HeadRoom BlockHead Headphone Amplifier
 There's a school of
history known as the "great man" school, which states that true human progress
is the result of outstanding individuals. Other historians hold that individuals are
molded by events and trends. Personally, I'm a huge believer in the "unreasonable
man" theory, which holds that progress is the result of individuals too talented or
too thick or too stubborn to accept that the law of averages applies to them.
Did Wellington win at Waterloo? Of course, but it wasn't
because he had the superior force or he held better ground or he was a superior tactician
to Napoleon -- he won because it never occurred to him to wait until he had a superior
force or better ground. As it so happens, Field Marshall Blucher's Prussians slogged
through eight miles of swamplike roads to flank the Imperial Guard on the left,
effectively turning the tide of the battle, but they arrived late in the day -- literally
at the last minute. Even Wellington called it "a damned near-run thing."
High-end audio is filled with unreasonable men -- you could
almost say it has been formed by them. Was the Krell KSA-50 a reasonable product?
No, it was overbuilt and inefficient, obviously the design of a man who wouldn't listen to
reason. However, it changed the way that amplifiers were designed.
Ditto for the Wilson WAMM. Who really needed a
$100k/pair loudspeaker? Who could have even conceived of one? Certainly not a man who was
impressed with what everybody knew about loudspeakers. Yet, 20 years down the road,
just about the highest accolade most speaker companies can come up with is "better
than a Wilson."
So when I call the HeadRoom BlockHead balanced headphone
amplifier a ridiculously over-built solution to a problem most people don't even know
exists, you must understand that what I'm actually saying is that it's solidly in the
tradition of those paradigm-shifting exemplars of high-end audio. And that it's historic.
And all.
I have a reasonable good ear in music
When I say the BlockHead is the solution to a problem most
people don't even know exists, I am referring to the universal custom of using a common
ground in driving a stereo headphone's two channels. An audio signal is carried over a
two-conductor cable -- that is to say, the signal travels to the speaker on one wire and
returns, completing the circuit, on the other, the ground. That's one channel. For
stereo, you'd need four conductors -- except you don't actually need four. You can
get by with a single wire (a "common ground") for the return leg of the signal.
I'm not sure when the convention of using a three-conductor
cable for stereo headphones began, but it might go all the way back to the
beginnings of the stereo era. At any rate, it simply became the way things were and nobody
ever gave it a thought, as far as I know.
Think about that for a minute: The custom of using a common
ground dates back to the '50s. Name any other constant in hi-fi from that period
that hasn't been seriously questioned. I sure can't think of one.
These days people even run separate ground planes on
circuit boards, fer Pete's sake! If that cuts down on interchannel
crosstalk, imagine how much a common audio lead has got to be affecting separation.
So one huge difference between the BlockHead and
everything else out there is that it runs discrete signal-carrying and ground-return
conductors to each earphone driver. And since every conventional headphone utilizes a
three-way connector, that means you have to buy headphones with special wiring harnesses
and two headphone plugs.
Two brands of headphone can be readily configured for this:
Sennheiser's HD 580 and HD 600 (which use the same connector) and Grado's RS-1. The
RS-1 can be purchased from HeadRoom configured for the BlockHead ($695) or you can have your
RS-1 modified by Grado (call for charges). If you buy the BlockHead, at least for the
moment, HeadRoom will throw in a pair of Sennheiser SD 600s (typically $299) if you
purchase either of two balanced wiring harnesses: the Clou Red Jaspis 212 XLR cable for
$350 or the Cardas Balanced Headphone Cable for $275.
All progress depends on the unreasonable man
The simplest way to describe the BlockHead is as two
of HeadRoom's Max amplifiers, linked by a common faceplate and a shared rear panel. The
two monoblock amps that make up the BlockHead are completely discrete units -- all they
have in common are those two pieces of casework. Each channel resides in its own
extruded-aluminum chassis; each has its own volume control and dual power supplies. The
unit requires two AC cables.
The faceplate is crenellated -- it reminded me of nothing
so much as New York's Moorish-Deco Armory, which I've always considered a nifty piece of
architecture. The two modules behind the front panel are obviously flipped 180 degrees in
relation to one another. At the center of the panel are two Neutrik XLR connections;
placed to the outside of those are four machined dimples containing lever switches
controlling (from the inside progressing outward) phase, filter, process, and gain. At the
outer ends of the faceplate sit the two channels' volume knobs. My sample came equipped
with Nobel potentiometers; for an additional $555, HeadRoom offers the BlockHead with
custom-tweaked stepped attenuators. (Talk about unreasonable, they buy Swiss-made Elma
24-position switches, disassemble them, remove the stock circuit boards and replace them
with custom-made boards with precision film resistors mounted to the contact boards. Geeze.)
 The rear panel is also mirror
imaged. Starting from the center and working outward are: an XLR input labeled crossfeed
in, an XLR output labeled crossfeed out, a grounding lift switch ("float" or
lift), an XLR for signal input, a power switch and an IEC mains socket. Engraved in the
casework at the top of the rear panel is a bit of typical self-deprecation by HeadRoom CEO
Tyll Hertsens: the words "The Original BlockHead" appear in quotes, followed by
Tyll's signature.
Keep those connections in mind; we'll get back to them.
The HeadRoom Max headphone amplifier was (still is, for
that matter) more than simply a step-up unit for driving headphones. Like all HeadRoom
products, it also contained HeadRoom's Crossfield Audio Image Psychoacoustic Processor
Circuit (CAIPPC), a nifty little psychoacoustic circuit that compensates for the extreme
left/extreme right/center of your head "blobby" spatialization effect that
bedevils headphone listening.
Human hearing can be phenomenally precise. Not, perhaps,
when compared to that of a bat or even a dog, but we are able to localize sounds in space
with astonishing accuracy. And when it comes to things like audio, ordinary, untrained
listeners can readily and repeatably hear sounds 50dB or 60dB below the noise floor of an
environment.
But try to understand how human hearing works and you'll
come to the conclusion that its creator had a bizarre sense of humor and a weakness for
meat-based plumbing products. Sounds traveling through the air vibrate a membrane, those
vibrations are mechanically amplified, and converted to pressure waves within a liquid,
which, in turn stimulates hairs, which fire off an electrical signal that stimulates the
thalamus, which finally stimulates the auditory cortex. Does that sound reasonable?
It doesn't even sound plausible.
So let's not delve too deep into how spatial hearing works,
let's just say that HeadRoom's little processor mixes a little of the left channel into
the right channel (and vice versa), adds some delay and some EQ and, ever so subtly,
removes that "headphone" sound from headphone listening. That's a super-simplistic
explanation for such a complex set of equations, but you can find out more from HeadRoom's website, as well as review
of HeadRoom's
Max.
Of course the BlockHead doesn't just use an ordinary CAIPPC
module. It doesn't even use a premium version of it -- it employs a reference
version, with carefully matched components and thin film resistors. And, since it's
dual-mono and balanced, it uses four of 'em. And remember those crossfeed inputs
and outputs on the back panel? That's how each amplifier receives the input from
the other to mix, EQ, and delay as part of the HeadRoom processing. In order to simplify
this, each BlockHead comes packaged with a pair of 13" DiMarzio balanced jumpers.
Because of the way the CAIPPC works, some listeners find
that the high frequencies sound "recessed," so HeadRoom incorporates a
three-position equalization "filter." One setting boosts the highs by about
3.5dB; the other seems to add about the same boost, only over a broader frequency range.
The gain switch enables the listener to adjust the unit for headphones of varying
sensitivities, although this function seems a strange addition when you consider how few
headphones are actually compatible with the balanced nature of the BlockHead.
There's another feature that might seem like overkill, but
I was extremely glad to see it. That's the ability to configure ground separately on each
channel. I've already employed the BlockHead as a monitor tool at two different recording
sessions, and you never know what kind of AC you'll run into in the field. Given the
universality of Murphy's Law, anything that allows you to cope with disaster is a
worthwhile addition.
A reasonable doubt is nothing more than a doubt for
which reasons can be given
Tyll Hertsens calls the BlockHead "the first
fully-balanced double dual-mono monoblock headphone amplifier." He's probably right,
but I think there's an extra "double" and probably at least a redundant
"mono" in there, too. But Hertsens' main point -- that he's gone waaay
beyond what's reasonable here -- is well taken. Each channel of the BlockHead is
essentially a stereo Max, only instead of using the two channels for right and left,
they're used for the two signal-carrying legs of differentially balanced operation.
Balanced operation is inherently costly; the circuit demands twice the parts.
That's not an insubstantial consideration when you're
talking about the kinds of parts HeadRoom has lavished on the BlockHead: Neutrik
connectors, Nobel pots (or even worse, that home-brewed version of the Elma), film
resistors, Burr-Brown 627 audio op-amps, Arvel-Lindberg toroidal transformers (four of
'em!), polyphenoline-sulfide film capacitors, and NASA-spec Vishay registers. It's an
impressive list.
Reasonable? Not hardly.
The wrong way always seems the more reasonable
My first BlockHead experience was actually with John
Atkinson's review sample. He was once again recording the vocal group Cantus, and he'd
graciously invited me to the sessions so I could write about them for his magazine (https://store.primediamags.com/subscribe/stereophile/5EKC).
As we were coordinating equipment transportation beforehand, I mentioned I intended to use
the BlockHead to monitor the proceedings. "Great," John proclaimed. "I have
one here, so I'll just take mine -- that way you don't have to carry yours on the
plane."
His sample, like mine, did not boast HeadRoom's stepped
attenuators. Could there be an audible difference between the stepped and unstepped
versions? Don't know and don't care. If there's one thing I hate worse than dual volume
controls, it's dual volume controls with stepped attenuators. This is my personal
hobbyhorse, I suppose; it harks back to an old preamp I had with 1.5dB steps between
settings. They were just too far apart. I wanted to adjust channel balance by .5dB or so,
not three times that amount!
Of course John wanted the stepped version since it
is crucial for him as a recording engineer to know that both channels are perfectly in
balance. Crucial, perhaps, but is it crucial to the tune of $555? He's
"pondering."
I haven't compared them, but everybody I know comes down on
one side of this issue or the other, and logic has nothing to do with it.
Man, being reasonable, must get drunk
While John fiddled with microphone placement and taped down
cables in the high traffic areas of the chapel of the Good Shepherd (located on the campus
of Shattuck St. Mary's School in Faribault, Minnesota), I started to familiarize myself
with the BlockHead and the specially cabled Sennheiser HD 600s it drove. I powered up
(twice) and very gradually began to ramp-up the gain on both channels. Soon, I found
myself surrounded with the noise of the wind through the junipers on the other side of the
stone chapel's stained glass, the sound of pews being moved so the group could stand in an
arc in front of the crossed cardiods, the burble of mememememes as one of the high
tenors warmed up his vocal cords, and suddenly, the voice of Eric Licht speaking over my
shoulder, "Could you hand me that socket wrench?"
I jumped, startled, and pulled off the Sennheisers as I
hastened to explain that I didn't have the socket wrench, only to discover that I
was by myself in the robing room. I had heard Eric through the BlockHead and the balanced
HD 600s. There was no electronic signature, no compression, no apparent noise floor
limiting what I could distinguish within the soundstage -- and certainly no indication at
all that I was listening through microphones, a mic preamp, a few hundred feet of cable,
the Nagra, or anything else. It wasn't "the next best thing to being there," it
was being there!
Oh my.
The next several days were intensely physically
uncomfortable. The frigid wind was still whipping across Minnesota's lakes, and yet we had
to turn the heat off in order to record. When the singers began to emit streams of ice
crystals with each note, we'd shut down the Nagra, turn up the heat, and try to get warm
again. Of course, John and I had located the recording gear in the unheated robing room,
which never got warm, so we just wore everything we'd packed. Lucky John had a hood on his
sweatshirt, but I'd brought my Fedora, which wouldn't fit over the Sennheisers. On the
last day there, I ran into a record store and bought the first knit toque I could find --
that clerk is probably still telling people about the fat, bald, middle-aged guy who was
into Mudbone.
The thing is, as cold and miserable as I was, I couldn't
stop listening to the BlockHead. It was so quiet, it was so real, and it was unlike any
kind of headphone listening I'd ever done.
In the four months that have followed, not much has changed
my opinion on that score. I monitored a friend's original electronica experiments with it
and thought a synthed bassline was going to vibrate me out of my listening chair. I may
have, in fact, dislodged a filling.
I also had an intensely visceral experience listening to Golijov's Yiddishbbuk [EMI
Classics 57356-2] for the first time. All of the power and delicacy of this complex,
passionate music washed over me -- yeah, right, washed over me like a freight
train. I was floored by the musical intensity of this recording, even as I was seduced by
its pure, musical sound. I've never heard any system walk that line between musical
intensity and dispassionate "tell it like it is" reportage the way the BlockHead
did.
But there are some minor details I ought to go into. First,
you'll note I haven't addressed HeadRoom's Crossfield Audio Image Psychoacoustic Processor
Circuit at all. That's because I've gone into in some detail in other reviews (see earlier
reference). I consider it an important component in making headphones sound more like
speakers responding in free air. I prefer listening to headphones with it activated.
Period.
The Reference version of the module that's included in the
BlockHead is every bit as good as it's billed. It's an elegant implementation of the
circuit, and if any component on the planet has the resolving power to unmask any inherent
noise or coloration in it, it would be the BlockHead. But, in fact, the CAIPPC is just as
quiet and musical under this electron microscope of an amplifier as it is in the Supreme
or the Max. And just as essential to its success.
However, just as the unbalanced Clou 212 Red Jaspis cable I
reviewed previously was unwieldy, the balanced version I've been using with the BlockHead
is stiff. A lot stiffer, actually. Between its weight and its relative lack of
flexibility, it tends to loosen the tiny little pressure fitting that connects it to the
Sennheisers' earpieces. This is a drag.
I want to try the Cardas balanced cable harness, which I
hear is a lot more flexible. (I've also heard raves about its sound quality, so I really
want to audition it.)
I also found that, with the best intentions in the world, I
tended to crank the BlockHead far louder than I would listen to speakers in free air.
Perhaps this was because the BlockHead was so free from any sense of distortion or effort
that I was unaware of the relative volume under the headphones. This is certainly a
possibility.
But I suspect it's also because what we typically call
"hearing" is actually something more like "experiencing" -- it
combines the output of several senses into the gestalt. I think there's something actually
tactile about really loud sounds and that listening through headphones does not completely
satisfy our need for that sensory input. So we listen louder.
I know we audiophiles tend to have a similar reaction to
the issue of location in prerecorded music. We desire an all-but-holographic certitude of
the musicians' relative positions to one another to an extent we never demand in listening
to a live event. Close your eyes in a symphony concert and try to locate the triangle's
precise position on stage. Chances are, you could be off by over 10 feet -- but if you
heard the same thing on a recording, you'd say it lacked detail.
I'm not trying to point out that we begin to confuse the
map for the territory -- that's built into the hobby, I suspect -- but I am saying you
need to be careful. Focus too much on holographic soundstaging and you only risk missing
the music itself (and, possibly, boring your loved ones -- but hey, that's what they're
for). Indulge too much in high sound-pressure-level listening on a system as clean as the
BlockHead/Sennheiser and you risk tinnitus or worse. That's not a flaw in the
BlockHead precisely, but don't hurt yourself playing with it.
A reasonable amount o’ fleas is good fer a
dog-keeps him from broodin’ over bein’ a dog
The very finest headphone system I had ever heard prior to
the BlockHead/balanced HD 600 was undoubtedly the Stax Omega II/SRM-007t, an $8500
electrostatic earspeaker/tube amplifier combination that, like the BlockHead/HD 600
system, seemed to evince a staggeringly low noise floor and an almost total lack of
coloration. If there were any true competition for the HeadRoom combo, the Omega would
almost certainly be the odds-on favorite.
And the two do share a lot. Toss a penny up in the
air and either of these models could let you hear the air rushing through Lincoln's
whiskers. And big? Good lord, you've never heard the intimations of infinity until you
listen to Pink Floyd's Echoes [Capitol 36111] through either pair.
But I ultimately tired of the sound of the Omegas, as hard
as that would have been for me to believe early on in my audition of them. As free as they
are from any boxy or smeared coloration, the Omegas (and all electrostats that I've heard)
do have a sound. Not so much a sound, even, as an attribute. They reach a certain
point in their portrayals of dynamics and they hang there. It's not exactly a sense of
dynamic compression -- of the sort you can certainly experience from some headphones and
even free-air loudspeakers -- it's primarily a sense of "that's all you get."
Once you reach that point (and it takes some doing to get there), you'll recognize that
the sound has always contained some degree of that character. Electrostatic headphone
sound is just so different from the colorations you've grown used to, it sounds at first
as though there are none. Harry Pearson used the expression "credit card
coloration," but I've never been precisely sure what he meant by it. Perhaps he
simply meant that electrostats have a set limit on their reproduction of dynamics.
That sense of unlimited dynamic potential is important to
me. To my mind, that's one of the chief differences between live and recorded sound. Not
everyone agrees with me, of course. Some people think the HD 600s sound soft in their
top end -- they might opt for the more immediate (and to my mind, slightly more
aggressive) sound of the Grado RS-1s with the BlockHead. It's even possible many people
might prefer the Stax Omega's sound to that of the BlockHead and any headphone.
Universal agreement isn't possible, of course.
But to my ears, the BlockHead/Sennheiser sound is as good
as headphones get.
It is the function of vice to keep virtue within
reasonable bounds
At the end of this total rave, however, I'm going to
backpedal furiously for a second. HeadRoom's own Max is probably the BlockHead's greatest
competition. At half the price of the balanced unit, the Max isn't exactly cheap, but
almost everything I've said about the BlockHead applies to the Max as well.
Except that I think the difference between the sound of the
Sennheiser HD 600s with the common ground and that of the balanced version paired
with the BlockHead comes down primarily to keeping the ground paths separate, not the
BlockHead's balanced circuitry. Split the ground on the Max and keep the signal separate
all the way to the HD 600s' drivers and I think the Max would be awfully hard to beat
for a lot less money.
But gee, that's just my opinion.
The product I actually auditioned, and the product that
actually exists, is the HeadRoom BlockHead balanced monoblock headphone amplifier and it
is, to my way of thinking, exactly as billed by its manufacturer. It is quite simply the
finest headphone system I have ever used. It delivers sound that's pure, emerges from
silence that most tombs would envy, and seems absolutely bulletproof. Buy one and be
confident that you actually own the best of something.
Again, that's just my opinion.
If you have the money and you need (and I leave it
to you to define need) the finest headphone amplifier and headphones currently in
production, the BlockHead is what you want.
As long as you realize you aren't being reasonable.
But whoever said great men have to be reasonable?
...Wes Phillips
wes@onhifi.com
HeadRoom BlockHead Headphone Amplifier
Price: $3333 (Nobel potentiometers); $3888 (stepped attenuators)
Warranty: Five years parts and labor
HeadRoom Corporation
521 East Peach Street
Bozeman, MT 59715
Phone: (800) 828-8184
Fax: (406) 587-9484
Website: www.headphone.com
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