Tandberg 10 XD Stereo Brochure 2
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Page 1
MODEL
10XD
STEREO
In the last year or two a steady stream of requests has come from
our marketing department for a Tandberg tape recorder that can
handle 10% spools. The requests have been put forward against a
background of recent developments in some of our most fruitful
export markets. The 10/2" spool was for a long time regarded as
almost the exclusive province of professionals. but now it Is
becoming fairly commonplace for keen amateurs.
When we started developing
the 9000X we were undecided
between the choice of a 7" spool
and a 10%" spool. Eventually we
decided on a 7" spool for a
number of reasons. One of the
reasons was the belief that the
particular design of the 9000X
c0uld give us certain experience
that we needed before we began
on the larger and more compli-
cated task of designing a 10/2"
spool machine.
Now we know that decision
was the right one. With the
knowledge and experience
gained from the 9000X project.
particularly during the develop-
ment and marketing stages, we
felt more able to tackle the
10XD. Besides. we were able to
include some features that the
market has now showed us it
wants.
It is clear from the exterior of
the 10XD that it comes from the
same stable as the 9000X and
the 9100X. This means that the
principles used in chassis con-
struction. the braking system
with friction brakes and elec-
trical brakes, the servo-control-
led tape tensioning and so on
are the same. The tape path is
the same. and all the audio
facilities and most of the circuit
design points have been bor-
rowed from the 9000X. At the
same time the 10XD has a
number of advantages over the
9100X as you will see from the
following detailed description.
101/2 spools
The facility for using 101/2"
spools is obviously the most
striking item of news. The larger
and more powerful spool motors
required to handle the larger and
heavier spools have been placed
in a new position to make room
for the spools. This has neces-
sitated changes in the lay-out of
the mechanical braking system
and the tape tensioning system.
Otherwise the same principles
which were used on the 9000X
and the 9100X have been re-
tained.
Spool sizes from 10%" down
to 5" can be used. For spools
with NAB hubs, NAB adapters
should be used. Two NAB adap-
ters and one empty 10/2" metal
spool will be packed with every
machine.
15 per second tape speed
The 10XD has three speeds. We
have chosen 15" per second as
the highest speed because this
speed is very much used by
professionals. In the old days
15" per second was necessary to
achieve satisfactory recording
quality. Today it is not so
important. However. this high
speed is important when it
comes to editing tapes. But
there is a price to pay and this
price is bad tape economy.
However, the Tandberg Cross-
field system gives exceptionally
good reSults right down to 3%"
per second. 30 with 15", 7%"
and 33/4" per second. the 10XD
should meet all the require-
ments of all the users.
Servo-controlled speed regula-
tion /d.c. capstan motor
The requirements we ourselves
placed on the tape speeds and
speed tolerances made it neces-
sary to abandon our traditional
system employing a hysteresis
synchronous motor and idler-
wheel transfer mechanism.
The choice fell on a servo-
controlled d.c. capstan motor
with belt drive between the
motor and the capstan/flywheel.
A more detailed description fol-
lows.
Capstan motor
We chose a d.c. capstan motor
which was able to run at the high
speed required (about 5000 revsl
min) without difficulty so that it
c0uld. via a suitable transfer
system. provide a tape speed of
15" per second. A conventional
d.c. motor with its brushes and
commutator can generate sparks
which lead to induced bursts of
noise in the magnetic heads and
amplifiers. To avoid this danger
in the 10XD we have employed a
brushless d.c. motor. The
brush/commutator system has
been replaced by Hall-effect
devices and transistors. The
motor functions according to
the following principle (see
figure).
E / gr.
wmmé?
The rotor is a permanent mag-
net. The stator has four wind-
ings. Placed on the stator there
are also two Hall-effect devices
displaced 90' from each other.
Hall-effect devices are semicon-
ductors with the following
characteristics: assuming a
constant current (i) and allowing
a magnetic field to go through
the device. we will get two
voltages out of the device (UI)
and (uz). The magnitude of
two voltages will be determined
by the magnitude of the mag-
netic field. In our motor the Hall-
effect devices are exposed to a
Cont. next page
Page 2
roughly sinusoidal magnetic
field when the motor rotates.
The voltages from the two de-
vices influence the transistor
circuits which are connected in
series with the individual wind-
ings. As a result the currents in
the windings flow in the correct
order determined by the position
of the rotor at any particular
instant.
Belt drive
Components forming the servo-control
system.
The capstan motor is mounted
at the correct distance from the
capstan/flywheel and the mag-
netic heads. A belt connects the
motor and the capstan/flywheel.
We could have chosen a direct
drive for the capstan. but our
experience tells us that this
arrangement can cause mecha-
nical and electrical interference
with the heads thereby adversely
affecting the SIN ratio and the
wow and flutter.
Servo-control
A d.c. motor is dependent on
one or another form of control
system to hold a given constant
speed. For any particular type of
motor it is possible to design a
relatively simple control system.
But in our experience these
simple control systems allow far
too much tolerance on the
speed. Furthermore they do not
correct for deviations in the
transfer system between the
motor and the capstan (devia-
tions caused by variations in
load and friction).
In the 10XD we have put
stringent requirements on speed
accuracy. We therefore chose a
servo-control system based on a
tachometer which senses the
rotation speed of the flywheel.
The 10XD has therefore a closed
system which eliminatestions in
the transfer system from the
motor.
NEWS FROM TANDBERG 10
With a precision adjustment
procedure a toothed wheel is
centred and clamped to the
flywheel. A semiconductor
speed sensing system consist-
ing of a light emitting diode and
a photo-transistor is m0unted so
that it bridges the teeth. When
the flywheel rotates the teeth
interrupt the light beam from the
diode to the transistor. The
output from the photo-transistor
is therefore a chopped waveform
(pulses) with a frequency that
directly depends on the rotation
speed of the flywheel.
The chopped waveform is
passed through an a.c.ld.c.
converter and compared with a
reference voltage. Undesirable
speed variations on the fly-
wheel/capstan result in a cor-
rection signal (the difference
between the output from the
a.c.ld.c. converter and the re-
ference voltage) being applied to
the motor to raise or lower its
speed.
A potentiometer permits the
three speeds to be adjusted
exactly. The system is stable
and therefore independent of
temperature, mains voltage, and
mains frequency. The tolerance
for the speeds is set to a
maximum of i 0.3%. As may
be seen in the performance
specification. the performance
for wow is also exceptional.
Because of the type of capstan
drive system used on the 10XD,
speed changes are carried out
electronically which means that
there is virtually no mechanical
work done by the speed selec-
tion knob. and it is very light to
operate.
A detail of the speed servo control
system.
As an accessory a PITCH
control can be delivered which
permits manual adjustment of
the tape speed within limits of
i 10% approx.
DOLBY N.R. B-TYPE
The Dolby noise reduction
system has turned cassette re-
corders into Hi-Fi equipment.
The principle of this system has
been described in a number of
technical journals and also in
earlier issues of News from
Tandberg.
The Dolby B system is em-
ployed in the 10XD. This has
brought a significant improve-
ment in the signal/noise ratio.
Tape hiss from modern tapes is
already very low and only during
for example, the most delicate
violin tones is it possible to hear
the hiss from the loudspeakers.
But with the use of DOLBY even
the most hyper-critical listeners
will be satisfied.
--.
The 10XD has a switch marked
«DOLBY N.Fl. B-TYPE» with four
positions. This switch makes it
possible to record or play with or
without Dolby. If the 10XD is
connected to a tuner. Dolby can
be used when recording stereo
transmissions. A filter is
brought in so that the stereo
pilot tone is substantially
attenuated. This is necessary for
the Dolby processor to operate
correctly. When the switch is in
the position «Dolby FM» record-
ings can be made of program-
mes that have been «dolbyized»
in the transmitter. The 10XD can
also be used as a decoder for
this type of «dolbyized» pro-
gramme when the tuner itself
does not have a decoder.
New logic control
The method we chose for driving
the capstan meant that the logic
control system for the spool
motors and solenoids had to be