JUNE 2001
by Steve Deckert

ZEN TRIODE PHONO STAGE WHITE PAPER

MODEL ZP-1 and ZP-1.5 and ZP-2

 

DESCRIPTION:

The 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.

The 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.

The 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 cartridges.

The 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.

ALL 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.

On 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!

OTHER 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 attractive.

Even 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.

In 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.

The 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.

The 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.

We 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.