that of
the Seventy/Seventy. There is none of the edgy bright "tearing"
sound when things get loud. In fact, with these amplifiers, you
probably will back off before playing them too loudly, whether because
there is some distortion we have yet to describe (a subtle one, of course)
or whether for the more aesthetically satisfying reason that when it is
too loud, the soft passages, with their exquisite pianissimos are just too
loud to be effective - in other words, too loud and the amp sounds out of
balance, and, thus, unlike the real thing. The range of dynamic
contrasts just fall apart at very loud levels. I should note that
when a tube in our pair of VACs, which were something less than factory
fresh, went out of spec, we were subjected to some of the brightness and
yuk-a-doodle-do sound of the Seventy/Seventy at clipping. Certainly,
those of you who are impatient will find the amplifiers' warm-up time of
approximately 100 hours frustrating, and the VACs really do sound cold,
thin, and unacceptable until well into burn-in. Even if after full
break-in you turn them off for a few hours, it takes, literally, hours for
them to come back into focus, which is why I dread turning them off.
The tube life, said to be about 10,000 hours, tempts me to do what I
cannot recommend that you do if you're not going to be around to keep an
eye on them. I am also not certain that I am entirely happy with the
bottom bass, which strikes me as both slower and phasier sounding (by
bottom, I mean in the 30 Hz region and below) than I would like, nor am I
certain that I am entirely happy with the area in which the string bass
predominates. With the romantic-sounding Triplanar arm, there was,
on string bass and the lower harp strings, richness, pluck, and
verisimilitude in what sounded like just right proportions. This was
not the case with either the
Graham or the Air Tangent, which sounded too "lean" and
slightly withdrawn. Likewise, with each of the preamplifier
combinations - specifically the Klyne phono stage and/or the moving coil
stage of a Modulus III feeding the Melos line amp (i.e., Mark Porzilli's
brilliantly designed headphone amp) - there was either too little or too
much. Only the combination of Jadis JP-80MC and Triplanar was right.
One can only say with authority that the VAC lets you hear all the
subtle (and not so) distinctions among these combinations.
The high frequency articulation of this amplifier borders on the
sensational and without any exaggeration. I'd suggest you snatch up
the Classic LP recut of the Reiner interpretation of Respighi's Pines
of Rome and put on the first cut, with its myriad high frequency
instruments all going at once. Normally, this section is too much
for almost any system, amp or otherwise, to handle. But with the
Renaissance One-Forty, each instrument is not only delineated separately
but remains tightly focused and at one point upon the stage, meaning that
the acute listener can hear deeply into scoring. And you'll
hear plenty, pleasantly upon the ear without any softening, from an
extreme left snare, played lower than usual and more softly than much of
the rest, to bell overtones that sound as if they are reaching up, with
transient truth, toward bat frequencies.
I mentioned the resolution at the soft end of the spectrum. At one
point in the Classic edition of Prokofiev's Lt. Kije (Suite), with
Reiner and the Chicago, there is a moment, after the third movement I
believe, when all the players shift in their sits - it is at the pppp
end of the spectrum, but nevertheless startling in its suggestion of what
happens when real men and women are making real music, and it brings the
Chicago experience back to life as if it were happening today, instead of
nearly 40 years ago.
After steady, but hardly enough, listening to the VACs, I am becoming
convinced that they are telling the truth and their (relative) closeness
to the real thing compared with all the conventional amps I can think of
is not the result of coloration or distortion, but simply of a superior,
if relatively ancient technology, ingeniously applied. While it
would probably be indiscreet and maybe even wrong to call the VACs the
best amplifier in the world, it's not exaggeration to say they are,
overall, the very best I've heard in my professional audio life, and they
are that because they put the music back
into high fidelity sound, where it has been, for so long, so sorely
lacking.
hp
VAC's Push-Pull Strategy
One concern sometimes expressed about push-pull amplifiers
by single-ended devotees relates to the way in which the opposing phase ("push-pull")
signals are derived. This is accomplished by the phase-inverter or
phase-splitter stage.
Most phase-inverters exploit the fact that the polarity of a
waveform on the anode of a tube is inverted with respect to the input on
the grid. In essense, the signal may be passed through an extra
active stage to obtain the interved signal. This inevitably changes
the signal somewhat, introducing anomalies into the composite push-pull
picture. This basic principle underlies the majority of
phase-inverters, including, although obviously, the long-tailed
(differential) pair. It is also seen in the absolute phase invert
functions of many preamplifiers.
Since different tube sections are used in the opposing signal paths of
such inverters, tube mismatch and aging can degrade performance. To
keep balance, many phase-inverters incorporate loop feedback in a way that
may degrade the sound. Further complications can develop if the
phase-inverter is required to do double duty, such as driving the output
stage.
These problems are avoided in the "first principles" [of] the
design of VAC Renaissance Series. The push and pull signals are both
obtained through a single Class A1 triode. Using both ends of the
cathode-to-anode circuit, a single contiguous electron flow (signal)
naturally creates the opposing phases. By careful design, the
reactive impedance of both phases is kept essentially identical, ensuring
symmetry of the push and pull waveforms. This stage is not burdened
with any other function, and purity is maintained.
Other push-pull problems due to tube cut-off or saturation are avoided by
strict Class A1 design of all Renaissance stages. Thus, at each turn
the Renaissance avoids what might be called a "Cuisinart"
effect.
The debate between push-pull and single-ended is complex and subtle, with
purist designs emerging from both camps. In the end, the ear must be
the final arbiter.
Kevin Hayes
Valve Amplification Company
The Renaissance One-Forty Amplifier
Technical and Design Considerations
The Renaissance One-Forty amplifier is a monoblock Class A all-triode
design. It operates in push-pull (with the exception of the first
6SN7), rather than single-ended fashion, as the designer, Kevin Hayes,
thinks that the advantages inherent in a push-pull circuit - cancellation
of even-order harmonic distortion, and elimination of DC magnetization at
the transformer - allow for a higher-fidelity design than a single-ended
circuit, which will not by nature cancel any harmonic distortion either in
the output stage or at the transformer, and which is not well suited for
high output power. He also
believes, among the many, that the triode tube, operating within its
design limits, is the most linear amplification device available.
The input stage begins with a 6SN7 operated under conservative
conditions, to preclude distortion. It acts as a single phase
splitter - the very same electron flow creates both push-pull signals;
thus, the signal is not being divided (with the potentional of both
split-halves not being equal) as is the case with most phase inversion
circuits. From there the signal
goes to four 6SN7 driver tube sections in what VAC calls a "star-driver"
configuration, said to eliminate high frequency loss. The output
stage uses eight 300B output tubes in push-pull parallel, each with its
own heater supply and self-bias network. The 300B, a filamentary
power triode, was chosen since it operates at a lower temperature than
other triodes as well as a lower plate voltage (and impedance), which
affords more reliable operation with better frequency response than other
tube types.
The Renaissance One-Forty also features a variable-feedback control.
Hayes states that when feedback is re-introduced into the circuit,
it may lower the overall level of distortion, but will add additional
orders of harmonic distortion which may be more objectionable overall.
For example: If an amplifier produces second harmonic
distortion, the introduction of feedback will create a second harmonic of
the second harmonic, the fourth harmonic. If it produces second and
third harmonic, the feedback-combined signal will produce second,
third, fourth, sixth, and ninth harmonics. Nevertheless, the
variable-feedback control is provided to match the amplifier with certain
difficult speaker loads. Rather than using feedback to provide a
(desirably) high damping factor, VAC chose to design its amplifier with a
low output resistance.
While a great deal of technological consideration and testing went into
design of the Renaissance One-Forty, Hayes, who has been experimenting
with electronics and building his own gear since he was a youth (and
who can quote chapter and verse from numerous electronic textbooks both
classic and modern at the drop of a diode) stresses that the ultimate
sonic arbiter was the ear, combined his lifelong love of, and familiarity
with, live music. In the tweaking of the design, it was not
surprising to find that changing even one wire could dramatically affect
the sound - he feels that the One-Forty is so revealing that is "ruthlessly
exposes any imperfections in its own implementation." The
amplifier also contains a ground configuration switch, to tailor the
amplifier's grounding scheme to the rest of the system - which will also
be audible when optimized.
FD
Amplifier Specifications
Type:
Tube Complement:
Input Impedance:
Output:
Frequency Response (1 watt):
Power Bandwidth:
Total Harmonic Distortion @ zero feedback:
Negative Feedback:
Weight:
Dimensions:
For more information about The Absolute Sound (R) please visit
their website, www.theabsolutesound.com