Shure | 994A | User guide | Shure 994A User guide

Shure 994A User guide
I L L L P H O N L D t l A W I R t 8383
March, 1941
Model 994A L i g h t Weight
C r y s t a l Record Reproducer
Model 994A L i g h t Weight C r y s t a l Record Reproducer
Model 9 9 4 Crystal Record Reproducer is intended f o r reproduction
of 10" and 12" lateral-cut records
and is designed t o give high-quality frequency response with medium output and unusually low record
wear. The c r y s t a l element is a Grafoil Bimorph
torsion u n i t with special-process and moistureproofing, completely shielded i n a c a s t metal
cartridge. The mounting is cushioned t o increase
i s o l a t i o n from the motor-board. The 994A reproducer has a base designed f o r s i n g l e hole mounting.
Low, record wear is assured by "BalancedTracking
(which maintains the horizontal project i o n of tAe needle closely tangent t o the groove
a t a l l times), by low needle-point impedance, and
the low needle pressure of 1-1/8 oz.
Model 99411 Light Weight Pickup is provided
with 12" leads.
APPLICATIONS: Model 994A Crystal Phonograph
Plckup w i l l give high-quality wlde
range reproduction with l a t e r a l - c u t
recordings a t e i t h e r 33-1/3 or 78 r.p.m. speeds.
The output voltage of the pickup is approximately 1 v o l t f o r an overall groove amplitude of
0.84 m i l a t 1,000 cycles which is s u f f i c i e n t t o
produce f u l l output from the audio stages of modern radio receivers and from moderate-gain audio
INSTALLATION: The Pickup should be mounted on the
motor-board so t h a t the a r c of
t r a v e l of the needle passes 1/4"
from the center of the record on the f a r s l d e of
the tone-arm pivot. A d r i l l i n g template Is furnished with each pickup t o f a c i l i t a t e motor-board
layout. The motor-board should be heavy and well
i s o l a t e d from vibrations of the motor and the
megohm or
put; the
ground or
The Pickup should be connected t o
the grid c i r c u i t of a vacuum tube
across a load resistance of 1/2
more. The coded conductor should be
t o the "highn slde of the amplifier inblack conductor should be connected t o
The 994A Pickup may be used with
any needle while s t i l l offering the
advantages of a Lightweight Pickup.
S a t i s f a c t o r y operation may be obtained with ordina r y s t e e l needles, precious metal-tipped needles
or sappare-tipped needles. Because of low needle
pressure and low needle-point impedance, needles
and records w i l l l a s t several times a s 1zng a s
when ordinary reproducers are used. The HighL i f t " arm provides f o r conlrmient needle changing.
shcald not be kekt
I f necessary, the length of the cable can be
increased considerably without excessive output
loss. Low-capacity shielded single conductor cable
Is s u i t a b l e f o r t h i s purpose. Make c e r t a i n t h a t
joints a r e well shielded t o avoid hum pickup.
Nothing should i n t e r f e r e with the f r e e motion
of the Pickup. Leads (or cable) should be a l l w e d
t o extend f r e e l y a t l e a s t two inches before making connections, so t h a t the pickup may r o t a t e
f r e e l y about its v e r t i c a l axis.
Sufficient cabinet ventilation should be provided t o keep the ambient temperature about the
pickup a t the lowest possible Value. I n any evetlt
the ambient temperature should not be allowed t o
(51.70 C. )
exceed 1250 F'ahrenhei t
Copyright 1939 Shure Brothers
Built-in "Balanced-Tracking", prsvided by the "needle-tilt
prlnelple i n the Model 994A Pfckup,
keeps the tracking angle (angle between hoF~zonta1
projection of the needle and the tanger:
t o the
record groove a t point of contact of needle and
r e c o r d l a t a negligible value throughout the e n t i r e
playing time of the record, A l a r g e tracking e r r o r
causes rapid record wear and impairs the f i d e l i t y
of reproduction, especially a t the higher frequencies. The Pickup should be locate; i n respect t o
the turn-table a s described under
t o derive the g r e a t e s t b e n e f i t from t h i s feature.
While imparting Its motion t o the mechanism,
the needle must be r e l a t l v e l y f r e e t o move from
s i d e t o s i d e i n the groove. The low needle-point
impedance of t h e Model 994A Pickup allows t h i s
Printed i n U.S.A.
f r e e motion, eliminating e x c e s s i v e t h r u s t and wear
on the s i d e s of the grooves. The needle Pressure
is only 1-1/8 ozs., insuring maximum record l i f e .
(necessary f o r l i f e - l i k e reproduction) some r e s i d u a l surface noise may be noticed, depending on the
condlt5on of the record.
Frequency response curves of the
9 9 M Record Reproducers obtained
on standard t e s t records a r e shown
i n F1g.A. This type of response i s very s a t i s f a c t o r y f o r high-quality reproduction of records
without t h e use of compensating c i r c u i t s .
Where maximum f i d e l i t y is n o t important, it
is possible t o decrease the audible needle-scratch
l e v e l by using t h e c i r c u i t shown i n Fig. C below.
This w i l l give a tone c o n t r o l e f f e c t s i m i l a r t o
t h a t found i n most r a d i o r e c e i v e r s and amplifiers.
I f the amplifier or r e c e i v e r used with t h e pickup
has a tone c o n t r o l f o r a t t e n u a t i o n of hlgher f r e quencies, the above c i r c u i t becomes unnecessary.
R-.25 MEG
The low frequency response below aPpI?OXimately 500 cycles depends upon the terminal res l s t a n c e a s shown i n Figure A. The u s e r can thus
a d j u s t the low-frequency response over wlde l i m i t s
by proper choice of r e s i s t a n c e of the input potentiometer o r g r i d r e s i s t o r . A value of 1/2 t o 1
megohm w i l l be s a t i s f a c t o r y In most cases. The
high frequency response i s n o t a f f e c t e d by the
value of t h e terminal resistance.
For more uniform o v e r a l l response, the low
frequency e q u a l i z e r c i r c u i t shown i n Fig. B, below, may be used, although I t Is n o t necessary or
d e s i r a b l e f o r most applications.
SURFACE NOISE : Surface noise or "needle s c r a t c h n
is produced by the passage of the
needle over the minute i r r e g u l a r i t i e s I n the s u r f a c e of the record groove. I n the
Voltage Sensivity:
l e v e l depends
lndlvldual recording,
With a standard recording the Model 994A has an output of approxlmately 1 v o l t f o r 0.84 m i l double displacement a t
1,000 cycles.
I n t e r n a l Impedance:
Equivalent t o 1,500 rmnf condenser.
Recommended Load
Impedance :
1/2 megohm o r more depending
upon the response curve rles i r e d . See Fig. A.
Model No.
f h s s u r e , low needle-po I n t Impedance, and low t r ~ ? k l n g , e r r o r , t h e r e
!s a Iainlmum of m r f a c ? noise from the. record.
Ho,iave r, due t o the wide range frecluency k s p o n s e
9uflr:= I I C I W P ,
w17;n low neealc
Code Word:
Cable Length:
Shipping Weight
13 oz.
Shure Crystal Record Reproducers a r e licensedunder p a t e n t s of the Brush Development Company. Shure patents pendlng.
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