Nippon DENON DCA-800 - Circuit Description

CIRCUIT DESCRIPTION
1. AUDIO SECTION
@ FET Input, FET Output
DCA-800 newly employs an operation amplifier which is a J-FET input type accommodating high-through rate digital source in the
input first stage of IC601, 602, 603. Also, in the output stage, employs a durable, highly reliable MOS FET which permits high-output
sound reproduction having a high-steepened, high-graded quality.
@ Sub-woofer
A sub-woofer signal is feasible by using VR603 to boost within the range of 0 ~ +16 dB to make balancing with the other channels
when sub-woofer input selector SW601 is set at INT. Also, this signal is processed with a -18 dB/Oct low-pass filter composed of
IC606. The filter's cut-off frequency is continuously variable within the range of 40 Hz ~ 120 Hz by VR604. (Fig. 1)
_ ® Crossover Circuit
An input signal applied to the front and rear channels can be processed with a -12 dB/Oct high-pass filter which is composed of
IC607,
608
by
using
SW602
at
need.
The
filter's
cut-off
frequency
is
continuously
variable
within
the
range
of
40Hz
~
120
Hz
by
VR605. (Fig. 1)
+16
Gain
(dB)
Sub
Woofer
Signal
———— Front/Rear Signal
Frequency
Also, the independence of SW601 and SW602 permits separate controlling of functions @ and @.
® Grounding Isolation
As
a
problem
of
amplifier
to
be
used
for
car,
the
grounding
position
difference
between
the
amplifier
and
the
in-dash
player
to
be
connected invites engine noise(en) overlap in the input signal.
In-dash Ployer ay Power Amplifier
if A(@s+€n)
«
Upon
this,
for
DCA-800,
the
primary
side
and
secondary
side
of
power
supply
ground
are
isolated
and
the
secondary
side
ground
i.e.
audio
ground to
the in-dash
player
is
connected to solve
this
problem. (Fig.
2)
es DCA-800
ANS
in-dash Player
2. POWER SUPPLY SECTION
@® Switching Regulator Controlling Circuit
IC801 (4PC494C) is an IC for switching regulator for control of DC-DC converter circuit.
The
pulse
switching
DC-DC
converter
circuit
is
output
from
No.
9
and
No.
10
terminals,
and
is
adopting
the
Fixed
Frequency
Pulse
Width Modulation Method.
When
REMOTE
turns
ON,
causing
TR818,
819
turn
ON
and
the
Pin
2)
is
supplied
to
the
power.
Upon
the
power
supplied,
the
standard
voltage
(5V)
which
is
built
in
IC801
emits
from
Pin
@
and
impressed
to
Pin
@
through
C808.
After
that,
the
voltage
at
Pin
@
gradually
reduces
voltage
to
ground
level
with
the
time
constant
of
C808,
R817,
however,
with
this
effects,
the
pulse
width
emitted from the Pins @, © of 1C801 gradually expands.
Accordingly,
occurring
of
rush-current
caused
by
the
steep
rise
of
power
at
REMOTE
ON
will
be
prevented.
(Soft
start)
This number of frequency is determined by C817 and R839.
Voltage
fluctuation
on
the
secondary
side
of
DC-DC
converter
caused
by
changes
of
power
voltage
and
load
is
captured
as
a
current
change
of
photo-coupler
(IC802),
and
the
pulse
width
is
changed
by
feedback
of
current
change
to
No.
10
terminal
via
VR801,
thus
the secondary voltage will be controlled.
® Toroidal Transformer
T801
of
this
unit
is
adopting
a
small,
highly
efficient
toroidal
transformer
and
therefore
the
stable
power
voltage
can
be
supplied
at
the time the output power is high.
3. COOLING FAN
Acooling
fan
is
newly
employed
to
this
unit.
This
fan
starts
running
when
the
heat
sink
temperature
becomes
approx.
70°C
to
lower
the temperature inside of the unit, thus each part of amplifier can perform stable functions.
4. PROTECTOR CIRCUIT
@® Protection of Speaker
C614 (uPC1237) searches various abnormalities and executes protective operations.
@ Overload Censoring
When
shortcircuit
or
overload
of
speaker
terminals
occurs,
current
at
(R630A
(B,
C,
D,
E,
F)
increases
causing
voltage
rise
of
this
resistance,
and
TR6O6A
(B,
C,
D,
E,
F)
turns
ON.
After
this,
due
to
turning
ON
of
TR608,
voltage
at
No.
6
terminal
of
IC614
increases by approximately 24V, and relay (RL601) turns OFF and separates the speaker from the amplifier.
@ DC Voltage Sensoring
Speaker
terminal
voltage
is
normally
approximately
OV
(DC).
However,
when
DC
voltage
comes
out
due
to
some
accident,
the
speaker is separated to prevent from breakage or burning damage.
if
DC
voltage
appears
on
the
speaker
terminal,
it
will
be
added
to
No.
2
terminal
of
IC614,
and
the
voltage
at
No.
6
terminal
is
raised up to approximately 24V, thus the relay (RL601, 602, 603) turns OFF.
e@ Acc OFF Sensoring
Acc
voltage
is
sensorate
via
R643,
ZD605
which.are
connected
to
No.
4
terminal
of
IC606,
and
the
relay
(RL601,
602,
603)
rapidly
turns OFF as soon as Acc becomes OFF.
@ Thermal Protection
When
temperature
inside
the
unit
rises,
resistance
of
thermistor
(TH802)
is
weakened
and
TR802
becomes
ON,
then
1C801
stops.
In case of abnormal high temperature, resonance of IC801 stops and then DC-DC converter circuit will be closed.
@® Protection Against at Excess of Primary Voltage
If
a
16V
or
higher
voltage
applies
to
the
battery
terminal
should
happen,
the
voitage
is
impressed
to
TR817
via
ZD801,
R841
and
TR817,
816
make
conduct.
Then,
IC801
stops
the
output
to
protect
against
abnormal
rise
of
the
secondary
side
voltage
and
breakdown.
DCA-800 Bm”