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The
Finishing Touch:
Arm mass, Compliance, MM - Capacitance,
MC - Impedance Loading, Replacement Styli.
Now
that you have made the basic alignment
of turntable, arm and cartridge correctly, and you have adjusted the
advised downforce as well, it is still possible that you are not entirely
satisfied with the sound. Check the loading of the cartridge first.
The
signal in the record groove is followed by a diamond tip. Thsi
tip is glued to one end of a thin rod, a cantilever, made of aluminum,
boron, byrillium, or sapphire. At the other end of this rod a
small magnet is attached. It moves in between coils. The stronger
the magnet and the larger the coil, the stronger the signal will
be. The arrangement of magnet and coils (the topology) is of course
of great importance. Magnet and coils determine the quality of
the signal being picked up: strength, frequency characteristic,
harmonious build up, and the level of distortion.
The aim of course is to retrieve the maximum signal from the groove
by optimizing the mechanical technique (the functioning) and by
the application of specific materials for the various components:
oxygen free coil wire, core material, magnetic material, rubber
damper, cantilever, diamond tip, connecting wires, cartridge housing,
and the distances between the individual parts and the arrangement
(topology).
All these were as important in the early days as today. The final
verdict is bny listening to the cartridge in the appropriate arm,
well set up and connected to the phono stage with the appropriate
specifications (Ohm and picofarad).
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A
moving magnet cartridge should be connected to the phono
stage of your (pre-)amplifier. This
phono input should be marked MM. It should have the right capacitance
to make the cartridge sound best. Test reports and the specifications
of the cartridge tell you its capacitance and what capacitive loading
is best.
The
capacitance of the input of the amplifier should more or less
match the value of the cartridge.
Of course a lot of scientific explanation could be done, but just
follow the general rule:
The higher the capacitive value of the input the duller the sound
will be.
Check the technical specifications in the manual of your (pre-)
amplifier. The capacitance of the phono input should be mentioned
there.
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The
Moving Coil Principle
The
drawing shows the principle of the cartridge: coils moving
in a magnetic field. All parts and also the arrangement (the
topology) are of course of great importance. They determine
the quality of the signal being picked up: strength, frequency
characteristic, harmonious build up, and the level of distortion.
The aim of course is to retrieve the maximum signal from the
groove by optimizing the mechanical technique (the functioning)
and by the application of specific materials for the various
components: coil wire, core material, magnetic material, rubber
damper, cantilever, diamond tip, connecting wires, cartridge
housing, and the distances between the individual parts and
the arrangement (topology).
All these were as important in the early days as today where
cartridge builders have chosen different materials and maybe
a slightly different topology, but the main principle developed
by Ortofon is still their starting point.
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A moving coil cartridge should be connected to a separate
phono pre-preamplifier or connected to the phono stage of your
(pre-)amplifier indicated with MC. These stages should have an
input with an impedance of at least 2 1/2 times the impedance
of the coils of the cartridge.
Again, the technical specifications of both cartridge and preamplifier
stage will tell you if the matching is correct.
It is of course possible to exceed the figure of 2.5 times. Say
for a cartridge measuring 40 Ohms, the impedance of the MC section
of your preamplifier should have a value of at least 100 Ohm.
In certain preamplifiers the impedance of the Phono Input can
be adjusted. Certain manufacturers prefer/advise to use a higher
figure than 2.5 times the impedance of the coils of their cartridges.
For the same 40 Ohm cartridge they can advise 500 or even 1000
Ohm. A higher value gives a more slender sound and gives less
"massive sound". A higher value can be achieved by inserting
a resistor in parallel.
Generally
the impedance of the Phono Input is an integral part of the circuits
as calculated by the designer.
You can alter the value if the impedance of the Phono Input. If
the value is rather high for the cartridge, it is possible to
solder a resistor in parallel (inside the connector for instance).
But then the sound may get slow, less defined and will have less
slam (bad transient response).
A
moving coil cartridge can also be connected to a separatepre-pre
amplifier. Here the values have to be similar. The input impedance
should at least be 2.5 times that of the mc cartridge.
Yet
another possibility is using a step up transformer designed
for a specific group of moving coil cartridges. In that case the
input impedance of the step up transformer should match (or only
slightly be higher than) the impedance of the coils of the cartridge.
That is why you just should not buy any
mc transformer, but one that matches the cartridge you use.
Check
the specifications of your cartridge and of your phono preamp,
preamplifier or step-up transformer and make corrections if there
is a mismatch.
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After
you have found that downforce and loading are correct, it still can
be that the low frequencies are not firm enough and that the mid and
high frequencies have a fuzzy character and lack detail and definition.
Or it
may be just the other way round: the sound is muddy, has a heavy quality
and lacks speed.
Lightness, speed, firmness and correct tonal quality, they all depend
on the right choice of arm for your cartridge. Or to be more precise:
the right combination of the effective arm mass and the level of compliance
of the phono cartridge, which actually is the elasticity, the easiness
with which the diamond tip can be moved.
As the
techniques of recording and record production and manufacturing were
improving through the years and attained unquestionable heights, the
manufacturers of turntables were conducting research and were designing
new turntables which incorporated specific solutions in order to make
the record player function in such a way that it does not interfere
with the delicate signal contained in the groove.
It was more and more apparent that the isolation from the environment
plays a key-role and had to be improved. Vibrations from the motor
should be eliminated completely. Mechanical feedback via floors, cabinets
and racks also should be minimized or possibly eliminated completely.
Hence the introduction by Mitch Cotter of the floating chassis which
was first incorporated in the famous Acoustic Research belt-drive
turntable which deals with these two problems in a most effective
way.
The
resonance of the suspension of the turntable should be low enough
to not interfere with the functioning of the cartridge.
It also should not interfere with the information of the audioband:
20 Hz. to far above 20.000 Hz.
To a
certain extend the (de-)coupling of platter and arm can also be achieved
by means of rubber feet instead of supple springs. Another, very popular
method applied to modern turntables is the use of cones or spikes.
Because of the reduced contact surface of a spike, only very high
frequencies can be transmitted and low frequencies are stopped completely.
With large rubber feet the coupling of lower frequencies is taking
place to a certain degree because of the large surface, and the midband
and high frequencies may be damped somewhat.
The
complex recorded signal is picked up by the cartridge which should
always be fitted firmly at the end of the arm. Never loosen the cartridge
screws or place a thin plate of rubber, metal or other material in
between the cartridge and the headshell. If you do, the result will
be incorrect attack and no real transient at all. Arm and cartridge
are to be considered as an entity.
The
suspension of the turntable should have a very low frequency so it
does not interfere with the music.
The cantilever
of the cartridge also functions like a spring and (de-) couples the
arm at the cartridge's end from the record, platter and base, while
at the other end the arm is fixed at the pivot (arm base).
A
heavy object needs a strong spring. Likewise heavy arms are only suitable
for cartridges with a sturdy cantilever. In other words: a cartridge
with a low compliance figure needs a heavy arm. And vice versa.
A lightweight arm needs to be matched with a supple spring, in other
words a very compliant spring which is the cantilever of a high-compliance
cartridge.
The mass
of the tonearm can vary from 4,5 grs. of an SME 3009 III to even 38
grams of the Fidelity Research FR-66S. And the Ortofon SMG 212 for
instance has such a heavy counterweight that the use with moving magnet
cartridges is not advised. That arm was meant for heavy Ortofon MC
cartridges for which the step-up transformer was incorporated in the
headshell.
These Ortofons had a low compliance.
The very heavy Fidelity Research FR-66S has an effective mass of 38 grs.
With the Fidelity Research moving coil cartridge FR1-Mk3F the resonance
is
very low: 6 Hz. Also the FR-64(S) arm has a mass of 30 grs.
which still is too heavy for a Denon DL103.
In
all cases the resonance of the arm-cartridge-system should be kept
outside the audioband and should not be disturbed by the fundamental
resonance of the suspension of the turntable. There should be a clear
division between turntable, arm and audio signal.
Turntable
suspension: 2 to 4 Hz.
Arm-cartridge resonance: 8 to 12 Hz.
Audioband: 20 to 20.000 Hz.
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Naturally
you will consult the literature of the cartridge manufacturer and
check reviews and technical tests in order to find out what arm mass
is advised. Likewise you will try to find the best cartridge for a
given arm. And: you can measure the cartridge-arm resonance by using
a test record (if you have one) and see if it is in the right region.
However
the question remains: What is the frequency of a specific arm-cartridge-combination
that makes the system sound best? Is it 8 Hz.? 12 Hz.? Or say 9.4
Hz.?
This
you can find out by carefully listening to the tests of a special
technical record, or just the music you are used to. So if the sound
is muddy, has a heavy quality and lacks speed, than the mass of the
arm is too high. You can try to find a lightweight headshell and see
if that helps. But you probably will come to the conclusion that the
only thing you have to do is to buy a cartridge with a lower compliance
which is suitable for the heavy arm, or buy a lighter arm suitable
for the cartridge you already have.
If
the low frequencies are not firm enough and the high frequencies sound
fuzzy, than the arm is too light for the cartridge you are using.
In that
case the situation is better because you just have to add a bit of
weight to the arm. Sometimes a little piece of metal of just one gram
glued on top of the headshell can already mean a significant improvement.
After adding the weight you have to adjust the downforce and the antiskating
force anew. Here also listening carefully will tell you if you have
to add more or less mass.
Another
important factor is the distribution of the mass of the arm.
If you
find that the arm mass should be greater you should nevertheless take
care that the added weight is distributed more or less evenly over
the length of the arm.
If the arm is too light to match the correct compliance of the
cartridge, adding a little piece of metal to the headshell can lower
the resonance and improve the tracking and clean up the signal.
In
this way you can optimize the quality the functioning of the cartridge
and the retrieval of the signal out of the groove so that the most
natural sound will be heard through your speaker systems.
Do not think it is done in a minute or two. Take your time. Because
after optimization you might think you did the job, until you listen
the next day and find that it needs readjustment.
Good luck and good listening.
REPLACING
AN MC CARTRIDGE AND
REPLACEMENT STYLI FOR MOVING MAGNET CARTRIDGES
Many
music lovers go for a moving coil cartridge when it comes to a precise
and natural reproduction.
Some people however prefer the sound of a moving magnet cartridge
when they talk about high fidelity. They consider that a moving magnet
cartridge has more swiftness and speed and is pleasant to the ear.
Each
design has its specific positive features.
Yet
the moving coil adepts have it easier when the time comes to change
a worn needle tip for a new one. For them the road to constant happiness
is a straight one. They just exchange their used cartridges for brand
new ones. And they will seldom be disappointed.
The
life of the moving magnet adept is not so sure and simple.
Especially
when he is using an older cartridge for which original styli are no
longer available and he has to submit himself to the mercy of a manufacturer
of discontinued needles. Most of the time these needles are not of
the same quality as the original ones. This is because the materials
used are not the same as the original manufacturer would use for
1) rubber damper (suspension block),
2) magnet (how large is it and of what type, material),
3) the cantilever (how strong is it, of what material is it made,
what is the shape and mass),
4) and the diamond tip (is it a nude stone, what is its shape, what
is its mass, and is it well polished).
If
you order a needle for a discontinued cartridge, be sure it is an
original specimen. If that is not available, check the functioning
of the replacement stylus and compare it to the original one, both
by eye and by ear.
It
is impossible that the replacement made by a different factory will
meet the standards of the original stylus.
But
the difference in sound should not be too great. If a replacement
stylus does not perform well enough, you should sent it back to the
seller. Because an impaired stereo image, a limited frequency band,
and a restricted openness will only irritate the listener. Of course,
the suspension of the stylus needs a break in time. This is certainly
true. But if the replacement stylus does not give a general impression
of its qualities right from the moment you have slided it into the
cartridge, there is no need for any break in time.
In order to avoid these problems it is advised to buy a modern quality
cartridge of which original needles will be available for at least
another five years. Another option is to send the MM cartridge to
a service for a new tip placed at the end of the original cantilever.
That will guaranty another 2000 hours of enjoyable music listening.
Ask The Cartridgeman or Alt Jouk van den Hul for possibilities and
prices.
Good
luck and good listening.
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