Semiconductors; Circuit Description; Block Diagrams - Adcom GFP-750 Service Manual

itfMM' GFP-750 Semiconductor
Block Diagrams
U359 74LS04
-
Hex
Inverter
Vcc A6
ft AS VS
At Y4
U68 74HC573
- Tri-State
Octal
D-Type
Latch
UATCH
OUTPUT
10 20 30
<0
$0 <0 TO »0
ONO
CONTROL
Output Latch
H = Ngh
level,
L = low
level
Coptrol _
Enable
Data Output
Qo s
level of
output before
sleacfy-state
L
H H
H
input conditions
were
established
L
H
H
L
Z =
high
impedance
L L
X
Qo
X
S
don't
care
H
X X Z
GFP-750
Circuit
Description
Power
Supply
The power
supply
consists of
two
supplies
each connected
to
a
separate
secondary
winding
of
transformer T1.
The
first,
a+12V
unregulated
supply,
is
formed by D41-D43
and
filter
capacitor
C40
and
is
used
to
power
the various relay
coils.
From
this
a
regulated
5V
line
Is
derived
by Q39,
C46
and choke
L45,
L47
to
run the control
circuitry of
U53, U68,
volume and
balance motor
drives
and
front
panel LEDs.
The second
supply
is
formed
by
rectifier
diodes
D19-D22,
capacitor
C23 and
the regulator
circuit
of
Q28.
This
-f-60V
supply
Is
distributed
to
the
preamp
circuit
of both <^annels.
Signal Path
The
selected signal
source
Is
switched
to
the preamplifier
circuit
through a bank
of
relays controlled
by
U53. Only
the
CD
source has an
option for
balanced
input operation.
If
the
CD
input
is
operated with
an unbalanced
source, external
jumpers
must be
placed
In
XLR
jacks J165
and
J175
to
connect
pins
1
and
3.
The GFP-750
is
shipped with
these jumpers
in
place
(part
# 22001445).
This shorts
10