Table of Contents
Advertisement
4.6
INVERTER
IC 8C is
configured
as an
inverting, unity gain buffer ampli-
fier.
Its
purpose
is to
maintain correct input/output polarity
with
the
suppressor section switched
OUT.
Components
R85, R86 and
R87 form an offset
adjustment circuit which allows any
DC
offset
at
the input of the
output amplifier
to be
matched
to an equal
offset
at the
output
of
IC 8C
for minimal "click"
when
the
suppressor
is
switched
IN or OUT.
4.7
OUTPUT AMPLIFIER
IC 8D, Ql,
Q2 and
additional components comprise
the
output
amplifier.
It
has
a
voltage gain
of 1.4
dB and drives transformer
Tl.
With switch
SI in the IN
position, input signal
is
connected
from the low pass filter through C84 and
R84.
C84
provides AC
coupling for
the signal.
R84
is
essentially ignored
by the
high
impedance input
of the Op amp.
With switch
SI in the
OUT position,
the signal
path
is
through
IC 8C.
The relatively low output
impedance
of IC 8C
effectively short circuits
the signal coming
through
R84.
This provides proper isolation between the IN/OUT
conditions
of the
bypass switch.
Switch
S2 in the
setup position places diodes CRl
and CR2
across
the signal line,
limiting the maximum peak-to-peak signal
to
approximately
1.2
volts
for
setup purposes.
4.8
HEADROOM INDICATOR
IC IB is a
half wave rectifier
with
its
input
driven
from the
variable gain amplifier.
The output
is
filtered
by R8 and
C4,
and
drives the negative inputs
of IC
2,
sections
A, B,
C
and
D,
which
are used as
window comparators.
The thresholds for the individual
sections are derived from
the
voltage divider consisting
of R9
through
R13.
4.9
POWER SUPPLY
The power supply
is
bipolar, employing two integrated circuit
voltage regulators, VR1
and VR2, to
provide low ripple,
±18
volt
DC.
Additional filter capacitors ensure power supply stability and low
noise
.
The pilot LED
is
connected across
the
positive
and
negative
sides
of the
power supply
to
indicate
the
power ON condition.
-
16
-
Advertisement
Table of Contents
