Studer J37 - Page 40

-
until the output Ievel of the
playback
amplifler, as
measured
on the
\IIVM, has
reached
a
maximum. The
potentlometer
should be locked
ln this
positlon
by means
of the lock-nut,
-
At 15 ips the bias is increased by turnlng
the corresponding
potentiometer
slowly
in a clockwlse dlrectlon and the
point
where
the WVM
across
the output reaches
r
maxlmum,
should be
noted.
The bias is now further
increased until the
output
Ievel has
fallen
agaln by about I.5 db, The
potentlometer
should be locked
tn this
position
by
means of the lock-nut.
E
2c Alignment of the Record Gain Control
It can be seen
from the technlcal
details,
that the
lnput and output levels of the machlne
can be
varied within
a
fairly wide range.
It
is only
a
questlon
of the
galn
of the two
ampllfiers. The tape
itself is
always
magneticaliy fully modulated in order to
achieve a hlgh slgnal-to-noise ratio,
The
galn
of
the
playback
ampllfier ls
matched
to a
fully
modulated tape,
as
descrlbed
under E I. The
setting of the
gain
of the record amplifiers should therefore be
adjusted so
as
to obtaln
a
fully
modulated
tape
from
the available lnput voltage.
The Procedure For
Setting
the
Gain
is
as
Follows:
E2d
-
Load
blank
tape,
select
deslred tape
speed and swltch to
"record".
-
Setthesignalqeneratorto 1000c,/sandfeedthedeslredinputvoltage
e.g. I.55V,
to the input terminals.
-
Measure the output Ievel of
the
playback
amplifler by means of
a WVM.
-
Set
the
potentiometer
"Levelu
(
"Pegel"
)
on the record
amplifier
(
correspondlng
to the tape
speed
in use
)
so
that
the output level of the
playback
ampllfler as
reao
on
the
WVM, is the same as from reference level of
the test-tape. The controls on
the
playback
amplifier
must of
course not be altered in
any
way.
Measuring the
Overall
Frequency
Response
-
Set
the
lnput voltage to the machine from the
slgnal
generator
so
that
the \ITVM
across the output of the
playback
amplifier reads
at
least
-20
db with the machine
switched to
"record".
(
333
c/s
for
7 I/2 ips or 1000
c/s f.or 15 ips.
)
-
At
the
same input voltage
at
both
speeds lnject t0 kc,/s
and adjust the trimmers on
the
record
ampllfier
marked
"Equalisation"
(
"EntzerrunS"
)
71/2" and
I5"
respec-
tively so
as
to obtain the same output
voltage
from
the
playback
ampllfler as for
333 c,/s
and
1000
c/s
respectively'
-
Repeat the measurements over the entire frequency
range from 30
c,/s to
15
kc,/s
with
a constant input voltage
and
note
the
results,
If necessary, the two
trimmers
may be re-adjusted
in order to obtaln the
smoothest
possible
frequency
response
within
the working tolerances
and
the
speclflcatlons.
Allgnment
of
Frequency Response of the
Sync-playback
Ampllflers
-
The frequency response
sectlon of the test tape
should
be
used
for thls
measuremenl
-
Check the output level for each
channel on the monitor output
and if
necessary
ad-
E
2e