TRIODE PHONO STAGE
REVISED FEB 2007
ZP3 phono stage has been in development for several years as a one-box alternative
to our ZP1.0 phono stage that used a remote power supply.
ZP1.0 was designed as a reference grade phono stage. To reach the performance level it
did, it required it's own dual mono remote power supply which
priced it out of reach for many people. You can read about
the work that went into it in the following two papers, Diary
of a Phono Stage" and Official
White Paper for the ZP1.0
then the ZP3
has been one of those pet projects of mine that I would
get out about every 6 months and try to make happen. I say
try, because I had set the a fairly high benchmark with our
ZP1.0 and didn't want to settle for anything less, especially in
the noise department. (That's where it always got sticky). It's
hard to build a phono stage in a single chassis that is as quiet
and one done with a remote power supply.
fact as I recall it wasn't all that easy even with a remote power
supply. When you build something as sensitive as a phono stage,
your dealing with around 40 dB of gain or more so a lot of the design
process is focused on the absence of noise and or hum. Part
of the thing that made it difficult in the first place was the point-to-point
wiring vs. using a circuit board.
that crazy design fest (above) that brought about the ZP1.0, one
of my favorite
sounding of the 5 best prototypes was actually the split passive RIAA
I had loosely based on a 2003 circuit by J. Epstein. Due
in part to my layout and point-to-point construction I had small noise/hum issues
with most of the prototypes including that one. For
that reason, the nice quiet active circuit is what went into production
and became our ZP1.0.
the years that followed and in response to requests for a less expensive
tube phono stage, I tried repeatedly to re-make one of my old prototypes
in a single chassis that was noise and hum free. If it could
be done it would drop the price significantly over a two chassis
design. My results always came close but I never as good as our
became obvious after awhile that chassis design and layout were
going to become the determining factors for success and they in
fact were. Once we switched the bulk of our amplifier line
over to the anniversary platform things began to fall together rather
nicely. The non-magnetic chassis created an eddy-free environment
that was far less prone to hum.
circuit is a split passive design with no negative feedback. It
uses a tube rectified and tube regulated power supply with a DC
heater supply. Execution of this circuit is unique in that
the B+ voltages used to drive the circuit are far lower than normal.
Similar circuits are using 330 volts to gain the maximum performance
from the 12AX7 dual triodes. The ZP3 is using a B+ of 244
volts to gain maximum liquidity and lengthen tube life. Rather
unconcerned about mathematical models and how good the circuit looks
on paper, the complete emphasis here is was on sound quality.
Lowering the voltage set the stage for several wonderful things
to happen. Things like greater sound stage depth, a more natural
and realistic image, a more organic timbre, less artificial
spotlighting of certain instruments and just a sense of ease. The
reason we listen to vinyl in the first place is because it doesn't
sound like CD's. I didn't want a phono stage that sounds like
a really good DAC but rather one that clearly makes a really good
DAC sound bad.
biggest question I'll be asked regarding the ZP3 is how can it possibly
be as good or better than the remote powered dual mono ZP1.0?
answer is that the ZP3 power supply is 150ma with only
a 30 ma current draw
from the circuit. That's about three times the size of the
ZP1.0's dual mono supply. The ZP3 also uses tube rectification while the ZP1.0's
was solid state rectified. Then the ZP3 takes it one giant
step beyond with tube voltage regulation. It is a serious overkill power supply for
a phono stage. It also uses a passive RIAA rather than active
and that eliminates having to use negative feedback. This
gives it better dynamics, better midrange presence, slightly more
detail and better depth.
ensure consistency in the noise spec for the ZP3, a circuit board
was developed for the RIAA section of the circuit leaving the rest
of it point-to-point like all of our other products. This proved
in the end to be the best of both techniques.
the high current and heat generating parts off the circuit board
ensures the high quality board will never fail or develop noise
with age because it will never heat up. Even the dual triode sockets
are chassis mounted (vs. mounted on the board) in such a way
as to make it impossible to put any pressure on the circuit board
during tube replacement.
board actually floats on the back of the ceramic tube sockets isolating
it from heat and vibration. The T6 aluminum chassis, combined with
a white powder coat finish, blocks heat and keeps the
tubes from punishing the circuit board. The rectifier
tube being the largest source of heat is isolated in the point-to-point
wired power supply section of the chassis.
keeping the interconnects from the optional rear jacks completely
off the board and keeping signal traces for the audio circuit incredibly
short we preserve fidelity. Long circuit board traces in the
signal path will not have the fidelity of good silver wire
in Teflon insulation.
feature of this design approach is the ground buss. As a designer
I've learned that the ground buss is perhaps the largest single
impact on the overall signal path besides components. A solid copper
rod is hard to beat. That makes the ground plane covering
the back side of the board in our ZP3 independent of the ground
buss rather than becoming the ground buss as is typical to do. The
overall ground scheme is now optimised with no current flowing through
the chassis and the board becoming it's own sub network located
at the end. Ground points are situated on the buss like
dots on a line and ordered least to most according to current flow.
front jacks that are standard on the ZP3 are located directly at
the front of the board and connected to it with 1 inch of flexible
silver/Teflon wire. This keeps the signal path leading into the
first input tube below 2 inches while maintaining total isolation
from the board. This way the jacks can never transfer any stress
to the board and slowly crack solder joints.
parts ie., resistors and capacitors used throughout the ZP3 are
audiophile components with 1% resistors and excellent sounding poly
caps. Selling our products on a 30 day money back trial means putting
your best foot forward so internal components and tubes are the
highest of quality and carefully tested.
of the sound is rather effortless, you have 4 tubes you can roll,
5 if you start trying different voltage regulator tubes.
handle Moving Coil cartridges, the same super hi quality Sowter
of England transformers that we used in the ZP1.0 series are being used as
the step up device. The advantages of using step up transformers
vs. just more gain are many. The blacker backgrounds and shimmer
on the top end are in and of themselves justification for the greater
expense and that's only two.
adjustable cartridge damping that was on the ZP2.0 is being employed
along with the Sowter transformers in a stand alone chassis and
sold as a separate product. This is because there are many
different Moving Coil cartridges with different specs. Most
of them fall into 3 categories, of which there are transformers
designed for each. There will be 3 models of the stand-alone step
up transformer called ZMC1, ZMC2, ZMC3. Each for a different category
of moving coil cartridge. All three will look identical and
be the same price making it easy for customers to trade-in one for
the other and so on.
go out to J. Epstein who's original circuit inspired my early prototypes,
and to J. Haggerman who was kind enough to offer his Cornet circuit
boards at one point along the way and let us modify them for
use in a ZP3. Even though that didn't end up happening, it
was much appreciated. (While the sound and implementation of these
three circuits is very different, the Epstein, ZP3 and
Cornet are using almost the same split passive RIAA scheme).
a final note I would like to suggest that many people who've never
gotten into vinyl can blame it directly on their phono stage / preamp.
I've heard enough phono stages that sounded no better than
a really good DAC to understand why so many people aren't turned
on to vinyl. I've seen cartridges and tone arms rotated until I was
dizzy when some of the worst performers turned out to be the best
after the right phono stage was employed. It really won't
matter how much you spend on a table, tone arm and cartridge if it
can't breath through a wonderful sounding phono stage. And a great
phono stage can easily sound better mated with a 300.00 cartridge
than an average phono stage will with a 3000.00 cartridge. I
wouldn't spend over $2500 on a phono stage without hearing a ZP3
side by side with it first.