Arcam Diva A80, Diva P80 Schematic

Service

DiVA

Manual

Issue 1.0

A80 Amplifier
P80 Power Amplifier

ARCAMARCAM

Bringing music & movies to lifeBringing music & movies to life

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Circuit description

o

A80/P80

!

Technical specifications

Circuit diagrams

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o L943AY

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Transformers

o

L916TX – 115/230VAC toroidal

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L917TX – 100VAC toroidal

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L907TX – 100VAC frame

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Exploded view diagram

o

A80

Mechanical & packing parts list

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o A80
o P80

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Circuit board silk screen

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A80

o

P80

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Circuit board parts list

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A80/P80 combined

Contents List

Circuit description.

Power supply.

The mains input to the unit is supplied at
filtered the Y Caps and locations C200 /C201 and X
cap at location C209, these are in-place to reduce
mains born HF interference and to prevent bridge
rectifier noise from leaving the unit.

The mains select switch at location
conjunction with the dual primaries on the 115/230v
transformers, the switch allows for the units to be used
in territories running a 115v or 230v grid when the
switch is set to the 115v position the primary windings
are connected in parallel.

Fig 1. Fuse value information.

Fuse location. Value.

FS200 T2.5A (20mm)
FS201 T2.5A (20mm)
FS200 (100v) T3.15A (20mm)
FS201 (100v) T3.15A (20mm)
FS202 (s.m standby 9v a.c rms) T500mA (s.m)
FS203 (D.C inline) T2.0A (20mm)
FS204 (D.C inline) T2.0A (20mm)

The standby Transformer TX200 continuously powers

digital

the
connected to the unit, this supply powers the Micro via
a regulating circuit based around regulator
special mention should be made of fuse FS202 as any
interruption to this supply will render the unit
completely lifeless and as such this circuit should be
checked before inspecting any other areas of the
board.

We will see that the main power transformer
supplies a separate secondary winding for the

–15v analogue

board locations FS203 and FS204, the failure of either
of these fuses will cause the op-amps connected to the
regulated rails to swing D.C. The regulator at location
REG 200 regulates the +15 rail and intern supplies the
+5V(A) analogue supply via the reference Zener at
location

The high level power amp A.C supplies arrive at
Con204 as a 4-wire supply this allows us to implement
a dual bridge network circuit with 4 individually
smoothed D.C rails these are labelled as +45(L),
+45(R) and -45(L), -45(R) we pull a –38v rail from this
point to form the VFD cathode bias voltage via R211
Con205 delivers the 3.3 V A.C supply to the main
board and then onto the display VFD via R203 (2R2
f.u).

DZ200

circuitry (+4.8v(D)) when power is

regulation stages via the two fuses at

and drive transistor

SK200

and is

SW200

TR200.

works in

REG 201

TX200

+15

and

Fig 2. Supply identification and related components.

Supply Related components
+ 45v L
+ 45v R

- 45v L

- 45v R

- 38v VFD
+15v (A)

- 15v (A)

+ 5v (A)
+4.8 (D)

Fil 1/Fil 2

Left power amp positive rail.
Right power amp positive rail.
Left power amp negative rail.
Right power amp negative rail.
Display cathode rail derived from –45v(R)
IC 300, 301, 302, 303, 304, 305, 306,
307, 308, 309 also including the input
clamp diodes all within the pre-amp stage.
IC 300, 301, 302, 303, 304, 305, 306,
307, 308, 309 also including the input
clamp diodes all within the pre-amp stage.
IC309 volume control
Input trigger stages, signal detect IC700,
delayed off IC703, IC701. Main micro
IC600.Remote pickup, Master reset
IC601, Over current detect-AC detect –
thermal cut-out IC600

3.3v~ filament supply.

Pre-amp.

The A80 Pre-amp has inputs for Phono, Aux, CD, Tuner,
AV, DVD and Tape. All inputs except Phono have a simple
resistor-capacitor 340Khz low pass filter to remove any
unwanted high frequency noise from the input signal/local
area, a pair of diodes on each input connected to the
+15/-15v rails prevent damage to the CMOS input
switching chips at locations IC300 and IC301, if any offset
is seen at the input the switching chips on a given input we
may suspect the failure of one of the input diodes.

Fig 3. Logic status of IC302 and 303 (switching chip).

Low= 0V High=4.8 (Cmos).

Input. A0
Phono
Aux
CD
Tuner
AV
DVD
Tape

The outputs of IC300 (L) and IC301(R) can be seen on pin
8 as a current signal and such this can not be viewed via
CRO although a 100 ohm resistor inline with the scope
probe may yield some results, from here we drive into line
drive op-amp IC307 (L) and IC308 (R) signal can be seen
at the output pin (1) and travelling into the volume control
chip (IC309) on pins 16 (L) and 9 (R) the output from the
Volume control is driven into IC307 at pin 6 (L) and IC308
pin 6 (R) and seen again on pins 7 on both IC307 and
IC308. After the Con 302 and Con 303 we drive directly

(pin 1)

Low Low Low

Low High Low

High High Low

Low Low High

High Low High

Low High High

High Low Low

A1

(pin 16)

A2

(pin 15)

Into the power amp stages but from this point we can
configure the unit as a separate Pre amp/Power amp
by moving the jumpers to the pin 2 and 3 of Con 304
and Con 305, and then remove the jumpers at Con
302 and Con 303 this may also be of use when fault
finding as we can effectively isolate the and D.C
offset/distortion problems coming from the Pre amp
stage to the power amp stages and test these stages
as a separate entity.

The Pre amp power up mute and power down mute is
controlled by the relay at location RLY300 A/B the
relay also triggers to mute the switching noise when
switching between inputs (see micro control/protection
and display section).

Power amp stages.

The main power amplifiers are of a Class A/B design
which use SAP “audio” transistors in a asymmetrical
current feedback configuration, Input and feedback
paths are D.C coupled and there is a active integrating
servo to remove D.C offsets from the outputs.

The basic principle of operation is as follows: Left
channel description given only, read all references as
5xx for the right channel.

The input level of the power amp stage is clamped by
the 3V9 zener diodes at positions DZ402 and DZ403
this protects the power amp input stages from gross
overload and subsequent damage R410 and R402 and
C416 in parallel form a 340khz filter.

IC400A is a V-I converter with a gain of 2 it’s output
will be a accurate amplification of it’s input voltage (i.e
the output voltage at pin 1 will be identical to the input
at pin 3 but twice the amplitude) the output voltage is
driven unto a 44 ohm load formed by R445 and R446
this op-amp is used in a slightly unusual configuration
in that it’s power supply pins are used as a current
output and the output pin is used as a current
feedback. Transistors TR404 and TR408 supply the +/­15v rails and act as cascades to pass it’s supply pin
currents through to the current mirrors.

The “feedback current” flows back from the power amp
output via R447-R450 to allow IC400A to swing it’s
output, this is why the term current feedback is used –
it’s is the current flowing in the feedback resistors that
sets the overall gain of the amplifier.

IC400B acts as an inverting integrator and it’s purpose
is to remove DC from the loudspeaker outputs. Any
positive D.C offset will cause the output of IC400B to
go negative thus increasing the current in it’s negative
supply pin and pulling the output voltage back to zero
R420 and C442 set the time constant of the integrator
so that audio frequencies are ignored

The transistors found at locations TR400 and
TR401/TR402 form the PNP Wilson mirrors and TR416
and TR411/TR417 form the Wilson NPN current mirrors,
emitter degeneration is provided by R405, R406 (+) and
R407, R408 (-).

R415 and R416 decouple the current mirror stages from
the main power supply stages to allow the bootstrap circuit
to operate this circuit is formed by C423 and C424 and the
Metal film 1 watt resistors at locations R452/R453, the
boots strap is provided to allow the output stage rails to go
up and down slightly with the output signal to the
loudspeaker, this enables the driver stage to fully saturate
the output drivers giving the greatest output and the best
thermal efficiency.

TR405 and TR407 are the Pre-drivers, TR412/TR414 and
R411/R434 provide a current limit of about 30mA under
fault conditions. R423 and R428 loosely couple the
outputs of the output drivers to the inputs of the SAP
output devices, this allows the output devices inbuilt
temperature sensing diodes to accurately control the
quiescent current of the output drivers as the temperature
varies, C425 and C405 ensure that both halves of the
output stage receive an equal A.C component.

The output transistors are TR413 and TR415 these are
specially designed for audio power use Sanken SAP15N
and SAP15P devices they provide a inbuilt 0W22 thick film
power resistor and temperature sensing diodes that track
the V

BE

versus temperature characteristics of the power
transistors allowing for accurate control of the quiescent
current.

R459 and C427 form the Zobel network which is provided
to ensure that the amplifier see a constant and resistive
load at high frequencies C421 locally couples the “High
frequency” and signal grounds together at the input stage
for the same reason. Any signs of burning or scorching of
R459 will indicate that the unit amplifier channel(s) have
been running unstable or oscillating.

The Bias should be set for minimum distortion (THD+N)
using a 0.5v rms 20 Khz sine wave into the CD input with
the amplifier set for full gain, the absolute maximum level
of Bias acceptable is 22mV measure across CON401 (L)
or CON 501 (R) the adjustment is made using RV400 and
RV500 we set the bias at the factory using an extremely
accurate Audio Precision-audio analyser.

If you do not have access to a distortion level meter
capable of 0.05% or better accuracy you may be able to
rough set the amplifier to a typical reading of 15mV (at
cold switch on).

Fig 4. Suggested blanket replacement parts for

power amp failures.

Location Description Model Part no.

TR413 Output driver + SAP15NY 4CSAP15N
TR415 Output driver - SAP15PY 4CSAP15P
TR410 Predriver + FMMT 497 4AFMMT497
TR412 Predriver + ZDT 6758 4AZDT6758
TR414 Predriver - ZDT 758 4AZDT758
TR405 Predriver - FMMT 597 4AFMMT597
TR401 Current mirror PNP BC859B 4A859
TR402 Current mirror PNP FMMT 597 4AFMMT597
TR411 Current mirror NPN FMMT 497 4AFMMT497
TR417 Current mirror NPN BC849B 4A849B
TR412 Driver bias + ZDT 6758 4AZDT758

Fig 4a. SAP NY/PY output driver information.

SAP 15NY SAP 15PY

Under output driver failure conditions the 0.22 internal emitter
resistor will usually go open, the resistor should be measured between
pins S and E.

S-E = 0.22 ohm.

Micro control/protection and display.

The micro is tasked with providing an instantaneous safe
operating area for both the amplifier and loudspeaker by
monitoring the below areas.

o D.C
o Over current

o

at both left and right channel outputs.

within either power amp stage.

Over temp

detection for both power amp stages.

o A.C present detection.

Please see fig 5. For voltage readings with regards to the protection

operations.

Within the A80 integrated amplifier these tasks are
performed by the H8 type micro at circuit location IC602,
within the P80 power amp version the tasks are performed
by the PIC micro at location IC603, the protection lines are
“daisy chained” to both micros regardless of witch one is
fitted.

To operate both micros require a constant stable supply
voltage, this is derived from the

+4.8v(D)

rail from
transformer TX200 and via regulator REG201 this supply
should be constant at anytime mains appears at the
amplifier power input.

Please note: This supply is protected from over-current
and over-voltage operation by the surface mount fuse at
location

FS202

T500mA and as such if the Amplifier fails
to power up this supply should be checked before making
any further investigations.

We also need to see a

X600

.

4.00 Mhz

clock at crystal location

The micro interfaces with the pre-amp stage input
selection

(see Fig 3)

and the volume control level
adjustment we also drive the VFD via the display
drive/keyboard scan micro at location IC800.

IC602 receives Keyboard scan data and RC5 from the
remote pick-up diode at location RX800. The
power on
switches

reset

can be found on the display board and

HI

(4.8v) after mains in.

master

Fig 5. Working status of protection lines and fault
status

.

Low =0v High = 4.8 (Cmos).

Location Fault Line Output pin Working

IC 601A AC present 2 High
IC 600A Over current 3 Low
IC 600B Therm prot (L) 6 High
IC 600D Therm prot (R) 11 High
IC 600C Therm prot main 8 Low
R634 D.C prot (L) N/A Low (D.C)
R635 D.C prot (R) N/A Low (D.C)
R663 D.C prot combined N/A Low