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TECHNICAL DATA
Orban Model
464A
at
the
top of
C129, which
is
charged
by
IC114b's
pin
7
through diode-
connected
transistor
Q109. IC114a
buffers
this
voltage
and
provides feedback
to
IC114b's
pin
6,
"telling"
IC114b
how
to
charge
C129,
C130
so
that
the
peak
value of
the
waveform on
IC114b's
pin 5
is
accurately followed.
To
achieve
the
very
fast
response
desired, the
peak-holding
capacitors
C129
and
C130
are
relatively small.
To
achieve a
sufficiently
slow recovery time
with
a
practical
value
resistor
(R222
=
22meg),
R222
is
bootstrapped
to
the
output of
IC
1
14a through R223.
R224
introduces
enough
DC
offset to
produce
approximately
0.5V
across
R222
at
all
times.
This
multiplies the effective
value of
R222
by
about
30,
and
slows
down
the
recovery time
as desired.
The
output of
peak
detector
IC114a
(pin
1)
is
applied
to
LM3916
bargraph
driver IC117. Other
than the
fact that
this
IC
provides
a
VU
(rather
than
a
linear) scale,
its
operation
is
identical to
the operation of
the
LM3914
used
in
the
IC116
socket
(see
above).
7.
Power
Supply
Unregulated
voltage
is
supplied
by two
pairs
of
full-wave diode
rectifiers.
The
nominal
unregulated voltage
is
±22
volts
DC
at
rated line voltage.
This
will
vary
widely with
line
voltage
variations.
Regulator dropout
will
occur
if
the
unregulated
voltage
falls
below
about ±17.8
volts.
Regulated
voltages
are
supplied
by
a
pair
of
overrated
500mA
"three-terminal"
IC
regulators.
Because
they
are
operated
conservatively,
they
can be expected
to
be
extremely
reliable.
Component-level
description:
The
two
pairs
of full-wave diode
rectifiers
that
supply
unregulated
voltage
located
in
package
CR3. The
rectifier
pairs
drive
energy
storage capacitors
C2
and
C3.
The power
transformer
T1
can
be
strapped
for either
1
15-volt
or
230-volt operation
(the
two
sections
of
the
primary
are paralleled
for
1
15-volt
operation
and
connected
in series
for
230-volt
operation).
The
pair
of ICs
which
supply regulated
voltages are "three-terminal"
IC
reg-
ulators
IC8, IC7.
IC8 and IC7
are
frequency-compensated by C4,
C5
at their
outputs
to
prevent high-frequency
oscillations.
Small 0.1nF/25V ceramic
ca-
pacitors
bypass
the
power
busses
to
ground
locally
throughout
the
board
to
prevent
signal-carrying
ICs
from
oscillating
due
to
excessive power-lead
in-
ductance.
(If
replaced,
C4
and
C5
must be
replaced
by
low-inductance
aluminum
elec-
trolytic
capacitors
only
—
see
'Tower
supply
problems"
on page
5-2.)
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