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

Circuit description

A80/P80

Technical specifications

Circuit diagrams

o L943AY

Transformers

L916TX – 115/230VAC toroidal

L917TX – 100VAC toroidal

L907TX – 100VAC frame

Exploded view diagram

A80

Mechanical & packing parts list

o A80 o P80

Circuit board silk screen

A80

P80

Circuit board parts list

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

(pin 16)

(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

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

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

(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

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