The most popular magnetic pickup made---also
one of the best and one of the cheapest---is the General Electric
"variable reluctance" cartridge, in which the stylus
is set in the end of a cantilever spring connected at its other
end to a small permanent magnet. The stylus and vibrates between
two iron pole pieces which extend up into the pickup chassis
and form the cores of two small copper-wire coils. The pole pieces
are yoked together at the top, close to the permanent magnet.
This creates a complete circuit-magnet through stylus bar to
pole pieces and back to magnet. As the stylus vibrates it feeds
this magnetic-flux circuit alternately through the two pole pieces,
inducing an electric voltage in the copper-wire coils. This voltage
is led off to your preamplifier and emerges from the loudspeaker
as musical sound.
Early GE cantilever stylus assemblies were
too massive to transmit very high-frequency vibrations. New GE
stylus assemblies, which fit the old cartridges, solve the problem.
Extraneous vibrations of the stylus and the lever are damped
pretty effectively by tiny elastic binding blocks.The GE comes
equipped with one stylus (for 78 or microgroove) or two styli
(one for each type of record) in a single cartridge. Anyone can
take out the old stylus and put in a new one on the GE pickup,
and the new two-stylus assembly is made in such a way that either
stylus can be replaced separately. Maintenance is simple-just
clean away the dust that gathers in the gap around the stylus.
GE's -new, 1958-model VR-11 is made to track at a vertical pressure
of only four grams. All the other variable-reluctance pickups
cost considerably more than the GE, and there is some question
about whether they are worth the extra money---except in a very
expensive rig. The German-made Miratwin has extra values, however,
for cheaper installations, too, because its output is five or
six times as great as the GE's, since it needs less "gain"
from the preamp. Among inexpensive preamps, where hum can be
a problem, the Miratwin may be a safer buy-especially since the
price difference between Miratwin and GE is now considerably
less than the price difference between an elaborate and a simple
preamplifier. The Pickering, which operates on somewhat different
principles, and offers reliable viscous-damping of resonances,
gives better high-frequency response than either the GE or the
Miratwin, which may or may not be worth the extra cost.
A new "moving magnet" pickup---the
Shure---is just coming onto the market now, and making a well-deserved
splash. Engineered to the smallest tolerances of any pickup,
the Shure is the most delicate and probably the most accurate
of variable-reluctance designs; the output is very low, usually
requiring a special transformer. Made to track at a vertical
force of less than two grams, the Shure competes on at least
equal terms with the fancier dynamic pickups, It costs as much,
In magnetic pickups the voltage which corresponds
to the motion of the stylus is induced in a stationary coil by
a "moving iron" element. In dynamic pickups the coil
itself moves. Generally speaking, this design produces an even
smaller voltage than the variable-reluctance magnetic design.
Thus dynamic pickups give extremely low output and require either
a top-quality preamplifier or a separate booster transformer.
The most popular of them is the Fairchild, in which the wire
coil is wound directly onto the duralumin bar that holds the
stylus. It is an extremely accurate pickup, and the least fragile
of the low-output dynamics. Fairchild makes only single-play
cartridges, which means that you must buy two (each of which
costs as much as a double-play GE) if you have both microgroove
and 78-rpm records. The cartridge must be returned to the factory
for stylus replacements minor drawback.
About the only disadvantage of the Fairchild
(except for its price) is that the magnetic field extends some
distance beyond the cartridge itself. If your record player has
an iron turntable, the magnetic pull will increase the effective
tracking weight of the stylus, speeding up both record wear and
stylus wear. Most people who want to spend $75 for their pickups
will also want to spend the necessary money for a machined-aluminum
custom turntable. For those who use this pickup with a record
changer, however, Fairchild makes a pad which sits on the turntable
and keeps the cartridge safely away from the pull of the steel
Many experts f eel that the new Electro-Sonic
Laboratories cartridge, especially in its imported Danish version
(the American model is built to a Danish pattern), is or ought
to be inherently the cleanest dynamic pickup, perhaps because
of the appealing logic of its design. It is, however, extremely
expensive (up to $100 for a single-play cartridge and balanced
arm; no dual-stylus model is made) and terribly temperamental
about working conditions. Like all pickups using magnets, it
gathers dust, and cleaning it requires elementary knowledge of
mechanics. In short, the ESL (as it is affectionately known in
the catalogues) is for hobbyists and specialists rather than
the average listener. Even here, it is seriously challenged by
the Shure and the splendid British Leak ($70 with arm), which
knowledgeable people say measures "flatter" than any
other pickup. But it has almost no vertical compliance---which
means it won't play warped records. The new Grado, just coming
on the market at the end of 1957, gains vertical compliance by
an ingenious plastic stylus bar and viscous-damped conical assembly.
This is the one, you may recall, that has the radium dot to ionize
Crystal and ceramic pickups operate on an
entirely different principle, chemical rather than electrical.
It has been known f or some time that a crystal made of Rochelle
salts will bend without breaking, and will give off an electric
signal when made to bend. In piezoelectric pickups the head of
the stylus (or, more commonly, a lever attached to the head of
the stylus) is inserted into the crystal or ceramic (a synthetic
crystal). Its side-to-side swing bends the crystal, and the result
is a fairly sizable electric signal. The piezoelectric pickup
has certain advantages over the magnetic. It gives off a much
larger voltage, which means that it can be used without a preamplifier.
Moreover, any extraneous noises that enter the system through
the pickup will be far less important, because the intrinsic
musical sounds are coming through with 60 to 70 times the strength
they would receive from a magnetic cartridge.
The induction coil that makes the electrical
signal in the magnetic pickup may in its wanderings come within
the field of the turntable motor and transmit a dose of 60-cycle
hum, while the piezo-electric pickup is impervious to stray magnetism.
Finally, the magnetic is unsatisfactory in moist climates, because
condensation forms between the poles of the magnet, eventually
corroding the guts of the pickup; the ceramic (not the crystal)
Nevertheless, a satisfactory magnetic pickup
is easier to design than a satisfactory crystal or ceramic. The
stylus in a magnetic pickup need push only a light coil of wire
or an equally light metal tube, while the stylus in the piezoelectric
pickup must bend a crystal. A baseball which hits a heavy wire
screen at 60 miles an hour may dent the screen; a locomotive
which hits the screen at that speed will go right through it.
In every pickup, the stylus moves at the same speed. If it is
to do more work, it must have greater mass.
The greater the effective mass of the stylus,
the less responsive it will be to the back-and-forth push given
by the moving wiggle on the phonograph record. It will have greater
inertia, greater tendency to keep traveling in whatever direction
it has been pushed. The strong low-frequency pushes, therefore,
will tend to drive the stylus right out of the groove. Keeping
the stylus in the groove will demand more stiffness inside the
pickup, more resistance to the free motion of the stylus. Most
piezoelectric pickups are therefore inaccurate at the lower f
frequencies. And the piezo-electric pickup is a constant-amplitude
device. The electric signal is caused by the bending of a crystal:
the greater the degree of bending, the greater the signal. Records
are cut, however, by a constant-velocity cutter, which makes
the strength of the recorded signal proportionate to the speed
with which the stylus whips around the wiggles. Low-frequency
signals become wiggles of considerable amplitude, and high-frequency
signals wiggles of infinitesimal amplitude.
Thus the piezo-electric pickup distorts the
recorded signal by giving a loud voltage to the low-frequency
notes and a soft voltage to the high-frequency notes. Moreover,
there may come a time, at very high frequencies, when the amplitude
of the wiggle is not sufficient to make the crystal bend, and
the piezo-electric pickup will not respond at all.
None of this is quite as bad as it looks.
As explained previously, high-frequency signals are boosted when
records are made, to mask surface noise; low-frequency signals
are attenuated, so that grooves can be kept narrow and lots of
grooves cut into a single disc. The piezo-electric pickup, in
boosting the bass signals and diminishing the treble signals,
acts to equalize the distortion built into the phonograph record.
While it will not boost or diminish on a curve that exactly matches
the "recording characteristic" of the record, it will
do a fair-enough job. And by eliminating the equalizer as well
as the preamplifier, it enables a big cost corner to be snipped
off. No piezo-electric pickup yet produced commercially will
respond throughout the audible range, but a few of the new designs
fit the stylus so closely into the ceramic that an electric signal
will be produced by wiggles as narrow as 14,000 cycles. From
14,000 cps to 17,000 cps, which is the utter limit of normal
hearing, represents a range of less than two whole tones in the
musical scale, so a pickup which responds to 14,000 cps is quite
adequate even for very high fidelity. Two piezo-electric pickups
are made for installation in a full high-fidelity rig: the Electro-Voice
Ultra-Linear and the Sonotone. Both companies make special preamps
to handle their pickups.
Among all the other piezoelectric pickups,
the experts have good words only for some Astatic crystals, the
Sonotone, the British-made Collaro and the Dutch-designed Ronette
ceramics. These would be adequate for low-cost hi-fi machines,
except that even the minimum hi-fi amplifiers now include preamplifiers
and are built for use with magnetic pickups. Most of the straight
amplifiers presently on the market do not even have an on-off
switch, let alone such refinements as a volume control. They
are meant to be used only with a separate preamplifier control
unit. So the crystal or ceramic cartridge fades away as a possible
buy for anyone building a set from individual components. Where
it is still important is in the packaged machine, usually portable
or table-top, which uses the stronger voltages from the piezo-electric
pickup to sidestep the expense of a preamplifier, and thus gives
value for money in the $125-$175 price range. People who are
looking to improve a well-loved package unit with a crystal pickup,
though, might try substituting a Ronette for the old crystal.
They'll hear the difference.
CAPACITANCE OR FM CARTRIDGES
The less work the stylus must do, the more
accurate the pickup can be. In magnetic, dynamic and piezo-electric
pickups the electric signal is generated by the motion of the
stylus itself, which requires a certain minimal bulk. Even with
the most careful engineering a vertical pressure of four to eight
grams is necessary to make such pickups work properly, and the
moving mass of the stylus must remain a measurable quantity.
If you could design a pickup, though, in which the signal voltage
was already there, and the motion of the stylus would merely
modify it, then...
Then you would approach the perfect pickup.
Literally hundreds of patent applications have been filed on
such designs, and a few such pickups have actually been manufactured.
The most successful of them is the Weathers, which is called
a "capacitance" pickup because engineers enjoy using
such words, or an "FM" pickup because it works similarly
to FM broadcasting. Briefly, the works of the Weathers pickup
consist of a fixed metal plate onto which is fed a very rapidly
oscillating charge, and a free-floating plate which in rest position
stands parallel to its neighbor, a tiny air gap away. The floating
plate is attached to the stylus. As the stylus traces the wiggles
in the groove of a spinning record, it causes the floating plate
to flutter toward and away from the charged plate. As the air
gap expands and contracts, the oscillating current is modulated
by the frequency of the vibration of the stylus.
The Weathers pickup cannot be bought alone.
You also need the Weathers box with the oscillator which feeds
the unmodulated and detects the modulated current, the way a
radio tuner detects an FM broadcast. The combination costs $40
with a sapphire or $55 with a diamond stylus. Since the Weathers
will not operate properly in any tone arm but its own, you had
better add $15 for the arm and buy the package. The advantages
of the Weathers are numerous. Since it tracks at a pressure of
only one gram, it wears both records and styli much more slowly
than any other pickup---except, perhaps, the Shure. A stylus
will last about 20 times its normal life in a Weathers pickup.
The moving mass of the stylus has been reduced to the point where
it is scarcely measurable, which means that the frequency response
is practically unlimited: the Weathers has tested out to 30,000
cycles. Because the vertical pressure is so low, the record can
played while resting on a center cushion no wider than the label.
The grooves never touch the turntable, and thus they pick up
much less surface dust than those of the average record.
But all this is balanced, in most households,
by the Weathers' one overwhelming disability: it is disgustingly
fragile. A cross look can give it a case of intermodulation distortion.
It must be fixed in place and left alone, and it is not recommended
for any household in which more than one person has access to
the phonograph. For bachelors, or people with unnaturally good
control over the spouse and children, the Weathers is excellent.
For others, it is just too delicate.
The Weathers pickup can be purchased with
any of five styli: a 78 diamond or sapphire, a microgroove diamond
or sapphire, or a "truncated" sapphire which will play
all kinds of records. Because of its exceedingly low tracking
weight, the Weathers can use an all-purpose needle without ruining
records. No other pickup today can make this claim. Some of the
cheap crystal pickups come with a single all-purpose stylus,
but they invariably chew up both vinylite and shellac records
in a very few playings.
A new and correctly shaped stylus will ride
in the grooves of a record with its weight on two points at the
sides of the groove. As the stylus wears, it will develop "flats"
at these two points. Now a 10,000-cycle wiggle, halfway through
a long-playing record, has a length of about .001 inch. If the
flat on the stylus has a length of .001 inch, the stylus will
simply ignore the 10,000-cycle wiggle. A worn stylus will therefore
cut the frequency response of the phonograph, regardless of the
newness of all the other elements. Worse, it will cut the record.
A sharp edge forms at the point where the hemisphere tip of the
stylus begins to flatten, and the edge gouges away the wiggles
in the record groove. At four grams of vertical pressure the
stylus presses on its two resting points with a weight of nearly
20 tons per square inch, and a sharp edge with such weight behind
it will soon ruin a record.
An osmium stylus, which is standard equipment
on crystals and ceramics of the second grade, will develop slight
flats after playing only two or three LP's and may begin to damage
vinylite records after as few as 10 playings (the wider groove
of the old 78 does less damage to the stylus and, generally speaking,
a 78 stylus will be safe enough for three times as many hours
as a microgroove stylus). Few people are willing to change needles
that often, and even if they were, the expense would be enormous.
No need for it: the the sapphire is much cheaper.
An average sapphire stylus will give about
35 or 40 long plays before it begins to scratch records. With
luck, it may go to 75 plays in safe condition. Since an LP plays
almost an hour, this is not an insignificant amount of music,
and in the average home would mean that the stylus would need
to be replaced every two months or so. For most pickups the replacement
cost is about $2. Pickups that must be sent to the f factory
for stylus replacement should not, however, be bought with sapphire
styli. The replacement charge on them is usually higher.
For LP's the recommendation is always the
diamond. The purchase cost of the stylus will run somewhere between
$8 and $16, but the diamond will last from eight to 30 times
as long as a sapphire, which means that it costs much less over
the long run. It also gives you fewer worries about what is happening
to your records. A worn stylus will ruin records long before
it begins to sound bad, and the man with a sapphire usually loses
part of the fun of his phonograph because he is listening for
that first sign of wear. A diamond should be good for at least
300 hours, and it may give 1,000 hours of listening before it
goes sour. There is a considerable difference between 300 and
1,000, and the man who lives far from the madding crowd may find
it difficult to decide when his stylus wants replacement. In
most larger cities, however, a record store or hi-fi shop will
have a 150-power microscope set up for the purpose of examing
styli-and you can see for yourself whether or not the tip is
BUYING A STYLUS
It is dangerous to try cutting corners on
the cost of a new stylus. When you buy a stylus you do not buy
just a tip, but a complete assembly which is a vital part of
your pickup. A "retip" soldered onto the old assembly
is likely to change the very delicate balance within the pickup
and produce distortion in the final sound. For the more common
pickups-notably the GE-stylus manufacturers such as Walco and
Tetrad produce perfectly good stylus assemblies which will work
as well as the manufacturer's own. For other pickups, however,
it is advisable to buy the stylus made by the company that makes
the cartridge. You have put a lot of money into a phonograph,
and the sound of that phonograph depends initially on the accuracy
of its pickup. It doesn't pay to save two bucks on a stylus and
distort the performance of the machine as a whole.
(Excerpts from the book
Hi-Fi All-New 1958 Edition)