A U D I O
P A P E R
DESIGN NOTES on the ZBox
2004 by Steve Deckert
THE MOTIVATION BEHIND the ZBox
of reasons I started this company was to develop products that would
benefit the most people vs. ego products that
few can afford. The later of the two is btw, far easier in my opinion.
The Zen Triodes are proof that I try to accomplish my missions.
Based on their quality and sound they could have easily been
repackaged in machined gold chassis and sold for top dollar in only
the elitist solon's. So based on this mind set when the decision
about what to do this year for a CD player came along the ZBox was
an easy choice.
To date I
have done two CD/DVD players. The first DEC343 - a Pioneer
player that I developed a tube output stage for. The second
was the DEC685 - a Sony player that I developed a different tube
output stage for. The only reason the second player came to
pass is because they discontinued the first player shortly after
I developed the mod. The reason the tube output stages were
different is because one took it's signal just before the final
output stage of the CD players original analog section and the other
took it's signal off the DAC ahead of the original analog section.
a year to the day, the Sony player has been discontinued and replaced
by a stripped out version of it's former self at just over half
the cost. It's a real shame because both of these players
made it into many happy customers hands with our mod's.
In my eyes
modding these players was a temporary solution to get a decent source
in more of our customers hands. My hope is to develop a good
tube DAC but these things take time. I've already done a good
portion of the development on a DAC but as many manufactures will
tell you we're in no rush with the current format wars.
So the question
became what to do in the mean time. Of course we'll still
offer the mod's to both the Pioneer and Sony players but you'll
have to supply the player.
As I look
around this year trying to find a decent player to mod, and dreading
the R&D involved because I'll have to design two or three different
circuits and listen to all of them, pick the most promising and
then continue to voice it to my liking. This is a process
that takes months. The new models of last years players are
not getting better, only costing less money. None of them
are real good candidates for a mod. At this point it looks like
I would have to jump into the next price level to find a good candidate.
I'm afraid after the mod's it would push past the 1000.00
mark - perhaps by a fair amount. This would take it out of
the intended market, we would sell half as many units and by the
time the year is up and I've recovered my development costs it will
THE CIRCUIT and APPLICATION
The ZBox is
a stand alone device designed to become a tube cathode follower
to the stock output stage of any CD player or DAC. It uses
a single 12AX7 tube (dual triode) to accomplish this.
The big question
when comparing this approach to either of our two previous modded
players is of course how will the end result compare?
On the original
Pioneer player my intension was to bypass the entire stock analogue
output stage and feed my tube stage from the DAC chip. To
make a long story short, it didn't work out that way. To keep
noise low and maintain a robust frequency balance I had to use all
but the last output stage in the original analog section to drive
my tube stage. Having only eliminated one of the solid state
op amps that make up the original output stage I was always amazed
at how good the end result was. People who were used to listening
to digital front ends costing $5000.00 were finding very little
if anything wrong with it.
On the Sony
player, the DAC setup is a little different. Interestingly,
the stock output of the Sony player had better sound than the stock
output of the Pioneer player yet when it came time to apply the
same circuit the end result was sub par. In the Sony the best
sound was to change the output stage to a Plate driven output with
gain and feed it directly from the output of the DAC chip.
As you might
expect the Sony player had a bit more inner detail than the Pioneer
but did nothing else any better. Imaging and soundstage on
both were excellent. I found the Sony to be a bit more analytical
while the Pioneer was a bit more musical. This is not what
I would have expected since I have so little respect for the surface
mount solid state output stages in consumer players.
that these solid state output stages were basically futile. When
you listen to them an compare them to a really good reference player
you can hear how literally broken the soundstage and imaging are.
You can also hear the frequency balance of the music change
with the transients. Sudden swells or peaks in the music excite
the output stage in a negative way resulting in notes that shout
at you for no good reason.
The fact that
the Modded Pioneer sounded so good should have been a clue, but
until recently I didn't realize you could actually fix to some degree
the damage these cheesy little output stages create. In comparing
the stock outputs of the original Modded Pioneer connected to the
ZBox with the modded outputs of the player I was again surprised
at how similar they sounded. The only large difference between
the two is that the modded outputs have one less op amp between
the DAC chip and the tube output stage. The voicing on each
sounded almost exactly the same, except that the stock outputs driving
the ZBox had a touch more weight.
same test to the Sony player I expected a greater difference in
sound and there was. The stock outputs feeding the ZBox had
close to the stock output voltage, while the modded outputs had
significantly more. The overall weight was better on the stock
outputs feeding the ZBox than it was on the modded outputs. The
modded outputs demonstrated the same increase in inner detail that
we heard when we compared it to the Pioneer player. However,
again the difference was there but not overwhelming. In this
evaluation the trade off was some inner detail traded for a less
analytical sound with more tone.
the ZBox to the modded outputs of the Sony player was a noticeable
improvement over the prior tests. This was a welcome result
because I didn't design the ZBox to filter things and make crappie
CD players sound better. Instead it was designed to have excellent
transparency so that it would also make good CD players and DACs
sound great. It's appeal should be to a wide market with both
entry level players and heavy hitters benefiting from its use.
to the guy with an inexpensive to moderate CD player or DAC... You
will no doubt wonder if adding a ZBox to your present player would
be more cost effective than having that player(DAC) tweaked or getting
a new player(DAC). I've heard a lot of tweaked CD players
and DACs. The upgrading of the internal power supplies, and
choice replacement of parts in the analogue section make a big difference
but not to the extent of simply adding a ZBox. The ZBox does
wonders for opening up the music and developing a natural sound
stage. It adds a wonderful sense of control and weight to
the bass. It makes the mid's sound way more organic and liquid,
and the highs shimmer without the grain or dryness. There's
just no substitute for a good all tube cathode follower circuit.
a couple of advantages to the ZBox approach that may account for
results it brings about. It is after all a tube output stage
that becomes a direct coupled cathode follower to any line level
source. That means it has the ultimate low impedance
output able to drive anything including long cable runs with the
same consistent sound all the time. Its also stand-alone with
it's own steel chassis offering total shielding of the output stage
from the RF in the room and the Digital noise of all the chips in
your player or DAC. It also has an earth ground via it's removable
power cord. It has been designed so that when you plug your
source (and amp) into it they also gain an earth ground, something
that many CD players and amplifiers don't have. It also has a variable
output via a simple to access control on the front. This allows
you adjust the output of your CD player to match your preamp or
become a volume control when driving an amplifier directly with
no preamp. With many DACs having high output (over 2 volts)
this allows you to tame it back down to a more usable 2 volt range
without loosing the dynamics you picked up from having higher output
in the first place.
tube itself is a huge advantage in that you can easily access it
and replace it with your choice of over 20 different brands each
with a slightly different signature. Some will be more dynamic,
some more airy, some more focused, etc. You will have control
over how it sounds. You can also use lower gain tubes such
as 12AT7 or 12AU7 when you feel like seeing what happens on a high
output DAC exceeding 5 or more volts. And while there are
probably more, one of the last things that comes to mind is the
fact that the ZBox is always on. It runs 24/7 so it develops
a consistent temperature eliminating parts drift for consistent
sound. It's always warmed up and ready at all times. The
heaters of both halves of the dual triode tube are in series with
10 vs. 12 volts of AC. Slightly starving the heaters like
this and series wiring are tricks I've learned along the way to both
improve the sound and make the tube last twice as long. Since
the tube never gets hot, you can grab it while it's on without consequence. For this reason it protrudes through the front of the chassis
as if it were a knob, in fact it looks just like one. This
makes changing tubes very easy to do without having to unhook stuff.
It's my feeling
that a guy with a so/so CD player or DAC (who's faced with purchasing
a new one and expecting substantially better sound) may be able
to spend less than half the money on a Zbox and get a better result.
Then later when a new player is purchased the Zbox is used
to elevate the performance of that new player to a level noticeably
higher than without it.
This is an
all tube cathode follower that can be used after any line level
device and or preamplifier. It has just under unity gain so
what you put into it is basically what you'll get out of it. The
ZBox is a device I've talked about making since the late 90's and
now is the right time for it.
is being built in a newly designed chassis with dimensions
of 2"H x 6"W x 11"D matching the basic size of the
original Zen Triode chassis so that it can be optionally slipped
into a hardwood base like our amplifiers. Otherwise it will
offer a clean stealth look with a high quality black powder coat
preserve the karma the ZBox was designed with an analogue pencil
Decware is a trademark of High Fidelity Engineering
Copyright © 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
2007 2008 by Steve Deckert