Decware ZTPRE v2 User manual

O W N E R S M A N U A L
Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com
Zen Triode Preamplifier
MANUAL NO. 02 REV. DATE: 11/2023
ZTPRE
v2

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INTRODUCTION
The Zen Triode Preamplifier (ZTPRE) is a fully differential-balanced all tube preamplifier that was designed 100% for
sound quality and therefor has nearly zero features aka bells and whistles. If it were a race car, it would only have
one seat and be pretty well stripped the bone for winning races.
This is not only fully differential balanced but fully dual mono with quad power supplies. Everything inside is hand
wired point-to-point with no circuit boards using only the best parts and wires.
NOTE: This is the owner’s manual for the 2024 model ZTPREv2. The only functional
difference between this and the prior model is that this one no longer has remote control of
any kind. Instead it is offered with high quality carbon volume controls or optional 48
position dual layer attenuators which favor performance over convenience.
OPERATION
The ZTPRE features a volume control for each channel to control your master volume. The output level is adjustable
with rear mounted attenuators each with 20 steps of adjustment. Simply turn these output level controls all the way
down so that no sound is heard and then raise the master volumes to the half way mark. Now slowly raise the
output level controls 1 click at a time until your amplifier / speaker combination reaches what you would call your
normal listening level.
Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com

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UNBALANCED INPUT OPTIONS
The ZTPRE is available with an optional transformer balanced input option making it possible to convert an
unbalanced input to a fully balanced input. When this option is used a single RCA jack is seen instead of a 3 pin
XLR jack. The advantage of this is in maintaining a fully balanced system. Using a RCA to XLR adapter jack in
place of this option will also work but will unbalanced the entire system which may or may not reduce sound quality.
It is important to understand that most balanced sources will have somewhere between 3.5 and 10.5 volts of signal
whereas most unbalanced RCA components will seldom have more than 2 volts. This means, even with the
balanced input transformer option, whatever you have plugged into it will still only have 2 volts and thus play much
quieter than your balanced sources causing you to have to turn the volume control much higher to reach the same
listening level. This is normal, but needs to be understood or else you might think something is wrong.
One nice trick when running a single ended source into the ZTPRE is to put a single tube gain stage on your source
to raise the voltage to around 6 volts or so. Decware makes a product that does this called the ZSTAGE.
Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com

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INPUT SELECTOR OPTION
The ZTPRE comes with optionally up to 3 inputs making it possible to select from 3 different source components.
The input selector is located on the top side of the unit just behind the face plate.
The input selector is set up from left to right meaning when you have it in your hand, fully counter-clockwise is input
# 1 and conversely fully clockwise is input # 3. The picture below shows the selector in position # 2.
The input selector switch is a rotary type (obviously) but perhaps not so obvious is that it uses silver contacts to
preserve signal integrity. It is set up with a 1/4 inch shaft being American made and is fitted with a chicken head
knob with a clear white line making it all too easy to not only see, but in the dark, feel, where it is set.
Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com
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2
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INPUTS

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IEC POWER CORD CONNECTOR / FUSES
The ZTPRE uses a standard high quality IEC connector making it compatible with all after market power cords
including our own DHC-1 which is recommended. Unlike so many “hi-end” components in this price range, this is
not a 75 cent IEC jack, but instead very high quality worthy of a good power cord. Even many aftermarket
‘audiophile’ power connectors are actually just gold plated 75 cent jacks so don’t be fooled.
The fuses are located on either channel of the ZTPRE and are rated at 2 amps each. Fuse specification is:
250V 2A Slo-Blo A 576-0313002.MXP
Physical Size is:
6.3 mm x 32 mm
The specification shown is available from mouser.com or you can call DECWARE at [phone] for replacement.
Also you can source your own fuses so long as they are the same physical size and rating. If you use an
“audiophile” fuse, make sure it’s not a standard ceramic fuse with a new wrapper or paint job as there are many fake
hi-end fuses available for 1000 times more than the actual fuse really costs. Your money would be better spent on
cables, or tubes.
NOTE: Installing the wrong size fuse or operating without a fuse could permanently damage your preamp if a tube
shorts. This would not be covered under the lifetime warranty and it is easy to know if the fuse specification was
exceeded.
The power switch activates both channels at the same time. As you know, the ZTPRE is a fully dual mono amplifier
which is why there are two fuses. These fuses cover both power supplies in both channels. Do not use larger than
a 2 amp slow blow fuse or your warranty will be void.
Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com

O W N E R S M A N U A L
OUTPUT LEVEL CONTROLS
The ZTPRE features an output level control for each channel which sets the output voltage of the ZTPRE to match
the amplifier’s input sensitivity. It is recommended for DECWARE amplifiers that have input level controls also known
as gain controls and also used as volume controls when no preamp is used, to have the output level of the ZTPRE at
full and experiment from there, whereas using the ZTPRE with non-DECWARE amplifiers it would be best to follow
this set up as your starting point:
Turn your amplifier ON and let it warm up a bit. While it warms up be sure your output level controls are turned all
the way down.
Turn on your source and raise the volume controls to the half way point. You will hear no sound yet, because the
output level controls are turned all the way down. Slowly raise each control one click at a time until the amps are
playing at your normal listening level. The ZTPRE output controls are now set. From this reference point you can
experiment with setting the output controls higher or lower and compensating with the master volume controls on the
front of the ZTPRE. Just go with whatever sounds the best. You are listening for dynamics, density, and a fullness to
the sound when you make these adjustments.
The output level controls come standard with ALL variations of the ZTPRE. They consist of 20 position gold contact
stepped attenuators using 1% precision metal film resistors with no leads and no circuit boards. There is no signal
degradation as a result of these controls.
Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com

O W N E R S M A N U A L
STUDIO OPTIONS
The small 1/4 inch plug you see above each of the three XLR input jacks on each channel are for switching when
there is more than one input and no rotary switch. In this case there is a toggle switch for each input channel
directly above the channel input. This eliminates the internal wire that would normally go to the rotary selector
switch. To use the switches you simply engage the one you want to hear on each channel. If you accidentally
engage more than one input on either channel, you will be able to hear both inputs simultaneously.
Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com

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TUBES
The ZTPRE uses 3 dual-triodes per channel to create a true balanced preamp. So if you look at this preamp and
think of it as a V6 race engine as its looks would suggest, it is actually a V12 using 12 triode stages to achieve audio
bliss.
ZTPRE is designed for the higher heater current requirements it’s factory tube compliment of 6N1P-EB tubes. These
are the smoothest and the warmest tubes available making use with digital sources particularly synergistic.
Replacement tubes are always available from DECWARE.
One of the unique features of the ZTPRE are the heater circuits. Each channel has it’s own AC heater supply which
was found to sound better than DC due to the inevitably higher current potential for the dollar, and the ZTPRE took it
a step further with a high voltage 18.9 volt supply rather than 6.3 volts. This requires all the heaters of all three tubes
on each channel to be wired in series. After extensive testing between AC, DC, it was found AC sounded better.
After additional testing between 6.3volts where each tube is wired in parallel vs. 18.9 volts where all three tubes are
wired in series saw another market increase in sound quality. It creates an interconnectedness between all the
tubes of the various channel and gives it the more transparent single ended sound the ZTPRE is famous for.
This means that if the heater burns out in one tube, all three will go dead just like old fashioned Christmas tree lights!
This is very rare of course but helps to know what can happen in rare cases.
The main rule with this type of circuit is that all three tubes should match as far as heater draw. See next page.
Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com

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TUBE HEATER CURRENT
The three tubes of each channel have the heaters wired in series which means that ideally you want all three tubes
to match. It definitely means that where the factory tube compliment of 6N1P-EB tubs are concerned, you either
have to run all 6N1P-EB’s or NONE at all. In other words, you can run 6922’s, good strong 6DJ8’s, or 7DJ8’s. Some
Russian 6N23P’s may also work well so long as they are relatively matched.
To be clear, you can NOT mix 6N1P’s with 6DJ8 or 6922 or 7DJ8 or any other compatible tube at the same time
without side effects. The reason for this is that the 6N1P has a higher current draw on its heaters than all of the other
tubes mentioned. Running tubes with miss-matched current draws like this can have effects like having your 6N1P
prematurely fail, or having one or both of the other tubes run with starved heaters causing higher harmonic distortion
which some people would actually like.
Also, when it comes time to change tubes if you notice one tube that has grown darker in appearance then the
others it is an indication that it was a weaker tube or had a heater that drew more current causing it to run hotter or
both. This is not a real sonic issue, but deserves explanation in so much that if you want all your tubes to balance
out perfectly and last the same amount of time aka wear evenly, then make sure they all match. Match the sections
of each tube and then match the tubes themselves. This will have little sonic benefit except over time, in that you’ll
get longer periods of time between tube changes.
The factory tube compliment of 6N1P-EB tubes have a rated life of 6000 hours.
Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com

O W N E R S M A N U A L
TUBE HEAT IN GENERAL
Due to the design of the ZTPRE’s tube layout, even if configured without a selector and completely covered by a
metal plate (worse case scenario) there would still be adequate ventilation for the tubes out the back so no worries
about overheating the ZTPRE however whatever was set on it would no doubt be overheated.
WARM UP
The ZTPRE has no unique requirements other than the typical warm up time associated with tube gear. After the
unit is turned on, the tubes will begin to warm up and glow and begin to pass signal after apron 30 seconds or so.
The best sound quality, as with all tube gear, will come some time after the 20 minute mark.
MAXIMUM ON TIME
There is no time limit or suggested maximum amount of time the ZTPRE can be left on. If left on indefinitely it will
have to be turned off for tube replacement every 6000 hours.
Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com