by Steve Deckert
ZEN TRIODE PHONO
STAGE WHITE PAPER
MODEL ZP-1 and
ZP-1.5 and ZP-2
Zen Triode Phono Stage is an active single ended RIAA phono amplifier
using a single triode tube per channel in the signal path. It comes
in three models, the ZP 1, 1.5 & 2.
ZP 1.0 has around 30 dB of gain making it suitable to drive most
power amplifiers directly, including a Zen Triode amp which needs
2 volts to come to full power provided you use a high output moving
coil or moving magnet cartridge.
ZP 1.5 has around 48 dB of gain and incorporates a permanently installed
silver coil step up transformers (by Sowter of England) making it
suitable to drive most power amplifiers directly, including a Zen
Triode amp, with low or high output moving coil and moving magnet
ZP 2.0 has the same gain, but offers dual inputs and a switch to
select between them. One input is direct (same as the ZP1) and the
other input uses the step up transformer (same as the ZP1.5) So
effectively it is the same as have BOTH the ZP-1 and ZP-1.5. This
results in a very flexibile unit with the ability to permanently
hook up two turntables or tone arms.
THREE units employee a variable input impedance on the input that
adjusts from 3.5 ohms to 50,000 ohms in 20 steps with the simple
turn of a knob. This not only allows you to set the specified input
impedance for a given cartridge but also lets you tweak it one way
or the other which you will find is the real secret to extracting
the full potential from your cartridge. It will effect dynamics,
bloom, the amount of total gain, effect frequency balance allowing
you to favor the bass or treble, can act as a compressor to tame
things down, or as an expander to flush things out.
the ZP-1 this loading circuit is directly on the inputs, but is
not in the signal path. On the ZP-1.5 this loading circuit is on
the output of the step up transformer (also not in the signal path).
This means we can alter the impedance of the step up transformer
far beyond it's usual 25 ~ 100 ohm range. In fact with this arrangement,
you can still use a high impedance cartridge like a Dynavector MC,
and several Moving Magnet cartridges as well. It effectively makes
it possible to use high impedance cartridges (up to 50 kOhms)with
the step up transformer. Imagine having three tone arms set up with
three entirely different cartridges and having one phono stage sound
right on all three!
POINTS OF INTEREST
These units all use a dual mono power supply in a separate remote
chassis. This is the exact same remote power supply that our ZTPRE
preamp uses. It offers vibration free noise free continuous operation
without generating any substantial heat. It can be left on indefinitely.
It packs 5 times more current than is used by the phono stage and
uses absolutely no solid stage regulation or chokes of any kind.
The cable that connects the two units together is of the highest
quality and about 1/4 inch in diameter so it is easy to use and
though the circuit uses only one tube per channel, you will see
three tubes in the unit. The reason for this is two fold. A) We
choose to series the heaters of three tubes to keep the heater voltage
high to reduce hum. B) It is our observation that making each channel
"aware" of each other through a common heater has some
very positive effects on musicality.
addition, the input is tied to the plates of the the third tube
which also adds positive things to the sound, although difficult
to explain without getting long winded. It truly falls under the
category of being a Zen thing.
chassis of the phono stage is a symmetrical split design with tubes
in one side and electronics in the other. This makes tube rolling
not only convenient but SAFE. There is a removable cover on both
sides of the chassis. Besides being the right size, and shape to
be very ergonomic to use, it also offers great isolation from resonance,
and has good RF rejection.
actual circuit incorporates an active RIAA stage using minimal feedback
which is detailed in the design log titled "Diary of a phono
stage". It was evaluated against over a dozen popular circuits
including reference grade solid state designs and found to sound
the best. The performance is very good, with very low noise, very
low hum, and very open and holographic sound.
feel the end result is comparable with any high priced tube phono
stages currently available, and better than anything comparably
priced by a long shot. For that very reason, combined with the hand
built point to point quality we will be extending our lifetime warranty
and 30 day money back trial to this product as well.