dbx 463X - RMS Detector Circuitry

Control
Voltage
Path
Is
also
sent
to
the
volts
when
the
Input
Match*
point
and
This
level
Is
RMS
Detectors
(general)
The
heart
of
the
level
sensing
circuitry
In
the
463X
Is
the
dbx
patented
RMS
Integrated
circuit.
This
IC
takes
an
ac
signal
at
Its
Input
and
produces
a
dc
voltage
at
Its
output
that
Is
proportional
to
the
true
rais
level
directly
In
dB.
The
Input
(pin
1)
Is
a
current,
requiring
a
resistor
1
n
.series
from
a
voltage
source,
and
acts
basically
like
a
summing
Junction.
This
Input
resistor
sets
the
nominal
level
at
which
the
output
(pin
7)
Is
0 volts.
This
output
Is
a low
Impedance
voltage
source
and
can
drive
external
circuits
directly,
the
scaling
of
the
output
Is
a
lY
a
£
S
«
+6m
y
/
J
B
;
th1s
dc
voltage
Is
a
small
amount
of
ripple
at
tw
2
c
« thc
1n
P“t
frequency.
The
*RMS
SYM*
trim
pot
adjusts
this
l?
pl
?
f?
r
perfect
symmetry.
Attack
and
release
time
constants
are
adjustable
with
external
components
connected
to
pin
6.
For
a
more
detailed
explanation
of
this
IC
see
dbx
application
note
AN110
RMS
Detector
(463X)
nwe
.
In
addition
to
feeding
the
VCA,
the
output
of
0A1
RMS
detector,
IC2.
The
output
of
IC2
(pin
7)
is
0.000
current
(pin
1)
Is
5.7
micro-amps.
This
Is
the
"Level
corresponds
to
an
input
level
of
about
-lOdBv
at
C12.
calibrated
exactly
via
R25.
For
example,
with
the
scaling
of
**-6mV/dB.
the
/onEri* J[
olta
?
e
(
at
TP6
)
*111
be
+120mV
when
the
Input
level
is
+10dBv
f
b
?
V€
]
eve
J
match
)
and
will
be
-120mV
when
the
Input
level
Is
-30dBv
(20dB
below
level
match).
The
RMS
symmetry
Is
adjusted
by R31
and
Is
»uri
b
inn
e
H-»
S
ef
h
tha
*
a
Input
signal
the
ripple
component
Is
a
pure
100
Hz
sine
wave
at
about
70mV
p-p
at TP11.
* «,*..*
*<
speed
at
which
output
of
this
detector
changes
when
the
Input
signal
suddenly
gets
smaller
Is
called
the
'Release
Rate*
and
determines
the
basic
rate
at
which
the
463X
will
*downward-expand*
or
gate
A?
e
nfii
nal
j It
115
rate
.
1a
sct
by
the
non-linear
capacitor
circuit
made
up
ul
0A
:P
and
Jts
associated
components
connected
to
pin
6 of
the
detector.
When
the
voltage
changes
at
pin
6
are
large,
this
circuit
looks
like
a
small
capacitor
and
sets
the
release
rate
at
125dB/second.
When
the
voltage
changes
are
small,
this
circuit
looks
like
a much
larger
capacitor
vith
a
release
rate
of
about
25dB/second.
This
unique
feature
eliminates
any
increase
in
distortion
at
lo*
frequencies.
When
connected
to
another
463X
for
stereo
operation,
pin
6
of
the
jetector
Is
tied
directly
to pin
6 of
the
detector
in
the
other
unit
via
the
ring
on
the
Stereo
Strapping
Jack.
By making
this
connection,
the
iudio
levels
of
each
unit
are
combined,
and
the
output
of
the
detector
at
m’
ri
7
Is
the
true
rms
sum
of
the
two
levels,
reqsrdless
of
the
relative
>hese
between
them.