Dual 721 - Tonearm and Suspension; Tonearm Design and Balancing; Tonearm Removal

Fig. 11
Tonearm suspension
28 27
41 201 72
50
40
53 58 48 36 54 38
____•_•_,.
BIS
IZ
311111 MM
Mir
......
Tonearm and Tonearm Suspension
The
feather-light,extremely torsion
resi-
stant
all-metal
tonearm is
suspended in a
gimbal.
Suspension is by
means of 4
hardened
and
precision
polished
steel points
which
rest in
precision ball
bearings. Tonearm
bearing
friction is thus
reduced to a
mini-
mum.
Bearing
friction vertical
0.007 p
Bearing friction
horizontal 0.015 p
as related to
stylus point
As
a result,
it
ensures most
favourable
pick -up
conditions.
Before
adjusting the
pick
-up force to
suit the
built-in
pick -up
cartridge
the
tonearm is
balanced with
the
scale
set to zero.
Coarse
adjustment is
carried out by
moving the
weight with
the
stem
(51), the
subsequent fine
adjustment
by turning the weight.
The balance
weight is
designed so
that pick -
up
cartridges having a
deadweight
of 4.5 -
10 g
can be
balanced. lt takes
the form of
a
double
anti-resonator
thus
absorbing the
vibration
energy in the
range of
tonearm
and
chassis
resonance. For
this purpose,
the
inner
part
weight is
matched to
the
tonearm
Fig.
12
58
53
50
62
64
233 -
210
159
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•
moullY
11.
230
231
232
214
234
156
38
54
55
51
111H11
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sommulan
resonance and
thus acts as anti-resonator
by means of antiphase
vibration. The outer
part of the balance
weight taking the form
of a higher balanced anti-resonator
prevents
transmission of partially occurring chassis
resonance to the
tonearm.
The
tracking
force is
adjusted
by
turning
the
graduated spring
housing
(58) incor-
porating
a coil
spring. The
scale has
mar-
kings for a
range of
adjustment
from 0 to
30 mN
(0 to 3 p)
which
permit
accurate ad-
justment of
the
tracking
force. One
grad-
uation in
the range
of 2 - 15
mN (0.2
-
1.5
p)
corresponds to
1 mN
(0.1 p), in
the
range
of 15 - 30
mN (1.5
- 3 p) to
2.5 mN
(0.25 p).
Removal of
tonearm (50)
from
bearing frame
1. Secure
unit in
repair jig.
Remove weight
(51)
unscrew
fixing screw (54).
Set
tracking force
scale to
zero.
2. Move unit
screening
an muting
into head
position.
Remove
plate
(133). Unsolder
tonearm
switch
(131).
3.
Move unit
into normal
position.
Turn
both
mounting screws
- SW 4.5 -
(55)
counterclockwise to the
stop of the
bear-
ing
frame
(53).
Attention!
Observe the
bayonet
mounting.
Slide
tonearm (50)
rearwards
and remove
it
upwards
from the
bearing
frame.
For
installation
proceed in
the reverse
or-
der.
Removal of
tonearm
assembly with
tonearm
bearing
Proceed as
follows:
73
1. Secure
unit in repair
jig. Set
graduated
spring
housing (58) to
zero. Arrest tone -
arm
(50). Remove
weight
(51).
2.
Loosen
tension layer (62)
and bring
tone -
arm (50)
in its
highest
position using
knob (64).
Fasten
tension lever (62).
Bring
knurled
ring (66) in
position
"3".
3.
Turn unit
upside down.
Remove screening
plate (133).
Unsolder
tonearm leads on
the
muting
switch.
4.
Remove machine
screw (217), hex
nut (218)
and
fillister
head screw
(70). Also re-
move transition plate
(268) and guard
plate (219).
12