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TAPE RECORDER 15
PLAYBACK
7.2 Model 15 G T — Group Trainer
INPUT
OUTPUT
AMPLIFIERS
AMPLIFIERS
Fig. 7.3 NORMAL
INPUT
PRONE
OUTPUT
AMPLIFIERS
LEVEL
AMPLIFIERS
Fig. 7.4 GROUP
Model 15 GT is mechanically identical to the stan-
dard version. The height of the cabinet has, however,
been increased to accomodate the extra electronics
that enables distribution of programme to a group of
11 participants, or recording of a group conference.
These two functions are named NORMAL and GROUP
respectively, and can be selected with switch on the
front panel. Block diagrams for the two functions are
shown in figs. 7.3 and 7.4. Three of the eleven ampli-
fiers are shown. The additional electronics comprises
11 input amplifiers with preset gain, and 12 output
amplifiers with variable gain. Output amplifier no
1 is used as group amplifier. A separate programme
amplifier is also incorporated.
7.2.1 Input Amplifier
Each input amplifier comprises transistors Q201
through Q203 with associated components. See dia-
gram at the rear of the manual. Signal from the
headset microphone is fed to the corresponding DIN-
socket pin 2. After amplification in Q201 and Q202,
the microphone signal is tapped off and fed through
the mixing resistor R209 to GROUP/NORMAL selec-
tor. In GROUP mode the same signal is also fed to
terminal 1 on amplifier board no. 15001 in the tape
recorder. Transistor Q203 provides further amplifica-
tion of the signal before it is fed to the output ampli-
fier for the headset.
7.2.2 Output Amplifier
Each output amplifier comprises transistors Q301
and Q302 with associated components. Output ampli-
fier no. 1 is used as a group amplifier and is supplied
with signals from all remaining output amplifiers
when the GROUP/NORMAL switch is in GROUP posi-
tion. The output signal from the group amplifier is
distributed via another section of the same switch to
the remaining output amplifiers (2-12) via the pro-
gramme amplifier.
Input signal to each output amplifier is supplied from
the corresponding input amplifier via potentiometer
R301. The signal is mixed with signal from the pro-
gramme amplifier at the top of R304.
The output signal from each output amplifier (2-12)
is fed to the corresponding headphone.
7.2.3 Programme Amplifier
The programme amplifier is built around Q220. The
input signal is supplied from the PREAMP output of
the tape recorder only when the GROUP/NORMAL
switch is in NORMAL position. In position GROUP,
this signal is mixed with signal from the group ampli-
fier. The programme amplifier output is connected
to R305 in all output amplifiers 2-12.
7.2.4 Adjustment of Signal Levels
Adjust R301 to obtain 0.8 V across headphone for
1 mV input and with R304 in output amplifier (Adj.
Stud. Phones), turned to maximum.
Adjust R304 in group amplifier to obtain 0.8 V across
headphone during playback for a tape containing a
400 Hz signal recorded at normal level, and with the
same setting for Adj. Stud. Phones as above.
Adjust R301 (Adj. Group Level) to obtain 0.8 V across
headphones 3 through 12, with 1 mV into microphone
input 2, and with GROUP/NORMAL selector in posi-
tion GROUP.
7.3 Model 15 F
This model differ from the standard model by the
remote control facilities for start, stop and rewind.
The remote control unit is a foot pedal connected to
the recorder with a 3-pin plug.
The pedal has three positions. In unoperated position
the tape recorder is in STOP. Normal forward drive
is accomplished by depressing the front part of the
pedal. Depressing the rear part puts the recorder
into rewind mode. When the remote control unit is
to be used, the operating lever must be in normal
forward drive position.
7.3.1 Mechanical Operation
The mechanical functions in connection with the re-
mote control equipment are operated by solenoids
controlled by microswitches and the pedal switches.
Start/Stop Solenoid
The start/stop solenoid controls an eccentric mecha-
nism operating the pressure wheel assembly. Wtien
current is passed through the start/stop solenoid, the
30
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