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THE DAVID HAFLER COMPANY

5910 Crescent

Boulevard, Pennsauken,

New Jersey

08109

Please reler to this

setial

number

in

all

communicaliong

regarding this equipment.

7

L

POWER PER

CHANNEL

BOTH CHANNELS

CLIPPING

MONO

OPERATION

DYNAMIC

CLIPPING

CAUTION:

For continued

protection,

replace

the

power

fuse only with the same type

and rating

as indicated

WARNING:

TO

PREVENT

FIRE OR SHOCK HAZARD, DO

NOT EXPOSE THIS

EQUIPMENT

TO

RAIN

OR MOISTURE.

@Copyright

1984. The David

llafler Company.

2

INTRODUCTION

The

P500

is a high

power

two channel audio

amplifier

intended for

professional

sound installations of the highest

caliber. Its levels of

performance

and reliability have been

amply

demonstrated in the success of its counterpart

in the

consumermarket, the DH-500, formore than2

years,

and

the number of those amplifiers which have been chosen by

sound

professionals.

The P500 adds notable convenience,

versatility, and

improved serviceability

in an even more

rugged

package.

The

rated continuous

power

output

from each

channel is 400

watts

into 4 ohms. The short term con-

tinuous

power

is

in excess

of 500

watts

per

channel

into

2

ohms.

This

is

more

than enough

to

disable

most

loudspeakers if

improperly applied.

Moreover, the

conservative rating method we

use,

and the design

factors which

contribute to

its excellent sound and

superior low impedance

drive capabilities,

necessi-

tate a

word

of caution about its

peak power potential.

Peak

power

outputs

can

be

more

than double

continu-

ous

ratings. Each

channel

is

capable

of delivering

more than 20 amps into a short circuit! And, in

monophonic applications, the

P500

can deliver in ex-

cess

of

800

watts

continuous

powerinto

8ohms.

Such

reserves of

power

must be treated with

understand-

ing, as the Hafler

Company

will not be responsible for

misuse, or consequent loudspeaker damage.

The P500 is available fully

factory

assembled, and also

as apartially assembled version which can be

completed

in

a few hours. Even in this kit

version, the output

amplifier

module, as well as the

control circuit board

module, are

supplied fully assembled and tested, so that the amplifier's

audio

performance

can be confirmed as meeting specifica-

tions as it was

packed

at the factory. The remaining as-

sembly

is

largely

mechanical, and this is further simplified

by

providing prefabricated

wiring

harnesses,

with

plug

terminals already installed.

These instructions assume no special knowledge, or fa-

miliarity with kit

construction. Thus, experienced techni-

cians may find some explanations more

detailed than they

would

prefer.

We urge

you,

however, to avoid

'skimming'

these instructions, for important details may

be

lost in too

rapid

a

perusal.

This

manual also includes full information

to

aid

the

ser-

vice

technician in field repairs, should they

be

necessary.

However, successful completion

of the

kit should not be

considered

sufficient basis for troubleshooting,

without

technical familiarity

and

proper

equipment.

The block di-

agrams and circuit description

will make it easier for the

technician to find his

way

through

the schematic

diagram,

and the

voltage

reference

points

identified

on the back

views of

the circuit

boards. The brief section

"

For Service

Technicians" is intended

as a

guide

to disassembly

for

ready access

to the modules, eitherfortroubleshooting,

or

to

return a

problem

module for factory

service in the

most

expeditious way. It is

strongly recommended

that the

complete manual, including the Pictorial

Diagram,

be re-

tained

for future reference, because the

diagram defines

wire

color codes

for reinstallation.

The P500 incorporates

a number of

protective

devices,

including separate

power

supply

fuses for B*

and B- on

each channel,

individual thermal

sensors on each

heat

sink, a relay

to

disengage the output if excessive

DC offset

is detected, a delay to avoid turn-on transients,

and acces-

sible output fuses on the back

panel

to

protect

the

load

(loudspeakers),

in addition to the

AC line fuse, which

is

not accessible from the outside, to conform

to certain

safety standards. It does not have, and

by virtue ofits de-

sign, does not

need

the thermal

tracking and current

limit-

ing

circuits

which are mandatory

with

conventional

bipo-

laroutput transistordesigns. The

power

MOSFETs

in this

circuit inherently

limit

the

current under abnormal

condi-

tions, thus avoiding

'thermal

runaway'. You

thus have the

dual advantages

of

greater

reliability from

simpler cir-

cuitry, and the elimination

of one of the chief causes

of

distorted extraneous

signals-the harsh

sounds

of the ac-

tuation of complex

protective

circuitry.

The fully complementary,

symmetrical

audio circuit is

direct coupled throughout

(except

for

a

protective

input

capacitor).

All silicon discrete semiconductors

are

em-

ployed

in aformatwhich is closely

relatedto the acclaimed

Hafler

preamplifier

circuit, and combined

with film

resis-

tors and

capacitors

of the highest audio

quality.

The speed

of the circuit-its slew rate-delivers unmatched

trans-

ient linearity. In refining the basic

Hafler MOSFET cir-

cuit, the overall loop

gain

was reduced by using

more

local

feedback in the input stage. This required

less compensa-

tion to stabilize the circuit.

with the result that it

was faster

overall.

With

the built in bandwidth

limitation atthe input,

all

other stages

are free of any transient overload.

3

I

Adequate ventilation

is a

primary

consideration in the

placement

of any high

power

amplifier, because of the

ap-

preciable

heat output. Air is drawn in through the foam

filters

on the sides. and exhausted to the rear. Make sure

this flow is

unimpeded.

The

filters must be

kept

clean-

just

slip

them out,

wash

them, and squeeze dry. Replace-

ments are available from the Hafler

Company,

but if

you

replace

them locally, make sure

you

use an

'open

cell'

foam for air conditioner filters.

The front

panel

is

designed to fit a standard 19" rackatT"

intervals. The feet

may be unscrewed from the bottom to

simplify such

installation. The front

panel

is rigid enough

to safely accommodate the weight of the amplifier, but

rear mounting

holes have also been

provided

in the

side

panels

to facilitate alternative means of securing the P500

when desired.

A

powertransformerof

this

size will radiate anoticeable

hum field, even though Hafler transformers are specially

engineered to reduce this effect. If the amplifier is likely to

be installed close to equipment which may be sensitive

to

such a field, such as microphone

amplifiers or other high

gain

audio stages,

you

should check for

adequate

clear-

ance.

INSTALLATION

CONNECTIONS

AC Line

Unless otherwise

marked, the amplifier will be con-

nected for

120 volt

AC

operation, as used in the

United

States

. For

use

with other line

voltages, connections

to the

barrier

strip inside the amplifier may be changed, as indi-

cated elsewhere in this manual. Two

jumpers

are

pro-

vided, but

in some instances one is

'stored'

,

indicated by a

loop

on one terminal

in the diagram. Never wire the

amplifier for a lower line

voltage than what is actually

supplied,

in an attempt

to obtain

greater power

output.

Such

operation

reduces safety margins, and

voids

the war-

ranty. Note that

the value of the internal AC line fuse

(near

the

power

switch) should be changed when

converting

from

the lower line

voltages

(120

or

less)

[

15 amp slo-bloJ

to the higher

ones

(200

+)l7t/2

amp slo-blol

,

or vice versa.

Other

fuse

values do not

change.

A

3-wire

grounded

power

cord is supplied. It must be

connected to a

properly grounded

(earthed)

AC receptacle

for adequate

safety. Neverbreak off the

ground pin

on the

plug

to avoid obtaining

the

prcper

adapter for 2-wire

re-

ceptacles.

High

power

output

puts

heavy demands on the

supply wiring.

If extension cables must be

used,

keep

them as short as

possible,

and

use

#14

gauge

or heavier

3-wire

cord. A single

P500 delivering

rated

power

will

heavily load

the typical 15 amp circuit. Multiple amplifiers

will most likely need

to be connected to independent cir-

cuits.

Input

Three

types of

input connections are

provided

on the

back

panel.

Only one input

signal to each channel may be

employed

at a time,

but since various input connectors to

each

channel are wired in

parallel,

additional amplifiers

may be driven

from the same source with appropriate

jumper

cables from an unused input.

Both

balanced and

unbalanced inputs can be accommo-

dated without the need

for accessory transformers.

(A

balanced input

utilizes

two signal

conductors,

plus

the

shield.

An unbalanced input, which is

usually

satisfactory

for short

cable runs, uses a single conductor,

plus

the

shield.)

The amplifier's circuitry which

provides

for a bal-

4

anced input

includes additional

gain

in that mode,

together

with a slight reduction

in bandwidth

and signal to

noise

ratio. An incoming unbalanced

line will work into

the bal-

anced input if it uses correctly

wired 2-circuit

plugs,

or if

two input

jumpers

are installed on the

back

panel

barrier

strip.

Two

5-pin

plugs

at the front of the PC20

control circuit

board

(behind

the level controls)

[JlA,

towards the

center

ofthe boardl are connected

for a balanced

line operation

as the amplifier is

supplied. If

you

choose

to

use

only un-

balanced inputs,

you

may shift these

plugs

to the

'B'

loca-

tion

towards

the front of the unit,

and thus bypass the

bal-

anced amplifier circuitry.

This

'B'

position

provides

2.35

volt sensitivity

(vs

1.5

volts), and offers

the lowest

amplifier noise and the

widest bandwidth. It shorts

the

'- '

input connections

to

ground.

Only if

you

are using bal-

anced lines, or if

you

need the additional

gain,

is there

good

reason to use the

amplifier's

'A'

provision

for a bal-

anced input. Thus

you

may want to change

the

plugs

on the

control

board if

you

work only with unbalanced

inputs,

so

the signal

passes

through

the least

number of amplifier

stages.

The

barrier

strip on the back

panel provides

an

easy

means of

'hard

wiring' the input in

fixed installations.

The

3 terminals

towards each

end of the strip are

the inputs.

Beneath each

they are identified

with &

*,

-

,

or a

grouftd

symbol.

For

an unbalanced

input, the

'-'

terminal

should

be connected

to the adjacent

ground

terminal

with a

jumper.

This

will override the internal

plug

connection,

if

it is set for a balanced

input.

The locking

Cannon XLR

connectors

are wired for the

IEC International

standard,

which connects the

#

I

to

the shield, or screen; the

#2

as the signal,

or'high'

side; and the center

#3

pn

as the

return, or'low' side.

Note that XLR connectors

in other equipment

are some-

times wired to the defacto

American standard.

which in-

terchanges the

#2 and #3

connections.

You should

check to see how other

equipment

you

use

is

wired, and

make all

your

connections

consistent. As the XLR

input is

presently

wired, an unbalanced

input

would

use

the

#

1

(shield)

and

#2

pins.

The

numbers are marked

on the

face ofthe back

panel

connectors.

Each

channel

provides

a

pair

of

3-circuit

non-shorting

phone

jack

inputs. These are wired

for a balanced input

with

the sleeve as

ground

(shield);

the tip is

'high';

and the

ring

is

'low'.

For an unbalanced

input, connect the sleeve

of a

2-circuit

plug

to

ground,

and

the tip

'

high' . The second

ofeach

pairofphonejacks

provides

aconvenient

means of

'daisy-chaining'

inputs to other

amplifiers

with

shielded

jumper

cables.

The input impedance

of the P500 is high

enough

that connection

of severat

P500

amplifier inputs in

parallel

will

not materially

affect

performance.

Ground

Reference

The two

center

terminals on

the back

panel

barrier strip

are connected with

a

jumper

as

the amplifier is supplied.

These

two terminals are

not

part

of the input wiring,

but

are instead

the tie

points

for

the chassis

ground

reference,

and for the

audio signal

ground.

Whether these should

be

connected,

or isolated, will

be determined

by

the relative

hum levels when

the overall svstem

is interconnected.

Output

The red

and black output

binding

posts

are heavy duty

to handle the

high currents which

may be involved. They

are

spaced for double

banana

plugs,

or

you

can connect

bare wire

ends through the

vertical holes in the shafts,

which

are visible when

the

cap is unscrewed. To be certain

that no

strands of wire are

unsecured, a tinned end, or a

spade lug

soldered to the wire

is recommended.

The

black output terminals

are connected to signal

ground

internally.

A

jumper

on the

center terminals of the

barrier strip

above the outputs

allows for the

connection

or

isolation

of chassis

ground

from the signal

ground.

The

black

output terminals

may be connected

together

(com-

mon

ground)

when

accessories

utilizing acommon

ground

system,

such as headphonejunction

boxes, are

employed.

The red

terminals

should not be

connected together.

Thus

you

should carefully

observe

proper

connections

when

using a common

ground

device, to be sure that there

is no reversal

ofground and

high side.

Select hookup wire

of sufficient size

to

preserve

the high

damping

factor of the

P500. The minimum recommended

wire size

is # 16

gauge

when

high

power

outputs

are ex-

pected.

Larger wire

sizes are recommended

for long runs,

or where the

speaker

impedance is less than

8

ohms.

Be sure to

maintain

phase

integrity

when

connecting

loudspeakers.

When multiple

amplifiers are used, all

speakers

which

are fed from a common

input source

should

be compared for

correct

phasing.

Monophonic

Operation

(Bridge

Output)

When very high

power

is desired, the

P500 is easily con-

verted

to a single channel amplifier

which can deliver more

than

800

watts

into an

8

ohm load.

The slide switch below

the output

grille

is moved

to MONO, and input is

provided

only to a LEFT

channel

jack.

The output

is taken

between

the two

RED terminals.

It must be

'floating'-that

is,

neither

side

can be

grounded.

In this mode the P500 can

drive a

70 volt distribution line

directly. In this mode, only

the left

gain

control is

operative.

OPERATION

Standard

practice

is to turn

power

amplifiers on last,

and switch them off

first. in the chain of electronics. This

minimizes the likelihood of damage to

the

load from turn-

on transients

generated

by source

equipment.

The

P500

provides

built-in

protection

from such transients by incor-

porating

a

delay of

3

seconds at turn-on, before the relay

connects the

load

(loudspeakers).

Some source equipment

may require a longer

delay to avoid their internally

gener-

ated turn-on

pulses.

If

you

wish to extend the

P500's

turn-on delay, contact the

Hafler

Technical

Service

De-

partment.

When the

P500

is switched

on, the

'Ready'

light will

glow

red at first.

If it does

not,

the internal

line fuse

(15

ampere slo-blo

@

120 volts) should be checked, or the

local

AC line as it, too, may

be

a

15

amp

circuit. When

the

relay

connects the load, the Ready light switches to

green.

If at any time DC

voltage

rises

to an unsafe

level

at the

outputs,

the relay

will

disconnect the load, and the Ready

light will

again

glow

red.

Very

high levels of low frequency

energy

can

sometimes imitate

DC

at the output, and might

activate

the

relay

protection

inappropriately. If this is the

case, the

level

of DC

protection provided

by the relay

can

be changed, with advice from the factory, if

you

wish.

Above

the Ready light

is a red

indicatorwhich is illumi-

nated

in the event

of thermal shutdown.

With

high speed

fan

cooling, it is unlikely

you

will

ever see this lighted. The

fan

continues to

run when

this light

is on, and operation

will

be

restored

automatically when

the temperature of the

heat sink drops sufficiently.

If this

OverTemp

light

comes

on again,

you

should

check for inadequate ventilation,

clogged airfilters, an extremely

low load impedance, oran

input which may

have dangerous signal

content

(such

as

oscillation).

Failing evidence

of this sort, the fan or the

amplifier may

have malfunctioned.

The fan operates at its

lowest

speed whenever

the

power

switch is on,

and it is

automatically

switched

to the two higher speeds when

heat

sink temperature

rises.

The

presence

of any

signal above

the

noise

level will

activate

the

green

'Signal'

lights for

each channel. The

separate red

'Clip'

indicators

above them are activated

by

a comparator

circuit which

triggers when

the output dis-

tortion level reaches

approximately

3Vo.

They

indicate

when

the demands of

the amplifierexceed

its output capa-

bility. Because the

dynamics of

good

source

material may

include steep waveforms

which

briefly reach these limits

for a small

fraction of a second.

normal actuation would

cause them to flicker so briefly that the eye

would miss it.

In the interest of

giving

maximum information,

we have

included a

'hold'

circuit

which

extends these brief

pulses

to about V+ second, so they will be

clearly

visible. How-

ever, these occasional flashes do not indicate that the

amplifier is being substantially overdriven.

Thus these

lamps may indicate

quite

differently from similarly

marked signal devices on some other amplifiers.

The left

and right

gain

(level

or volume) controls

are

precision

31 step attenuators designed for

very low distor-

tion. In the monophonic bridged mode, the left channel

control determines the

gain

of the

amplifier.

Unless

there

is a specific

purpose

for an intermediate setting

(such

as

level matching), the

gain

control on any

power

amplifier

is

usually fully advanced. That is the setting for which the

amplifier's sensitivity is specified.

As

supplied to

you,

the P500 will accommodate either

a

balanced or an unbalanced input at maximum sensitivity

(1.5

volts for full output). A direct input

which

bypasses

some stages, can be

used

only with unbalanced lines and is

available with an intemal

plug

change.

[The

two 5-pin

plugs

near the

center

of

the PC20

control board must be

moved to their forward

positions.l

The direct

input has a

sensitivity

of 2.35 volts for full output.

A balanced line

(2

conductors

plus

shield) should be

employed

when

the elimination of

hum and interference in

long lines is of

great

importance.

Unbalanced

(single

con-

ductor

plus

shield) lines should connect the

'- '

input

side

to

ground

(as

with a mono, or

2-circuit

phone plug).

The

barrier

strip

on the back

panel

ofthe P500

provides

an easy

way of adding

jumpers,

to

be certain.

Terminals

2-3

and

6-7 are marked

'Un-Bal'

for that

purpose,

and

these

jum-

pers

are

effective on all input connectors.

Be sure the AC line can supply adequate current,

par-

ticularly if

you

are using more than one

high

power

amplifier. The

P500 is

fused

for 120 volt

lines with a 15

ampere

Slo-Blo

line fuse.

In

the event of supply failure,

also check the AC mains fuse or circuit breaker

if it is the

same current rating, as it may have

opened first.

On

high

power peaks,

the

amplifier may

draw

so much current that

the

line

voltage

will

drop

noticeably. This can result in

dimming

lights,

but more important,

it may affect audio

quality,

because the lower line voltage may interfere

with

proper

operation of some of the

source electronics con-

nected to the same circuit.

Output

Fuses

The two fuse holders on the back

panel

are for

load

pro-

tection. They do

not

protect

the amplifier

itself, though

if

fuse

values

higher than 10 amps are

installed, the

internal

fuses

may

blow

first with excessive

output current.

If the amplifier

produces

a

low level distorted signal, the

most

likely cause is a blown output

fuse.

This

low signal

occurs because the fuses

are in the feedback circuit,

and

thus there is some coupling

to the output. If one

of these

fuses blow, it

does not indicate malfunction-simply

a

very high output signal, or a very

low impedance

load.

If the manufacturer

of

your

speakers

recommends

a

specific fuse value

for their

protection,

you

should obtain

3AG

type fuses of that value,

and substitute

them for

the

ones supplied.

We

do

not recommend the use

of a slo-blo

type fuse for speaker

protection.

Because

the choice

of

fuse size is up to

you,

and because

the

P500

can

deliver

substantially more

power

than

most speakers

can safely

tolerate,

the Hafler Company

cannot assume

any

responsi-

bility for damage to the

load

(loudspeaker).

The output fuses supplied are rated at 5

amperes. This

value

provides

a moderate amount of

protection, yet

will

allow substantial sustained full

power

output.

Continuous

duty full

power

sine

wave

testing,

however, will blow

these fuses. Iffull

power

tests are to be undertaken,

par-

ticularly at

very

low load impedances, output fuses

of

10

amps or larger will be required. When

performing

such

tests, voltage losses due to

long

AC

lines should be com-

pensated

for.

A 2 amp fuse into an

8

ohm load

permits

continuous

power

up

to

32

watts, but it

will

tolerate

brief

peaks

up

to

the amplifier's full

rated

power

output.

A

3

amp fuse al-

lows

72

watts continuously

into

8

ohms, or 36

watts con-

tinuously into 4 ohms. 5

amps

passes

200

watts continu-

ously into

8

ohms, or 100

watts into 4 ohms.

If

more than one

pair

of

loudspeakers will be

connected

in

parallel

to

the amplifier,

proper

speaker

protection

would dictate that

each speaker be

separately fused,

since

when they are operated

in

parallel,

the

combination

of

lower impedance and

the higher

power

handling capacity

would assume a much

larger amplifier output

fuse.

krj

tl

6

ASSEMBLY

INSTRUCTIONS

The

P500 amplifier

is a versatile component

with sophis-

ticated circuitry which has been

made remarkably easy

to

build by individuals with many

years

of experience in the

design and engineering of the finest

performing

audio

kits,

and

in

the

preparation

of their manuals.

There are three basic

rules for success in electronic

kit

building:

1.

Read the instructions carefullv. and follow them

in or-

der.

2. Make secure solder connections,

which are bright and

smooth.

3. Check

your

work carefully after each

step.

Kit building should

be fun, and

we

are certain

you

will

find this to be so. Assembly will

be faster and

more enjoy-

able if

you

have someone help

you

by

reading

the

steps

aloud and selecting the required

parts

as

you proceed.

Fa-

tigue increases the risk of error, so take a break rather than

push

to

early completion. There are relatively few sepa-

rate

components in this design,

to

make

it easy to

pack

everything away, if need be.

Your

work

area should have

good

lighting, the

proper

tools, and a

place

where the large

pictorial

diagram can be

tacked to the wall within

easy

reach

for checking.

The

tools should

include:

1. A

40

to

60

watt

pencil

soldering iron

with

a3ll6"

or

smaller

tip

which

reaches

700'F.

2. 60140

(60Vo

tin) ROSIN

CORE

solder,

1/16"

diameter

or

smaller.

3. A damp sponge or

cloth

to wipe

the hot tip of the

iron.

4.

Awire stripping

tool forremoving insulation.

This

can

be asingle-edge razorblade, but inexpensive stripping

tools are safer.

faster and easier.

5.

A

medium-blade screwdriver

(about

ll4"

wide).

6. A

#

| or #2

Phillips

head screwdriver.

7. Needle-nose

pliers

(a

long, narrow

tip).

8.

Diagonal

or side-cutting small

pliers.

9. Large

"gas"

or

"slip-joint"

pliers.

10.

A

ll4"

"Spin-tite"

nut driver may

be

helpful,

but

is

not necessary.

Proper

Soldering

There are

four steps to making a

good

solder connec-

tion:

Make a

good

mechanical

connection

to hold the

wire

in

position

while heat and solder is applied.

Heatthe

junction

of

the

wire and lug, or eyelet, with the

bright, shiny tip of the iron.

3.

After heating for a

couple

of seconds, apply

solder to

the

junction.

It should melt immediately

and flow

smoothly around both surfaces.

4.

Allow

the connection to cool undisturbed.

The

general

procedure

is to

use

a hot iron for a short

time to heat a connection, then add solder with the iron

still in

contact. Remove the solder

once it flows, and then

remove

the iron. A cooler iron applied

for

a

longer time is

more likely

to damage components, or

lift

the copper cir-

cuit

pattern

from

the boards. A break in the

etched circuit

can be mended by simply soldering a small

piece

of

wire

across it. Do not allow much build-up of solderon the

tip of

the iron, or it may fall into adjacent circuitry.

Remember that the connection is made by the

solder,

not

by mechanically attaching the

wire to the terminal.

Usually

the

wire

is

looped

through the

lug and

crimped

in

place

,

but

some

prefer

to

just

place

it through the hole and

rely

on the stiffness of the

wire

to

hold it while soldering.

Eyelet connections, of course, are handled this

way.

Good

solder

connections

are essential for trouble-free,

noise-free

operation.

A

good

solderjoint

does not require

much solder around the conductors. Never

"butter"

par-

tially melted solder on the

joint,

as it is

useless.

A

good

connection

looks smooth

and bright because

the solder

flows into every crevice when the

parts

are

hot

enough.

The iron

must have a bright, shiny tip to

transfer heat eas-

ily to the

junction.

That's why the damp sponge should be

used frequently to wipe the tip, and occasionally

you

must

add a small amount of solder to the tip, too. If a connection

is difficult to heat,

"wet"

the tip

with a

small blob

of solder

to

provide

a bigger contact surface to the

joint.

Once

the

solder flows around

the conductors,

any movement must

be avoided for a few seconds to allow a

good

bond. When

cool, check the connection by

wiggling the wire. If in

doubt, or if the connection is not shiny, re-heat the

joint.

Excess

solder may be removed from a connection

by heat-

ing it and allowing the solder to flow

onto the iron,

which

is

then wiped on the sponge.

ALL

SOLDER USED

MUST BE ROSIN CORE

Never use acid core solder

or any separate flux

in elec-

tronic work. Silver solder is

also not suitable. If

in doubt

about unmarked solder,

always obtain a fresh

supply of

rosin core solder. We

recommend

60/40

for

easiest use.

Do not confuse it with 40160,

which is harder to

melt.

When

soldering to an eyelet or hole on the

board, insert

the wire from the components side,

and apply the iron

to

the bottom, leaving some bare wire exposed

so that

you

can see that the eyelet is then filled

with

solder

for a secure

bond.

A round wooden toothpick is suggested

so that

you

can heat and clear an eyelet of

solder if it hinders

your

inserting the wire. Some builders

prefer

to clear

every

eyelet first with a touch of the iron and

toothpick. Others

connect the

lead

by bringing it up to

the

centerofthe

eyelet

on top of the board, applying the

iron from the bottom

of

l.

2.

the board, and

pushing

the lead in as the solder in the

eyelet melts.

Ifthe

wire

has first been

"tinned,"

usually

no

additional solder

is

necessary,

but it is a

good practice

to

push

the

wire

through, and then back it up a bit, to be sure

solder frlls the

eyelet. On the bottom of the board, make

certain a bright, shiny flow is

evident from the

wire onto

the

circuit

pattern

on the board.

"Tinning"

refers

to

the

process

of applying a light coat-

ing of solder to the bared

wire

end.

This keeps all the

strands secured, and also makes a

good

connection easier.

Simply touch the

wire with

the iron

for

a couple

seconds,

and apply solder. Allow the excess to flow away onto

the

iron.

When

properly

done, the wire is uniformly bright,

and no larger than before.

If any components are

unfamiliar to

you,

checking the

pictorial

diagram should

quickly

identify

them. Or,

the

quantities,

and the

process

of

elimination as

you

check the

parts

list, will help.

The

pictorial

diagram is necessarily

distorted

to some extent for clarity, so

that

you

can trace

every

wire in

a single overall view for verification as

you

work.

You may wish to

check

off on

the diagram

as

you

solder

each

location.

To

"prepare"

a wire means

to cut the designated

amount from the length of that color, and strip about

ll 4"

of insulation from each end. The wire supplied in the kit is

#18

and

#22,

so

you

can set adjustable wire-strippers ac-

cordingly. The transformer leads

are

#16, and the line

cord is

#

14. Be careful that

you

do not nick the wire when

you

strip

it

(that

can happen more easily if

you

do not use

wire strippers)

for that

weakens

it.

Whenever

a

connection

is

to be

soldered.

the

instruc-

tions will so state, or

indicate by

the symbol

(S).

If more

than one

wire

is to be soldered to the same

point,

they

will

be indicated

by

(S-2), (S-4),

etc. If soldering is

not

called

for, other connections have

yet

to be made to that termi-

nal. They would be more difficult if the connection

was

already soldered. Every connection in the kit

will

be

sol-

dered when

it is complete. After soldering a connection,

it

is best to clip off any excess lead length to minimize the

possibility

of a short circuit

(as

on switch

lugs,

where

ter-

minals are

very close together), and for

neatness.

Handle the

circuit boards carefully. They represent a

major

part

of the

kit

cost. Stand-up components, such as

transistors, should

be checked

when

you

install the mod-

ule,

to

be sure all leads are separated.

Take the time to be accurate and neat, and

you

can be

sure that

your

completed amplifier

will

meet the

per-

formance of a factory assembled

unit,

and can continue to

perform

properly

for

years

to come.

Check

your

work, and

make sure the entire step has

been

completed before

plac-

ing a check mark in the space

provided,

and continuing on

to the next step.

COMPLETING

THE PSOO

For safety

in shipping, the

power

transformer

and

the

amplifier

power

module have been temporarily

fastened to

the chassis,

and a few screws secure chassis

metalwork.

These should all be removed,

and the hardware

so em-

ployed

should be included

when counting and

sorting kit

parts.

A

couple

ofegg

cartons

are helpful

for sorting hard-

ware items. A count of each item checked

against the

parts

list will enable

you

to differentiate

similar

parts,

and iden-

tify

unfamiliar

items. Take

particular

note that the 4 black

sheet metal screws which secure the

power

module

may

be

confused

with the #6-32black screws.

Also,

there

are

4

self-tapping #6 screws,

with

slots

in the tip, and 4 oval

head Phillips

screws which look much

like the #4-40

screws. The

#6 nuts

can be separated

from the

#4 nuts

by

sliding them over a

#4 screw.

Be

particularly

careful in handling

the amplifier module

and the

separately

packed

control

circuit board,

that the

leads

of upright

components are not stressed by

bending.

These two elements account for the

major

cost

of the

amplifier.

Set the cover, the two side

panels,

the front face

plate,

the

power

transformer and the

power

module to one side,

along with the

PC-20

control circuit board

and the two

large

capacitors.

These will not be utilized for some

time.

The initial steps will secure as many of the smaller compo-

nents as

practicable,

to minimize the risk of misplacement

during assembly.

I

n

Select the

front

panel

(with

4

rectangular holes),

the 4

plastic

standoffs with spring latches in the

tips,

and

the 4

self-tapping slotted tip

5l16'

screws.

Like all of the chassis metalwork, the edges of

the

front

panel

bend towards the inside.

Mount the

standoffs

on the inside

of the

panel

in the holes

above

(and

below) the 3 vertical openings.

For

later access. each standoffshould be

mounted so

that the spring latch in the tip

projects

up

towards

the top edge

of

the front

panel.

2

!

Select the

power

switch

and

two

black #6-32

screws. Install the

power

switch on the

inside of

the front

panel

with the lugs towards

the

bottom

edge of the

panel.

Set

the front

panel

assembly

aside.

3

n

Select

the

back

panel,

the two XLR 3-pin

sockets,

the

4 Phillips

oval head

ll4"

screws, and four

#4

nuts. Install each socket from the outside

of the

panel

with

the

locking

tab

at the top, at locations

XL

and

XR.

4

!

Select the 4

phonejacks,

the 4 flat fiber

washers,

the 4 shoulder fiber

washersn the

4

flat metal

3/8"

washers

(two

slightly smaller

washers are

used

elsewhere),

and

the four 3/8"

nuts.

Install

thejacks

below the XLR sockets as follows: Place

a shoul-

der washer on the collar of the

jack,

with the nar-

row shoulder side up; install the

jack

from

inside

the

panel,

centering the shoulder to insulate the

jack

from the

panel;

add the flat fiber

washer on the

outside,

followed

by

the metal washer and nut.

Tighten each

jack

when

it is

positioned

so that the

center connecting

lugs

of each

pair

face each

other. See the

pictorial

diagram.

a

5

n

Select

the

8-lug

barrier terminal strip,

the internal

tooth

ground

lug,

two

#6-32

black screws and two

#6

nuts.

Place the

ground

lug on the inside,

point-

ing down

under the

right channel input

jack,

when

you

install

the barrier strip on the outside,

below

the

phone

jacks.

6

!

Select the two red output terminal

assemblies, and

two of the solder lugs.

The red terminals will

be

installed

from the outside in

the two center

(*)

holes

below the barrier

strip as follows: The base

of each terminal

and its mating

plastic

washer

are

formed with shoulders which

have a flat which

must engage the

flat in the

punched

hole in

the

panel.

When these are

properly

located,

secure

them with

one nut

which

is tightened fully. Then

add the solder lug,

pointing

upwards, followed by

the second

nut which

is

also

fully tightened. Then

bend

the solder lug away from the

panel

at

right

angles, so

it is

parallel

with the terminal

post.

It is

imperative

that each nut be firmly

tightened, so

that

these terminals can handle

the

amplifier's

high

output

power

without

the distortion

which

can

occur from a loose

connection. A nail or the Allen

wrench

through

the shaft hole on the outside will

help to keep

the hole vertical.

7

E

Select the two

black output terminal assemblies,

and the two solder lugs.

Install these terminals as

before. on

either side of the red terminals.

8

!

Select the two round 2-piece fuse holders, the two

thin rubberwashers, the two

ll2"

lockwashers and

the two l/2" nuts.

Place

the rubber washer on the

fuse

post

first, and install it from the

outside. Se-

cure each with a lockwasher

and

nut

so that

the tip

lugs

point

away from the other fuse holder.

9

[

Select the AC line cord and the

plastic

strain relief.

Note that

one

conductor has aribbed exterior. The

ribbed

conductor will be cut shorter later, and it

will

be easier if it is on

the inside

when it

passes

through the

back

panel.

13" from the cut end ofthe

line

cord make a

tight

'V'

by bending

it

back

sharply

on itself. Install the strain relief as shown,

with the smaller

end of the strain relief nearest the

cut end of the line

cord. Crimp

the

two halves

of

the strain relief around the wire at the

'V'

with

heavy

pliers,

to

partially

form it before insertion

into

the back

panel

hole AC. Then

grip

the

larger

diameter of

the strain relief with the tips of the

pliers,

squeeze it

tightly, and insert the end of

the

cord and

the strain

relief

through the back

panel

hole from the outside. The relief

snaps into

posi-

tion

when

it is fully inserted.

The

two conductors and the

ground

wire of the

line

cord must be separated without cutting through

the insulation

on any conductor. The outer con-

ductor will be kept its full length. The inner ribbed

conductor, and the

green ground

wire in

the

middle

should

be cut off6" from the back

panel

surface.

Carefully

separate

the 3 insulated conductors

all

the

way

down to

within

1" of the strain relief. Set

the back

panel

assembly aside temporarily.

10

n

Selecj the bottom

plate,

the 4

rubber feet, and 4

black#6-32 screws. Fasten the feet

on the outside

of the holes

near

each corner, to

which threaded

studs have been affixed on the inside.

11

n

Select the two dual

fuse clips, and

4

sets of #4

hardware.

Install one

set of clips at the

pair

of

holes near

the

center of the bottom

plate.

Fasten

the

other set near the left

edge of the chassis.

12

n

Select the single fuse

clip and one set of #4 hard-

ware.

Install the

clip in the front right

corner in

front of

the two dimples

in the bottom

plate.

13

!

Select the 14 screw

terminal barrier strip, and 4

sets of

ll2'

#6

hardware. Install the barrier strip at

the right rear

corner ofthe bottom

plate.

14

n

Select the

plastic

enclosed relay, the

'L'

shape

relay

bracket,

3

sets

of #4 hardware and a #4

lockwasher.

Fasten the bracket to the relay

by in-

serting

the screws

through the bracket first, with

the foot of the

bracket

pointing

away

from the re-

lay,

at the opposite

end from the lugs.

Install

the

assembly close to

the barrier strip on the

bottom

plate,

with

the

lockwasher

under the foot.

15

[

Select the

3l4" #6 screw, a #6 nut,

and the

1"

square

rectifier

diode block. The terminal

marked

'+'

(which

may have

a

locating

stud) should

be

po-

sitioned

next to

the relay bracket, and

the rectifier

installed

through

the adjacent hole.

o

16

n

Select the two

round

capacitor brackets, 6

sets of

ll2' #6 hardware, the two

314"

# 10 screws, and

two

#10 nuts.

Note the

location

of

the bracket

clamps, and the direction of insertion of the clamp

screw

in

the

pictorial

diagram

for later access. In-

stall the large

bolt

in the

clamp

of each bracket

loosely, and mount the brackets in the two sets

of

holes

(3

each) in front of the rectifier. Before tight-

ening

any of

the bolts,

temporarily install one of

the large

capacitors

and make the clamp snug.

Now tighten the mounting bolts for that bracket,

and remove the capacitor. Do the same

for

the

second

bracket.

17

E

Select the two l-ll2' metal

standoffs, two #4

screws, and the two #4lockwashers. Install

a

lockwasher below the standoff at the hole in front

of

each

fuse clip.

Set

the bottom

plate

assembly

aside temporarily.

You

will

be using a soldering iron

regularly from now

on. Be sure to maintain a bright, light coating of solder

on

the tip, and

wipe

it frequently. When soldering to

a hole

(eyelet)

on the board,

you

may first

need

to clear the

hole

by

touching it

with

the iron,

and

using a

round wooden

toothpick

to

open

it.

A small

amount of

solder added to the

tip of the iron

will

provide

better

heat transfer, so that the

iron will not have to remain in contact

with

the circuitry

for

long. The solder should flow

into

the hole. Bare

wire

ends

should be twisted tightly, and tinned before connecting to

a hole,

so

that

strands do not separate when inserted. Do

not

push

the wire all the way

up

to the insulation. Leave

some bare wire exposed on top so

you

can see

when the

solder has flowed around the wire. After a connection

cools, wiggle the wire to be sure of a

good

connection

(no

sign of movement). Wires are identified by the tracer,

or

stripe

color-a

white wire with a blue tracer is called a

blue wire.

18

n

Select the small PC-22 circuit board

with two

LEDs mounted on it, and the 17" harness

which

has one solid white wire, and

2black

wires, with

loop terminals at one end.

Connect

the bare black

wire ends

(they

are interchangeable) to holes

#4

and #5 from the front side

of

K,-22.

and solder

them on the back.

!

Select the

32"

harness with

3

plugs

at one end, and

the miniature slide switch.

The switch will be con-

nected at the

'break'

in this

harness, where

only

one

(black)

wire is continuous. Note

that the cen-

ter row of switch lugs is offset

as manufactured.

Orient the switch so that

the wide spacing to the

outside row is at the bottom,

and bend the bottom

row upwards, to a uniform spacing.

The bent

lugs

will

be

#7, #8

and

#9. This will

provide

more

clearance for connections close

to the chassis

when

installed. With the back

of the switch facing

you,

and the

#l lug at the top left,

place

the

long

(plug)

end of the harness

off to the left.

At

the

break,

5

wire ends come from the

left, and

3

from

the right. Do

not

confuse the

green/black pair

on

the

left, which is about the same length. Connect

both the black

wire from the left and the black

wire

from

the

right to lug #7.

(S-2).

Connect

the red

wire from the right to

lug #8.

(S).

Connect

the

red

wire

from the

left

to

lug #9.

(S).

Connect

the

yel-

low

wire

from the left

to lug #4.

(S).

The

paired

blue

wires

from the

left are interchangeable. Con-

nect one of them to lug #1.

(S).

Connect

the other

blue

wire

to

lug

#2.

(S).

Connect

the

yellow

wire

from the right to

lug

#6.

2l

n

Select

the 3000

ohm resistor

(orange/blacklredl

gold),

and clip

its leads to ll2"

(or

less).

Connect

one

lead to lug #5.

(S).

Connect

the

other

lead to

lue #6.

(S-2).

22

!

Select

the large amplifier module.

Stand

it upright

with the fan towards

you,

and its

attached

3

leads

protruding

to the right. Place the

switch harness

underneath

with

the

switch at the center

rear, and

the long

plug

ends to the

left.

On

the right side,

connect the red

wire

to eyelet

#

|

on the

rear

edge

of the right circuit board

(the

uppermost

eyelet).

Connect

it from the outside

(front

surface) of the

board. and solder

it from the back of the

board.

Connect

the corresponding black

wire to eyelet

#2.

(S).

The black

wire of the

yellow/black pair

is

not

connected,

but serves only as shield.

It has

been secured

with

tubing. Connect

the

yellow

wire

to

eyelet

#A, which is about 1" below the top cen-

ter of the board.

(S).

When

you

cannot solder

a

wire

from the back

side of the board, it is very

im-

portant

that a) all strands of

wire

enter

the

hole; b) that

you

do

not

use

an excessive amount

of solder, so that neither it,

nor

the

hot iron will

contact adjacent components and damage

them;

and c) that the solder flows into

the hole so that a

secure connection is made to the circuitry

on the

back side of the board. If necessary,

you

could

dismount the board to

sain

access to

the back.

20

'

'{li'zk'

rNq)

19

!

Select the 9" harness triad ofred,

green

and black

wires with a

plug

on one end.

Connect

the

bare

wires to the front of PC-22, and solder

on the back

as follows: Red to hole #3

(near

the

red LED);

black to hole #2;

green

to hole # 1. Set this

assem-

bly aside.

10

23

!

On the left side,

projecting

from either

side

of

a

plastic

wire tie, is

a black/green

pair,

and a black/

yellow

pair.

Connect the

green

wire to

(the

lower)

eyelet

# | on the rear.

(S)

. Connect

the

correspond-

ing

black

wire

to eyelet #2.

(S).

Connect

the

yel-

low wire to

eyelet

#B nearthe

centerof the board.

(S).

Be

careful

that heat

does

not

damage the

adja-

cent diode.

Connect

the corresponding

black

wire

to eyelet #E

atthe base of the rear

potentiometer.

(S).

Set the module assembly aside.

24

E

Select the main wiring harness

and the bottom

plate

assembly.

Lay out the harness on the bottom

as shown in the

photograph.

The

red/yellow

group

of

4

wires

to the relay should be

placed

under the

relay. The

two

groups

of

5

wires each, which con-

nect

to the module, should

be bent upwards.

25

n

Select one of the small capacitors

(103M).

Strip

two

pieces

of insulation, each

314"

long, from the

thicker red wire supplied

in the kit, and slide a

piece

over each capacitor lead.

Connect

one lead

to rectifier

diode block DB lug #

1,

around

the base

of

the

lug.

Because other wires will be

connected

to these lugs with

slip-on spade connectors, it is

important that these wires

(this

lug will be soldered

later) not

go

through the hole in the lug, but are

instead wrapped

low around

the base, so that

when

solder

is applied, it will not

interfere

with

the

spade

connector

to the upper

portion

of the lug.

Connect

the

other capacitor lead to DB lug #4.

(S).

Place

the capacitor

down out of the way. Be

certain

that

no

bare leads can

touch the metal case of the diode

block.

tl

29

30

26

n

There is one brown wire, and one thicker

red wire

from the trunk of the harness, that connect to

the

rectifier. Strip each of these

leads

ll2" . Connect

the brown

wire

to the base of

DB lug #1.

(S-2).

Connect

the red wire to DB lug #2.

(S).

Since

no

spade connector will be used on lug #2(the

*

ter-

minal). this wire mav be connected to the

hole in

the terminal.

27

n

Select the single

green

wire from the trunk of the

hamess, strip it ll2"

,

and connect it to

DB htg #3.

(S).

No spade connector

will

be used

on this lug,

either. Check to

make sure no bare wires can touch

the metal rectifier

case.

28

n

The

4

wire

group

of black, red and 2

yellows

con-

nects to the right side of the relay.

Connect

the

black wire to lug #B.

(S).

Connect

the two

yellow

wires to lug #9.

(S-2).

Connect

the red

wire

to

lug

#6.

(S).

I

The black,

green

and 2 blues 4-wire

group

con-

nects to the left side of the

relay.

Connect

the black

wire to lug #A.

(S).

Connectthe2

blue

wires to lug

#7.

(S-2).

Connect the

green

wire to lug #4.

(S).

E

The single red

wire

coming

down

from the left

module

group

(this group

was bent upwards) con-

nects to FL lug

#1.

(S).

31

[

The left front

group

of

wires

contains 2

redlgreen

pairs.

Connect

the 2

red wires to

FL

lug #3.

(S-2).

Connect

the 2

green

wires to FL lug #4.

(S-2).

I

A single

green

wire

comes

down

from the right

module

group

(bent

upwards).

Connect

this

green

wire

to FR lug #6.

(S).

n

Near the metal standoff at the front

center is a

single red wire and a single

green

wire.

Connect

the

green

wire to FR lug #8.

(S).

Connect the

red

wire

to FR

lug #7.

(S).

34

!

Prepare a heavy

gauge

6-112"

green

wire.

Connect

one end

to FL lug #2.

(S).

Place

this wire off to the

left.

35

!

Prepare a heavy

gauge

6-112"

red wire.

Connect

one end to

FR

lug #5.

(S).

Place this

wire

off to the

left.

36

n

Preparethe 4"

piece

of

the

very heavy

gauee

(#14)

white wire. Connect

one end to the single

fuse clip

FC lug #1.

(S).

Select

one of the spade

lugs, and

solder it to the other end.

The

proper

way

to

attach a spade lug to

a wire is to

first cut the bared

wire end to the right

length

(no

more than 1/4") so that the

insulation will be sec-

urely

gripped

by the

longer, outer tabs,

while

the

wire does

not

protrude

into the spade clamp

area.

Tin the bare

wire

end. Bend

the shorter, middle

set

of tabs tightly around the

bare wire, and then bend

the longer tabs around

the insulation. Then

flow

solder into the

joint

around the bare

wire, keeping

the solder away

from the spade

section.

37

n

Set

the bottom

plate

assembly aside, and

select the

power

transformer

and two spade lugs. Solder

a

spade

lug

on each of

the two shorter, solid

red

transformer

leads.

38

n

Select one of

the

loop

terminal lugs. Trim the bared

end

of

the

long

red/yellow transformer lead

(do

not

confuse it

with

the brown/red) to no more than

ll4" . ttn it. and install the terminal so that the end

of

the

wire

just

protrudes,

enabling

the

iron to heat

it

properly.

Solderit, making sure sufficient solder

flows inside

the terminal, but stays clear of the

loop

portion.

Pointing the wire upwards may

simplify soldering.

39

!

Select the

6

position

fanning strip

(U-shaped

ter-

minals). The six transformer leads will be cut to

different lengths so that they can

all be secured to

the hole in the end of the strip, and then

bent at

right

angles as each enters its terminal.

Trim the

leads

at 3/8" intervals as follows:

Black 7" from the exit hole of the

transformer.

Black/Red 6-518"

Black/White

6-114"

Brown 5-718'

Brown/Red 5-112"

Brown/White

5-118"

Strip each lead 114", and tin. Insert

the Brown/

White

lead in the terminal nearest the

hole end of

the strip. The bare

wire

goes

through the loop,

and

the

pointed

tabs are crimped snugly around the in-

sulation.

Solder,

making sure the

loop is filled, but

lay the strip flat to keep solder away from

the

U-shaped

portion.

Do the same with the other

leads in sequence: Brown/Red, Brown, Black/

White,

Black/Red, and Black.

40

E

Select the

plastic

wire

tie. Secure

all

6

of the leads

from the fanning strip to the end hole. The tie can

be used only once, as it locks once the

tail is

pushed

through

the open head from the flat side.

Cut

off the excess tie.

41

n

Set

the

transformer

aside, and select the back

panel

assembly and the rerrraining spade

lug.

Strip

the longer conductor of the line cord bare for 3/

8"

,

being careful not to cut any strands. Twist and tin

the

bared end.

Attach the spade lug, crimping the

long outertabs tightly around the bare

wire as well,

since the insulation is too thick to include

it.

(S).

42

E

Select the

remaining loop

terminal. Strip

the

shorter, ribbed conductor ofthe line cord

(not

the

green ground

wire) bare for

318"

,

and twist

and

tin

the end. Install the terminal and

solder

it well.

It

is

a tight fit, so solder does not flow easily into the

terminal, which

is important. Heat the

wire

end

when

the terminal is

pointed

upwards, and the sol-

der

will

flow down.

43

n

Strip ll4" from the

green

line cord

ground

wire,

twist and tin the end, and

connect

it to the

ground

lug at the end of the barrier strip.

32

33

t2

The following

connections to the back

panel

will be

made with

the lighter

gauge

wire

of the specified colors.

44

E

Prepare two 1-314" lengths of red

wire.

Connect

one

wire

from JA lug # I to JB lug #6.

Connect

the

other wire from

JC

lug #7

to JDlug

#12.

45

E

Prepare two 2"

red wires.

Connect

one from JA lug

#

I

(S-2),

to XLlug#Z.

(S).

Connect

the otherwire

from

JC

lug #7

(S-2),

to

XR

lug #2.

(S).

46

E

Prepare a l-112" red wire.

Connect

one end to JB

lug#6.

(S-2).

Connect the other end to BS

lug # 1.

Whenever a

wire

connects to one of the terminals

on this strip, be sure it is wrapped tightly to hold it

until it is soldered..

47

!

Prepare a 1-114" red wire.

Connect

one end to JD

lug# 12.

(S-2).

Connect

the otherend to BS lug #8.

48

!

Prepare a 1-112" blue wire.

Connect one

endto

JA

lru'g #3.

Connect

the other

end to JB

lug #

4.

49

[

Prepare al-ll4" bluewire.

ConnectoneendtoJA

lug#3.

(S-2).

Connect

the otherend to BS lug #2.

50

n

Prepare

a

l-112" blue

wire.

Connect one end to JB

lug#4.

(S-2).

Connect the otherend to XLbottom

lug #3.

(S).

51

n

Prepare a 1-112"

green

wire.

Connect

one end to

JC

lug #9,

and the other end to JD lug #10.

52

!

Prepare

another

l-112"

green

wire.

Connect

one

end to

JD

lug #

10.

(S-2).

Connect the other end to

XR lug #3.

(S).

53

[

Prepare

al"

greenwire.

Connectone

endto JC

lug

#9.

(S-2).

Connect

the other end to BS

lug #7.

54

!

hepare

a2-114" black wire, but stip ll2"

of insu-

lation from one end. Pass the

longer bared end

through JA lng#2 and connect it to JB

lug #5.

Sol-

der only lug #2.

Connect

the other end to XL

lug

#1.

(s).

55

[

Prepare al-112" blackwire. Connectone

endto JB

lug #

5.(S-2). Connect

the other end to BS

lug #3.

56

!

Prepare

a2-114"

black

wire, but strip 1/2" of insu-

lation from one end.

Pass

the longer bared end

through

JC

lug #8,

and connect

it to

JD

lug #11.

Solder

lug #

8. Connect the

other end to XR lug

#

I .

(s).

57

!

Prepare a

l-314" black

wire.

Connect

one end to

JD

lug#11.

(S-2).

Connectthe

otherendto BS

lug

#6.

58

!

Prepare

a2-3l4"black wire.

Connect

one end to BS

lug #5.

Connect

the

other end

to the

ground

lug at

the

end

of

the strip.

(S-2).

59

n

Select one of the small disc capacitors

(

103M), and

cut each lead to

ll2" . Connect

one lead to BS lug

#5.

(S-2).

Connect the

other lead

to BS

lug #4.

60

!

Prepare a2" black wire,

but

strip

1"

of insulation

from one end.

Connect

the

shorter

bared end to BS

lug#6.

Wrap the

otherend first around

BS

lug #4,

and

then connect it to BS lug #3. Solder

lug #4

(capacitor

lead too).

t3

61

E

Select

the

18" harness with two

plugs

at one end.

At

the other end. the wires are in

2

groups

of

3

each, one of which

has a blue

wire,

and the other

has a

green

wire.

It is important that the respective

red and

black

wires

be

paired

with

the correct

color, if the twisting has

been

loosened. The

blue

set is shorter.

Connect the blue

wire

to BS lug #2.

(S-2).

Connect the corresponding red wire to BS

lug #1.

(S-2).

Connect

the corresponding black

wire

to BS

lug

#3.

(S-3).

62

E

The

other triad of wires will

be connected

to the

right

channel inputs.

Connect

the

green

wire

to BS

lug#7.

(S-2).

Connect the red wire to BS lug #8.

(S-2).

Connect

the

black

wire

to BS lug #6.

(S-3).

63

n

Select the shortest of the 3

jumper

wires with a

loop terminal at each end.

On

the

outside

of the

back

panel,

connect

it

between BS

screw terminals

#4

and #5. Set the back

panel

assembly

aside.

64

n

Select

the bottom

plate

assembly, the

power

mod-

ule assembly, and two #4-40 screws.

Place

the

module in its approximate location. Install the

switch

on the

rear lip

of the bottom

plate

at

SW,

making

sure

that

no strands of

wire

can touch

the

chassis, or other

than their intended terminal

lugs.

65

f

Place the 3

wires

from under

the module towards

the right

rear corner

of the

chassis.

The switch

wires

go

under,

not

behind, the module. Select

the

4 black sheet metal screws. and fasten the

module

to the

bottom

plate.

66

E

The following connections will be rnade to the left

circuit board eyelets on the forward edge of the

board. The

wires will

be installed from

the front

(outside),

but should be soldered on the inside.

The eyelets are numbered from 3 to 10,

with #3 at

the bottom.

Clear

the holes of solder

with a

tooth-

pick

first, and tin each wire before

insertion, so

that all strands are secured. Good

solder

connec-

tions are essential, especially to the heavier

wires

which

carry

the full output

power,

so

you

should

be sure there is sufficient solder for

a smooth con-

nection

to the circuitry

on

the back

side.

Connect

the red wire

to

eyelet #3.

(S).

Connect the blue wire to eyelet #5.

(S).

Connect the

shorter

brown

wire

to eyelet

#6.

(S).

Connect

the black wire to eyelet #7.

(S).

Connect the

longer

brown

wire

to eyelet

#8.

(S).

67

n

Select

the

green

wire from FLlug

2,

andconnect it

to eyelet #10.

(S).

68

!

The following connections will be made to the

right

circuit board.

The eyelets are numbered

starting

with #3 at the

top.

Connect

the

green

wire to eyelet #10.

(S).

Connect

the shorter brown wire to eyelet #8.

(S).

Connect the black

wire

to eyelet

#7.

(S).

Connect the

longer

brown

wire

to

eyelet #6.

(S).

Connect

the

yellow

wire

to eyelet

#5.

(S).

69

n

Select the

red wire from

FR

lug #5, and

connect

it

to eyelet #3.

(S).

70

n

Select the triad of wires from

under

the

power

module

(two

are

heavy

gauge),

and

place

it under

the

pair

of brown wires, and

under the

group

of

5

wires at the center rear, and

behind

the relay.

Select one of the two

3"

jumper

wires with loop

terminals.

Connect the

shorter

heavy wire from

the module, and one

end of thisjumperto TS screw

#

1. Make all of

these connections from the rear of

the terminal strip.

When more

than one loop is attached

to

a

screw

terminal, it is important

that the loops be

posi-

tioned or

bent so that each makes a flat

contact

with

the surfaces above and

below it, because

of

the

high currents involved.

NOTE: The

placement

of

this

jumper,

and other

wiring

to screw terminals #1 through #7 in these

instructions

is intended for a nominal

120 volt

AC

line.

If

your

line voltage is different, refer

to

sepa-

rate instructions

in this manual for appropriate

connections to the screw terminals.

71

n

Select the other

3"

jumper,

and

connect

one

end,

together with the

green

wire from

under the

mod-

ule to TS screw #3.

72

!

Select the two large

capacitors, and install them in

their

brackets with the

(+)

terminal

towards

the

front of the amplifier.

Be sure the capacitors are

tight against the chassis, and

tighten the bracket

clamps.

73

n

Select

the heavy metal2-112" strap

and

2

of the

318'

#

10 SEMS

screws with lockwasher

attached.

Install the strap between

the

(-)

terminal of the

front

capacitor

and the

(+)

terminal

of the rear

capacitor,

with

the single

hole on the right side.

74

n

Select 2

of the black screws, and that

portion

of the

hamess which has

6

black wires with loop termi-

nals.

Connect

three of them to the strap

with one

screw, and the others

with

the other

screw, using

the holes on the left.

'Fan'

them

out so that a

good

solid contact is made.

75

[

Select the remaining two 318" #10 SEMS

screws.

Connect

the triad of red wires at the front to the

(+

)

terminal of the front

capacitor. Connect

the triad

of

green

wires to the

(-)

terminal of the rear

capacitor.

76

E

Select the

long

harness

with

the PC-22 circuit

board

in the middle. Connect the bare end of the

heavywire nearthe

circuitboard

to

FC

lug#2.

(S).

Connect

the loop terminal

at the

other

end

of this

heavy wire to TS screw #6

from

the rear, together

with

the

jumper

from TS

3.

77

n

Connect

the loop terminal on the shorter black

wire of

this same triad to TS

screw #7 from the

rear, along

with

the

(longer)

heavy

wire loop

ter-

minal from

under

the

power

module.

Connect

the

corresponding longer black wire

loop

terminal

to

TS screw#4, along with the

jurnper

from TS 1.

t

I

i

t

14

78

n

Place the back

panel

assembly behind

the bottom

plate.

Select

the

group

of

5

wires at the center

rear

ofthe bottom

plate.

Feed

the separate single black

wire

under the 6

wire

group

which is connected to

the input strip, and connect it to

the

bare

wire

jumperbetween

lugs BS

3

and BS 4.

(S).

79

[

Select the

red and

black

pair

from this

group,

and

connect the black

wire

to the lug on output

termi-

nal RB.

(S).

Connect the

red wire

to terminal

lug

RR.

(S).

Make sure these output terminal lugs are

well soldered,

and tight.

80

n

Select the

green

and black

pair,

and connect

the

green

wire to output terminal lug LR.

(S).

Connect

the

black

wire

to terminal

lug LB.

(S).

81

n

Select the

pair

of brown wires at the center

rear.

Connect

one

wire

to the tip

lug

of fuse

post

RF.

(S).

Connect

the other wire to the side lug.

(S).

82

n

Select the

pair

of brown

wires

at the

left rear.

Con-

nect one wire to the tip lug of LF.

(S).

Connect

the

other wire to the side lug.

(S).

83

n

Select 4

of

the

black screws and fasten the back

panel

to the bottom

plate,

making sure

no wires are

trapped.

84

n

Connect the shorter ribbed conductor of the

line

cord to TS screw #14fromthe front.

85

fl

Loosen

the 6 screws, #8-#13, on the TS terminal

strip, for about

3

turns.

Now

turn the

chassis up-

side down, and shake out any

wire

clippings

or

other debris.

86

E

Turn the

amplifier

up on

its right side, and bring the

power

transformer close to its

position,

on its side,

with the leads to the rear. Twist the 2

red leads

together,

and slide the spade

lugs

over

DB termi-

nals

#

I and

#

4. Make

sure they are fully on. Select

one black screw. and fasten

the Red/Yellow

lead

to the strap between

the

2large

capacitors.

87

I

Select 4 each

of

the ll2"

#

10

screws, nuts, and the

large

flat

washers. Make sure no wires are trapped,

and fasten the

power

transformer in

place

with a

washer above each foot. and the screw

heads on

the outside.

88

!

Install

the fanning strip on the transformer leads to

TS screws #

8

through # 13. Be sure all the screws

on this strip are fully

tightened.

89

n

Select

four 10 amp fuses, and the single 15

amp

slo-blo fuse. The 15 amp fuse

goes

in

the

single fuse

holder, and the other fuses in

the two dual fuse

clips.

90

n

Select the

front

panel

assembly,

and the

remaining

small disc

capacitor. Cut its

leads to 314" . Connect

one

lead

to PS

lug #l around

the

base

ofthe

lug.

(S).

Keep the

lead, and the solder,

clear of the

main

part

of the

lug to

provide

a

good

contact

for the

spade lug. Connect

the other

lead to

PS

lug #2 in

like fashion.

(S).

91

n

Select

the rack mount face

plate,

the two handles,

and the

four 5/8"

slotted hex head #10 screws

and

lockwashers, along with the front

panel

assembly.

To

prevent

marring the finish,

protect

the work

surface

with

a towel. Place

a lockwasher over each

screw, and fasten the face

plate

to the

front

panel

with the screws into the handles. Make

sure these

screws are tight.

92

n

Select the PC-20 control circuit

board, the two

larger

(approx.

ll2")

flat metal washers, and

their

two nuts.

Carefully

fasten the control

board to the

front

panel,

making sure the LEDs

fit into the face

plate

holes, as the small boards

are eased over the

spring

clip

latches. Do not flex the board

and con-

trol connections unnecessarily

as

you

secure this

assembly with the

control

washers

and nuts.

93

n

Bring the front

panel

close to the bottom

plate,

and

install the small PC-22 circuit

board over the

clips

on the standoffs

power

switch,

with the

red LED near the center

line

(top)

of the front

panel.

94

n

Stand the amp on its right

side with the front

edge

extending over the

work surface. Select 4

of the

black screws.

Slide

the spade

lug from the fuse clip

wire onto

PS

lug #1.

Slide

the

line cord spade

lug

onto

PS

lug#2. Make sure these

are fully engaged.

Fasten the bottom

plate

to the front

panel,

making

sure no wires are trapped.

DO NOT MOVE

THE

AMPLIFIER BY THE HANDLES UNTIL

THE

SIDE PANELS

ARE

INSTALLED.

95

!

Select

the two

plastic

cable clamps,

the 2 small

flat

washers, and the two

#4-40 screws. Slip

a clamp

over the input harness

near the front center.

This is

composed of two

triads of wires, each

terminated

with a

5-pin

socket

plug.

The clamp

goes

behind

the secondwire tie. Place

awasheroverthe

screw,

and with the

cable

clamp on top of PC-20,

secure

it

to the central metal standoff. Place

the other cable

clamp

over the left harness,

which

comprises

the

three

pairs

of wires which are terminated

with

2-pin

plugs.

Secure it behind

the

3rd

wire

tie

and

the

left

comer

of

PC-20

in

like

fashion.

96

n

Note that

plug

connections are

polarized-that

is,

the

plug

goes

on only one

way without forcing.

Connect

the wires to the control circuit

board as

follows: The red/green

pair

near the fan to the

2-pin

plug

near the center

rear of the board. The

single black wire from the large capacitors

to the

post

near the center of the board.

The triad from

PC-22

near

the

power

switch to the right

rear

corner.

The

S-wire

plug

from the main

harness at

the centerto

the right edge ofthe board.

The

pair

of

(shorter)

blue wires on the left harness

to the left

front corner

of

the

board. The other

pairs

in this

group

connect to the 2-pin

sockets at the front

center-the

green

to the

left,

and the

red to the

right

channel.

The last 2

plugs

have

a choice ofthe

front or rear

pairs

ofconnectors near the

front

cen-

ter of the board,

depending on whether

you

intend

to use balanced

orunbalanced input circuitry.

The

locations toward

the

center,

or rear, of the board,

l5

marked

JlA, are those

which

provide

for a bal-

anced

input,

together

with

maximum sensitivity.

We suggest

that these

be

used unless

you

know

that

you

intend

to use

the direct

(unbalanced)

in-

puts.

The

plug

with

the

blue wire

goes

to the

teft

side,

and

the one with

the

green

wire

is forthe

right

channel.

97

[

Select the

two

side

panels,

the two

pieces

of

foam

filter,

and 14 screws.

Slip the

foam filters

into

the

grilles

from the

outside,

make

sure no

wires

are

trapped,

and secure

the

panels

to the chassis.

98

!

Select the

L-shape

Allen wrench,

the two knobs,

and

the two

set screws.

Slide a set screw

onto

the

wrench,

and

install

it in the knob.

Tighten

each set

screw

onto the

flat ofthe

control shaft.

99

I

Check that the

3

pieces

ofadhesive-backed

foam

are in

place

on

the transformer

and fan housing,

and that

the rubber

grommet

strip is

on the top

of

the front

power

module

bracket.

100

[

Before securing

the cover,

check that the

power

switch

is off.

Plug the unit in, and switch it on

briefly

to make sure

the fan turns freely. Then turn

it off.

and install

the cover with 14 screws.

101

n

Select the appropriate

size fuses

for output load

protection,

and

install them

in the back

panel

fuse

holders. The

size

of the fuse determines

the

level

at

which

speaker

protection

is

provided.

The

5

amp

fuses

supplied will

offer some

protection

to high

powered

speakers,

but absolutely no

protection

is

provided

with

fuse sizes

of 10 amps or more.

How-

ever,

if

you

intend

to test the amplifier with

full

power

sine waves,

10 amps is the minimum

needed,

and

at very low impedances with

maximum

output,

the internal fuses

may blow first

if

the output fuses

are higher than

l0 amps.

102

n

Affix

the serial number

label to the bottom.

Check

the

position

of the

mono-stereo switch for.your in-

tended

use. You may also wish

to secure the Allen

wrench

to the

underside with tape.

AC

LINE

CONNECTIONS

FOR

OVERSEAS

USE

I ine

voltages

other

than

the

120 volts

USA

standard

may

be accommodated

with

altemative wiring

to the screw

terminal

strip

behind

the

power

transformer.

These

are

diagrammed

below.

In some instances,

one of the short

jumper

wires is

simply

'stored'

as

a loop

under one

terminal.

If a line

voltage of

200-240 volts

is

provided,

the

15 ampere ito-Uto line fuse

should

be replaced

with

a

7Vz ampere

slo-blo

fuse in the

single fuse

clip in fronf

of the transformer.

l6

SERVICE

POLICY AND

LIMITED

WARRANTY

The

P500 Power Amplifier has been carefully en-

gineered

to

provide

many

years

of use

without

requiring

any

maintenance or servicing.

Factory assembled

units

are

subjected to many

physical

and electrical tests before shipment. The amplifier module

assemblies of kit units are similarly tested to meet

per-

formance

specifications

prior

to

packing.

In

spite

of this,

shipping damage

does occur,

a kit

may

not

be

assembled

properly,

or human error interferes, so service may be

needed.

The David Hafler

Company

provides

complete

service facilities at

the

factory

to

make any necessary re-

pairs.

Because many of the

components

in this refined de-

sign are

not

readily

available

through local sources, and

the

performance

of the

unit is

likely

to be compromised

with

"similar

type" substitutions, we strongly recom-

mend factory service,

or obtaining the

requisite

parts

from

the factory.

It is

the owner's responsibility to

return

or

ship the

unit

freight

prepaid

to the factory

service

department

and to

provide

insurance in transit.

Units

shipped

freight collect

will not be accepted.

For units

to be repaired under war-

ranty, a copy of the dated bill of sale must accompany the

unit.

Use

the

complete

original

cafton

and all

packing

mate-

rial to ship

your

amplifier. The

kit

packaging

is designed to

accommodate the

completed unit.

Enclose

with

the unit

the following information:

1. Complete

shipping address

(Post

Office

box numbers

are not acceptable, except for correspondence).

2.

The serial number, if

it

is not on

the unit.

3. Copy

of dated

bill

of sale if repairs are

to be made under

warranty.

4. Description of the malfunction. If intermittent, be sure

to indicate.

5. You may also wish to attach

your

address directly to

the

unit, or

to

the

line

cord.

All service work

is

guaranteed

for

90

days.

Warranties

appiy to

the

original

purchaser

only. The

warranty is void

if the amplifier has been modified

without

factory authorization; or if

parts

have been substituted

which, in the factory's

judgment,

are not suitable; or if the

amplifier has been either

physically

or electrically abused,

or used for some

purpose

for which it was neither designed

nor intended. The

warranty

on the transformer is void if

the

leads

have been cut too short for re-use.

Technical assistance

to help

you

locate

the source of a

problem

may

be

obtained

by calling orwriting the Techni-

cal Services Department. Phone

(609)

662-6084

between

8

A.M. and

4:30 P.M.,

eastern time.

It

is helpful

to

know the

serial number

of the unit, and the results of any tests

you

have

performed.

However, we do not recommend that

you

attempt

your

own servicing unless

you

are

knowl-

edgeable in this regard.

If

you

choose,

it is

possible

to

return only a

portion

of

the amplifier for factory service,

with some disassembly

on

your part.

This assumes that

you

are certain

the

prob-

lem lies

only in

the returned

portion,

and that

you

assume

full

responsibility for reinstalling it correctly, since a ser-

vice

warranty

cannot be extended

for other than the actual

portion

serviced and any malfunction caused

by improper

reinstallation is

your

responsibility. Because the trans-

former is so heavy, and a

problem

there

is most

unlikely,

its removal by disconnecting

a few leads is a logical

choice.

The balance of the amplifier should be insured

for

$800.

It is also

possible

to unsolder the

power

output

mod-

ule, and return it, if that is

where

the only

problem

lies.

However, it requires much more care in

packing.

to

pro-

tect the delicate components

on the

circuit

boards, and

many

connections must be unsoldered,

so there is more

risk of reinstallation error. It should be

insured for

$400.

The service

fee for the

power

output module is

$50.

Likewise, the

control circuit board

may be readily re-

moved for service, and returned separately. It should be

insured for

$200.

and the service fee for it

alone is

$20.

WARRANTY FOR KIT-BUILT UNITS

The

parts

in a

P500

kit are

warranted for a full

year

from

the

purchase

date. If

a defective component

is found on

a

circuit

board or in a

kit, simply return the individual

part

to

the factory

prepaid

together with the

serial number and

the

date of

purchase,

and it will be replaced

at no charge.

If

you

cannot

locate what is wrong

with

your

P500,

re-

turn it to the factory

along with a copy of

the dated bill

of

sale,

and a check for

$75.

Ifthe cause

ofthe

problem

is a

defective

part,

the unit

will

be

repaired and returned

to

you

transportation

prepaid,

and

your

$75

/ess the shipping

charges

will

be returned to

you.

If the

problem

is found to

be

an

errorin

your

assembly of the amplifier,

the amplifier

will be

put

in

proper

working order, tested to be

sure it is

meeting specifications, and returned to

you

(freight

pre-

paid

within the

continental U.S.).

Excess

shipping charges

for expedited service,

or

overseas

delivery are

your

re-

sponsibility. At the sole discretion of the

factory service

department, if the time required for

diagnosis, repair

and

testing,

and the nature of the malfunction

warrants it, a

portion

of

the submitted repair fee may be

rebated.

This

warranty

is

void if the kit has not been completely

assembled or if other than

rosin core solder has

been used.

Units

assembled with acid core solder or

paste

flux

will

be

returned unserviced.

WARRANTY FOR FACTORY

ASSEMBLED UNITS

The

P500

is warranted for

3

full

years

from the

purchase

date including

parts

and

labor and normal

shipping costs

from the factory to the owner within the continental U.S.

The owner is responsible for

returning the unit to the

fac-

tory and must submit a copy of the dated

bill of sale.

This warranty

gives you

specific

legal rights. You may

also have other rights which vary from

state to state.

17

FOR

SERVICE TECHNICIANS

The

P500 has been

designed in modular

fashion with an

eye to easy service

accessibility.

Remove the

cover first,

and

then the side

panels

if necessary.

Do not attempt to

move the amplifier with

the front

panel

handles, once

the

side

panels

have

been separated.

The

AC line fuse is

below the

power

switch. The

dual

fuse holders on

either side of the fan are

l0 amps, for B+

and

B- . Failure of any of

these usually indicates a more

involved

problem,

unless the amplifier was

being tested at

maximum

power

into a

low

impedance load, with

output

fuses larger

than 10 amps.

If the

problem

is a weak,

dis-

torted

output, the only

problem

may be a blown

output

fuse

(back

panel).

Some signal is heard with

a blown

speaker

fuse, because

they are in the feedback loop.

If factory

service

of the entire

unit is in

order, it is

quite

easy to remove

the

power

transformer,

and thus

save half

the weight,

and

greatly

reduce

the risk of damage

in

transit.

Transformer

problems

are extremely

unlikely. A

fanning strip

secures most

of the transformerleads

to the

barrier strip,

spade lugs

connect

to the rectifier,

and the

red/yellow

lead

is unscrewed

from the

capacitor strap.

If a

problem

has been isolated

to the amplifier

audio cir-

cuitry, that

alone can be removed

for factory

service, or

easily dismounted

for diagnosis.

Four sheet

metal screws

secure

the

power

output

module

to the chassis. The

ther-

mal

protection

devices, and

the fan speed resistors

are lo-

cated on

the bottom of

the module.

If the module is

to be

disconnected,

three wires

go

to screw

terminals on

the

transformer

barrier

strip, and it is easiest

to dismount

the

stereo/mono

switch from

the

chassis,

rather

than unsolder

the

input leads

to the board, since

that harness

can be un-

plugged.

Then only

connections

to the front

edge of the

boards need

be unsoldered,

and tagged for reinstallation.

To

dismount

the control circuit board,

first remove the

knobs and

the control nuts. The

board is secured

by

two

rear screws,

and spring latches

on the front

panel

standoffs

to the LED

boards. If

you

only need access to the

bottom

of the

control board,

just

remove the rear

screws, and

carefully separate

the front

panel

assembly

(with

the

board) from

the chassis.

CIRCUIT

DESCRIPTION

The

P500 amplifier components

have been selected to

protect

against

failure, and all

parts

are operated

conser-

vatively

to assure unaltered

performance

and

proper

op-

eration for

many

years.

The semiconductors

have been

thoroughly researched

and selected

for minimum noise

and distortion

plus

maximum reliability

in sustained use.

Power

Amplifier

Circuit

The amplifier

stages

are fully

DC coupled, with a

dual

differential

pair

for the

input, and a fully

complementary

MOSFET output

stage.

Transistors

Q3, Q4, Q5,

and

Q6

form the

input differen-

tial stage

while

Ql

and

Q2

are the

constant

current sources

for the input

pairs.

Potentiometer

Pl adjusts the output

offset

voltage.

Transistors

Q7, Q8, Q10,

and

Q11

are

the second

gain

stage and

are the

predrivers

for the

output stage drivers

Q12

and

Ql3.

The drivers supply

the current necessary

to

drive

the MOSFETs.

An adjustable

voltage reference

is formed by transistor

Q9

and

potentiometer

P2. Thus the signal

sees the bases of

transistors

Q12

and

Q13

tied together.

P2 adjusts the

vol-

tage to

bias the amplifier

for class AB

operation and

therefore

determines

the

quiescent (idle)

current in the

driver

and output stages.

Thermal stability

is assured by

the

positive

temperature

coefficient of the

power

MOS-

FETs. The

usual thermal tracking

methods are not

re-

quired.

The

driver

and output stages

are fully

complementary.

Q14, Q15,

and

Q16

are

N channel MOSFETs

in

parallel

for

the

positive

half of

the signal, and

Q17, Q18,

and

Ql9

are P

channel MOSFETs

for the negative

signal

half.

There

is none of

the usual volt

amp limiting

in the P500.

Diodes

Dll, Dl2,

D13, and Dl4

prevent

the

gates

of the

MOSFETs

from

being overdriven

in the event of

abnor-

mally high

signal levels.

The output

current is limited

only

by the

B+, B-

,

and

the speaker

(output)

fuses.

AMPLIFIER CIRCUIT

ta

RELAY

CIRCUIT

Relay Protection

Circuit

The

relay circuit has a

3

section low

pass

filter which

prevents

signals

above 10

Hz

from opening the

relay.

This circuit allows DC to

pass

to

ICl07A

and IC107B

which

senses any offset above

3.5

volts, opening

the

relay to

protect

the speakers.

Rl32 andRl33 form the reference

for

the

positive

offset detector IC107A, Rl34 and

Rl35 form

the reference

for the negative

detector

IC107B,

Cl15's

charging

time is the time

delay

at turn on, and after

any

relay

actuation.

D106

and

C116

form a

quick

discharge supply

that

opens the relay immediately

when the

amplifier is turned

off.

Balanced

to

Unbalanced

Line

Circuit

IC101 and

IC102 are buffers to keep the input impe-

dance to the summing stages IC103A and IC103B inde-

pendent

of the input. This allows P102 to

null

out

any

common

mode signals on

the input

lines.

Moving the input

plug

from J101A to Jl0lB

will bypass

the balanced to

unbalanced

circuit.

Clipping Detector Circuit

P.122,R123,

and P103 adjust the amplifieroutput

signal

to the same level as the input. Rl18, Rl19, C106, and C107

shape the frequency response of the input signal to match

the

amplifier.

The two

signals

are compared

by IC105, and

any difference is amplified and triggers the

one shot mul-

tivibrator IC106 which liehts LED D202.

Signal Present Indicator Circuit

Any signal that is more

than the

reference set by Rl15

and

Rl16 drives the output of ICl04

negative, lighting

LED

D201. R201 and C201 integrate

this signal to reduce

the flicker in the LED.

Mono

Operation

When 52 is switched to MONO

the

right

channel's input

is shorted to

ground

and the output of the left channel is

connected to the inverting

input of the right channel

through

R44. A third section of

53

disconnects B* from

the right

channel clipping indicator. In mono the load is

connected across

the two

red

output connectors. Neither

of these may be

grounded.

When

determining the load im-

pedance

for

the

amplifier

in mono each channel

"sees"

one half the load

impedance.

Power Supply

The

power

transformer may be

wired

for 100, 120, 200,

220.

or

240 volts

AC lines. Never wire it for

less

than

the

incoming

mains voltage. Thermal breakers

TBI and TB2,

located on the heat

sinks, will turn off the amplifier in the

event of

overheating. The over temperature LED

on

PC-22lights

when a

breaker

opens. In series with the fan

are two resistors, R45 and R46,

which reduce the fan speed

for

quieter

operation.

With

increased heat sink tempera-

ture, thermal

sensors TSI and/or TS2 will short out these

resistors,

raising the fan speed. A current inrush

limiter

TRI in the AC line input

reduces the initial turn-on surge

for longer component

life.

BALANCED TO Ut{BALANCED LINE CIRCUIT

CLIPPING DETECTOR

CIRCUIT

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ATI

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DETECTOR

lCTB

SIGNAL PRESENT INOICATOR

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Hafler P500 Amplifier User manual

Hafler P500 Amplifier User manual

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