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DESIGN
NOTES
By
Steve Deckert
INTRODUCTION
If
a guy was to build an all-out preamp
with the intention of using it in a
world class reference system there might
be few things he would realize right
off the bat. Things like - What
would be the point in having monoblocks
if you're going to drive them with a
stereo preamp? To keep from undoing
some of the benefits of using two or
more mono amplifiers, the preamp would
also have to be dual mono. That
means no parts including the power supplies
are shared between channels.
He
also might realize that since channel
separation is the theme behind dual
mono, balance controls or ganged volume
pots are out. The only way to
do it right would be to use two separate
volume controls.
Having
the luxury of experience, he would know
that a fundamental reason why lovingly
hand-built gear always sounds better
than production "off the shelf"
gear is the absence of circuit boards
and the attention to detail. That
means the preamp would have to be hand
built.
So we started with that, a good foundation,
and applied everything we know about
to effect what is now the ZTPRE. The
ZTPRE was more than challenging and
more than an accomplishment when you
consider the design goal.
The
design goal was to have this preamp
be so good, you couldn't hear it in
front of a Zen Triode amplifier. Our
Zen Triodes have only 2 resistors and
1 capacitor in the single path, no hook-up
wire, and only 11 solder nodes between
the input and output jacks. It's
transparency has become legendary and
it has been able to reveal the weakness
or imperfections of every preamp we've
tried in the $2500 to $4500 range. To
get the ZTPRE invisible when used in
front of a Zen is something I honestly
didn't think would be possible.
We
achieved the design goal, with the added
goal of making the unit equally at home
with all other amplifiers in hopes that
people with large investments in high
power systems, especially solid state,
could have some Zen magic too.
Steve
Deckert
DETAILS
ABOUT THE DESIGN
The Decware
ZTPRE is a vacuum-tube preamplifier using a dual mono design
that features a single ended dual triode gain stage for each channel.
It also has dual volume controls and was designed for those people using
mono blocks to preserve the almost infinite stereo separation dual mono
setups are capable of. It also has a separate power supply that is dual
mono for stone quiet operation in front of any amplifier. Of utmost importance
is the fact that these units are hand wired point to point with minimal
amounts of (silver/Teflon)
wire. There are no circuit boards or solid state parts to contaminate
the sound. Even the LED is located in the power supply. The signature
is free of contamination and over analytical regulation.
It also features
a sealed internal chassis that houses the tubes which are also shielded.
This chassis is isolated from the main chassis for a combination that
eliminates the need for tube dampers, and prevents RF noise for pitch
black backgrounds.
The dual
mono power supply features a seriously overbuilt package for each channel
with a separate DC filament supply of over 50,000 uf. In fact the power
supply for this unit could power 5 ZTPRE's without any strain. The non
magnetic chassis means no physical hum or vibration to annoy those midnight
listeners. The absence of heat it testament of it's overbuilt design and
makes it possible to turn it on and forget it. The ZTPRE can be left on
365 days per year without problems if you want, meaning it's always warmed
up and ready when its time to perform.
The circuit
itself uses the SVETLANA or SOVTEK 6N1P dual triode, one per channel. It can also
be used with 6DJ8's or 6922's with an added resistor to the heater supply.
When these dual triodes are paralleled to drive a line level signal they
create a high current driver stage capable of driving most any amplifier
without having to use two stages. This has proven to be THE ticket for
uncompressed dynamics and speed. With a single stage like this, there
is only one cap in the signal path and only two resistors. Backed with
its power supply, the speed is uncanny.
Using a special
series heater circuit the heaters of both channels become one, and therefor
respondent (or aware of) each other in a self balancing way that lets
the music breath with less effort. We feel this corrects the only possible
detriment of dual mono designs and that is that if the left hand doesn't
know what the right hand is doing, there is usually spotlighting or other
stresses heard in the sound stage. This is of course my subjective description
of the result, no need to get your calculators out!
The internal
layout of this unit has painstakingly evolved over 50 some units to a point
where it no longer changes. The unit has been selling unchanged since
then for several years now and is not
subject to being UPDATED to sound better
in the future. This is it - can't
get any better. The in depth feedback from all
our customers has helped to accomplish a voicing and performance that works
on anything from a single ended triode amp, to a huge pair of solid state
mono blocks.
Amps that have high input sensitivities of less than 1 volt
will enjoy the cathode output of the ZTPRE. Considering that most
all sources have a minimum of 2 volts
of output means that these high input
sensitivities require you to actually
turn the volume down, not up. Important to understand
is that it took almost a year to solve the problem of how do you attenuate
without squashing dynamics like every
other preamp does. As opposed to using a resistor
to ground to divide the voltage for lower output (A method that is suicide
for detail), the cathode output is the
only natural way to attenuate without squashing dynamics by pulling voltage
to ground. For amps that need a little gain, the ZTPRE has plenty when
used in anode mode. There is a setup switch on the back to change from
one to the other.
Biasing any
circuit is a huge factor in how good it will sound. As a manufacture you
usually have to play things safe and run it down the middle, however any
tube guru will tell you that biasing an amp on the system it will service
sounds best and always changes from one system to the next. Since biasing dictates warmth,
soundstage presentation, dynamics, whether or not the unit is aggressive
or laid back, you can see why it would be different in any given room
as to which way is better. On the ZTPRE there are two settings for the
bias, one laid back, one aggressive. The adjustment is made via a switch
on the back. (By aggressive we mean dynamic with added presence)
Coupling
capacitors also have a major part in dictating speed, detail, air, space,
clarity, and so on. Some sound warm, some dry, some fast, some slow. Again,
the same cap regardless of type will sound great in some rooms and less
than ideal in others. The ZTPRE has two sets of coupling caps selectable
via a switch on the back. For hard core listeners, this feature alone
is rather amazing (and required) stuff.
The combinations
of signatures that can be yielded from these set up switches effectively
give you NINE different versions of the ZTPRE. How flexible is that? We
think of it as an insurance policy that the unit will become your reference
preamp for life.
The input
selector is very NON ERGONOMICALLY placed on the rear of the unit between
the two pairs of input jacks. This was done to eliminate the internal
wire and fidelity loss associated with rotary switchers at a price.
The unit
comes stock with ALPs pots which have a wonderful sounding taper and well
suited for moderately priced sources. However, audiophiles who prefer stepped attenuators
may have their ZTPRE built with our GoldPoint units for an extra cost.
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