Cambridge Audio Alpha-9 Service Manual

H R I ALALPHA 9/9P SERVICE MANUAL

ARCAM ALPHA 9/9P SERVICE MANUAL

Issue 1 Serial No. 001 - (Paul Newton July 96)

Circuit Description

Input/Output Selection

The Alpha 9 integrated amplifier has 6 line level
inputs and optional phono input selected by use of
the motorised ‘listen’ switch, SW201.

The use of the 'record' switch SW202 allows
recording of one source whilst listening to another.
The Processor/Tape 2 switch, SW207, allows tape
monitoring of a 3 head tape deck connected to the
Processor/Tape 2 sockets. It can also be used to
allow input signals to be routed to an external
surround decoder for processing before being
routed back to the Alpha 9.

Tone Control & Preamp Out/Power Amp In

The tone control stage on the Alpha 9 is based
around a dual op-amp Z2. The first half provides
a buffer stage for the tone controls and the second
one with its frequency dependent feedback is used
as the tone control itself.

The output of the tone control then passes through
the balance control RV201 and then onto the
power amp stages and the preamp out buffer
stage formed by Z203.

The tone controls and balance pot can be
bypassed by use of the 'direct' switch SW205.

The Alpha 9 can be driven from an external
preamplifier source by moving the internal switch
SW206 to disconnect the Alpha 9 preamp stages
from the power amp.

Power Amplifier

The signal from either the Alpha 9 input sockets or
an external preamp enters the power amp stage
via C12 and R35.

Q11, Q16 form a long, tailed pair driven by the
current source formed by Q18 and Q19.

Q6 is the Class A stage driving the quasi
complementary output stage of Q4, Q5, and
mosfet's Q1, 2.

The Alpha 9 and Alpha 9P utilize an auto bias
circuit to maintain the correct quiescent current
(IQ). The circuit works by monitoring the voltage
across the 0.22 ohm resistors R1, RA1 and
comparing it to a voltage derived from the - 44v rail

via R24. Both these voltage are fed into the inputs
of comparator Z3. If the voltage across the 0.22
ohm resistors increases the output of the
comparator goes high impedance and Q15 is
turned off. This causes capacitor C72 to discharge
and reduce the bias on the base of Q17 which
reduces the IQ. Conversely if the voltage across
the 0.22 ohm resistors is low then Q15 is turned on
more and C72 charges and increases the bias on
Q17 and so increases the IQ. Under signal
conditions a low frequency, variable mark/space
ratio, waveform can be seen on the collector of
transistor Q20 as the bias is being automatically
adjusted.

Z1 is a d.c. servo used to maintain a low d.c. offset
at the speaker outputs.

Power Supplies

The Alpha 9/9P is powered by a toroidal
transformer with 2 sets of secondary windings.

The main windings are used to provide +/-44V
D.C. after rectification and smoothing by diodes
D201-204 inc. reservoir capacitors C201, 202.

The second winding is rectified to provide an
unregulated supply voltage for the motor driver ics,
Z402 (for the volume control) & Z403 (for the listen
selector).This unregulated supply is also smoothed
and regulated with a simple stabilizer circuit (zener
diode D402 and associated components) to
provide a stable voltage for the micro controller
Z401.

Protection/ Mute circuit
The protection and mute functions are carried out

by Z501. This performs turn on delay, d.c. offset
detection and thermal cutout. It also displays the
status of the amplifier with the use of a bicolour
LED - 'Green' for ready and 'Amber' for when the
speakers are disconnected internally because of a
fault condition or on initial power up whilst the 5
second switch on delay mute is operating.

If the unit suffers a current overload the protection
circuit may latch and the unit will not reset until it
has been switched off and on again. If the
protection is activated by a thermal problem the
unit will begin to operate again when it has cooled
down.

The thermal cut out operating point is set by the
thermistor TH501, mounted close to the output
device heatsinks.

Disc Stage (optional)

H R I ALALPHA 9/9P SERVICE MANUAL

The optional phono stage board available for the
Alpha 9 provides amplification and RIAA
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. The
negative feedback loop around IC2, R7, 8, 9, 10
and C3 provides the active low frequency RIAA de­emphasis.

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.

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 holding the pcb to the
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
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

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 6­7 mV.

H R I ALALPHA 9/9P SERVICE MANUAL

Alpha 9 Integrated Amplifier Parts List

Ref. No. Description Part No.

C1 ELST 100U 25V 2N710

C2 PEST 47N 63V 5% 2K347

C3 ELST 100U 100V 2N710B

C4 PCRB 100N 100V 5% RA 5mm 2H410

C5 PPRO 680P 5% 63V RA 2D168

C6 PSTY 56P 160V ENCAP 1PF% 2F056

C7 ELST 10U 50V 2N610

C8 ELST 100U 25V 2N710

C9 PEST 15N 63V 5% 2K315

C10 PEST 15N 63V 5% 2K315

C11 PPRO 220P 5% 63V RA 2D122

C12 ELST NON POLAR 10UF 35V 2U610

Alpha 9 Integrated Amplifier Parts List

Ref. No. Description Part No.

C106 PSTY 56P 160V ENCAP 1PF% 2F056

C107 ELST 10U 50V 2N610

C108 ELST 100U 25V 2N710

C109 PEST 15N 63V 5% 2K315

C110 PEST 15N 63V 5% 2K315

C111 PPRO 220P 5% 63V RA 2D122

C112 ELST NON POLAR 10UF 35V 2U610

C113N PPRO 220P 5% 63V RA 2D122

C114N PPRO 220P 5% 63V RA 2D122

C115N ELST 10U 50V 2N610

C116N PCRB 100N 100V 5% RA 5mm 2H410

C117N PCRB 100N 100V 5% RA 5mm 2H410

C13N PPRO 220P 5% 63V RA 2D122

C14N PPRO 220P 5% 63V RA 2D122

C15N ELST 10U 50V 2N610

C16N PCRB 100N 100V 5% RA 5mm 2H410

C17N PCRB 100N 100V 5% RA 5mm 2H410

C18N PPRO 100P 63V 5% RA 2D110N

C19N PPRO 100P 63V 5% RA 2D110N

C20 PEST 15N 63V 5% 2K315

C21N ELST 10U 50V 2N610

C22 PCRB 100N 100V 5% RA 5mm 2H410

C23 PCRB 100N 100V 5% RA 5mm 2H410

C25N PPRO 2N2 5% 63V RA 2D222

C26N ELST 10U 50V 2N610

C71 ELST 10U 50V 2N610

C118N PPRO 100P 63V 5% RA 2D110N

C119N PPRO 100P 63V 5% RA 2D110N

C120 PEST 15N 63V 5% 2K315

C121N ELST 10U 50V 2N610

C122 PCRB 100N 100V 5% RA 5mm 2H410

C123 PCRB 100N 100V 5% RA 5mm 2H410

C125N PPRO 2N2 5% 63V RA 2D222

C126N ELST 10U 50V 2N610

C172 ELST 100U 25V 2N710

C173 ELST 100U 25V 2N710

C201 ELST 10m 50V RA 32mm 2N910

C202 ELST 10m 50V RA 32mm 2N910

C205 PPRO 4N7 63V 5% RA 2D247N

C206 PPRO 4N7 63V 5% RA 2D247N

C72 ELST 100U 25V 2N710

C101 ELST 100U 25V 2N710

C102 PEST 47N 63V 5% 2K347

C103 ELST 100U 100V 2N710B

C104 PCRB 100N 100V 5% RA 5mm 2H410

C105 PPRO 680P 5% 63V RA 2D168

C207 ELST 10U 50V 2N610

C208 ELST 10U 50V 2N610

C209 ELST 10U 50V 2N610

C210 ELST 10U 50V 2N610

C301N CERD 1N0 63V 20% RA 2A210

C401N ELST 1M0 25V 2N810

H R I ALALPHA 9/9P SERVICE MANUAL

C402N CERD 10N 63V 20% RA 2A310

C403N ELST 1M0 25V 2N810

C404 CERD 10N 63V 20% RA 2A310

C405N CERD 10N 63V 20% RA 2A310

C406N CERD 10N 63V 20% RA 2A310

C407N CERD 10N 63V 20% RA 2A310

C408N CERD 10N 63V 20% RA 2A310

C409N CERD 10N 63V 20% RA 2A310

C410N ELST 10U 50V 2N610

C411N ELST 1U0 50V 20% RA 2N510

C501 ELST 100U 25V 2N710

C502 ELST 1U0 50V 20% RA 2N510

C503 ELST 100U 25V 2N710

C504 ELST 1U0 50V 20% RA 2N510

D104 ZENER 10V 400MW 3C11004

D106 ZENER 22V 400MW 3C22004

D201 RECT F ER MUR420 4A 220V 3B420

D202 RECT F ER MUR420 4A 220V 3B420

D203 RECT F ER MUR420 4A 220V 3B420

D204 RECT F ER MUR420 4A 220V 3B420

D401N RECTIF ER 1N4003F 1A 200V 3B4003

D402N ZENER 5V6 400MW 3C05604

D403N RECTIF ER 1N4003F 1A 200V 3B4003

D404N ZENER 5V6 400MW 3C05604

D405N ZENER 5V6 400MW 3C05604

D406N SSDIODE 1N4148 75V 3A4148

D407N RECTIF ER 1N4003F 1A 200V 3B4003

D408N ZENER 5V6 400MW 3C05604

C505 SUPPR CAP 4N7 250V 2K247

C506 CERD 10N 63V 20% RA 2A310

C507 CERD 1N0 63V 20% RA 2A210

C508 CERD 1N0 63V 20% RA 2A210

C509 CERD 1N0 63V 20% RA 2A210

C510 CERD 1N0 63V 20% RA 2A210

C511 CERD 1N0 63V 20% RA 2A210

C512 CERD 1N0 63V 20% RA 2A210

C601N PPRO 220P 5% 63V RA 2D122

C602N PEST 15N 63V 5% 2K315

C603N CERD 10N 63V 20% RA 2A310

D1 ZENER 10V 400MW 3C11004

D2 RECTIF ER 1N4003F 1A 200V 3B4003

D3 ZENER 10V 400MW 3C11004

D501 RECTIF ER 1N4003F 1A 200V 3B4003

D502 RECTIF ER 1N4003F 1A 200V 3B4003

D503 RECTIF ER 1N4003F 1A 200V 3B4003

D504 RECTIF ER 1N4003F 1A 200V 3B4003

D505N RECTIF ER 1N4003F 1A 200V 3B4003

D602 ZENER 5V6 400MW 3C05604

F501 INS COVER PCB FUSEHOLDER F022

F501 FUSEHOLDER 20mm PCB 8S004

F501 SPARE FUSE 20mm 1 6A AS C12166

FS502 INS COVER PCB FUSEHOLDER F022

FS502 FUSEHOLDER 20mm PCB 8S004

HS1 ALPHA9 & AV50 HEATSINK E801HK

HS201 HEATSINK TO220 13 DEGC/W F005

HS201 HEATSINK CL P TO220 13/8 6 DC/W F006

D4 ZENER 10V 400MW 3C11004

D5 ZENER 5V6 400MW 3C05604

D6 ZENER 22V 400MW 3C22004

D101 ZENER 10V 400MW 3C11004

D102 RECTIF ER 1N4003F 1A 200V 3B4003

D103 ZENER 10V 400MW 3C11004

HS202 HEATSINK TO220 CL P 23DEG/W F004

KP1 KWIKST K PAD S/A 25 X 12mm F157S

KP2 KWIKST K PAD S/A 25 X 12mm F157S

L1 INDUCT 2U2 15x25mm AD2018 7D002A

L101 INDUCT 2U2 15x25mm AD2018 7D002A

LED601 LED RED/GREEN 5MM 3D002

H R I ALALPHA 9/9P SERVICE MANUAL

LK401N JUMPER 3 WAY x 125mm L815CA

LK501N L NK BANDOL PREFORM 10mm 1X010A

LK601 JUMPER 3 WAY x 125mm L815CA

MI MAINS SWITCH SD33P NSULATOR E00301

MS MAINS SWITCH SPACER E66901

PL1N 2WAY MOLEX VERT MALE CONNECTOR 8K6201

Q1 TRANS POWER MOSFET IRPF240 4K240

Q2 TRANS POWER MOSFET IRPF240 4K240

Q3 TRANS LF SS P 2SA1085 4A1085

Q4 TRANS LF SS N 2SC2547 4A2546

Q5 TRANS LF SS P 2SA1085 4A1085

Q6 TRANS LF SS P BC556B 4A556

Q7 TRANS LF SS N BC546B 4A546

Q8 TRANS LF SS P BC556B 4A556

Q109 TRANS LF SS N BC546B 4A546

Q110 TRANS LF SS P BC557B 4A557

Q111 TRANS LF SS N BC547B 4A547

Q112 TRANS LF SS N 2SC2547 4A2546

Q113 TRANS LF SS P BC557B 4A557

Q114 TRANS LF SS N 2SC2547 4A2546

Q115 TRANS LF SS P BC557B 4A557

Q116 TRANS LF SS N BC547B 4A547

Q117 TRANS LF SS N BC547B 4A547

Q118 TRANS LF SS N BC547B 4A547

Q119 TRANS LF SS N BC547B 4A547

Q120 TRANS LF SS N BC547B 4A547

Q121 TRANS LF SS P 2SA1085 4A1085

Q401N TRANS LF SS N BC547B 4A547

Q9 TRANS LF SS N BC546B 4A546

Q10 TRANS LF SS P BC557B 4A557

Q11 TRANS LF SS N BC547B 4A547

Q12 TRANS LF SS N 2SC2547 4A2546

Q13 TRANS LF SS P BC557B 4A557

Q14 TRANS LF SS N 2SC2547 4A2546

Q15 TRANS LF SS P BC557B 4A557

Q16 TRANS LF SS N BC547B 4A547

Q17 TRANS LF SS N BC547B 4A547

Q18 TRANS LF SS N BC547B 4A547

Q19 TRANS LF SS N BC547B 4A547

Q20 TRANS LF SS N BC547B 4A547

Q101 TRANS POWER MOSFET IRPF240 4K240

Q102 TRANS POWER MOSFET IRPF240 4K240

Q402N TRANS LF SS P BC557B 4A557

Q403N TRANS LF SS P BC557B 4A557

Q502 TRANS LF SS N 2SC2547 4A2546

R1 RES MO 3W 5% 0R22 KOASPR3 1Q922

R2 RES CF 1W 1R5 5% 1E815

R3 RES CF 1W 5R6 5% 1E856

R4 RES MF FU W3 100R 5% NFR25 1G110

R5 RES MF W4 470R 1% 1H147

R6 RES MF FU W3 100R 5% NFR25 1G110

R7 RES MF W4 470R 1% 1H147

R8 RES MF FU W3 100R 5% NFR25 1G110

R9 RES MF W4 1K0 1% 1H210

R10 RES MF W4 1K0 1% 1H210

R11 RES MF FU W3 220R 5% NFR25 1G122

Q103 TRANS LF SS P 2SA1085 4A1085

Q104 TRANS LF SS N 2SC2547 4A2546

Q105 TRANS LF SS P 2SA1085 4A1085

Q106 TRANS LF SS P BC556B 4A556

Q107 TRANS LF SS N BC546B 4A546

Q108 TRANS LF SS P BC556B 4A556

R12 RES MF FU W3 220R 5% NFR25 1G122

R13 RES MF FU W3 470R 5% NFR25 1G147

R14 RES MF FU W3 470R 5% NFR25 1G147

R15 RES MF W4 1K0 1% 1H210

R16 RES MF W4 18K 1% 1H318

R17 RES MF W4 5K6 1% 1H256

H R I ALALPHA 9/9P SERVICE MANUAL

R18 RES MF W4 2K7 1% 1H227

R19 RES MF W4 2K7 1% 1H227

R20 RES MF W4 4K7 1% 1H247

R21 RES MF W4 330R 1% 1H133

R22 RES MF W4 2K7 1% 1H227

R23 RES MF W4 100R 1% 1H110

R24 RES MF W4 220K 1% 1H422

R25 RES MF W4 18K 1% 1H318

R26 RES MF W4 2K7 1% 1H227

R27 RES MF W4 5K6 1% 1H256

R28 RES MF FU W3 10R 5% NFR25 1G010

R29 RES MF FU W3 470R 5% NFR25 1G147

R30 RES MF W4 100K 1% 1H410

R31 RES MF W4 120K 1% 1H412

R54N RES MF W4 1K8 1% 1H218

R55N RES MF W4 1K0 1% 1H210

R56 RES MF W4 56R 1% 1H056

R57N RES MF W4 100K 1% 1H410

R58 RES MF W4 330R 1% 1H133

R59 RES MF W4 27K 1% 1H327

R60 RES MF W4 1K0 1% 1H210

R61 RES MF W4 33K 1% 1H333

R62N RES MF W4 820R 1% 1H182

R71 RES MF W4 15K 1% 1H315

R72 RES MF W4 15K 1% 1H315

R73 RES MF W4 15K 1% 1H315

R74 RES MF W4 15K 1% 1H315

R75 RES MF W4 10K 1% 1H310

R32 RES MF W4 47K 1% 1H347

R33 RES MF W4 470K 1% 1H447

R34 RES MF W4 47K 1% 1H347

R35 RES MF W4 2K7 1% 1H227

R36N RES MF W4 5K6 1% 1H256

R37N RES MF W4 6K8 1% 1H268

R38N RES MF W4 6K8 1% 1H268

R39N RES MF W4 12K 1% 1H312

R40N RES MF W4 6K8 1% 1H268

R41N RES MF W4 10K 1% 1H310

R42N RES MF W4 12K 1% 1H312

R43N RES MF W4 470R 1% 1H147

R46N RES MF W4 100K 1% 1H410

R47N RES MF W4 4K7 1% 1H247

R76 RES MF W4 12K 1% 1H312

R77 RES MF W4 220K 1% 1H422

R78 RES MF W4 120K 1% 1H412

R79 RES MF W4 33K 1% 1H333

R80 RES MF W4 1K5 1% 1H215

R81 RES MF W4 2K2 1% 1H222

R82 RES MF W4 100R 1% 1H110

R83 RES MF W4 4K7 1% 1H247

R84 RES MF W4 18K 1% 1H318

R101 RES MO 3W 5% 0R22 KOASPR3 1Q922

R102 RES CF 1W 1R5 5% 1E815

R103 RES CF 1W 5R6 5% 1E856

R104 RES MF FU W3 100R 5% NFR25 1G110

R105 RES MF W4 470R 1% 1H147

R48N RES MF W4 4K7 1% 1H247

R49N RES MF W4 1K8 1% 1H218

R50N RES MF W4 6K8 1% 1H268

R51N RES MF W4 100R 1% 1H110

R52 RES MF W4 6K8 1% 1H268

R53 RES MF W4 2K2 1% 1H222

R106 RES MF FU W3 100R 5% NFR25 1G110

R107 RES MF W4 470R 1% 1H147

R108 RES MF FU W3 100R 5% NFR25 1G110

R109 RES MF W4 1K0 1% 1H210

R110 RES MF W4 1K0 1% 1H210

R111 RES MF FU W3 220R 5% NFR25 1G122