Advertisement
ALPHA 9/9P SERVICE MANUAL
ALPHA 9/9P SERVICE MANUAL
The optional phono stage board available for the
Alpha
9
provides
equalization for both moving coil (MC) and moving
magnet (MM) cartridges.
Transistors Q2-5 and their associated components
provide the extra gain required for moving coil
cartridges when required Z1 forms a flat response
gain stage with the gain set by R3 and R4. R5 and
C2 provide a low pass filter used as the high
frequency part of the RIAA de-emphasis.
negative feedback loop around IC2, R7, 8, 9, 10
and C3 provides the active low frequency RIAA de-
emphasis.
The pcb mounted switch selects between MM or MC.
The board is powered by +/- 15V regulated rails from
the main pcb and the +15V rail is then regulated to
6.3V by Q1 and D1, D2 to power the moving coil
stage.
TEST POINT
DC VOLTAGE
TP1
+ 5V
TP2
+9.6V
TP3
0V MUTE ON +2V MUTE OFF
TP4
0V VOL UP +5V VOL DOWN
TP5
+5V VOL UP 0V VOL DOWN
TP6
+15V
TP7
-15V
TP8
+44V
TP9
-44V
amplification
and
RIAA
The
Disassembly For Servicing
1.
Remove the top cover and front panel.
2.
Remove 2 screws securing the sub front to the
chassis sides and 3 screws holding the
subfront to the chassis base.
3.
Remove 3 screws
chassis. These can be found close to the large
heatsink and also near to the mains inlet
socket.
4.
Remove 5 screws from the rear panel, one at
each end and 3 along the bottom edge.
5.
Remove the transformer bolt.
The pcb,
with the rear panel, transformer and
subfront attached, can now be pulled backwards out
of the unit.
TEST POINT
DC VOLTAGE
TP10
0.5V
TP11
0.5V
TP12
-2V
TP13
-2V
TP14
+2.2V
TP15
+2.2V
TP16
+6.8V
TP17
0V MUTE ON +2V MUTE OFF
The IQ voltage measured across the 0.22 ohm
resistors R1, RA1 or R101, RA101should be about 6-
7 mV.
holding the pcb to the
Advertisement
