Sinclair Project 80 Technical Information

I

=llnEl=lr

PROJECT

80

Constructional

and

technical

information

on Sinclair

project

80

modular

hig

h-f

idelity amplif

ier system.

;

tl

Contents

lntroduction Section

numbering

Modules available Part

1: Complete Systems

AB 25w

stereo amplifier using PZ6

and2Z40s

AB1

Lavout

AB2

Shopping

list and suppliers

AB3

Notes

AC A

stereo

record

player

with

tuner

PZS

plus

2 Z40s

AC1

Lavout

AC2

Shopping

list

AC3

Notes

AD A tuner

for use with

AB

AD1

Layout

AD2 Shopping

list

and

suppliers

AD3 Notes

A1 .4 Templates

Choice of cabinet Positioning of modules and

wiring

Preamp and

AFU,

tuner and

decoder Power amplifier Earth

point

Power supply

A3.5 Mains

wiring

Output

wiring

Input

wiring Use of other modules 240/260 PZs/PZ6 PZ8 Project

60 tc12 Other

modules

Alterations and additions

to basic layouts Plugs and sockets Headphone socket Power-on indicator Fault finding

Part

ll: The Individual

Modules

AJ.O

43.7 A4

44.1 A4.2

44.3 A.4.4

44.5

44.6

A5 A5.1

t\3.2

A5.3

Ab

B B6

86.1

8,6.2

86.3

B9

89.1

BA BA1

t5 t\z

B43 B44 BA5 B46 B47

8A7.1

Connections

8A7.2

Types of aerial

BA8 Tuning

indicator

Project 805 Layout Parts list Notes Additional

information

on

systems Mounting details Preamp, tuner,

AFU

and

decoder

240,260

and

PZ8

PZ5 and PZG

Tuner

and

Decoder Power supply Decoupling High voltages Low voltages Applications Use

with amplifiers

other than

Project 80 Tuner Circuit

description

Circuit

diagram

Component

layout Performance Connections See Section

BO

Aerials

Switched

tuning

and fine

tuner

Common

faults Decoder Circuit

description

Circuit

diagram

Component

layout Performance Connections See Section

86

Tuners

other

than P80

Tape

recordlng

Common

faults Alignment Control

Modules

Stereo

80 and

AFU

Stereo

80 Circuit description Circuit

diagram Layout Performance Connections Power

supply AFU Description Circuit Layout Specification Connections Power supply Over-ride switch Use with amplifiers other

than Project 80

Common

faults

Z.40 andZ60

Connections Power, output,

speakers and

heatsinks

Output

power

Sound

level Loudspeakers Heatsinking Power suppliers Gain Common

faults Z.40 Description Circuit Layout Performance Applications Amplifier

for

crystal

pickup

260

Description Circuit Layout Performance Switch-on-surge

suppression Applications Full bridge circuit

for 60w DC amplifier Power

supplies Performance PZSA

PZ6

AE

AE1

AT,Z

AtrJ

A A1

41.1 A1.2

A1.3

4

A A

A

4

+

6

A

5

o

6 6 6 6

6

U

8 I I 9 9

31

q

10

9 9 I 9

v

9

q

10

10 10 10 10 10 10 11 11 11 11 11

13 13 13 13 13 13 13 13 13

'13 13

14

14 14 14 14 14 14 15

15

t5

15 15

t3

tb

16

16 16 16 16 17 17

11

17 17 17

'18

1A

11 18 19

tv 19 19

'19

IY

lv

19 20 20 20 20 21

21

zl

LI

21 21 22

z5

22

23

zq

24 24 24

ZJ t4

.A aA

zc

26 zo

lo

2t 27

a1

27 28

28 28

BA9 BAlO BB BB1 B82 B83 B84 BB5 B86 B87 B88 B89

BB1 O

c

cA1 CM C43 c44

LA5

c46 CB1

C82 C84

CB5 c86 c87 CBB cB10 D D5 D6 D6.1 uo.z D6.3 D6.4 D6.5 D] D10 DA DAl DA2 D43 D44 DA9 DA9.1 DB DB1 DB.2 D83 D84 D88 D89 D89.2 DB9.4 E E4 EA&EB

tAl

EB1

cru

EB2

trAJ

E83 EAlEB5 EAlE85.1

Description

Circuit Layout

Connections

PZ5l6

Mains connections

A3

43.1

A5.Z AJ.J

A3.4

P25 PZ6 PZ5 PZ6 P25 P26

EAIEB5.1.1

Fuse and switch

EA/E85.1 .2

110v

operation EA/E85.2 Output EAIEB10 Common faults PZS

and

PZ6 EC PZg EC1 Description EC2

Circuit

EC3 Layout

ZI

27 21

28 28 29 29

EC4 EC5

trLO

F FA

FAI

F43

Performance Connections Voltage adjustment Other

parts

Project

805

masterlink Description LayouI

Appendix Service

and

Guarantee

Modules in

groups

B C & D are intended to work from a

power

supply

of

group

E or from any other source of voltages between

25

and 35

(some

modules down to

12v

and some

up to 55 volts).

The

power

supply should

be chosen

in

conjunction

with the

power

amplifiers: it will

also

drive whatever

preamp

modules

you

choose.

B

Signal sources

BA FM

(VHF)

Tuner

intended

to

receive FM

transmissions, 88MHz

to 108MHz.

BB

Decoder

intended

to

be used in

conjunction

with the tuner to

convert

it

to stereo

receotron.

These two modules could be

installed

{with

a

PZS) to work with an

amplifier other then a

project

80.

It is also

possible

to use the decoder

with

tuners other than

the

proiect

80 tuner to convert them to stereo.

C Preamps and control systems

CA Project 80 Preamplifier. A stereo

preamp,/control

unit. lt

is

the

heart of any amplifier made from

project

80 modules.

CB

Active Filter Unit

(AFU).

An optional addition to extend the basic

facilities

of the

project

80.

lt is intended to improve

performance

where

old

records

are used, or

when

cl'reaper turntables are

used.

CC SO Decoder. For

quadraphonic

sound an SO decoder,

two

more

power

amps and

possibly

a second

power

supply are added

to

the

existing stereo unit. The decoder also

has its

own

tone and volume

controls

for the rear channel. The decoderis covered by a separate manuat. D Power

amplifiers

DB 260 for

all systems

up to25W

(8

)

or

40 W with 4 .

For

higher

powers

(up

to 50W into

15

or 80W

into

8 ) two

260's

can

be

used

back-to-back. The full advantage of a 260 over the

240

can only be

realised when using PZ8 to

power

the system.

DA

240

for all systems up

to 18W RMS

into 4Qspeakers. E Power supplies EA PZs suitable

for

smaller

domestic situation of 5

+ 5W stereo or 10W mono. EB PZO a higher

powered

version for up to

25W

total output

(12W

+

12W

into 8 O).

240's will normally be used with

PZ5

or

P76. Although

260's

can

be

used, there is no advantage unless a

PZ8

is chosen.

PZ5

and

PZ6

are

both mains operated and

\220-240

volts)

and

can be adapted for

1 1 0-120v ooeration.

EC PZ8

a high

powered

voltage stabilizer

with sophisticated

protec-

tion circuitry

built in, and

performance

tailored to match two

260's

working

into

BQ, delivery

25 + 25V1

. The PZ8 can also

power

other

combinations

but the total audio outputs

from it will be limited to

about 50W

(e.g.

50W on

mono, or

25 + 25W

stereo, or

4 x 12Yz\N

on

quadraphonic).

The PZ8 is not

mains

powered

and requires a separate

transformer

rated at

40V,2A.

F

Other

parts

FA Masterlink

a connecting

panel

with

output and

input sockets

fitted.

FC

Switch

module containing a

mains switch and neon indicator.

These two

modules are included

in

the

Project

805

which

also

contains the

Project 80

Preamplifier 2

240's and

PZ5 with ready

tagged

wires to

allow

solderless assembly.

Project

805

is covered in

lavout EA.

29 29

2q

30 30 30 30 30

30

Apology We regret

that, due

to circumstances

beyond

our control, the layout

and design

of this first edition

of the Project

80 manual has been

rushed.

We apologise for

any resulting

errors and inconsistencies

but if

you

have

any comments, criticisms

or suggestions

the author

will be

pleased

to

consider these when the next

edition is reprinted.

Introduction

This manual describes Project

80 high fidelity modules for

the home

constructor.

Part

One deals with

some complete

projects

for the

home constructor

and

gives a pictorial

layout

of each, with a

shopping

list

and

details

of some suppliers. Layout

AE deals with

Project 805

specif

ically.

The beginner is

strongly recommended

to follow one

or other of

these

projects

exactly, but the rest

of Part One

gives

additional

information

on complete systems

and

hints

for those who wish

to

depart

from

the suggested layouts.

It is not

possible

to list all the

pitfalls

that

can occur but if

commonsense

is

used and the hints

are

followed,

even the complete

beginner will be

able to assemble his

project

into

whatever case or

system

he wishes

-

and he will

get

excellent results first

time.

When wiring the modules,

you

may find it helpful to

colour the

wires

on our

layouts. For instance,

you

could

colour all

the wires

connected to the

power

supply + ve in red

and say to the

-ve

in

green.

There

will then be far less chance

of a

mistake

when wiring.

Section 46 is

about

fault finding

-

just

in

case

you

do make

a

mistake in

assembly, or something

goes

wrong. lt includes

a

step-by-step

chart which will help

you

find most likely faults.

Part

Two of the manual deals with

the individual modules,

unit-by-unit. lt

gives

circuit diagrams,

performance

and technical

information,

as

well

as listing many interesting

and useful applica-

tions for the individual modules.

Section

numbering

By

its very nature, a modular system

is flexible - new modules

are

announced

from time to time.

This manual is therefore

planned

so

that there is a logical

place

for information on

new modules. The

manual

is also laid out so that as

far

as

possible

it is in the order

you

want it - the

first thing

you

will

want is to assemble

your

new

system

-

so the

practical

projects

come

first. Only if

you

are

departing

from one of

these will

you

need the

rest

of

Part

One

(with

the exception of Section

A1 which deals

with mounting the modules).

Part Two is numbered as consistently

as

possible

so

that

Sections

BA2,BB2, CA2, etc. are

all circuit diagrams,

whilst B86, CB6,

DB6

are

all information on

power

supply

requirements. Where two

modules have common

information, e.g. tuner and

decoder, which

have

identical

power

supply requirements, rather than

include

this

information

twice

as

846 and

B86, it is included as Section

86

there are no Sections

8,46 or B86.

240

and

260 have much common

information included

in Sections

D5,

D6, D7

and

D10. The

power

supplies

PZ5 and

PZ6

are

very

similar

so that common

inforrnation on these is included

as EAr'EB

when

it

does

not include the PZ8.

Modules Available The following

list shows

all the

modules which

are available, or

projected,

at

the

time of

printing.

The modules are

grouped

into four

sections

lettered

to coincide with Part ll

of

the manual: B

signal

sources, C

preamps

and control

units,

D

power

amplifiers E

power

supplies

and F other modules.

AB 1

PZ6/Z40layout

Part 1:

Complete

Systems

AB

25w

stereo

amplifier

using PZG

Shopping

list Z.40 Project 80 Preamplifier AFU

(optional)

PZ6

lor

PZ5)

Cabinet,

metal, 19" x6" x2"

approx

3 5

180"

(A

type)

DIN

sockets and

plugs

2 2pin

DIN speaker sockets and

plugs

1 2

pole

mains

switch

(toggle

type)

1 Miniature

panel

mounting fuse holder

1

Cable

clamp

(for

mains cable)

2 Heatsink

blocks

(for

240 mounting)

1

Resistor

(120Olw)

for tuner + ve feed

(PZ6

onlv)

(see

nore 2)

22

684 x

%

"

screws

(see

note

1

)

18 6BA nuts

1

6BA

%

"

screw

(for

earth

point)

6 684

solder tags

1

yd

stereo microphone cable

1

yd

stereo microphone cable

3

vds

assorted colours

flexible

wire

as

required:

3 core

mains

cable

Suitable cabinets

are available

from: H L

Smith & Company

278 Edgware Road

London W2

(Plain

aluminium chassis, undrilled)

NSMHC Sales Limited (National

Society for Mentally

Handicapped

Children)

17

Pembroke Souare

London W24EP

(Aluminium

chassis with slide-on wood surround)

West Hyde Developments

Limited

Ryefield Crescent Northwood Hill Middlesex

H46 1NN

(Black

cabinet

with wooden

end

panels punched

ready for various

combinations of

modules)

West Hyde

can also supply all

hardware,

etc., to suit their cabinets

or

your

local shop should be able to supply allthe required items.

AB3 Notes

l. The Z40s

are

mounted

on

heatsink

blocks as shown in

41.2. The nuts and bolts

indicated

above assume that

block has 684 tapped holes - if

you

use nut

and

fastening for the blocks

you

will need 8 less

%" screws

four extra l " screws

and

nuts

lfor %"

block).

2.

The box is wired

so

that the

complementary tuner

(Section

AD)

plugs

into the tuner socket and draws

power

from

the

amplifier, therefore there

is

a connection

from PZ6 +

ve to Pin

4

on

the tuner

socket to

provide

h.t. This wire

should only

be

fitted

if

a tuner

is

to be used.

The resistor shown in this + ve feed line is not reouired

when

a

PZ5 is used.

3. Using a PZ5 instead

of

the PZ6 will reduce the

output

power

(see

section E4) but will have little other effect except for

a

slight increase in hum level when using the tuner,/decoder.

AC

A

stereo record

player

(and

tuner) using PZs

AC 2 Shopping

list

2 Z.40

1

Project 80 Preamplifier

1 Project 80

tuner

{

1

Project 80 decoder 1 optional 1 PZs 1

Plinth with deck 1

100

pF 25V

capacitor

(for

tuner and

decoder)

1 5

DIN

socket

2

DIN speaker socket

1

Coax

aerial socket

1 Panel

mounting fuseholder

1 double

pole

mains switch

1 metre stereo

microphone cable

3

metres assorted colours

flexible wire

AB2

2

Iia

the bolt ano

PZS/240

plinth

lavout

3

metres mains

cable aluminium foil for lining 68A

1/q"

Screws

68,4 1"

screws

68A

Yr" spacers 684 nuts 6BA solder

see also section A5.3.

43.6.

Output wiring

From

9 on the 240

orZ60 the

output

wire

corrnects

(via

a

2000uF

capacitor

on

the 260

only) to the

output socket,

and to

any

headphone

sockets

you

may have fitted.

lf

any

of

this wiring

is anywhere

near the input

wiring of the

preamplifier,

or any

other modules, interaction

can occur

as some of

the

output signal will

then

feed

back to the input.

Keep

output well

away from

the

input

and

also twist the output earth

and

live

leads together. A3.7. Input

wiring

Shouid

usually be

screened - but if it is

short

(4"

or

so)

and does

not

pass

near

any

mains

or output wiring,

screening is not necessary.

Thus,

in

our

plinth

layout

we have

not used screened wires

from the

tuner to the

Stereo 80, but we have

used

screened wire from the

pickup.

A4 Use of other modules

in

our

layouts

44.1

740 or Z.60

The 260

is longer

than the 240. lt

also

requires

an additional fairly

bulky

output capacitor

(see

section D.5). The

output capacitor is

part

of the

output wiring and must

be treated

accordingly.

It

should be noted that

there

is

no advantage in

using the 260

instead

of the 240

unless a PZ8 is used,

although with l5Ospeakers

and a

PZ6,

the supply voltage

can be increased

to about 40

to

give

a

useful

power

increase.

A4.2.

PZ5 or 6

These are

physically

and electronically

interchangeable.

However,

when using a PZ6,

additional

heatsinking

will be required

(see

section

D 6.4.). The

PZ6 will result in

a slight improvemenr

in hum level

when

the

tuner

is

used. A4.3. PZ8 The

PZ8 is not

physically

or

electrically a replacement for

the PZs or

6

and

the

transformers commonly available for the PZ8

are

large

(about

10

x 8 x Bcm). lf the transformer

is to be housed in the same

case then this will need to be considerably larger

than the PZ5l6

case. The PZ8 must not be

used

with Z40s

unless its output

voltage

is reduced

{see

section

EC6)

but

if

this

is

done it does result in

a

considerable improvement in

performance.

The PZ8

also should be chosen where

sustained high

power

operation is required. PZS and 6 are small

and after a while

get quite

hot

at

higher

powers.

lt is, of course,

quite possible

to mount the

PZ8's

transformer remote from the PZB

proper.

A4.4. Project

60

modules

The

earlier

project

60 modules

are compatible with

project

80 except

that the

Stereo 60

gives

more

output then the

project

80

preamplifier

so the

gain

of the 230

and 250 is less than

that of the 240

and 260.

However, the

gain

of the 260 has

been

kept

deliberately low

so that

it is

still compatible with

the earlier Project 60.

When

using

project

80 control modules with 230

or

250 the

gain

of

the

230

or 50 will

need to be increased.

A4.s. tcl2

lt is

possible

to use an lC12 instead

ot a240. The lC12

should have

its

gain

set to

100

as explained in

the instructions.

A4.6.

Other Modules

There are

other makes

of

modules

available and it is

orobable that

most of these will

present

no

problem

when used

with Project

80

provided

they use

a similar

power

supply

voltage

and have a

negative

earth. Such combinations,

however, are

beyond Sinclair's

control

and we cannot

predict

results nor can

we

advise as

to the compatibility. A5 Alterations

and additions

to basic layouts A5.1. Plugs and Sockets We

strongly

recommend

that

you

stick to the

DIN

type

plug

and

sockets as

we lrave, but

if

you

use

different types remember

that the

mechanical mounting

on many of these

is

also a signal connection. lf

you

use

a metal chassis

this must be insulated or an earth loop will

form causing

hunr, distortion and

instability. This in

particular

applies

to

jack

sockets

and

phone

sockets.

Do not use

jack

sockets

for the loudspeaker: many

types cause a

short

circuit as the

plug

is inserted or withdrawn

and

this is undesirable. A5.2. Headphone socket A 3

pole

jack

socket can

be used

for connecting

headphones

provided

the

resistors shown

in the diagram are

fitted.

These

resistors will be between

10[)and

470Q lower values

for inefficient

low

impedance

phones

and

higher for high

impedance 1ypes.

220!Jis

most

often

used.

A 5.2.7

Headphone socket wiring

We have used a

slide type switch

to switch the

speakers off

. This

can

be a toggle or other

double

pole

switch but

you

cannot use

the

switch commonly

fitted to

the

jack

socket or

the

resistors will not be

in circuit.

The

headphone socket and

switch are

part

of

the output

wiring

and

should be

kept well away from the

input connections.

lf

you

wish to

mount it on the

front

panel,

mount

it to the

right

of

the

oreamD

and AFU.

On

Project 805,

when

adding

headphones,

the two

links shown

below

must be broken or

the switch on the

headphone

circuit will

not

mute the soeakers.

A5"3.

Power-on

indicator

It is simple

to fit an

indicator lamp

to

shcw

when the

power

is

switched on.

There are

two recommended

types of indicator avail-

able,

both

can be obtained

with

lens for

panel

mounting to

give

a

decorative appearance.

Neon indicators make sure

you purchase a proper

mains neon

indicator with built in resistor

for

direct

mains

operation.

You will

probably

want to mount the

neon

on

the front

panel

with

the

mains switch

-'

this is alright

provided

care

is

taken, and

in fact

mains

switches

are available with built-in neon

indicators to

show

when

power

rs

on.

The neon

indicator

should be connected

between L I N connec-

tions to the

PZ5l6

(or

the corresponding terminals on

the

switch).

Do

not

position

the

neon nearthe

input

circuitry,

not

only can

this

induce hum but neons can cause an annoying

'buzz'

in the speaker if

wrongly

positioned,

so

we

prefer

the next type of indicator.

LED

Indicators

are now readily available.

These work Jrom

dc

so

must be connected between

tve the

power

supply,

via a suitable

lirniting

resistor,

and earth.

A current of about

20mA

is suitable for

most

LED's so

choose a

resistor of :

1K

l4w

for PZ5

'1

K5

1w for PZ6

2K2

1w for PZB

The LED,

working

from dc, can cause no

problem

wlth hum etc-,

so

can be

positioned

anywhere

on the

front

panel.

With

the

PZ5,

however,

it

will tend to

flicker with music because the

power

supply

voltage

vafles.

We use

LED as

the indicator for the stereo beacon

in

the decoder.

46.

Fault finding

It is not the

intention,

in this section, to

teach

how to

repair a

module.

but

it

is

quite

simple

to trace

the fault to one

particular

module.

ls

the

fault in both channelsT ls it the

same

in

both channels?

lf

so,

then is it sensible to assume that one component

or

wire

causes

the

trouble in both channels, or the

power

supply is at fault. A faulty

power

supply

can cause hum, or non-functioning

but is not likely to

cause distortion.

Has the fault been

present

since

the

project

was assembled? lf so,

it is

probably

something

in tl.re wiring or layout. Or did the equipment

fail

after some

period

of use?

This is usually one module

failing.

lf there are apparently

different

faults in

both channels then

maybe there

are two

faults.

The commonest

failures are

in the

power

amplifiers

-

which are

subject to

most misuse and

can

fail from overheating - or

in the

PZ6.

which

is not itself

protected

and

can fail if one

power

amplifier

f ails.

There

are

'faults'

which

are

not due to anv module.

but a combination of layout and wiring. These include hum, motorboating and overheating

(sometirnes).

Also, sometimes a

project

does

not live up to the constructor's

expectations, but

it works. Maybe the user

did not know what to

expect, but more

likeiy the trouble is caused by a

bad choice of

layout

or the other

apparatus

ls incompatible.

The following test

procedure

will be

able to

locate for

you

almost

any

fault which is likely to arise.

Each

step

gives you

either a

conclusion

or an

additional

test to make with expected symptoms.

lf

you

get

one

of the symptoms

indicated

proceed

to the

test whose

number

follows the symptom.

Further information is

given

in other

sectlons of the manual as explained.

1.

a)

Different faults are

presented

in different

inputs

2

b)

Fault is not

present

on tape input, but

is

present

in

c)

d)

e) f)

D.U. ano

rao

Fault is only

present

on

pickup

input

Fault is

only

present

on tape recording

from

(but

is

not

present

on

llstening to)

record

or

radio input

Fault

is

only

present

on

rad input

The

same

fault is

present

on all

three inputs

4

tr o

l

A

5.2.2

Detail of

break in M/L track

breaks

11

2.

lgnore one fault

(the

most

minor one) and search for

the most

obtrusive

fault first.

e.g. if

one

input is distor-

ted on

one

channel

and another is completely dead,

look for

the cause of the dead input

3.

Either

there is a fault in

the

preamplifier

(which

is

unlikelv).

or two

separate faults are

present,

look for fault

on one

input

at a

time

4. The

pickup,

or connections

to

it

are faulty or incorrect

or the

pickup

alignment is wrongly set up. With

a

screwdriver

short together

pins

3 and

5 on the

pickup

input socket. lf the

amplifier modules

are correct both

channels

will

perform

in the same way.

a) both work

properly,

or show exactly the same fault

pickup,

DIN

plug

or wiring to deck is incorrect.

b) both channels

go

dead

there is a short circuit in

pickup,

DIN

plug

or wiring between

them or in the

screened wire connecting the DIN

socket to the

preamplifier.

c) nature

of

fault

does not change

at all.

There

is a fault

in the

preamplifier

on

pickup

input.

5. Since the

signal

in

the speakers

is

clean when listening

to records

(or

radio)there is no fault in

the amplifier but

the tape recorder is

not suitable or wrongly wired

or

wrongly matched. See section

C,A7.

6. Tuner

or

decoder is faulty. Try

test 4 on tuner input and

if fault is in

tuner see section 810.

7.

a) Both channels are faulty but do not have

the same

fault

b) Fault is

present

on one channel only, the

other

channel works

properly

11.

c)

Both

channels show the same fault

Search for the major fault

on one channel only, ignore

the fault

on

the

other channel

(e.9.

if

one

channel is

dead and the other working but distorted

-

look for

the cause of the non-working

channel

first).

Exchange

speakers so that the one which was

plugged

into the left channel is now

plugged

into

the right chan-

nel and

vice-versa.

a)

fault remains

on same speaker, then this

or

its wiring

is

at fault

b) fault

changes to other speaker

Select

pickup

(or

tuner) and

play

some music. lf

you

have

tested

properly

this far,

only one channel will show

the fault

you

are trying to

trace.

With

a screwdriver

short together

pins

3 and 5

on the

pickup

(tuner)

input

socket.

This

shouid have no

effect

(if

it does,

go

back

to test

4).

Switch

off, connect a wire between

5 on

right 240

(60).

Switch on again

and with both volume controls turned up: a)

Both

channels

are

dead,

then there is

a short circuit

from

5 to

6

on the

240,

or frorn

5 on the

240

or

from

5 or 6

on

AFU

(if

used)

or from

14

or

15

on Stereo B0

(if

you

do not use an AFU),

or

from

the

wiring

between AFU,/preamplifier

and 240

(60)

to earth.

b) both channels work

(properly

or with some distor-

tion or hum

etc). then the

240's

(or

260's)

are

work-

ing

and the fault is in the

preamplifier,

AFU

or its

wiring.

lf

you

have an AFU: c) fault remains unchanged Short together

pins

2

and 3 on the

AFU.

a)

fault

does not change AFU

or

its wiring is

faulty.

b)

Both

channels

go

dead - there is

a short circuit f rom

2

or 3 on AFU or f rom

14

or 15

on Stereo 80

to earth.

c)

Both

channels work,

the

preamplifier

is at fault.

The 740

(260)

or

its wiring is

at

fault. Exchange

all

wiring from leftZ40 onto the right hand 240 and vice

versa.

a) fault is now on other speaker, then this 240 is at fault. b) fault is on same speaker: there is a fault in the wiring

to this

240.

Swop

wires from left to right,

one at a

time, to locate

it.

Both

channels are: a) Dead b)

Overheating and

the

system does not work

(a

loud

buzz or

hum may be

present) c) Too loud d) Not loud enough e)

Distorted

at high

volume

only

f ) Distorted at all volume control levels

g)

Overheating,

but system works with

or

without

some distortion or

hum

etc.

Working but high hum level

lf

you

use PZB: one 260 has

possibly

failed

or there

is a short in the + ve

power

wiring. The PZ8,

detect

ing

this,

has

shut off causing both

channels

to

go

dead

(note

that svmptom

13b

cannot

occur

unless

the PZ8 is at fault). Disconnect

oin

B on one

260

at a

time to see which is

at

fault. lf

this does not locate

the trouble then maybe the PZ8 is at fault

or the

wiring.

PZ6: lf there is a

short, or one

240

has failed, the

PZ6's internal fuse will

have blown. This failure will

usually be

preceeded

by a very loud hum

at switch

on,

followed

by a click and silence.

See section

EB10

lf f

use

has

not blown and the amplifier is dead:

PZ5: a failed 240,

or a short,

will

not immediately

damage

the

PZ5

but will cause a loud buzz

on both

channels and overheating in the Iailed Z4O

and the

PZS. The PZ5 may fail

only if the fault

is sustained.

Disconnect

B to each 240 ln

turn to locate the

fault. lf the PZ5

gets

hot

with all + ve wires

discon-

lbtof

4&6

12.

13

14

14 16 16 1l 18

19

20nl

14.

a)

b)

c)

15

8.

9.

B 9

13

9

11 12

15

nected it is faulty lf the

systern

is

dead

15

Amplifier is dead. There

was no hum/buzzloverheating before the failure

nor is there

any click or noise at

switch on, nor is there any residual

noise or hum in

the spea ker. The mains f

use

has

blown, or the mains wiring

or switch

is faulty. A mains fuse will

not usually blow for

no

reason so when replacing

check the circuit

and take

care when sw,itching

on.

These

faults

are to do with

the amplifier

gain,

input

matching

and speaker efficiency.

See section CA7 and D]. This is the

symptom

of a true

power

limit.

Maybe

the

PZ5

needs to be changed for a PZ6.

See section D61.

ls the distortion

on all

inputs?

ls it

on only

loud

passages

of

music?

The symptoms

do not indicate

a specific

fault

and could

be caused by the tuner,

pickup,

wiring or

preamp.

Overheating can be

caused by

instability

caused by lay-

out

problems (see

section A3) when it

will be worse

at

high treble

control settings and high voiume

settings.

It may

occur even if no music is

played

and

rnay

be on

one channel

or

both. A 10 F

caoacitor connected be-

tween

pins

1

and 8 on each

power

amplifier

may

cure

this.

lf

the overheating is

only

present

when music is

playing

at a high volume level,

then

heatsinking is

inadequate

(see

section D64).

Hum

cannot

arise in the

modules themselves

and

is

in-

variably

caused

by layout,

wiring

and screening

prob,

lems

see section A3.

Hum can

also occur in

the tuner

(see

section

BA10).

10

16.

11 . 18

19.

12

20.

Part

ll: The Individual Modules

B Tuner

and

Decoder

BO

Power Supply

Both tuner and decoder are

designed for the same supply

voltage

range

(23

-

30V) and

draw the

same

current

(40mA

max at 30V).

Power

input

numbering and supply

decoupling

arrangements

are

identical:

1 is + ve input, 2 is decoupling and 4 and 7 earths.

86.1 Decoupling Where an unstabilized supply

is used

(e.9.

PZ5, or where

power

is

drawn

from the main amplifler),

hum andlor instability

may occur.

To

overcome

this a

1000uF 25v

caoacitor

must be connected from

2

to earth. The same capacitor

can be used for the tuner and

for

the decoder

by connecting both

pins

2

together to the capacitor's

+ ve termrnal.

The ve of the capacitor can

be

connected

to earth on the

tuner/decoder

box as shown

in fig AD.1. However,

if

this does

not

entirely

remove hum

it

may be

necessary to run a separate

wire from

the

capacitor's

ve

to

the earth

point

on the amplif

ier

concerned.

86.2

Fligh-Voltage

Use

For driving the tuner

(or

decoder) fronr a voltage above 30 a

resistor,

R, must be

fitted in series with the + ve supply line.

This resistor's value is found

f rom the formula

v

30

Ko

40

When both tuner

and decoder are

used this

resistor is halved

in

value and

both

prns

1

are

connected

together to one end of

the

resistor whose

other end connects

to

+ ve

power

input.

The resistor should

be

rated at more than

i.2 x R watts for one

module

only or

4.8 x

R *atts for both.

1 000

In

practise

the

formula will not

give

an available value so the

nearest

value up to

15% higher

or

Iower than that calculated will be

used.

Thus f or

PZ.6

(35v)

220 Q

could be used, /zw,Ior

one module.

PZ.6

'

both modules

use

120Q1w

PZ.B one

module: 470[)1w

PZ.B two

modules:

270\l2w

86.3

Low-Voltage

Use

1-l

-

22v

(well

smoothed)

may be

fed into

point

2.

11 - 17 volts use is

possible

if the following modifications are made:

1.

Replace

D2

(tuner)

or D1

(decoder)

by

a 9v

1w

zener taking care

to observe

polarity.

2.

Replace

R17

(tuner)

or

R2

(decoder)

by a 6S0resistor.

J.

heeo | | - l/v Into

prn

z.

4.

The tracking

may need realigning if

this is done.

lf instability

or hum occurs a capacitor

must be

connected across

the

new diode

use

1000rF 12v.

89 Use with

amplifiers other than

Project

80

Tuner and

decoder draw 80mA max between them. This can

usually

be taken from the

power

supply inside

the amplifier with which they

are

to be used.

Fig. AB 1 shows an amplifier made from Project 80. Note

the use

of

DIN sockets and in

particular

that only three

pins

on

the tuner

input are

normally used. We have therefore

connected one of the

spare

pins

to the + ve of the

power

supply to

power

the tuner

of

AD,1.

lf

your

amplifier

has

a

-ve

earth and uses DIN

plugs you

can

probably

make the same arrangement inside it,

or

you

may have to

add an additional

insulated

terminal

inside

the amplifier for + ve

ourpur.

It is

best

to

add

the

extra

resistor

(section

8.6.)

inside the

amplifier

so

that

in

the event of a fault

in

the tuner connecting wire,

the

amplifier's

power

supply is not short circuited and damaged.

We

have

fitted the resistor thus in

our

examole.

BA Project

80

FM Tuner

BA1 TechnicalDescription The

printed

circuit aerial coil,

T1,

provides

matching to either

75Qor

300{)aerial systems.

lt is

tuned

by

one

half

of the matched dual

varicap diode VC1. R.F. signals are applied to the

self oscillating

mixerTRl,

TR2via R3. Printed

circuit coil

T2 is

tuned by the second half of VC1. The amplitude of oscillation across T2 is limited by D1 and the freouencv is:

Fro

=

Fr

-l-z

2

where

Fro is the local oscillator

frequency

F, is the incoming

R.F. frequency

F2 is the

l. F. f requency

1 000

BA 2 Tuner crrcuit

13

For

3O0Qinput

is

fed

between

pins

6 and

8

with

5 connected

to

earth

direct.

8A7.2.

Types

of

Aerial

Ultimately

the

choice

of

an

aerial

will

depend

upon

yor.rilo.al signal

strength.

Your

local

radio

dealer

should

know

what'signal

strength

exists

in

your

area,

or

in

U

K' the

BBC

engineeing

informition

service

provides

details

of

signal

strerrgth

uni

aouatuga

of

their

transmitters.

Stereo

reception

requires

a

much

better

aerial

system

than

does

mono

receptlon'

It

is hardlv

possible

to use

too

good

an

aerial

and

commercially

made

aerials

are

available

with

upto

six

elements'

Forbestresu|tstheaerialshouldbemoUntedashighaspossib|e

preferably on

the

roof

'

A simple

diode

can

be

made

as

shown

in

fig'

8A7

2 1' where

two

pieces

of

wire

are

connected,

one

to

the

inner,

one

to the

outer

of

ih"

.ou*

to

form

a

'T'

aerial,

5' across

the

tips

of

its

'arms'

The

wire

is taoed

or

pinned

to

a

piece

of

wood.

BA

7.2.7

SimPle

diPole

aerial

F, is

fixed

by

the

mid

point

of

the

passband of

the ceramic

filter

X1

and

is

approximately

10.7MH2.

Note

that

the

R'F

signal

mixes

with

twice

the

local

oscillator

frequency

to

product

the

I F RVl

is

the

tuning

control,

and

RV2 and

RV3

set

the

tuning

range

and

tracking:

RV2

determining

the

L.F.

and

RV3

the

H

F end'

Note

that

the

A.F.C.

adjustment,

RV4, also

controls

the.

varicap

supply,

thus

it

is

necessary

to

set

the

A.F'C.

before

adjusting

the

tracking

Tem-

perature

compensation

is achieved

by the

use

of a

thermistor'

TH1'

The l.F.

coil

L'l is tuned

to

the

l.F.

passband

by observing

the

waveform

at

the

collector

of

TR2.

TR3

amplifles

the

l F output

from

the

mixer

and

provides matching

to

the ceramic

filter,

Xl The

output

from

X1 is

fed

into

the

balanced

coincidence

detector

lC1

' A

adjusts

the

phase

of

the signal

in the

detector

circuit

and

should

be

sei

to

give

a symetrical

'S'

curve

with

a

F.M sweep

signal

applied

lcl

hai a

limiting

circuit

before

the

detector

stage

which

provides

a

very

good

degree

of

a.m.

rejection.

The

A'F'C'

voltage

is derived

from

8 of

tCt

via R13,

R14,

R15 and

is

used

to control

the

voltage

apolied

to

VC1.

With

the

A.F.C.

switch

out

RV4

provides the

reference

voltage.

De-emphasis

of SCpS

is

fixed

by C13.

Should

75sS de

emplrasis

be

required

(North

America)

a

1200pF

capacitor

should be

wired

across

C13.

For stereo

operation

with any

decoder,

C13

must

be

disconnected

by cutting

across

the

printed

circuit

at

points

marked

,X"

The

supply

rail

is stabilised

at

12 volts

by

the

zener

diode

D2'

The

diagram

below

shows

a simple

radio

aerial

that can

be

made

for

use

in

a car.

A

piece

of

brass

rod

is

soldered

to

the

centre

ConnectionofaUHFp|ugandbent45o.TherodmUstbeinsu|ated from

the

skirt

oi

the

plug,

which

can

be

done

by

filling the

plug

bocly

with

Araldite

or similar

epoxy

adhesive.

BA4

Size Tuning

range

Aerial

type Sensitivity Audio

outPut

Output

load

imPedance

Distortion Power

requtrements

Typical

Performance

85x50x20mm

87.5

to

108 MHz

75Oor

3000

5mV

for 30db

signal

to

noise

(mono)

300mV

for

75KHz deviation.

100mV

for

307o

modulation

not

less

than

10K!l

<0.3o/o

at

l

KHz

and

75KHz deviation

23 to 30v

(max.

40mA)

BA5

Connections

to

the tuner,

shown

numbered

in

fig are:

1

+ ve

powPr

23-30v

2 Decoupling

(see

text)

3

Audio

output

4 Signal

and

Power

(-ve)

earth

5

Aerial

centre

tap

6

Aerial

inPut

7 Alternative

earth

8

Aerial

inPut

BAO

Power

suPPlY

see section

B.6

BA7

Aerials

BA7.1.

Connections

You

may

use

either

a 3000one

or

a

750one

75(l

is

more

common

in

U.K.

but

30QOis

used

in

many

other

parts

of

the

world.

Our

layout

(section

4) shows

a

75!)aerial.

For750:

connect

screerl

to

5

and

the

inner

core

to

6'

Note

that Din

5

is connected

by

the

aerial

socket

to

earth'

14

BA

7.2.2

SintPle

car

aerial

I

1l

(rcl)

l0yfOV

4

(rcl)

BA

8

Tuning

meter

BA8

Fitting

a Tuning

Indicator

Using

the circuit below, it is

possible

to fit a 50-0-501r,4

centre

zero

metre

io indicate whether the module is accurately tuned

or

not.

Setting up

is

quite

simple, the

10K

preset pot.

should be adjusted

with the AFC

our

and the module tuned off station, i.e.

jusr

noise

on

the output.

The meter should be set to read zero, or centre

scale.

Apartfrom the meter and

10K

preset pot.,

the only

other compon-

ents required are a22KSl resistor and a

10pF

electrolytic capacitor,

which can

be

omitted

if the resultino

'flutter'

of

the meter is

not

objectionable.

BA9

Switched

Tuning

and

Fine

Tune

By breaking

the circuit

between

points

DC

and

GF

it is

possible

to fit

prese

t

potentiometers

and

appropiate

switching

The

circuit below

shows the details.

Note also that

a separate

switch

position

has

been used to

enable

the existing variable

control

on the module

to be used

(position

1).

Position

2

on

the

switch

allows a fine

tuning control, VR1,

to be

used in conjunction

with the

existing tuning.

Switched tuning or fine tune

could be a very

useful addition for

car

radio

use.

BA10

Common

Faults

Hum:

cauged

by inadequate

power

supply smoothing.

Fit the

cap-

acitor

mentioned

in 84.6.

Motorboating:

caused

by

poor power

recommended caoacitor.

Interference:

especially

when the tuner

supply

stabilization: fit

the

is

mounted

on wood short-

wave interference

may occur between

stations. This should vanish

when a station

of

good

strength is tuned in. lt

can be reduced

however by mounting

the tuner

on

a metal

plate

(or

lining the front

of

the wood

panel

with metal foil beneath

an insulating layer),

and/or

by linking

5

to

7 via a 1nF

capacitor.

Noise.

Between stations

you

will

get

a noise like frying

eggs. When

on station it should disappear. lf it

does not, the

aerial

is

probably

inadequate- A

poor

aerial will cause

a

great

increase

in noise when

stereo

is being received.

AFC button

throwing the station off tune. This means

the set is

out

of alignment,

probably

because it has

been screwed down

too

tightly onto a metal surface,

or the area of metal indicated

in the

template has not been removed

properly.

Alignment.

lt should not be necessary

to

realign

the tuner

and as the

ad.iustments are interdependant

we do not

give

details in

this manual

but only

on

request

(S.A.E.

please).

Service. Experience has

shown that faults in use

are

rare

-

Most

of

the

tuners returned

to the Service Department for

'repair'

are in fact

working

properly

and the fault is in

the user's installation.

BB

Stereo

Decoder

BB1

Technical

Description

The Multiplex

input

signal is fed into

3 on the

decoder. L2

and C6

are the

first 19KHz

filters,

L1

and C7 are the

second. L3 is

the 38KHz

filter. lf this is

shorted

out decoding does

not

occur and mono

receotion results.

When

a stereo

station is being received

the

decoder

causes the

LED to illuminate.

D'l is a zener

diode

to stabilize the

supply voltage.

BB 2 Decoder

circuit

L2

I I01

C11

,T

T,

10

I I

16V

6 11

12

l3 10

lcl

3 4 ) 7 1r

VR3

BA 9 Switched and fine

tune

15

B84

Typical

performance

Size

4-l x

50

x

20mm

Input

impedance

20K t)

Load

imoedance

not less

than 22K{)

Separation

30dB minimum

BB5 Connections 1

+ ve

power

(23

-

30V)

2 decoupling

(see

86)

3

inout

(from

tuner)

4

Earth

(signal

&

ve

Power)

5

Output

left channel

6 Output

right

channel

7 Earth

(alternative)

B86

Power Supply

See

section

B

6

BB7 Use with tuners other

than P80

Although the decoder

is intended to

work with P80 tuner

it will in

fact

give

excellent

results with many other

tuners and may even

give

passable

results

with a VHF

transistor

portable,

which is not

intended

for stereo

reception,

provided

the signal strength

is

very

good.

887.1

Connections

There are only two

wires

needed between the tuner and decoder:-

a signal

wire from the tuner Multiplex

output to

3 and an earth

wire

from

the tuner to

7.

Connections to the amplifier are made

from

pin 4 (earth)

5 and 6 via screened wire.

lf tuner or amplifier's

power

supply

is

ve earth of the correct

voltage a

+ve

power

supply

wire may

be connected via an

appropiate

resistor

(See

section 86) from

pin).

Otherwise if a

separate

power

supply

(or

battery) is

used +ve

and

-ve

supplies

connect

to terminals 1

and 4 respectivelV.

lt is

possible

to run

the decoder from

a 12V

battery discorrnect

D1

and

connect the

12V

in its

olace.

887.2

Tuners

without

multiplex

output

Most

tuners which

do

not have

a special

multiplex

output

(or

socket

for a decoder)

were

designed

for

mono

reception

and

even if

to

ffi

BB 7.2 Typical

FM detector

Circ.

conversion to stereo

is

undertaken the

quality

of the receiver may

make

good

stereo

reception impossible. A

poor

1F

strip will invari-

ably

result in

poor

separation.

It is not

possible

to supply detailed conversion instructions for

any

particular

tuner

and

the conversion can

sometimes be

very

difficult

even

for

an experienced engineer.

The following

notes

are

for

guidance

only:

When modifying to stereo

you

must expect to up-grade

the aerial:

the signal that

gives perfect

mono may well be totally

useless for

slereo. Fig. BBl .2

shows a typical VHF detector circuit. The exact circuit

and

values vary

considerably from set to set but the

audio ouput,

point

A, is usually easy to locate

as

it feeds

(via

a switch

perhaps)

into the volume control. Locate components

Cx and Rx, which will

havevaluessuch

that Cx

x Rx'-50,000

where C is in

pF

and

R in k{J,

Cx is the deemphasis

capacitor and must be removed. lt may also

be necessary to reduce in value

or to

remove

entirely, Cy, which is

for

1 F rejection,

or

poor

separation may result.

These components can be difficult

to spot and it may be

necessary to ask the

receiver's

manufacturer for

advice.

The decoder's multiplex input,

3, will

accept the signal from

point

A.

887.2.1

Transistorsets

Most

transistor sets

without

MPX

outputs are transistor

portables.

The

de-emphasis

capacitor

is in the region

of

10pF.

These may

only

give

indifferent stereo and in

particular

are

unlikely to

give

any results on their built

in

aerial except

in

very high

signal

strength areas.

887.2.2 Valved tuners Mostly these are of older

design: the

resistors in the discriminator are

higher

in value than for

transistor circuits and

the de emphasis

capacitor

will be about

1sF.

5W 1

l-\. f\: \^./r

\/

n{n

vv

::::::

A \."l

IJ

BB 3 Decoder

layout

BB B

Filter

circuit

2

dr decodel

'1ftr

1OOO pt

a.

explaired in

82;

to

St 80

(

4 or7 dftoder

)

earth

pinT

of St 80

T

B88

Tape recording

On

stereo

transmissions

a

certain

amount

of

residual

19 and 38KHz

switching

frequency

may

remain

in the audio

output

from

the

decoder.

This

does

not

matter

for normal

music

listening

but, on

tape

recording

it may

interfere,

with

the

recorder's own

erase

and

bias

oscillator

causing

whistles and

noise.

l{ this occurs

the circuit

of

fig. B88

can be

interposed

between

decoder's

output

and

preamplifier

input.

The circuit

must

be duplicated,

one

for each channel.

BBi0

Common

faults

Noise on

stereo,

not

present

on

mono or

when

mono switch

is

in.

This

is

invariably caused

by a

poor

signal strength

so a better

aerial

is

needed.

Stereo

reception

is

far more critical

than

mono

and

requires

a

much

better signal.

Stereo

beacon

operates

between

stations

this

may happen,

the

beacon

can

be activated

by noise,

and

does not

indicate a

fault.

Hum and/

or

motorboating:

the decoupling

capacitor

oJ section

82

is

requrred. Poor separation:

usual

cause of

this

is

that

the

decoder's alignment

is

disturbed:

the alignment

is critical

and

may

be disturbed

by

excessive

vibration.

Usuallv only

Ll needs

re-alignment.

Service.

Experience

shows

that

very

little

goes

wrong

with de

coders,

at the

rnost all

they

require

is slight

re-alignment

C

Control

modules

:

Preamp

and

AFU CA

Project

80

Preamplifier

CA1

TechnicalDescriPtion

TRl

is a virtual

earth stage

with C4,

C5,

R5 and

R6

as

feed

back

comDonents

and

R1 in series

with

the inductance

of

the magnetic

pick

up as

the source

of

impedance.

The circuit

in fact utilises

the

inherant

properties

of

the

pick-up

in

its

equalization

:a

typical

pick

up

has an

inductance

of

450mH and a

resistance

of 5009

For ceramic

pick-up

the

source

impedance

which

matches exactly

a

ceramic

pick-up

with

typical capacity

of

500pF

is changed

by

R2.

For radio

the

network R3,

R4, C1 and C2

is switched

in.

The radio

input should

be fed

from a resistive

source of

less than

50K.

Tape

monitor

facility

is

provided

between

TR1

and the

tone

controls,

which

are

a conventlonal

virtual earth

arrangement

around

TR2.

Since

separate

controls

are supplied

for each

channel

a balance

control

is

not

required.

Power

supply

is to

pin'1

,

decoupled

via R19 and

C16.

CA4

Typical

Performance

Size

260 x 50

x

20mm

Output

100mV

+

3dB

for specified

inputs.

lnputsensitivities

(

PU1

3mVmagneticPU

a )

"

300mV

ceramic

PU

source

impedan""t

)

radio

100mV

25K

max'

\

taoe

30mV

10K max.

Tape monitor

output

30mV

from

47K

Frequency

response

2OHz

ro

1511112

+

1dB

Frequency

range : bass

+ 12dB

-

14dB at

100H2

Frequency

range: treble

+.11d8 12dB at

10KHz

S/N

ratio 60dB

Power reouirements

12v

to 35v.

Maximum

output

(30V

supply)

2.5V rms.

CA5

Connections

1

+ ve

power

+ 12 to 35V

2 Right

)

3 Left

I

pick

up

point

4 Earth

!

5

Left

)

6

Right

i

radio

input

7 Earth

\

CA 2 Stereo B0 circuit

,aT

1H

-'+

o

n.i

rv

?

I

1l

CA 3

ST

B0 layout

B

Right

input

9 Left input

10 Right

output

1 1 Lefi

output 12 Earth 13

Earth,

signal

and

-

11 !"rl \ o,,ou,

l3 rrrgnr

t

CA6 Power

supply

Although

the

preamp

will function

over the full

range 12

to

35V the

overload margin

is reduced

as the supply

voltage

drops:

at

12V

the

maximum

output is 1V.

Replacing

R19

by 1K will

increase

this

to

2V

rms.

Above

35 volts

C16's

voltage

becomes

exceeded,

which

will

not

damage

it until

severe

overload

occurs. However

it is

best to fit

an

additional

resistor

in

series with

1

--

use

10K

for 40

50 volts

and

22K

for

50

-

70

volts.

CA7

Inputs

and Outputs

CA7.1. Magnetic

and ceramic

pickups:

Virtually

all magnetic

pickups

will

feed

directly into

the input

with

PU1

selected.

The

only

exceptions

are low impedance

devices,

such

as the Ortofon,

which

need

a matching

transformer.

Ceramics feed

the input

with

pU2

selected.

There is

a considerable

variation

in

output from

pickup

to

pickup

so some of the higher

output types

may require

a

very

low volume

control settrng.

CA7.2. Flat

inputs:

radio

and tape. The

radio input

has

a sensitivity

of

100mV

and the tape

30mV. Almost

every

signal source

you

may

wish to use

will feed

one or

other of these

inputs,

but if

you

wish to

reduce

the sensitivity

of either

one the

alternator

of CA

7.4.

can be

used.

CA7.3 Tape

output is 30mV.

lt cannot

be increased,

but

should

you

wish

to reduce

it then

the

attenuator

of CA7.4

can be

used.

CA

7.4.

attenuator. The

figure

shows

a

skeleton

preset pot

wired

with

screened leads

for input

and output. Input

lead

is from

the tuner

or tape recorder

and output lead

feeds

to the

preamplifier's

input_

Used on tape

out, this

feeds

the attenuator's

input

and the

attenuator's

output feeds

the

tape recorder's

input.

The

preset

can

be anyvalue

between 10K

and

100K,22K

or

47K

generally

being

best.

The

preset

should

be

adjusted for

best results.

CA8 Mono

Use

lf

a mono

source

(e.9.

tuner

without

decoder,

or a mono

lape

recorder) is

used

pins

5 & 6 or

8 I 9 can

be

joined

together.

Any

input

fed

to

either

will

then

be amplified

bv

both

channels.

For recording

into mono

recorder

it is

quite

permissible

to

join

pins

10

and 11

together,

this

will not

affect

the

channel

seoaration

through

the

amplifier in

normal

use.

CA 7.4

Altenuator

I

t_

>

I ape

Input

and

output

connections

l

J

ve

power

1B

CA10

Common

faults

Hum

The

preamplifier

cannot

generate

hum

within

itself

but

it can,

if

mounted

or used

incorrectly,

pick

up hum

from outside.

The cause

of the

hum must

be located and

rectified.

Noise.

This consists of

a steady

fluctuating crackling

or

'frying'

sound.

lt is

uncommon

in the

preamp.

lf

the

preamp

is the cause

then

it will be

present

with all

inputs disconnected

but

not with

the

volume

turned

fully down.

There

is arr irreducible

level of noise

on

any

preamplifier.

Service.

The maiority

of

preamplifiers

returned

for service

have no

fault:

the troubles

are caused

bv the

way it is

mounted or used

CB

Active

Filter

U

nit

CB1

Technical

Description

Tr1

with

its associated

components

is a Sallen

and

Key type

low-pass

(scratch)

filter whose

effect

is

varied

by

RV1. Input

is to

3

(or

2)

and

no

input isolating

capacitor

is included

since

this

component

is in the

preamp's

output.

When driving

the

AFU from

an

input other

than

Stereo

80, a

capacitor

must be

included.

The

scratch

filter's

output,

from Tr1's emitter,

is fed to

the rumble

(high

pass)

filter arranged

around

RV2. Output

is

{rom

6

(or

5).

Supply

voltage

is

fed to

1 and

decoupled

by

R7 and C6.

r,.

'I.-

CB

2 AFU circuit

C86 Power

supply

The

AFU

will operate

from below

12V

to 50V. The

maximum

output

is voltage dependant and

if

clipping

occurs at lower

voltages R7

can

be reduced to

6K8

or so.

lf the AFU is to be used with an amplifier other

than

project

80, it

can

be run

from its'

own separate

battery. In this case R7 can be

short

circuited and a 9V battery

used it will

last

many months as

consumption

is very

small.

C87 AFU

'override"

switch

The layouts that

incorporate an AFU

leave it

permanently

in circuit.

However even

at minimum cut. the

AFU does impose a lirnitation on

frequency

response especially

when fed

from a high impedance.

It may be found desirable,

therefore to

incorporate

an override

switch to cutthe

AFU out of circuit.

To do this a

4

pole

change over

switch

is needed, wired as

in

the

diagram below.

Note that the

resistors and capacitors

are optional

but

if they

are

omitted operat

ion o{ the switch

will cause norse.

Cts4

TypicalPerformance

Size

Source

impedance

Frequency

response

(f

ilter at

0)

Low

pass

(scratch)

High

pass

(rumble)

CB5

Connections

1 + ve

power

2 Input

left

3

Input

right

4 Earth

{signal

& ve

power)

5 Output

left

6

Output

right

7 Alternative

earth

CB

3 AFU

lavout

108x50x20nrm 10K maximurn

36Hz

to

22KHz

-

3dB

-3dB

variable

22KHz

to 5.5KHz.

slope

12dB

per

octave.

-28d8

at28Hz.

slope 9dB

per

octave.

AFU

layout

19

_prf

6

-

on5

0l_--."

z

[F___pn3

l

I

)

illl Rs l00K

AMPLIFIERS VOLUME CONTROL

TO

POWER

l--

srAGE

LH CHANNEL.

TO

POWER

l_{ srAGE

'

RH

CHANNEL.

CB 8.2

Detail of amplifier

CB

7

Aver-ilde

switch

CB8 Use with

amplifier

other

than Project

80

Most stereo

amplifiers

include

a

tape link

with

monitor

facility. The

AFU

can

be arranged

to

plug

into

this

tape connection

and run

from

its own

power

supply.

lf the

amplifier

is negative

earth

then it

can

be used

to

po\

/er

the

AFU and

a separate terminai

can be

added for

the

+

ve lead.

In

the

diagram

below we

have

assumed

that

the

5

DIN

tape monitor

socket has

been replaced

bv a 6

tvpe and

the

sixth

used for

this +ve

connection.

Fig.

C88.1

shows

the AFU

wired

for

this.

Note

the

use of

'l1rF

capacitors

in

series

with

pins

2

and 3.

The

AFU will

not work

if

these

are omitted.

Corrected in

this

way

the

amplifier's

tape monitor

switch

becomes

an AFU

override.

Note

in fig.

C88.1.

and

C88.3.

that

all screens

are connected

at

one end, but

at the

other

only

one screen

is

connected

to

the

plug/socket.

The

other

screens

are left floating.

lf the

amplifier

does not

have

a monitor

facility

it must

be modified

bywiring

the appropiate

connections

and fitting

a 6

DIN

socker.

The best

place

in most

amplifier

circuits is

just

before

the volume

control, which is

usually

fitted

just

before

the

power

amplifier

as in

fig. CBB.2.

The

connection

must

be

broken

as shown.

Fig.

CB 8.3.

shows how

the DIN

socket is

wirecl.

In this

application

it is

also

possible

to fit

an AFU

override

switch

(CB7).

lf

the AFU is

used

off its

own battery

a

5

pole

2

way

switch

could be used

for this

override

-

the

spare

pole

being

used

to

switch

off the AFU.

C B B. I AFU

wired

f

or tape

socket

CONNECTIONS. TO A.

F.

U.

c

B.

8.1

6

DIN

PLUG

VIEWED

FROM

REAR

OF

PLUG

CBl0 Common faults

Lack

of effect. Invariably

this fault

is not

caused by

the AFU but

by

the speakers

or by

sub.jective

effects,

The

average

person

can hear

frequencies

up

to

'l4KHz

a few

people

can hear

higher

than this

(up

to

19KHz)

but

this drops

off

with age

and some

older

people

can only hear

up to 11KHz

or so.

But there is

not very

much

sound content

in normal

music

above

'l2KHz

and the

speakers

may not respond

very

weli

-

so the AFU

nray

appear only

to have

effect at maximum

cut.

A

similar effect

occurs at low

frequencies,

especially

with

smaller

loudspeakers

which may

have very little

response

below

150H2.

The

rumble filter may

then have

very little

audible

effect.

Distortion,

controls interact

when

in use from

an

input

other than

Project 80. The AFU

does

not have

an isolating

capacitor

at

it's

input,

tl.ris is included

in the Project

B0's output. lf

the feed

to

the

AFU has a direct

dc

path

the contrcil

operation

wiil be reduced.

See

section

CBB.

Serice. The majority

of AFU's returned

for

service

are not faulty.

The

users are

experiencing

a subjective lack

of effect

as explained

above.

D

Z40

and 2:60

Z4O and760

are very

similar in

their

uses

and

applications.

They

are

in many

applications

interchangeable

and for

the

most

part

will be

dealt with

together.

Information

which

applies

specifically

to one

of

other is included

in

sections DA

and

DB.

D5

Connections

Pin 1 Power

-ve

and output

earth

2

Signal earth

6 PIN

DIN SOCKET

VIEWED FROM

OUTSIDE

TO

AMPLIFIERS

'

HT

LINE

CB 8.3 Wiring for

AFU

socket

20

r

of the amplifler,

the input

level

and the loudspeaker's

efficiency

and

inpedance.

So long

as the sound

output

is

undistorted,

these

are the

only factors

imposing

any limitation,

lf therefore

the

sound level

from the

system

is

too high

one

of these factors

must

be altered.

Gain alteration

is

covered

in section

D7

and'input

level'in

section

C47.

D6.3. Loudspeakers

The

two factors

which

determine

how much

sound

a

given

loud-

speaker will

give

out with

an amplifier

are its

efficiency

and

its

rmpedance.

Efficiency ls

rarely

quoted

by

the manufacturer,

but

probably

varies from

0.5% to 10%

a

range

of

20

to 1.

Other

things being

equal the 10026

efficiency

will

give

20

times

as much

sound as

the

0.5% one. lmpedance

is

always

quoted

and is usually

quoted

as 4,

B or

16!la

change

of only 4 to

one. The impedance

change

above from 16!lto

4Ocould

give

arr increase in

sound

of only 4

times.

However

a speaker

does not have

a

fixed

impedance

if

you

were to

actually measure

an

Bf]speaker

you

would

get

an

impedance

varyrng between

perhaps

5f)and 20Q.

Some

'B[)'

speakers infact

fall

as low

as

2i:

at

certain freouencies.

When

choosing

a speaker

therefore

a listening

test is

to be relied

on far more

than any

written

specification:

the impedance

in

particular

is

only a

guide

and is not

important.

D6.3.1.

Permissible

impedance

240's

and 260's

are

both

quite

safe into

normal

speakers

which

varV

between 4t)and 16t2.

lf speakers

at the

low end

of this

range

are used

for high-volume

level

there is

however

a chance

of

some over

heailng. High

impedances

above

'l

6flare

rarely

met

but will

do no harm.

Both

amplifiers

are saf e into

even ar)

open circr-rit.

Low

impedances,

i.e.

below 4O,

will,

on both

amplifiers,

cause

heating,

lf the

load is

applied for

too long,

or is

a direct

short-circuit,

heating

rnay

be excessive

and will

cause damage.

This

is especially

true

of 240

and 260

used

at or near

the

top

of their

permissible

r,perattn0

voltaUe

ranges.

Electrostatic

speakers

are not

suitable

for use

with the

240,

but can

safely

be used

with the 260.

D6.4.

Heatsinking

The

260

\or

240)

when

working

hard,

gets

hot

(the

two

transistors

mounted

on

the black

fin

dissipate

this

heat).

lf

the amplifier

is

worked

too

hard

and

this heat

is

not removed,

these

output

transistors

will

get

too hot

and will

fail. The

purpose

of heatsinking

is

to remove

this heat.

Normally

the amplifiers

will

be

assembled

into

a metal

chassis

and

this

will be

used as

the hearsink.

Fig.

A1.2.

shows

some

ways in

which

a 240

or 260

can be

mounted

using

a metal

block

to ensure

good

flow

of heat

to

the

chassis.

In high

power

situations

this

sinking

is very

important

and it is

also

important

that all

contact

surfaces

through

which

heat flow

(i.e.

which

contact this

block)

should

be flat

and free from

burrs

round

the

holes.

A light

smear

of

silicone

grease

or heatsink

compound

is

also advisable.

The

amount

of heat

generated

(and

thus

the

need for

heatsinkino)

will increase:

with increasing

supply

voltage

with

decreasing

speaker

impedance.

with

increased

output

volume.

Thus,

with a PZ5, you

will

not normally

require

any heatsinking.

The

PZ5

is therefore

used

in our lavout

in

a olinth.

With

the PZ8,

heatsinking

must

be used

not

onlV for

the 260,s

but

also for

the PZB

itself.

You

will

also need

better

heatsinking

where

the

amplifier

is

used

for

high

powers

rather

than

the for

normal

domestic

use.

As

a test

of

your

heatsinking

-

feel

the black

fin

of the

amplifier.

lf

this, under

all conditions,

remains

only warm,

then

your

heatsink

ing is

adequate.

lf it

is much

too

hot

to touch

--

then

vour

heatsinking

needs

improvement.

D6.5.

Power

supplies

Normally

theZ40

will

be used

with

a PZ5

or

pZ6

and the

260 with

a

PZ8.

However,

the

power

supply

will

determine

how

much

oower

the.amplifier

can

supply

(see

section

E4)

and

this will

determine

heatsinking

requirements

(section

D6.4.).

The

table

below

shows

roughly

how

much

current

the 260

takes

at various

power

levels.

The

240

will

be similar

up

to 35V

operation.

3

A

5 6

l

8 9

Signal earth Feedback

"earth"

Signal

input

Alternative input

"earth"

Feedback

point

+ ve

power

Input

Output

to

speaker

D 5 240/260

wiing

The

circuit

above

shows the

connections

to one 240

or 260

used

with

a simple volume

control.

Note

the use

of a central

earth

point

with

separate

wtres

run

to

each of the

connections

shown.

This

point

should be

situated

so

that

the wires

to terrninals 1, 2

and 3

are short

(not

more than

3").

Note

also that

with a 240

only,

the wire

to terminal 2

can be

omitted

(2

and

3 are irrternally

connected

in the

amplifier).

C1: input

capacitor.

This

must be

used in

all cases

except

with

Stereo

B0 or AFU

driving

the

amplifier. 1pF

50V

will do for

all

purposes

although 100nf

to

1Opf

can be

used.

C2:

output capacitor.

This

is required

only with a 260.

Choose

2000irf

50V although

other values

can

be

used with

B{l

or

1b(/

speakers

(1000pf

and 500pf

respectively).

Reducing

the value

of this will

reduce

extreme

bass response.

The voltage

rating

should ideally

be

the

same as the DC

supply

voltage

used,

but

can where

size is

important

be reduced

to half

the supply

voltage"

C2: only needed

where

a

poor

power

supply is

used

(e.g.

dry

batteries)

or

where

leads

to

power

supply

are

longer

than 3"

or so. lt

should be rated

at a working voltage

not less

than

the chosen

power

supply voltage

and can be

between 1Opf

and 100pf

where

longer

supply leads

are in

use. With

batteries

it

should

be increased

to

1000pf,

or even

5000pf with

smaller

batteries.

RVl:volume

control. A

log type

should

be

chosen

-

47K

max. for

240

or

100K

max. for

260. Lower

values

can be

used,

depending

upon the

signal

source feeding

the

amplif ier.

D6

Power

supplies,

speakers,

power

and heatsinking

fhe 240

and

260

have

a constant gain

that

is

to

say that

the

volume

level

from

the

speaker

will

be

solely

dependant

upon

how

loud the

input

signal

to

the

amplifier is.

The

gain

can

be

altered

as

stated

in D7.

However,

if too

much

input

is

given

the output

signal

will start

to

drstort

at a certain

level.

This

level

of distortion

is

the

,maximum

output

power'

and is

dependant

upon

the

power

supply voltage

used

and the

loudspeaker's

inpedance.

A

graph

showing

this

dependance

is

given

for

the

260 in

section

D84,

and

the curve

from

the 240

is

similar

except

that

this

must

not

be used

above

35v d.c.

Output

power

is

not

a measure

of the

sound

level

you

will

hear

from

the

speaker

-

since

in normal

use

you

shoulcl,never

require

to

use

the

amplifier

anywhere

near its

maximum

power.

Although

increasing

the

power

supply's

rating

will increase

the

maximum

power

output

it will

have no

effect

on the

sound

at the

level

you

normally

use

-

unless

you

are

using

the

existing

system

at its limit.

D6.2

Sound level

The

level

of

sound

coming from

an

amplif ier

depends

upon

the

,gain,

ZI

50v

40v 30v 20v 10v

1.9A

(40w)

1A

(30w)600mA

(18w)

1.5A

(35w)

800mA

(19w)

450mA

(10w)

'l

.1A

(20w)

600rnA

(10w)

300mA

(5w)

700mA

(7w)

400mA

13.5w)

150mA

('l

.5w)

300mA

(1

.5w) 200mA

(.5w)

75mA

(0.3w)

DA

3 240

layout

These

figures

are based

on continuous

sine-wave

operation

and in

practlse

current

consumption

will

be far less

-

sav

lz

-

3/c

for

loud

pop

music

and % % for

normal

domestic

listening.

D6.5.1

Battery

Operation

Because

of the low

current

consumption

batteries

are a very

suitable

power

supply;12V,18Y

or

24V

are suitable

combinations.

Remember

however

that for

a

power

of 5W f rom

the

amplifier

the

battery

may have to

give

up

to

10W,

so don't

expect too

much from

a small battery.

The battery

should be

able to

supply the

current

indicated

above.

For

battery

operation the

capacitor

shown

as C3 in

D5

must be

included

but itsvalueshould

be increased.

1000pF

is

to be

considered

the minimum

value

but larger

values

(5,000rrF

or

10,000pF)

are

advisable especially

with

smaller

sizes of

battery.

This

capacitor

must be rated

at a working

voltage

equal

to or

greater

than

that

of

the

chosen battery.

D7

Gain

As

supplied

the Z4O has a gain

of approximately

110

times

and the

260

about

55

(this

means that

it aZ60

is

put

immediately

in

place

of

a

Z40,the

260 will

not

sound

as loud).

This is

done

so the

260

can be

used with

the earlier

project

60

system. In

both

amplifiers

the

gain

is

controlled by

two resistors

-

R8

I R6 in

240

and

R8 & R7

in 260

-

such that

the

gain

in

approx.

DA

2 240

circuit

R16

TR7

C6

1m0

25V

nt/

Ot22

R2

t,7K

A

R12

t,7

0

5K6

R7

10K

TR4

R9

LK7

22

r

R8- R6

(or

R7)

R6

(or

R7)

On

both

amplif

iers the

gain

can

be increased by

fitting

an

external

resistor

across

pins

4 I7

: 4-l

on the

240

or

1

k8 on the

260 will double

the

gain.

The resistor can

be decreased further

if more

gain

is

required,

but will not

normally be less than about

10Q

on

the

240

or

180 on the 260

(giving

a

maximum

gain

of around

500).

D10 Common

faults

In any

power

amplifier

the

devices most

likely to fail are those

which

do

mostwork

-

i.e. the output

transistors

Trl 1 t

12. lf

one or

both

fail the

amplifier and

power

supply

may overheat

and

it will be

obvious

that a severe

failure has occured.

The

protection

on

240

and

260

will make this sort of

failure

uncommon

-

except where

heatsinking

is inadequate.

Overheating

during

normal

use may simply

indicate that

heatsinking

is inadequate

(see

section

D6.4.) but

it

can

also

indicate instability,

in which case

it may

well occur on one channel

only.

Instability

is

caused

by excessive

lead lengths or

layouts which

place

outputs

and

inputs

too close

together

DA Z4O

DAl

TechnicalDescription

The

input

signal

is applied to

Tr1's base, which compares

it with

part

of

the output

and amplif

ies the difference.

Tr2 matches Tr1's output

to

Tr3. and

orovides

a

limited maximum amount of

drive to Tr3.

On

positive-going

half cycles

Tr3 drives the output transistor

f rJ

directly

and

if the current through

Tr7 is excessive a

voltage is

developed

across

R16,

which turns

Tr5 on removing

drive

from Tr3

and

thence

protecting

the outpUt.

On

negative

half cycles

Tr8

is driven by

phase

inverter

Tr4.

Excess

current

on this

half cycle

is detected

by R17, causlng

T16

to conduct

and

reduce the

drive to

Tr4.

DA4

240

performance

Size Supply

voltage

Ouiescent

current

Power

output

Distortion Input

impedance

55xB0x25mm

tr 55 0.c.

15mA typical

(

t

5mA)

at

35v.

12w rms 8!lat

35v.

20w rms 4!lat

35v.

0.1%

at

10w, 80,

l KHz .

90kf/

+ 10%.

DA 9.1

Amplif ier for crystal

pick-up

DB

2 260

circuit

A

R1

39K

A

R20

0n1

A

TR3

c2

10n

R2

39K

C1

10

TR6

A

TR12

R 21

10

R5

t,7

0

A

tKf

100K

R6

39K

C5

2P2

D5

R11

D6

A

z5

,

DB 3

260 layout

T16

provides

a constant

current Iimit

on negative half

cycles.

Tr3 is a constant

current'tail'for

Tr1

and 2 to make

sure voltage

variation

does not

alter

performance.

The

outputtransistors(Tr11

and Tr12)

are driven

bv Tr9

and Tr10.

and

the

current through

Tr11

is sensed

across

R19. lf it rises.too

much Tr5tunrs

on, limiting

the drive

to Tr9. Tr5

is also

turned

on by

excess voltage

across Tr11,

sensed

bV the

divider

chain R13

and

R15, so that

the limiting is

of

power

in

the

output transistor.

Tr7

performs

a complementary

function

on

the negative

half

cvcle.

-f3tZ

55x98x20mm 10-50 DC l BmA

at

45u

approx.

25w

into

Stlat 50v

40w

into 4!lat

50v

.02o/o

aI

10w,

BOat l KHz

100k

*

10%

70db 'l

5Hz to

200KHz

+

3db 55+5% 4!)or

greater

Safe

open circuit

Supply-voltage

dependant

current

limit into

low impedances

depends upon

output

capacitor

used

(100

with 2,20OuF

into

8Q

at

1

KHz)

The curve

below shows

how the

power

output varies

with

supply

voltage for

various loudspeakers:

D88

Switch

on surge

At switch

on, depending

upon

the

power

supply

used, a large

surge

may be

present

in the loudspeaker.

The PZ8

Mark 3 includes

a circuit

to

limitthissurge

but with

other

supplies it

can be severe

enough to

damage

a small

speaker of 3!lor

so.

S/n

ratio

70

oo.

Frequency

response

30Hz to

'l00KHz

into

8[iat 1w.

Voltage

gain

1 10

+ 10%.

Permissible

load

impedance

4.

8

or

16t].

Protection

safe

ooen circuit.

3A

current limit

into low

imoedance.

Damping

factor

50

with

8fl load.

Power

bandwidth

30Hz

to 35KQHz +

3 db.

Input sensitivity

90 mV

(for

12w

into

Bl)).

DAg Applications The 260

may be

used

instead

oI aZ40

in

these applications.

However,

the

260's

gain

is

about half

that of the 240

so this mav need

to be rncreaseo. DA9.1 Amplifier lor

crystal

pick

up

The circuit above will suit

a simple

record

player.

Omit R2 unless mor'e

gain

is required

(see

section

DA.7).

R1

can be increased to reduce the

output. lt will also increase

bass

resoonse.

C1 affects treble: increase it for

more treble, reduce for less.

C2 need only be fitted if R2 is

added.

DB

Z60

DB1

TechnicalDescription

Tr1 and Tr2

from

a long

tailed

pair

used to

compare dc

and

ac

conditions on

the input with

those

at the output.

Input

conditions

are,

at dc, the

potential

on the

junction

of

R1

I

R2 and,

at ac, the actual input

signal.

The

output conditions

are the dc

potential

on the

output but

onlv

a

part

of the

ac

level,

defined

by R7

and RB. Tr1's

collector

shows

an

output

proportional

to the difference

in input

and

output, which

is

fed

to Tr4. Tr8 is in

series with

Tr4 to

provide

a current limit

so the

output transistors

have the

same

amount of drive

availability

at

all

supply

voltages.

Tr8

only limits drive

on

positive

going

half cycles.

.A

D84

Performance

Size Supply voltage

Ouiescent current

Power

output

Distortion Input impedance S,/N

radio

Frequency

response

Voltage

gain

Permissible load

impedance

Protection

Damping factor

r

DB 4 Power

outlet

curve

Fig.

DB.8 illustrates

an additional

circuit

which

can be

added to

reduce this

surge.

One

circuit may

drive

several

260s,

but

the

capacitor

C1 should

be doubled

for two

260s,

trebled

for

three. etc.

DBg

Applications

DB9.2 Full

Bridge

Circuit for 60w

The circuit

of

DB9.2.1

shows how

two Z60s

can

be connected

back-

to-back in

a full bridge

to double

the output

power.

Each 260

in

effect operates

into half

of the

speaker.

Speaker impedance

should

DB 9.1.2

Oscillator

outouL

VOLTS

OUT

(RMS)

POWER

SUPPLY

VOLTAGE

(DC)

DB

9.2.1 Full

bridge circuit

be 8O

or more,

since

with

an

8[l

speaker

each

260

,sees,

4O

and will

(from

fig

D84)

give

approximately

40w

into

this

4f] load

(from

bOv

supply).

Thus

both

together

will

drive

an SOspeaker

at up to

80w.

(fig

D89.2.1)

Similarly

the circuit

can

give

up to

60w

inro l6e

(each

amolifier

operates into

8Oand

gives

30w).

Care

must

be taken

with

the wiring

which

should

be

as short

as

possible.

Fig

D89.2.2

shows

the

wiring

of

the bridge

with

the two

amplifiers

mounted

aboul

1/2"

to

1"

apart

(one

of the heatsink

blocks

shown in

fig

A'l .2 is

ideal).

Note

in

particular

that

pins

1-1

,2-2,3-3

are

joined

together

with

one wire

f rom

each

pair

to

the

earth

point.

POWER SUPPLY

DB

9.2.2

Full

bridge

wiring

This

arrangement

can

suit two bridges,

with

a common

point

for

both.

Heatsinking

is

of

prime

importance

on the bridge

-

a 60w

bridge

may have to dissipate

30w itself,

so all

surfaces in

contact

must

be

flat and all holes

must

be deburred.

Silicone

grease

must

be used

to

ensure

good

heatflow.

One

PZB will

drive

two

bridges

-

but

will

slightly

restrict

full

output

with SQ,speakers.

lf

maximum

power

is required,

two

pZgs

can be

used

(when

two

transformers

will

be needed),

one for

each

bridge.

Two

earth

points

can

now

be used

-

one

for

each

bridge

/

PZ8

combination.

40

a

t

:30

i

Rzo

F f o F

3ro

20

25 30

SUPPLY

VOLTAGT

+

VE

SUPPLY

-D

7 260

a

+PlN7260b

10

0

KJI

DB

B

Switch-on

surge

z5

The

output capacitors

are included

to

give

some

protection

against low impedance

loads

at

low

frequencies,

and

to

ensure that

any slight DC

imbalance

does not

cause current

through the

speaker. Note that if

the bridge's

gain

is to be increased,

only the

gain

of the first 260

should be

altered.

DB

9.2.3 Full

bridge mounting

Fig D89.2.3

shows how two Z60s

are mounted on one heatsink

block, with

a

'floating

earth

point'

between them. Wires

go

from

this

point

to

power

supply,

chassis,

preamp,

etc. lf two bridges

are used with a common

power

supply, the inset earthing is best.

Terminals

1-1

,2-2,3-3

are connected with one wire from each

pair

to

the common

earth

point

for all four

amplifiers.

D89.4. DC Amplifier

This

application

is not

suggested for the less

experienced con-

structor.

DB

9.4.1

DC

amplifier

The figure

shows the basic connections for

using the 260

as a

dc

amplifier.

Note that

a split

power

supply voltage is

used. This

supply

must be symmetrical

but can varv between

5-0-5 and

25-0-25.

However, use at high voltages

can

result in

excessive

current

if

the

load is of low resistance

and this could destroy the amplifier

R1 and R3, D1

and

D2

and RV1 are included

as a

'set

zero' circuit

to adjust the

zero voltage

level

on

the

output. The setting will

be

somewhat dependant upon the

source impedance connected

be-

tweenterminals5S6.

Inputs Fig. DB9.4.2. a &

b show two input

circuits - a is a virtual

earth

inverting

mode

input and the

gain

will

be approximately

'

Zf)

100K

R4.

b is a non-inverting input, which

should be used from

a low

source

impedance to minimise

offset voltaEe. R5

(2K7)

can be added if

necessarv.

D89.4.2 a +

binputcircuits

Absolute maximum ratings Assuming

the amplifier is well

heat-

sinked, so

that the transistor

case temperature does not rise

above

50

C, the transistor maximum dissipation

is 50w. This heatsinking

will be difficult in

practice

because

of thermal resistance from

case

through transistor insulating mica

and heat fin to the heatsink

proper,

so the

specifications are for

guidance

only and are not continuous maxima. Supply voltage maximum

23-0-23v. Load current maximum 44. Load resistance maximum must

alwavs be less than

Vs2 and Vs, which

ever

is

the smaller.

200

6

Thus with a

23v

supply,

Vs2

gives

2.6

and Vs

gives

3.8.

200

6

In

practice

load impedance

should be

greater

than 4O

Inductive

loads lf the load is highly reactive

a series resistor is

necessary. With motors using brushes

a very'spiky'back EMF

is

given

and the circuit below is suggested.

lou

25V

Reversible

DB 9.4.3 Motor

drive circuit

E

Power

Supplies

E4

Specif

ications

The

power

supply chosen will

determine the

power

output

obtained

from the whole

system so that, it a PZ5 is

chosen, this

will limit

the

output to around

12w

total

output into 40.

With

the PZ6 the

output

will

be

25w

total into

SQor 4O(e.9. 12w +

12w into

80,

11w

*11w into 4O

but

about

20w into

4O

with

onlv

one channel driven).

The PZ8

will drive

240's fully

(if

it's voltage

is reduced

to 35)

into

any

impedance, and

will drive

the

260 at full

power

into BQ.

However,

into

4{lthe

PZ8's current

limit starts

to operate

to

give

extra orotection.

the

full 40

+ 40w will

not be

reached

with both

channels

driven simultaneously.

Thus

in the table

below,

expected output

powers

are

given

for

various combinations

of

power

supply. Columns

1 t 2 apply

to

240

butwon't

be affected

much bv

use of a

260. Column

3 is with a

PZ8

set

at

35v, with

240 or

260

(260

here will show

increased

power

into

4Q, of

25 & 25w). Column

4 is a normal

PZ8 at 50v

with 260's.

3.

4. PZB PZg reduced 50v 20+20

30+30

tz+ tz z5+ z5

7

+7

14+14

20 45

tz

z5

714

Both channels

driven

4

Q

8A

150

One

channel

driven

4

O

80

15 [)

1.

2.

PZs

PZ6

6+6

11-F11

4%

+ 4Y, 12+

12

3+3

7+1 820 5%

13 4l

EA/

EB

PZ' 8

PZ6

EA1 PZS

Description

The

PZS consists

of a

centre

tapped transforrner

feeding a

full-wave

rectifier

with a

2000pF reservoir

capacitor,

to

give

a no-load

output

of

approx.

28v.

The transformer

has a twin

primary

for series/parallel

operation

on

220v or

1 10v ranges.

EB1 PZ6 Description

The

PZ6 uses

the same transformer

as the

PZ5 but feeding a

bridge

rectifier

to

give

approx.

56v dc on

the

1000pF

capacitor.

At switch on,

there is no

voltage

on

the output,

but the voltage on

the

junction

of

R1 I R2

forward biasis D1, slowly charges

up C2.

Tr4's

base rises and

it

passes

slowly

increasing current

to Tr3 I Tr1.

The output

voltage starts to

rise until about 9v

when

ZD1 becomes

forward

biased.

Tr4 now compares

the zener

voltage on

its

emitter

with a

proportion

of the output

voltage

fed back from VR1, and

adjusts

drive

to

Tr1 I 3 to stabilize

the output

voltage dependant

upon the

setting

of

VR1.

Fs1 is a

fuse to

give

some

protection

and this

will infact blow after

a few seconds

on a

heavy overload

if 3 or 4 speakers are

in use.

lf a direct short

circuit occurs

across

the output however,

transi-

stors

mav

fail

as

well as

FS1 so if the

fuse has blown the

rest of

the circuit

should

be tested before

replacing.

To test the circuit

disconnect

it:

+ I

-

outputs,

replace

FS1 by a

1a slow blow

and switch

on,

with a voltmeter across

the output. The

voltage

will rise

quickly

to about

15v and

will

then

slow down,

stopping

at

35v. VR1 should

now adjust

the stabilized

voltage

between

20

and 50v

approximately.

EA5 Connections EA5.1. Mains conneutions Live

(L)

and

neutral

{N)

are connected

via appropriate

switches and

fuses

to L 8 N on

the PZ5/P26.

Earth

connects

either directly or

indirectlv

to the chassis

(-ve

terminal).

EAs.1.1.

Fuse

and

switch

Whilst the output

(dc)

of the

power

supplies does not

require f urther

EA

2 PZS

circuit

EB

2 PZ6 circuit

protectlon it is strongly

recommended

that a

fuse be inserted

in

series

with the

mains connections

to the

transformer.

For PZ5 and

PZ6 this can be

250mA

anti

surge.

For

the

PZ8 transformer

it

should

be

500mA

anti surge.

lf the

fuse also

provides power

to other equipment

(e.9.

the

turntable

motor)

then this

rating will

need to be further

increased.

A two

pole

switch

should

be used

in the

mains to

provide

complete

isolation.

EA5.1.2.

1

10v

operation

To change

from

22Ov

to

110v the

red

and

pink

wires from

the

transformer

(at

present

connected

to

land B in

fig. EA.3) should

be

unsoldered.

Now connect the

red

wire to the same

land as is

connected

the mauve

wire, and connect

the

pink

wire to the same

land

as is connected

the orange

wire.

For

1 10v

operation

the f use

rating should

be doubled.

To change

from

1 10

to

220v

the above

procedure

must be

reverseo. EA5.2. Output Output

of

the PZ5,/6

is between

+ & terminals.

The - output

is

isolated

from the

chassis.

EA10 Common faults - PZ5

The

PZS's

circuitry

is so simple that

there is very little to

go

wrong

with it and it

will

even

survive a short circuit across

its output

for

some

period.

Overheating

lf the transformer

gets

hot it is usually

because

one

of

the

amplifiers

is at fault.

Disconnect both Z40s and when the

PZ5

has cooled

down switch on

again. The PZ5 should

remain cool.

Faulty diode. Occasionally

one or other

diode may fail open-circuit or

short

circuit. Open

circuit failure

will

cause an

increase

in hum level

(and

a

hum frequency

change from

100 Hz to

50

Hz) but may

not

be

noticed.

A short circuit

diode

will

cause overheating.

Both con-

EA 3 PZ5 layout

27

L-

-{I-

G G

C1

-

F

I I F

I

Oemitter

TRl

acdlector

EB 3

PZ6layout

ditions

can be tested with an ohm meter, or by disconnecting one

wire

from

the transformer secondary:

if the PZS functions in this

condition

then the diode that is not disconnected is working properly. Service. About two

thirds of PZSs returned for service do not have

any

fault at all.

EBl0 Common faults - PZO The

PZ6 is not

protected,

but includes a fuse to restrict damage. lf

the fuse blows,

then it is

possible

that

other

damage has occured. lt

is not safe

to replace the fuse and

put

the PZO back

in

circuit, since

other

damage can cause

the

PZ6's voltage to increase to 55v

(which

is the normal off-load

voltage across C1). To test, disconnect the

PZ6

from

circuit,

replace

the

fuse

(1A

antisurge)

and switch on.

Measure the output voltage, which should be adjustable between

20

and 50 approximately.

lf this is correct, then it is safe to test the PZ6

in

circuit.

Fuse

repeatedly fails.

lf

speakers are

of

low impedance

(5

or less)

and

the volume

os turned too high, the fuse will fail with

no other

damage occuring. lf this happens

the

fuse

may be uprated to 1.25A

antisu!'ge. lf the mains fuse repeatedly fails,

then the extra equip-

ment driven

off

the fuse may

be at

fault,

or the wrong type

of

fuse mav be in use. Overheating.

The PZ6 in use does

get quite

warm,

especially

when

tuner and

decoder

are

in use from it,

or when high volume levels

are

in use.

lt is

unlikely that a

fault

causing

overheating could occur

within

the PZ6

without causing severe

audible symptons. The PZ6

transformer should

not

get

much

too hot to touch.

Service experience

shows

that

PZ6

failure

often

accompanies failure

of

one

power

amplifier. When

an amplifier

fails,

the PZ6 should

be

checked.

EC PZB

ECl

CircuitDescription

Tr4 and 5

form a long-tailed

pair

which compares

the reference

voltage on

ZD1 with that

present

on the

slider of VR1.

lts

output

26

controls

the

Darlington

'triple'

Tr1

,

2

and 3 in

such a way as to

minimize the difference

between the two.

At

the same time, if the

output

voltage

is at its nominal value

of

50v, T16 is

turned hard on by the reference developed

on

its

base by

R10

and R11. The tail

current through the differential

pair

is

then

limited by the zener voltage,

less Vbe in Tr4,

across

R8. As

the

output current through Tr1 increases its

base voltage increases

by

virtue

of the

increasing

voltage drop in R1. As

the base voltage

on

the

triple

rises, R4's

current

increases, drawing

more current through

Tr4

until, when Tr4 is

conducting the whole of the

available tail

current the

circuit stops stabilizing and the

output

voltage

falls as

current limiting occurs. The

circuit thus

gives

a limited

current of

between 4-6

amps at 50v, see the curve.

lf

severe limiting

occurs

the

output voltage drops. This

could

result

in over-dissipation in

Tr1, but the reduced output voltage

causes T16

to turn off, through R10

and

R11,

further reducing the

limited current

and dropping the output voltage. Positive

feedback

occurs and the

circuit'trips'

into

a sensing state when it

cannot

give

more

then

200-250mA.

Tr1

still dissipates,

about

10

watts

(200

mA at

50v

across it) but D1-D3

are in intimate

thermal contact

(being

mounted

on

the heatsink

below the transistor)

and

prevent

thermal

runaway

-

in fact both

the high current

and

low

current limits

are

reduced

slightly when

the circuit is hot.

The

circuit rests in its

sensing state safely

-

until such time

as the

overload vanishes,

when the

output voltage rises

and the circuit

turns

back

on again.

An

additional

attractive feature is the

circuitry

of

Tr7, D4

and

C4.

Before

switch

on C4 is discharged. At

switch

on

it

charges up

through

R5 and TrTs

base. The value

of C4 is then

effectively

multiplied

by

the

gain

of Tr7 and thus

charges very

slowly, with it

rises

the output voltage.

Thus to start with,

the output

current is

heavily

limited

(200mA).

lt is therefore incredibly

gentle

to the 260s,

which,

depending

on output capacitors

and speakers,

take

2-15

seconds to

switch on. During

this time many limitations

and

inter-

actions

occur between the

slowly rising

potential,

the

slowly in-

creasing

current limit,

the charging

output capacitors,

and the

switch on

performance

of the 260. The

noise

present

in the 260 may

l

63v

i

(ov)

'

1

.,1

:

'

:

I

r

+{+

r

F,

f,i,=

rlt,:.

:lri^

aa

:1

ll

,rR7

f

--.I"u

C

)

.

)

r"""11

,113

'F'

.

{

o,I,

ri

. *1""f.

i

r;],", .,_J1

,\.n-,

-1:i;

'

a

t t .Rt

tovl

..^{'ou

I

'n^u

:^"'

i'l;

,

!,

Rr

-.,u

ll_,^0..

=c3

b4I

o.o'D' c?

^..

\

IP

-

'.

';.i:

r

1t1

'

,i00!- ' \'

:^.:

cr*

!!.y

ll :

""

,|r,1,"

I 22!

MrN

..j,|o^--r.sv.

,+,

i''.

-j__

-

,;;-

ia:

* ASSUMING 46V n. INPUT

01250

....1,'

0v

L.,l L_

'

TRr

(

r5v)

()VOLTACIS

RLrftRtO

IO

+v. Of C1

EC 2 PZB

circuit

be anything from a dull

woomph woomph to a zzipp-squeak.

lt is

entirely safe

however.

EC4

The

curve shows

the re-entrant current limiting on the

PZ8 Mark

111,

and how this behaves with a

resistive load. Refer to the

technical description for more information.

At A the circuit has switched on and stabilized, under no

load. As

the resistive loading is increased the current rises until B is reached

(5A).

Limiting now

occurs

until at C the

output

voltage sensor works

EC

4 Performance

curve

and the unit switches down the

resistor load line

to

D.

As

the

resistance is increased current remains

constant

(limited)

but

voltage rises

to E.

The

sensing circuit now switches the unit

back. uo the load line to F

20

10

1

q

, o

EC3

PZB layout

s

*xxw*;x-f,T*ffi

*

29

JLJI

JL |-JLJL

JLJLJI JL,I.

JL

Note

the

line from C to E: this can

be

plotted

as the

trip current

for

varying

stabilized

voltage setting of

VR1 - the

pecked

trace

shows

the

current/voltage

curve at

20V.

EC5

Connections

Input.

The PZ8 requires

an

input in the

region of

40v ac,

which must

be supplied

from a transformer.

A suitable

transformer

will be

rated at

24

continuous,

with

an

output

voltage

of not

more than

45v maximum.

lf the output

voltage

is reduced

then

the input

can be

reduced also.

Input

voltage can

be

made

up to20o/o

less than

the

required output

voltage.

A

suitable

transformer

is the

MTl04 or

105.

avallable

from Henry's

Radio and

most other component

retailers.

ON

NO ACCOUNT

MUST MAINS

BE CONNECTED

DIRECT

TO

THE PZ8.

40V

ac

inout connects

to the terminals

on

the PZB

marked

Output.

+ ve and

ve outputs

are marked +

and

-.

The

-ve

outDut

is connected

to the

heatsink,

ECO

Voltage

Adjustment

The PZ8's

voltage

is adjusted

by

means of

VR1, between

a

maxi-

mum of about

6Ov and

20v

minimum.

A voltmeter

is required

to

measure the output

voltage if this

is

readjusted.

EC7

Mounting and

Heatsinking

PZB's mounting

and

heatsinking

requirements

are

the same

as those

of

the 260, covered

in

Section

D6.4 and

A1.2.

EC10 Common

faults

Failure of

the PZ8

is rare because

of

its sophisticated

protection

clrcuitry.

No output.

PZ8, working

into a

damaged

Z6O, may

detect this

damage

and shut

itself off,

giving

no

output.

This does

not indicate

a

fault

in the PZ8.

Disconnect one

or other

260 to

locate the

fault.

Overheating.

The

PZ8 will overheat

if heatsinking

is not adequate:

see

Sections

A1 .2 and

D6.4.

An area of

copper on

PCB

has overheated.

The PZB has

two thin

sections

of

copper on

its board,

in series

with the

rectifier, to act

as

f uses.

These

can only

fail if the

rectifier is destroyed.

When replacing

the

rectifier,

these can

be bridged over

with one

strand

from a

7/0016 flexible

wire

(fuse

rating about

7,A).

F

FA

Other

Parts

P.805

Masterlink

FA1 Description

The P.805

masterlink

contains input sockets

for

pickup,

radio and

tape

recorder connections,

and

speaker output sockets,

with

con-

necting

points

for the other modules

in the

project.

30

FA

3

Masterlink

laYout

It also

has alternative

connections,

by

means of

push-fit

wires,

for

pickup,

when the

whole

project

is

to

be

plinth-mounted. Facilities

are also

provided

for connection

of

headphones.

The masterlink

also contains

decoupling capacitor

for use

with the

tuner

(see

Section

86.1) and

attenuators

(variable

resistors)

for radio

and

tape

recorder

inputs to the

Stereo 80.

lt also contains

resistors

in

pickup

input for use

with high output

cartridges.

FA3

Layout

Note RV1 and

RV2 are not

included

in the'masterlink

which

is

matched to

the P.80 tuner.

lf a

different tuner,

with a

higher output,

is

used,

RVl and

RV2 can

be added.

Use

47K

pots,

R3,4,5

& 6 are

not fitted: space

is left so that a

PZ6 or

PZB

can

be

used

(subject

to

laboratory testing)

at a

later date.

Appendix

Service

and

guarantee

All

Sinclair

Project 80

modules are covered

by a

24

month

guarantee

during

which time we

will rectify at no charge,

any

fault within

the

module which

is not caused

by misuse,

subiect to

the following

conditions.

1. The item must

be returned as a

module i.e. not

wired into the

customer's

own

box - direct

to us,

properly packed

so as to

avoid

damage.

2. A letter must be included

stating

your

name and address

(block

capitals

please),

where and

when

purchased,

the nature of the

f au lt.

3. The item must

not have been damaged

by misuse or

inexpert

attempts

at repair, or

have been

modified either electrically or

mechanicallv

f rom the conditions

in which supplied, other than as

described

in this manual.

Please

note that we cannot

undertake to answer

letters sent

in

with

equipment

for

repair,

although every

effort will be

made to

oo so.

Under

no circumstances

can we accept equipment

back wired

up

unless

a

has been

made in writing.

We regret

we cannot undertake

to

service

equipment

brought

in

personally,

while-you-wait, unless an appointment

has been made in advance. Where the equipment

is not covered by the

guarantee

for any

reason

we will

normally

be able to service on

a standard charge

basis. The standard charges

are

f1.50

each

for 240 and

260

and

12.00

each

for

all other

modules.

These

prices

do nor

include VAT

which must

be

added.

This fee should be sent

with the

item for

reDalr.

Spare

parts

are available

for those who wish to do their own

service

-

price

lists

are available

on

request.

Cash

with order only

prease.

Naturally spares are

free if evidence

is

shown

that the failure

is

under

guarantee.

TOP

a-

a--

Y

-r

AFU

Templates

TOP

I

Tuner

Remove area marked----when

mountino on metal.

Switch

Unit

TOP

Masterlink

++

rr

o n

TOP

/+"

(6mm)

-d Y

rh

\r

Preamp

-f--

$

tfr"." holes

7e"

(3mm).

+ These

holest/."(5mm).

Q1

written

by

Richard

J.

Torrens

illustrated

by Stan

North

Published by Sinclair

Radionics

Ltd.. London Road.,

St.

lves., Hunts PE17 4HJ

Designed and

Printed

by Photo

Precision Ltd.,

St.

lves, Hunts

Publication number TFOI