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3
O!ERA
TING
INSTRUCTIONS
3.1
CONTROLS
AND
ADJUSTMENTS
FIG. 3 - 1
OPERA TING
CON
TR
OLS .
The D-60 'contains all the facilities essential for a
high performance amplifier.
The inp
ut
level controls
are
mounted on the front
panel.
Each
control should be adjusted for the de-
sired amplifier gain or output level.
When
the con-
trol is fully
CW,
the gain is 26db
as
determined
by
precision 1 % resistors in the D-60's feedback loop.
3.2
THE
PROTECTION
MECHANISMS
The
D-60 is protected against the common hazards
which plague power amplifiers, including shorted,
open, and mismatched loads; overloaded power
supplies; chain destruction pheomena; input over-
load damage;·and high frequency overload blowups.
Protection against shorted and mismatched loads
is provided
by
an
instant-acting limiter which in-
stantaneously limits at the volt-ampere product to
the
maximum
safe-
st
r
ess
va
I
ue
for the outplft
transistors.
The
area in which the amp will drive the load with-
out being V-I l
im
ited is depieted by the-'
1
cross-
hatched areas of Fig. 3-2. . ,
•,
If
a load initiates protection in the amplifier,
it
can
be
detected
genera
I
ly
by
watching the transfer
characteristics of the amplifier
on
an
oscillo-
scope or
by
plotting t
he
load's
V-I
behavior,
if
known,
on
to
Fig.
3-2. In applications where the
.load is a loudspeaker, amplifier protection will be
evidenced
by
distortion in the speaker. T
he
audible
effect ranges from something resembling cross-
overnotch distortion to a snapping sound, depend·
ing
on
the over-all load characteristics. Speaker
systems which are truly 4 ohms
or
greater will
not initiate the protection system.
The
AC
line for
120VAC
is
fused with a 2A, 250V
type
AG
fuse (on 240, 250VAC,
lA
type
AG)
. T
he
use of any other type of fuse will invalidate the
warranty.
All the amplifier's voltage-amplifiers circuitry is
designed to
be
inherently current-limited. T
he
r
e-
by,
if
any of the devices should fail, (which is
ex
-
tremely unlikely) no damage will occur to the rest
of the stages.
The input stage is protected against overdrive
. damage
by
-
a,-
series i imiting resistor should the
input signal level ever become very excessive.
17
The
amplifier featur
es
a controlled slewing-rate
which, coupled with the V-I limiter, protects the
amplifier from blowups when fed large
RF
input
signals.
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