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ALPHA 9/9P SERVICE MANUALALPHA 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)

1 2 3 4 5 6 ... 18 19

Inhaltsverzeichnis

Seite 1

ALPHA 9/9P SERVICE MANUALALPHA 9/9P SERVICE MANUALARCAM ALPHA 9/9P SERVICE MANUALIssue 1 Serial No. 001 - (Paul Newton July 96)Circuit DescriptionInp

Seite 2

ALPHA 9/9P SERVICE MANUALALPHA 9/9P SERVICE MANUALAlpha 9P Power Amplifier Parts ListRef. No. Description Part No.C1 ELST 100U 25V 2N710C2 PEST 47N 63

Seite 3

ALPHA 9/9P SERVICE MANUALALPHA 9/9P SERVICE MANUALD104 ZENER 10V 400MW 3C11004D106 ZENER 22V 400MW 3C22004D201 RECTIFIER MUR420 4A 220V 3B420D202 RECT

Seite 4

ALPHA 9/9P SERVICE MANUALALPHA 9/9P SERVICE MANUALQ116 TRANS LF SS N BC547B 4A547Q117 TRANS LF SS N BC547B 4A547Q118 TRANS LF SS N BC547B 4A547Q119 TR

Seite 5

ALPHA 9/9P SERVICE MANUALALPHA 9/9P SERVICE MANUALR106 RES MF FU W3 100R 5% NFR25 1G110R107 RES MF W4 470R 1% 1H147R108 RES MF FU W3 100R 5% NFR25 1G1

Seite 6

ALPHA 9/9P SERVICE MANUALALPHA 9/9P SERVICE MANUALR511 RES MF W4 18K 1% 1H318R512 RES MF W4 18K 1% 1H318R513 RES MF W4 33K 1% 1H333R514 RES MF W4 47K

Seite 7