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AMPLIFICATION
PHONO STAGE ESSENTIALS
So why might you need such a phono stage? Some
amplifiers have a dedicated turntable input with
a phono stage built in, but many amplifiers don’t,
especially those made during that time when vinyl
seemed to be a thing of the past, before it became
cool again. Solution — put a standalone phono
stage between turntable and amplifier.
But it may also be worth upgrading a phono
stage even if you already have one. The quality
of built-in phono stages in amplifiers is variable
— all products are built to their price, and lesser
circuits like the headphone output and phono
stage can often get minimal funds. Similarly some
turntables today have their own phono stages built
in, so that they can work with any amplifier —
but you may achieve better sound by bypassing
that and using a dedicated phono amp instead.
The reason? This is the most delicate signal
in hi-fi, and handling it is one of the greatest
challenges in audio engineering. The signal which
comes from a turntable is produced only by the
tiny movements of a magnet attached to the
needle, inducing current in a surrounding coil
of wire. Or, instead of moving the magnet, you
can attach the coil to the top of the needle and
surround it with a magnet instead — moving
coil, instead of moving magnet. With no power
supply, no internal amplification for this process,
the result is a tiny electrical signal, its potential
down in the single millivolts, compared to the
two full volts that come from a digital source.
Moving-coil cartridges are the lowest of all, often
below a single millivolt.
Such a low signal will be a thousand times
more prone to interference than your normal
line-level signal — and that’s a very good
argument for keeping the initial treatment of your
phono signal physically apart from the higher-
powered functions going on inside an integrated
amplifier, especially one with digital processing.
Pro-Ject’s S2 further protects against external
interference by having its housing made of an
aluminium/metal sandwich construction, with the
external finish available in either silver or black.
Secondly the quality of that initial treatment
can have an enormous effect on the final sound.
The application of thousand-fold amplification
prior to that of your main amplifier means that
any added noise or distortion is magnified, as
will be other characteristics such as the quality of
channel separation.
And the phono stage does not only amplify.
It also applies EQ — indeed a massive dose of
EQ. Vinyl fans often go on about purity, but the
whole vinyl path to playback is squeezed through
two curves. The first is applied prior to cutting
the disc, tilting the frequencies up to reduce
bass frequencies and raise the treble. Then in the
phono stage a reverse curve is applied, boosting
the bass and curbing all that extra treble.
Why do this? Because the reduced bass content
qat the initial stage makes LPs easier to cut and
safer to play, since large bass fluctuations create
such deviations in the groove that the needle’s
tracking ability can be compromised. Meanwhile
the downward treble adjustment on replay allows
a reduction of hiss and clicks while bringing the
music content back to its original level.
So the use of emphasis and then de-emphasis
allows safer and easier mastering, and some
advantages to playback. The cost is the jiggery-
pokery of phono EQ curves.
Making things still more complicated, there
were originally many different curves used by
different record companies; early amplifiers could
switch between the more common ones. But
thankfully RCA Victor’s ‘New Orthophonic’ curve
has been a de facto global standard for records
since 1954, becoming known as RIAA equalisa-
tion, so phono stages today just adhere to this.
It’s not a simple curve — there are three transition
points where the curve is redefined. Pro-Ject
quotes a maximum 0.4dB deviation from the
RIAA curve for the Phono Box S2.
All of this is why phono stages can make such
a difference to the sound of a turntable, and why
they can sound so different to each other. They
mould the signal at a very early and delicate stage,
and even small differences become amplified
into large ones. So a good phono stage can easily
outperform those within amplifiers by merits of
signal isolation and more dedicated design.LISTENING
And the Phono Box S2 proves a good phono
stage. We used it first with a visiting turntable
equipped with a relatively modest AT-VM95E
phono cartridge, under $80 if bought separately.
We checked the specs for this straightforward
moving-magnet cartridge — load impedance
47kohms, load capacitance 100 to 200pF, and the
gain we left at 40dB as recommended for other
moving magnets of 4mV output. So that meant
clicking up three of each eight DIP switches —numbers one, three and seven. And we made
direct comparisons with three other phono stages
— the one available in the turntable itself, the
stage in our resident Musical Fidelity preamplifier,
and (rather rudely, given its price) the impeccable
phono input of Yamaha’s 5000 Series preamplifier,
which has its own set of tuning options.
One clear conclusion is the confirmation of
how much difference phono stages can make to
the overall sound. On Pink Floyd’s ‘Animals’ closer
Pigs on the Wing pt2, the turntable’s built-in phono
stage sounded clear enough, but switch to the
Pro-Ject, or indeed any of the other three, and the
panned acoustic guitars were tonally filled, from a
thinner jangle to a richer, more real acoustic guitar
tone. The vocal was also more solid, even more
central, which you’d think a tracking trait rather
than being subject to the phono stage’s variation,
but it sounded as if the left-right treatment from
the turntable’s own internal circuit was not as well
matched as Pro-Ject’s dual mono circuit design,
which delivered a firm non-slipping central image.
At the start of Keith Jarrett’s trio’s Flying pt 1
there didn’t seem much to pick between the
renditions of Jarrett’s solo piano, but once Gary
Peacock’s drums and Jack DeJohnette’s drums
entered, the differences were far clearer in the
depth and richness of the bass tone, its ability to
deliver the microdynamics of a firm pluck over a
light one. The ride and China boy cymbals were
held more smoothly in check by the Pro-Ject’s
balance, whereas the turntable’s in-built phono
stage added a little too much ‘sting’; the Pro-Ject
was simply more musical. We loaded a recently-
acquired LP of Tears For Fears’ ‘Seeds of Love’,
hearing it on vinyl for the first time through the
S2; it took a full 40 minutes out of our reviewing
time, simply enjoying this richer version of the
album — and unmasking a vocoder vocal track
doubled behind verses and bridges of Sowing The
Seeds of Love — never before noted, and heck,
we’ve played that album a lot.
The synth pad and electric vocal on Jeff
Lynne’s ELO’s Sun’s Gonna Shine was given a