This page was written several years ago and
is mostly a collection of different ideas I started out with
to improve the PL-12D. Most of these ideas I experimented
with and some of them turned out unnecessary - the most
drastic improvement was to better isolate the turntable from
sound feedback; this coupled with improving the audio
circuitry formed the basis of the eventual product.
Contents:
Why choose
the PL-12D?
Wiring
Tone arm
Headshell
Mechanics
Chassis
Platter
Plinth
Paintwork
Why
choose the PL-12D?
When I originally posted this online
a few years ago, one question which several people
asked was why I was using the PL-12 when there were
other 'better' turntables to spend the
effort on.
One turntable often mentioned was the Goldring Lenco, indeed these are good
turntables and they naturally have a heavier build quality
than the stock PL-12. Also the Lenco has
infinitely adjustable speed right from 16rpm through
to 78rpm - there are still not many turntables which
can match this.
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Linn Basik on a Goldring
Lenco |
My honest reason for not using the
Lenco is that I find the levels of wow and rumble on
idler drive turntables unbearable. This is just a
personal opinion, probably I've been spoiled by
digital music and spending the last 15 years
listening for wow and flutter on cassette decks -
different people listen for different aspects and
for me, I can forgive a lot of shortcomings but wow
and flutter isn't one of them, it really drives me
mad.
Also, the platter on the Lenco is
partly recessed which means it makes a difficult fit
for modern tone arms such as Jatco or Linn, there are ways around this (and
I've tried several ways to get Linn Basiks to work on
Lencos well, I really prefer to use the Linn arm
base as it's sturdier), but it does put an obstacle in the
way. Eventually the best way seemed to be to mount the Linn as-is and make up the extra height
difference with good quality platter mats.
There are also turntables such as
Thorens, there are great and I've owned a TD-160
myself - but they're really beyond the scope of what
I'm looking for to use as a base, again they do have
their own limitations and problems when it comes to
modifications.
Also there are various other mass
produced Japanese turntables from the vintage era,
why not use those? Most later mainstream Pioneers
resorted to large amounts of plastic for
construction (officially called 'low resonance
polymer' or 'polymer graphite' or similar), the
resonances of these materials are often through the
roof and because of their moulded nature are very
difficult to modify or otherwise reinforce or
acoustically damp. Some of the higher end vintage Pioneers
(PL-550 etc.) were actually very nice turntables with
good arms and were instead constructed mainly from
wood products and aluminium, but again these can be
difficult to modify a great deal without hugely
altering the design of the turntable.
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A repainted PL-12D. To get this quality of paint
finish takes time. |
Two things to remember about the
PL-12D are that firstly, they are plentiful and
quite inexpensive to buy. Secondly, during this era
(mid 1970's), the Japanese were at the top of their
game with regards to audio equipment; they were
innovating at a high rate, the Dollar (or Pound) to
Yen exchange meant that they could manufacture their
product on Japanese soil and sell it cheaply in the
West.
Add this to the PL-12's inherent simplicity
and you have a product which although cheap at the time,
contained quite a high grade of engineering and quality of
materials, and an overall build quality better than any
turntable you could buy for less than £800 today.
Audio for me is, above anything
else, a hobby. I own some high end equipment and
some low end equipment and respect both for what
they are. If you can understand this then you can
understand why I've put so much time and thought
into improving the humble PL-12.
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Wiring
The original audio cables are fairly
good quality, measure lower on capacitance per metre
than some 'better' interconnects which you can buy
today - really, for a stock PL-12 on average
quality cartridge, they're good enough. After trying
home built studio grade pure silver 8 mm cables on
one of my Technics turntables many years ago I'm a
convert to the difference a clear signal path can
make to the delicate signal from the stylus and the
drastic improvement it can make to the soundstage,
even on a vintage deck. Of course, silver cables are
expensive and for a PL-12D (and probably my SL-150),
completely overkill. But oxygen free copper (OFC) is
far more affordable and still a solid upgrade from
what was there originally.
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The interconnects I used to
use. Much better than the originals but
still slim enough to fit without too much
cutting. |
The whole idea is to work around the
original tone arm, the original internal wiring is
plenty good enough for the arm; tone arm wiring
upgrades can get expensive, if you use some of the
more expensive esoteric wire you're beginning to
creep near to the cost realm of armless turntables
and upgraded arms. 6 or 8mm shielded OFC cables work
very well when coupled with good quality metal
barrelled plugs, a good upgrade for the cost. Also,
the PL-12 arm doesn't rewire easily, the inserts at
the headshell end especially tend to cause problems
and you risk damaging the arm just to get access to
the connectors inside. There is a case to be made
for tone arm rewiring but after all, it's a short
length of wire, screened inside an earthed metal
tube, so interference isn't a problem (no tone arm
wiring is screened, after all).
Even less expensive higher quality
wiring like Litz copper or similar will undoubtedly
have better conductivity and higher frequency
performance than the old stock wire
would but the difference would be minimal over such
a short distance. Screened interconnects are a different
matter, screened cables inherently will present
capacitance between signal and screen (ground) and
inductance along the signal and will
easily load the delicate phono signal.
To reiterate, there IS a reason for
better tone arm wiring and I'm not trying to argue
otherwise - but it's not the most important part of
the turntable, choice of cartridge and cabinet
acoustics will have a far greater impact on the
sound.
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Tone arm
The stock PL-12 arm is, for its age
and cost, a very good quality arm. It's reasonably
solid, has good quality bearings, will take just
about any combination of headshell and cartridge.
That's not to say that there aren't better arms
around, there most definitely are, but nowhere near
this price range. You'll expect to pay
upwards of £150 for a good arm alone - far, far more
than you'll ever pay for an unloved PL-12. I did
consider fitting an aftermarket arm,
the PL-12 would certainly be a good candidate for an
arm upgrade - it's got a solid metal surface to bolt
onto, the platter is relatively high which should
mean that most modern arms will fit well regarding VTA (Vertical Tracking Angle).
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Headshell
The original headshell was made from pressed
aluminium and had a lattice style pattern cut into it. Nice
for aesthetics but not great for sound, replacing this with
a more solid cast aluminium headshell is much better for sound - more
rigid and less vibrations. The arm on the PL-12 has a
universal headshell connector and will take virtually any
headshell/cartridge combination, the sky's the limit here.
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Mechanics
The PL-12 is really as simple as
they come. The motor is a basic shaded pole
induction motor which is synchronous, depending on mains voltage frequency in order to run
at the correct speed. Many vintage turntables used
these type of motors, if designed well performance
can be good. There's no facility for speed control
and so the tightness of the drive belt and the
size of the motor pulley are the two major deciding
factors when it comes to platter speed, without modifying
either the pulley or changing the mains frequency
(NOT a trivial thing to do) there's no way of
altering the speed of the turntable. However, it's
a simple system and that's a good thing, one reason why these
turntables last so well.
The motor itself is good quality and
sits on its own sub chassis suspended by three
rubber mounts (which luckily don't seem to
deteriorate with age). The main platter bearing is
brass bodied and is rigid and also easily good
enough for the purpose, when cleaned and filled with
a good quality oil it should be relatively smooth
and rumble free. In all honesty, I find a good
quality car engine oil of a thicker grade to be more than enough to
keep turntable main bearings quiet and working well,
if an oil can handle bearings in a car engine
spinning at peaks of around 6000rpm and exposed to
massive forces and do that with minimal wear and
noise then it can easily manage a turntable bearing
which never sees more than around 5kg of weight at
under 100rpm.
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Chassis
The deck on the PL-12 is steel.
Steel, like any other material, will become excited
at a certain frequency and will resonate, sending
that resonance back town the tone arm and into your
speakers. One thing that the PL-12 and Goldring
Lenco have in common is that they both have a mild
steel chassis - a tad under 2mm in the Lenco
compared to around 1.5mm in the PL-12. I did
consider several ways of dampening the chassis, the
two favourites were either cutting thick material
(preferably hard rubber or MDF) and bonding it to
the chassis underside, or using thick soundproofing
sheets which I already use on other audio equipment
- or even a combination of both of these. The idea
is to make the chassis as acoustically 'dead' as I
can, any improvement here will certainly be
reflected in better sound quality and tone.
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Platter
The original platter is cast
aluminium and quite lightweight, remove the rubber
slip mat and it will ring like a bell if you tap it.
There are ways to dampen this, I had several ideas
including filling the central underside section of
the platter with a compound to damp it, also bonding
some sound deadening material to the underside of the
platter, perhaps even using non-ferrous screws or
bolts . The motor doesn't have huge torque output
and the arm isn't height adjustable so care is
needed not to increase the overall height of the
platter or to increase its weight too much. The
stock arm could be height adjusted but this
would complicate things greatly. The slip mat cuts
resonance of the platter a great deal, so I don't
feel it's a major issue on the PL-12.
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Plinth
This is where we get to what I feel
is the PL-12's main weakness
- resonance and vibration. The plywood case is
really a nice touch even if it is only laminate,
give it a tap however and notice how hollow it
sounds. Better still, turn up the volume and tap the
case while playing a record and see what you hear.
This is the very reason higher end eccentric
turntables tend to use very heavy, low resonance
materials for the critical parts of the plinth and
platter (resin, marble, solid timber etc).
Of course, you can remove the lid
and lose some of this resonance, but the plinth is
still acting like a microphone, amplifying any
vibrations through the sensitive pickup and feeding
it back into the amplifier - after all, a turntable
is a transducer and in this sense, you can
really think of it as a crude microphone,
the polar opposite to a loudspeaker. A completely
new plinth manufactured out of heavier materials
would be great, but the original plinth is doing a
good job of supporting the deck assembly, nothing
wrong with modifying it to
lower its resonant frequency and damp any
vibrations. Just like with a loudspeaker cabinet,
the thicker the cabinet walls, the better the
loudspeaker behaves at lower frequencies and the
less coloration the cabinet adds to the sound.
25mm (1") MDF is a good choice, the
plinth is relatively small so this material should make a
very rigid box with drastically cut resonances, add
a solid base panel and some rubber isolated feet and
you have a vast improvement over the original
design. The plinth can be made slightly deeper to
perhaps incorporate some bracing or some acoustic
padding, although it's wise not to go too far with
this idea for aesthetic reasons. The modified plinth
can then be veneered (something unseen on the PL-12
after the original prototypes in the late 1960's) in
walnut to compliment the cabinet on Pioneer's high
end amplifiers or receivers or in another wood
finish entirely (Black Ash springs to mind, then
venturing into more exotic woods such as Rosewood
and Maple, even a striking, straight grained timber
such as Zebrano if you're feeling brave).
I also toyed with the idea of taking
the isolation a step further still. The original
design suspends the deck on compression springs
which rest inside the plinth, each spring is a
slightly different stiffness to balance the weight
at each corner. These springs are filled with foam
pads which act as crude shock absorbers to damp the spring
effect and prevent the deck bobbing up and down
endlessly, although in reality I don't see these as
necessary. The new, heavier plinth could be fitted
with an extra sub base and that connected to the
bottom panel via springs or rubber isolators.
After some thought I decided against drastically
changing the suspension; it seemed like a great deal
of extra complexity for no gain, the tension springs
which I would have used could themselves contribute
more problems than they solved.
Finally, fitting three feet instead
of four may also help decrease vibration feedback. The reason
for using only three feet is because they can be
arranged in a
tripod arrangement, a tripod is inherently more
stable than a regular plinth which had four feet.
Although there's only a single foot at the rear now,
in practice stability isn't a problem as the centre of gravity
of the turntable is still quite low.
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Paintwork
Originally these were painted matte
graphite from the factory. A nice, smart subdued
finish but not outstanding among a stack of silver
audio components. There's something about the look
of well finished, highly polished surfaces on a high
end turntable, against all the polished metal it can
add a stunning finishing touch and never seems to
become outdated.
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PL-12D painted Roman Bronze metallic. |
The original deck plate to which the
arm and platter are mounted is pressed steel and this
has a smooth, uniform surface and is hence an ideal
candidate for gloss paintwork. The deck is sanded
and then several coats of high build primer are
added then wet sanded and more primer applied if
necessary.
Once the priming coat is finished, it's
smoothed and opened up with another light sanding
and then the first colour coats are applied with an
airbrush (an airbrush needs more investment in
equipment, but the resulting finish is far finer than an
aerosol can could ever achieve). Always better to build up gradually with
thin rather than thick coats, more so on metallic
colours where the metallic flecks need to be
distributed evenly in the coat of paint and not sink
to the bottom of the coat. Lacquer is then added,
usually 6 coats or so to get a really good finish
and the finished deck is then cut back and polished
by hand to get a mirror finish.
Dark or autumnal colours tend to
look the best, colours such as dark metallic reds
and greens, also lighter colours such as gold. I
painted prototypes in black - both solid and
metallic, both colours work well. The original Roman
Bronze metallic is a matter of taste I suppose but
it did look good to me, it would look very striking
with a pale wood (ash or beech or similar) plinth.
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