Electro-voice 7300a Operation manual

'^~J\

Sedrol6ice*

ty

7300A

®

I

STEREO

POWER

AMPLIFIER

OWNER'S

OPERATION

AND

SERVICE

MANUAL

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

Table

of

Contents

1

2

3

4

5

7

ELECTRICAL

.

1.1

120

V

ac,

50/60

Hz

Power

Connections

.

1.2

220/240

V

ac,

50/60

Hz

Power

Connections

INSTALLATION.

2.1

Rack

Mounting.

2.2

Ventilation

.

SIGNAL

CONNECTIONS

3.1

O

2

.

2

Q

.

2

0.0

Q

A

.

2

0.4

.

2

0.4.i

VM/a.iCllia.Xiing

ITOWcr

ijUoofcJo

WiUii

a

uiiiii

xjKjaxM.i:>

...

.

3

<3

n

.

3

0.0

o

3.5.1

Calculating

the

Maximum

Length

of

Cable

for

a

Specified

Damping

Factor

.

4

,

.

4

0.0

3.7

Compression

Driver

Protection

Capacitors

.

,

.

5

OCTAL

ACCESSORY

SOCKETS

PROTECTION

SYSTEMS.

5.1

Load

Protection

Circuitry

...

5.2

Amplifier

Protection

Circuitry...

5.3

Protect

Indicator.

6

OPERATION

..

6.1

Dual

Mode

of

Operation

6.2

Bridge

Mode

of

Operation

IN

CASE

OF

PROBLEMS

.

8

SPECIFICATIONS

9

SERVICE

INFORMATION

...

9.1

Trimpot

Adjustments

.

9.2

Equipment

Needed

.

9.3

Adjusting

R39,

the

LF

Cancel

Trimpot.

9.4

Adjusting

R26,

the

BIAS

Trimpot

..

9.5

Adjusting

R23

and

R24,

the

Negative

and

Positive

Current

Limit

Trimpots

......

9.6

Checking

the

Short

Circuit

Current.

9.7

Ordering

Replacement

Parts..

•

9.8

Factory

Service.

•

9.9

Technical

Assistance.

13

14

15

i

Electro-Voice

®

a

Mark

IV

Company

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

(BOTH

SIDES)

1

ELECTRICAL

Two

amplifier

models

are

available.

One

model

hats

a

50/60

Hz

power

transformer

with

two

120

V

ac

primary

windings.

These

windings

may

be

wired

in

parallel

or

series

for

operation

at

either

120

V

ac

or

220/240

V

ac.

The

ot¬

her

amplifier

model

is

for

export

into

countries

where

the

ac

line

voltage

is

100

volts,

50/60

Hz.

The

sections

refer

to

the

first

model

with

the

dual

120

V

ac

pri¬

mary

windings.

1.1

120

V

ac,

50/60

Hz

Power

Connections

The

amplifier

is

provided

with

the

primary

of

the

power

transformer

strapped

for

120

V

ac

operation

from

the

factory.

Refer

to

Figure

2a

for

the

wiring

details.

WARNING!

Verify

that

the

power

transformer's

primary

circuit

configuration

is

correct

for

the

intended

ac

line

voltage

BEFORE

applying

power

to

the

amplifier.

1.2

220/240

V

ac,

50/60

Hz

Power

Connections

The

power

transformer

has

two

120

volt

primary

windings

which

can

be

connected

in

parallel

for

120

V

ac

line

voltages,

or

in

series

to

meet

220/240

V

ac

re¬

quirements.

Use

the

following

procedures

to

re-strap

the

primary

of

the

power

transformer

for

220/240

V

ac

applications.

1.

Make

sure

the

amplifier

is

not

connected

to

2

iny

pow¬

er

source.

2.

Remove

and

save

the

eleven

screws

securing

the

top

cover.

There

are

three

screws

on

each

side

and

three

along

the

top-rear

edge

of

the

chassis.

In

addition,

you

must

remove

the

two

inside

screws

al¬

ong

the

top

edge

of

the

front

panel.

Refer

to

Fig¬

ure

1

for

the

exact

screw

Figure

1

Top

Cover

Removal

locations.

3.

Locate

terminal

blocks

TBl

and

TB2

located

on

the

side

of

the

chassis

near

the

rear

input

PC

board.

Reconnect

the

leads

as

shown

in

Figure

2b.

4.

Install

the

top

cover

with

the

eleven

screws

previou¬

sly

removed.

Two

screws

are

longer

than

the

others

removed

from

the

sides

and

rear.

These

longer

screws

install

into

the

rearmost

position

on

each

side

of

the

chassis.

5.

Install

the

5A

fuse,

Littelfuse

Type

SAB

5A

/250V

slo-blo

326-series

ceramic

body

or

equiv¬

alent.

2

INSTALLATION

2.1

Rack

Mounting

The

amplifier

may

be

installed

in

a

standard

19

inch

equipment

rack.

It

requires

bVi

inches

of

vertical

rack

space

and

secures

to

the

rack

cabinet

with

the

four

rack

mount

screws

and

cup

washers

provided

in

the

hard¬

ware

kit.

2.2

Ventilation

The

amplifier

must

be

adequately

ventilated

to

avoid

excessive

temperature

rise.

It

should

not

be

used

in

areas

where

the

ambient

temperature

exceeds

60

°C

(140

°F).

To

determine

the

ambient

air

temperature,

operate

the

system

in

the

rack

until

the

temperature

stabilizes.

Measure

the

ambient

air

with

a

bulb-type

thermometer

held

at

the

bottom

of

the

uppermost

amplifier.

Do

Electro-Voice

®

a

Mark

W

Company

1

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

not

let

the

thermometer

touch

the

metal

chassis

because

the

chassis

will

be

hotter

than

the

ambient

air.

If

the

air

temperature

exceeds

60

°C

(140

°F),

the

equipment

should

be

spaced

at

least

1.75

inches

apart

or

a

blower

installed

to

provide

sufficient

air

movement

within

the

cabinet.

WARNING:

Do

not

operate

the

amplifier

within

a

completely

closed

unventilated

housing.

3

SIGNAL

CONNECT¬

IONS

3.1

Input

Connections

Balanced

input

connect¬

ions

may

be

made

to

either

the

Vi"

phone

(TRS)

or

the

female

XLR

connectors.

For

single-ended

in¬

puts,

strap

the

low

(—)

input

to

ground

(pin

3

on

XLR

or

Ring

on

Va"

phone).

Otherwise,

the

elect¬

ronically-balanced

input

stage

will

see

6

dB

less

input

signal

level

than

with

a

balanced

input.

Refer

to

Figure

3

for

typical

input

con¬

nections.

3.2

Line

Output

Connect¬

ions

The

XLR

and

Vi"

phone

connectors

are

wired

in

parallel.

2

of

the

XLR

is

the

Tip

of

the

Vi"

phone

connector,

and

3

is

the

Ring.

Since

the

input

imped¬

ance

of

the

electronically-balanced

input

stage

is

high

(15

kohms),

there

is

minimal

loading

on

the

signal

source.

When

the

input

connections

are

made

to

one

con¬

nector,

the

other

may

be

used

as

an

auxiliary

line

output

to

feed

other

high

input

impedance

equip¬

ment.

Refer

to

Figure

3

for

possi¬

ble

applications.

3.3

Output

Connections

Output

connections

eire

made

to

the

binding

post

connect¬

ors

located

on

the

rear.

The

Red

post

is

the

high

(-I-)

output

and

the

Black

post

is

the

low

(—)

out¬

put.

Refer

to

Figure

4

for

typical

output

connections.

3.4

Output

Cable

Selection

Speaker

wire

size

plays

an

important

part

in

quality

sound

systems.

Small

wire

gauges

can

waste

power

and

reduce

the

damp¬

ing

factor

at

the

speaker

termi¬

nals.

This

can

add

coloration

and

muddiness

to

the

sound.

To

help

offset

this

problem.

Table

I

has

been

assembled

to

enable

you

to

calculate

the

power

losses

in

the

speaker

cable.

3.4.1

Calculating

Power

Losses

with

8

ohm

Loads

To

calculate

the

total

power

loss

in

the

speaker

cable,

multiply

the

power

loss

per

foot

(or

meter)

of

the

2-wire

cable

selected

from

Table

I

by

the

len¬

gth

of

the

cable

in

feet

(or

met¬

ers).

For

example,

suppose

an

in¬

staller

uses

160

feet

of

10

GA

2-

wire

cable

with

an

8

O

speaker

system.

The

total

power

loss

in

the

cable

is:

Total

Power

Loss

in

cable

=

0.0509

watts/foot

X

160

feet

=

8.1

watts

Does

this

mean

that

whenever

the

amplifier

produces

200

watts

of

output

power,

191.9

watts

(200

watts

minus

8.1

watts)

will

he

delivered

to

the

8

ohm

load"?

NO!

The

actual

load

impedance

is

8

ohms

plus

the

resistance

of

the

cable

(0.00204

ohms/foot

times

160

feet)

for

a

total

load

impe¬

dance

of

8.3264

ohms.

At

the

8

G

rated

output

power,

the

output

voltage

is

40

V

rms.

Therefore,

the

amplifier

produces

192.2

watts

with

this

load

instead

of

200

watts.

This

was

calculated

by

2

Electro-Voice

®

a

Mark

IV

Company

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

This

example

illustrates

the

im¬

portance

of

using

the

proper

wire

size.

3.4.2

Calculating

Power

Losses

with

4

ohm

Loads

To

calculate

the

losses

when

using

a

4

ohm

speaker

sys¬

tem,

multiply

the

loss

at

8

ohms

by

3,

In

the

above

example,

the

10

GA

wire

would

consume

24.3

watts

of

power

while

the

18

GA

wire

would

waste

155.7

watts

-

more

than

half

of

the

amplifier's

4

ohm

power

rating.

3.5

Damping

Factor

The

higher

the

damping

factor

rating

of

an

amplifier,

the

greater

the

ability

of

the

amplifier

to

control

unwanted

speaker

cone

movements.

When

a

signal

drives

a

woofer,

current

flowing

through

the

voice

coil

creates

a

magnetic

field.

This

field

interacts

with

the

permanent

magnetic

field

in

the

gap

and

forces

the

combination

cone

and

voice

coil

assembly

to

move

outward.

When

the

signal

is

removed,

the

assembly

moves

in¬

ward

but

its

momentum

causes

it

to

overshoot

its

resting

point.

This

overshoot

will

dampen

itself

out

eventually

but

the

unwanted

mov¬

ements

can

add

considerable

dis¬

tortion

products

to

the

sound.

In

the

process

of

moving

inward

through

the

magnetic

field,

the

voice

coil

assembly

generates

a

current

of

opposite

polarity

to

the

original

signal.

This

current

induces

a

voltage

or

“back

EMF”

which

travels

through

the

speaker

wire

to

the

eimplifier’s

output.

The

lower

the

amplifier’s

output

impedance,

the

faster

the

over¬

shoot

of

the

voice

coil

will

dampen

out.

The

output

impedance

of

an

amplifier

can

be

calculated

by

dividing

the

rated

output

impe¬

dance,

typically

8

ohms,

by

the

damping

factor.

The

7300A

has

a

damping

factor

rating

of

200

which

corresponds

to

an

output

Electro-Voice

®

a

Mark

IV

Company

3

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

impedance

of

0.04

ohms.

3.5.1

Calculating

the

Maxi¬

mum

Length

of

Cable

for

a

Specified

Damp¬

ing

Factor

Specifica¬

tion

at

the

Load

The

damping

factor

rating

is

typically

never

realized

at

the

load

because

of

the

resistance

of

the

cable

(and

other

factors

such

as

the

contact

resistance

of

an

output

relay

or

the

resistance

of

an

output

fuse).

The

damping

fac¬

tor

at

the

load

should

be

30

for

general

paging

systems

and

50

for

high

fidelity

music

systems.

Econ¬

omics

usually

dictate,

however,

that

these

numbers

are

cut-in¬

half.

The

resulting

damping

factor

at

the

load

should

be

based

on

experience

and

customer

satis¬

faction.

Once

a

minimum

damping

factor

is

determined

for

a

parti¬

cular

type

of

installation,

the

following

equation

can

calculate

the

maximum

length

of

2-wire

cable

which

can

be

used

to

ach¬

ieve

the

minimum

damping

factor

specified

at

the

load:

Max.

Length

of

2-wire

cable

in

feet

ZL

—

Zo

=

_M

_

DCR/ft

where

ZL

is

the

load

impedance

to

connect

to

the

amplifier;

Zo

is

the

amplifier’s

output

impedance

(0.04

ohms

for

the

7300A);

DF

is

the

minimum

permissible

damping

factor

at

the

load;

and

DCR/ft

is

the

DC

resis¬

tance

of

the

2-wire

cable

per

foot

from

Table

I.

The

same

equation

can

be

used

to

calculate

the

maximum

cable

length

in

meters

by

substituting

Table

I

7300A

Power

Losses

in

2-wire

Speaker

Cable

Power

Cable

Cross-

Power

AWG

DCR/ft

Loss/ft

Sectional

DCR/meter

LossAneter

(GA)

(a/ft)

(watts/ft)

area

(mm^)

(a/m)

(watts/m)

6

0.00081

0.0201

13.30

0.00264

0.0661

8

0.00121

0.0302

8.36

0.00421

0.1051

10

0.00204

0.0509

5.26

0.00669

0.1669

12

0.00324

0.0809

3.31

0.01063

0.2650

14

0.00515

0.1286

2.08

0.01691

0.4210

16

0.00819

0.2043

1.31

0.02685

0.6667

18

0.01302

0.3244

0.82

0.04289

1.0609

20

0.02070

0.5148

0.52

0.06764

1.6627

22

0.03292

0.8163

0.33

0.10658

2.5950

the

DCR

per

meter

value

from

/

1

Zo

\

Table

1.

(Pout)(DCR/ft)

\

DF

ZL

1

Let’s

use

the

equation.

Suppose

ZL

equals

8

ohms,

Zo

=

0.04

ohms,

and

the

minimum

damping

factor

at

the

load

is

25.

In

addition,

18

GA

cable

is

preferred.

Then,

the

maximum

length

of

18

GA

cable

which

can

be

used

to

achieve

a

damp-ing

factor

of

25

at

the

load

is:

8

—

(0.04)

_25_

=

21.5

feet

0.01302

O/ft

Sometimes

it

may

be

necessary

to

locate

the

speaker

100

feet

or

more

away

from

the

amp-lifier.

In

this

situation,

a

much

larger

gauge

cable

is

required.

How¬

ever,

this

may

not

be

practical

or

economical.

The

size

of

the

2-

wire

cable

can

be

greatly

reduced

by

stepping

up

the

output

volt¬

age

of

the

amplifier

to

70,

100,

140,

or

210

volt,

using

an

output

transformer,

then

stepping

down

the

voltage

at

the

load.

Such

a

system

is

shown

in

Figure

5.

The

maximum

length

of

2-wire

cable

in

this

situation

can

be

ap¬

proximated

from

the

following

equation:

Max.

Length

of

2-wire

cable

in

feet

where

V

is

the

stepped-up

voltage

of

the

system;

Pout

is

the

rated

output

power

of

the

amplifier;

Zo

is

the

output

impedance

of

the

amplifier

(0.04

ohms

for

the

7300A);

ZL

is

the

load

impedance;

DCR/ft

is

the

DC

resistance

of

the

2-wire

cable

per

foot

from

Table

I;

and

DF

is

the

minimum

permissible

damping

factor

at

the

load.

Suppose

a

210

volt

system

were

used

at

a

600

watt

power

level

to

drive

an

8

ohm

load

with

a

mini¬

mum

damping

factor

of

25.

Using

the

same

18

GA

cable

as

before,

the

maximum

length

can

now

be

198

feet.

Power

companies

use

this

technique

to

trsinsfer

large

amounts

of

power

over

great

dis¬

tances.

3.6

Speaker

Protection

Fuse

Selection

Sometimes

it

may

be

de¬

sirable

to

use

in-line

fuses

(fuses

in

series

with

the

output)

to

pro-

4

Electro-Voice

®

a

Mark

TV

Company

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

Figure

6

High-voltage

Distribution

System

tect

loudspeaker

^sterns

(or

the

amplifier).

It

is

difficult,

however,

to

determine

the

proper

fuse

value

with

the

correct

time

lag

and

overload

characteristics

to

match

the

limitations

of

a

speaker

sys¬

tem.

The

values

shown

in

Table

II

should

serve

only

as

a

guide.

To

use,

determine

the

power

rating

and

load

value.

Then,

select

a

standard

value

fuse

of

the

value

to

the

one

listed

in

the

table.

Table

II

Calculated

Output

Fuse

Values

Power

4ft

8ft

16

ft

(watts)

Load

100

3.70

2.62

1.85

150

4.54

3.21

2.27

200

5.24

3.70

2.62

300

6.42

4.54

3.21

400

7.41

5.24

3.70

600

9.07

6.42

4.54

The

values

are

calculated

for

fast-

blow

fuses

which

carry

135%

of

their

current

rating

for

an

hour

but

will

blow

within

1

second

at

200%.

Other

fuse

values

may

be

calculated

for

different

power

levels

from

the

following

equation:

Fuse

value

=

(Pout

X

ZL)

^

amps

ZL

X

1.35

where

Pout

is

the

output

power

rating

of

the

amplifier;

and

ZL

is

the

load

impedance.

Use

32

volt

fuses

if

possible;

they

typically

have

the

lowest

internal

resistance

which

will

help

mini¬

mize

deterioration

of

the

damping

factor

at

the

load.

Refer

to

the

example

in

Figure

4.

3.7

Compression

Driver

Protection

Capacitors

Compression

drivers,

used

for

mid

to

high

frequency

sound

reproduction,

are

much

more

sus¬

ceptible

to

damage

from

low

freq¬

uencies

than

large

cone

loud¬

speakers.

Even

though

an

elect¬

ronic

crossover

may

be

employed,

problems

may

arise

in

the

cables

between

the

crossover

and

the

power

amplifier,

or

from

mis-

adjustment

of

the

crossover.

Either

of

these

situations

could

apply

low

frequency

signals

or

hum

to

the

driver

and

cause

damage.

To

prevent

a

potential

mishap,

Electro-Voice

re¬

commends

using

a

capacitor

between

the

amplifier

and

the

compression

driver

to

suppress

low

frequencies

and

possible

DC.

Refer

to

the

example

in

Figure

4.

In

choosing

a

value,

one

must

be

careful

not

to

interfere

with

the

crossover

frequency.

As

a

general

rule,

select

a

capacitor

whose

break

frequency,

with

respect

to

the

load,

is

3

dB

down

at

approximat¬

ely

V

2

of

the

high

pass

comer

fre¬

quency.

Mylar

capacitors

with

at

least

a

100

volt

ac

rating

are

recom¬

mended.

Table

III

shows

the

re¬

commended

capacitor

values

for

use

with

8

and

16

ohm

drivers

at

popular

crossover

frequencies.

Table

III

Compression

Driver

Protection

Capacitors

Crossover

8ft

16ft

Frequency

Driver

500

Hz

80

^iF

40

liF

800

Hz

50

|iF

25

liF

1000

Hz

40

ii?

20

^lF

1250

Hz

33

jiF

16

nF

2000

Hz

20

|iF

10

^iF

3150

Hz

12

^F

6

|iF

4

OCTAL

ACCESSORY

SOCKETS

Two

octal

sockets

permit

a

variety

of

plug-in

accessories

to

be

used

with

the

amplifier.

Normally,

one

“U”

jumper

is

inserted

be¬

tween

octal

socket

pins

8

and

1,

and

another

between

pins

7

and

6.

These

jumpers

must

remain

in

place

for

the

amplifier

to

operate

when

not

using

any

accessory

modules.

To

use

with

an

accessory

Electro-Voice

©

a

Mark

TV

Company

5

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

module,

remove

(and

save)

the

jumpers

and

install

the

module

making

sure

the

key

on

its

center

post

aligns

with

the

groove

in

the

female

socket.

For

operation,

refer

to

the

instructions

provided

with

the

module.

Schematically,

the

module

will

be

inserted

between

the

input

connector

and

the

bal¬

anced

input

stage.

Electronic

modules

are

powered

from

a

bipolar

15

volt

supply

in

the

amplifier.

The

supply

is

cap¬

able

of

supplying

up

to

25

ma

DC

of

current.

Currents

in

excess

of

25

ma

DC

may

prevent

the

amp¬

lifier

from

disengaging

from

its

built-in

protection

mechanisms.

5

PROTECTION

SYS¬

TEMS

5.1

Load

Protection

Circuitry

Each

channel

independ¬

ently

protects

its

load

from

start¬

up/shutdown

transients,

DC,

and

large

subsonic

signals.

5.2

Amplifier

Protection

Circuitry

A

unique

current-limiting

circuit

waa

designed

specifically

for

the

amplifier.

It

features

a

variable

current

limit

which

is

a

function

of

the

output

signal

volt¬

age.

As

a

result,

the

amplifier

can

deliver

the

rated

currents

into

rated

loads

but

substantially

lim¬

its

the

current

into

low

impedance

or

shorted

loads

(shorted

output

terminals).

Once

the

short

is

re¬

moved,

however,

the

amplifier

will

resume

normal

operation.

A

dual

speed

fan

is

also

incorp¬

orated

to

provide

efficient

cooling

under

the

most

demanding

condi¬

tions.

When

the

heatsink

temp¬

erature

at

the

fin

tips

reaches

approximately

88

"C

(190

°F),

the

fan

automatically

switches

to

high

speed

operation.

As

the

temper¬

ature

cools

to

approximately

78

°C

(172

°F),

low

speed

operation

is

once

again

resumed.

The

heatsink

is

also

thermally

equalized

to

prevent

the

output

devices

nearest

the

fan

from

op¬

erating

at

a

cooler

temperature

than

the

devices

at

the

opposite

end.

This

minimizes

the

thermal

gradient

across

the

heatsink

and

forces

the

devices

to

operate

at

more

nearly

the

same

tempera¬

ture.

This

equalizes

the

lifetimes

and

reliability

characteristics

of

the

output

devices

so

that

no

one

device

becomes

the

weak

link

in

the

chain.

Should

the

heatsink

temperature

of

a

channel

remain

excessively

high,

the

affected

channel

will

shut

down

automatically.

When

the

output

devices

cool

to

a

safe

operating

temperature,

the

chan¬

nel

will

automatically

resume

normal

operation.

5.3

P

rotect

Indicator

The

“PROTECT”

LED

does

not

turn-on

abruptly

as

others

may

do;

its

intensity

is

allowed

to

vary.

As

a

result,

its

degree

of

brightness

serves

as

a

relative

indicator

of

the

severity

of

the

current

operating

conditions

e.g.,

the

brighter

the

LED,

the

greater

the

stress

on

the

cha-

nnel(s).

This

provides

a

visual

notification

well

in

advance

of

any

impending

shutdown.

Although

the

channel

may

still

operate

with

the

LED

apparently

at

full

brightness,

a

total

shut¬

down

will

occur

within

a

few

sec¬

onds

unless

the

operating

con¬

ditions

improve.

If

a

shutdown

does

occur,

the

channel

will

re¬

sume

normal

operation

as

soon

as

its

devices

have

cooled

to

an

acceptable

temperature.

6

OPERATION

6.1

Dual

Mode

of

Oper¬

ation

In

the

dual

mode

of

operation,

the

channels

may

be

operated

independently.

After

installation

and

hookup,

verify

that

the

mode

switch,

located

on

the

rear

panel,

is

in

the

“DUAL”

position

and

rotate

the

level

controls

fully

counterclockwise

(full

attenuation).

Input

a

0

dBu

(0.775

V

rms)

nominal

signal

level

and

apply

power.

Slowly

increase

the

level

controls

until

the

desired

output

power

is

obtained.

If

either

“CLIP”

LED

illuminates,

reduce

the

output

with

the

channel

level

control

or

reduce

the

input

signal

level

at

its

source.

WARNINGS

Never

attempt

to

con¬

nect

the

outputs

of

the

two

channels

in

parallel.

6.2

Bridge

Mode

of

Oper¬

ation

After

installation

and

hookup,

verify

that

the

mode

switch,

located

on

the

rear

panel,

is

in

the

“BRIDGE”

position.

Ro¬

tate

both

levels

controls

fully

counterclockwise

(full

atten¬

uation).

Input

a

0

dBu

(0.775

V

rms)

nominal

signal

level

into

channel

1

only

and

apply

power.

Slowly

increase

the

level

control

of

channel

1

until

the

desired

output

power

is

obtained.

If

either

“CLIP”

LED

illuminates,

reduce

the

output

level

with

the

level

control

or

reduce

the

input

signal

level

at

its

source.

CAUTIONS

Be

sure

that

no

input

connections

are

made

to

channel

2

and

that

its

level

control

is

fully,

counterclockwise

(OFF).

WARNINGS

The

bridged

output

mode

provides

a

true

halanced-to-

ground

output.

Do

not

use

any

test

equipment

to

test

or

evaluate

this

amplifier

which

does

not

have

floating

grounds.

7

I

n

Case

of

Problems

Please

check

the

following

items:

6

Electro-Voice

®

a

Mark

IV

Company

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

1

.

2

.

Verify

that

the

amplifier

is

properly

connected

to

an

ac

power

source

and

that

the

source

is

active.

Verify

that

the

input

connections

are

properly

made.

Refer

to

Figure

3.

FAX:

(616)

695-1304

Electro-Voice

Customer

Service/Repair

8324

Doe

Avenue

Visalia,

CA

93219

U.S.A.

Tel:

(209)

651-7777

FAX:

(209)

651-0164

3.

Verify

that

the

output

connections

are

properly

made.

Refer

to

Figure

4.

Check

the

input

and

output

cables

for

proper

wiring

and

continuity.

5.

C

heck

the

signal

source

and

the

load.

6.

Insure

that

the

two

jump¬

ers

for

each

octal

socket

are

properly

installed

(if

not

using

optional

plug-in

modules).

7.

Insure

that

any

accessory

modules

installed

do

not

draw

more

than

25

ma

DC

of

current.

8.

Check

that

the

mode

switch

is

in

the

desired

position.

NOTICEj

Repairs

performed

by

other

than

authorized

warranty

stations

(Dealers)

or

qualified

personnel

shall

void

the

warranty

period

of

this

unit.

To

avoid

loss

of

warranty,

see

your

nearest

Electro-Voice

authorized

dealer,

or

call

Electro-Voice

Customer

Ser¬

vice

directly

at

(405)

324-5311,

FAX

(405)

324-8981,

or

write:

Electro-Voice

Customer

Service/Repair

10500

West

Reno

Oklahoma

City,

OK

73128

U.S.A.

Electro-Voice

Customer

Service/Repair

600

Cecil

Street

Buchanan,

MI

49107

U.S.A.

Tel:

(616)

695-6831

Electro-Voice

®

a

Mark

IV

Company

7

operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

8

SPECIFICATIONS

Bridge

mode,

8

or

16

O:

39

dB

Conditionss

1.

0

dBu

=

0.775

volts

rms.

2.

Dual

mode

ratings

are

for

each

channel.

3.

Both

channels

operating

at

rated

output

power

unless

noted.

4.

120

volt

ac

line

input

voltage

maintained

for

all

tests

unless

noted.

Continuous

Rated

Output

Power:

(20

Hz

-

20

kHz

at

less

than

0.1%

THD)

Dual

mode,

4

D:

300

watts/ch

Bridge

mode,

8

O;

600

watts

Dual

mode,

8

D:

200

watts/ch

Bridge

mode,

16

O;

400

watts

Input

Sensitivity

for

Rated

Output

Power:

(Ref.

1

kHz,

±0.15

dB)

Dual

mode,

4

Cl:

Bridge

mode,

8

fl:

Dual

mode,

8

fl:

Bridge

mode,

16

fl:

Maximum

Input

Level:

(Ref.

1

kHz)

Input

Impedance:

(Ref.

1

kHz)

Balanced:

Unbalanced:

+0.1

dBu

(0.78

V

rms)

+0.1

dBu

(0.78

V

rms)

+

1.2

dBu

(0.89

V

rms)

+

1.2

dBu

(0.89

V

rms)

+20

dBu

(7.75

V

rms)

15

kO

15kfl

Continuous

Rated

Output

Power

to

Subwoofer:

(20

Hz

-

1

kHz

at

less

than

0.1%

THD)

Dual

mode,

4

0:

375

watts/ch

Bridge

mode,

8

0:

750

watts

Dual

mode,

8

O:

225

watts/ch

Bridge

mode,

16

O:

450

watts

Polarity:

Positive-going

signal

applied

to

2

of

XLR

or

Tip

of

1

/

4

"

TRS

jack

produces

positive-going

signal

at

(+)

output

terminal.

Maximum

Midband

Output

Power:

(Ref.

1

kHz,

1%

THD,

@120

volts

ac

line

voltage)

Dual

mode,

4

O:

Bridge

mode,

8

O:

Dual

mode,

8

O:

Bridge

mode,

16

O:

>400

watts/ch

>800

watts

>250

watts/ch

>500

watts

(Ref.

1

kHz,

1%

THD,

@108

volts

ac

(10%

sag))

Dual

mode,

4

fl:

>325

watts/ch

Bridge

mode,

8

fl:

>650

watts

Dual

mode,

8

fl:

>200

watts/ch

Bridge

mode,

16

fl;

>400

watts

(Ref.

1

kHz,

1%

THD,

@100

volts

ac

(17%

sag))

Dual

mode,

4

O;

>230

watts/ch

Bridge

mode,

8

O:

>460

watts

Dual

mode,

8

fl:

>175

watts/ch

Bridge

mode,

16

fl:

>350

watts

Headroom

(Before

clip):

>1

dB

(Ref.

1

kHz,

1%

THD,

any

mode)

Frequency

Response;

10

Hz

-

90

kHz

(Ref.

1

kHz,

1

watt

output,

+0/—3

dB)

Power

Bandwidth:

20

Hz

-

20

kHz

(Ref.

1

kHz,

+0/—1

dBr

where

0

dBr

=

rated

output

power

in

any

mode)

Voltage

Gain:

(Ref.

1

kHz)

Dual

mode,

4

fl

or

8

fl:

33

dB

Phase

Response;

(Any

mode)

20

Hz:

<+25°

20

kHz:

>—15°

THD:

<0.1%

(lyp.

<0.01%)

(Any

mode,

30

kHz

measurement

bandwidth)

IMD

(SMPTE

4:1):

<0.05%

(Typ.

<0.01%)

(Any

mode)

TIM

(DIM

100);

<0.05%

(Any

mode)

Rise

Time:

<6

psec

(Any

mode,

10%

to

90%)

Slew

Rate:

Dual

mode,

4

or

8

D:

>30

V/psec

Bridge

mode,

8

or

16

fl:

>60

V/psec

Damping

Factor:

(Dual

mode,

8

fl)

20

Hz

-

1

kHz:

>200

20

kHz:

>75

Crosstalk:

<75

dBr

(Ref.

1

kHz,

0

dBr

=

rated

output

power

into

8

ohms,

single

channel

operating)

Noise:

>100

dB

(Below

rated

output

power,

A-weighting

filter,

8

fl

8

Electro-Voice

®

a

Mark

TV

Company

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

dual

mcxlG,

50/60

Hz

ac

line

frequency)

Amplifier

Protection;

Shorted

output

term¬

inals,

Over-temperature,

RF

interference

Load

Protection;

Startup/shutdown

trans¬

ients,

DC

faults,

Sub¬

sonic

signals

Cooling;

Heatsink:

Thermally

equalized

3/16

in

aluminum

black

ano¬

dized

heatsink

Fan:

Thermostatically

con¬

trolled

dual

speed

fan.

Approximately

50

CFM

at

low

speed

and

100

CFM

at

high

speed.

Ball

bearing

fan

has

mini¬

mum

life

rating

of

50,000

hours

at

25

®C

ambient

temperature

Output

Topology;

True

complementary

symmetry

with

grounded

collectors

(no

mica

insulators

means

better

heat

transfer)

Output

Type;

Dual

mode:

Unbalanced,

each

channel

Bridge

mode:

Balanced

Output

Devices:

Total

number:

16

devices

Pdmax

rating:

250

watts

Vceo:

250

volts

DC

Ic:

16

amps

DC

Tjmax:

200

°C

Controls

and

Switches;

Rear:

Mode

switch

Front:

Two

input

level

controls,Power

switch

Front

Panel

Indicators?

Power

LED,

Clip

LED

(x

2),Protect

LED

(x

2)

Connections;

Input:

W

phone

(x

2),

Female

XLR

(x

2),

Octal

accessory

socket

(x

2),

powered

with

±15

volts

DC

at

25

ma.

Output:

5-way

binding

posts

Power:

6

ft

(1.83

m),

3-wire,

16

GA

power

cord

with

NEMA

5-15

plug/IEC

Fuse

Type;

Littelfuse

Type

3AB

10

A/250

V

Slo-Blo®

326-

series

ceramic

cartridge

body,

or

equivalent

(for

120

V

ac

use)

Power

Requirements;

120

V

ac,

50/60

Hz,

1000

watts

(configurable

to

220/240

V

ac).

100

V

ac,

50/60

Hz

model

available.

Operating

ac

Voltage

Range;

Operates

from

line

voltages

as

low

as

90

volts

(at

reduced

output

power)

assuming

a

120

V

ac

nominal

line.

Power

Consumption/

Heat

Produced;

(Both

channels

operating

in

dual

mode

with

1

kHz

sinewave

input

signal

at

stated

output

power

into

4

D

loads)

idle:

72

watts/0.245

kBTU/h

l/8th

max

midband

power:

720

watts/2.100

kBTU/h

l/3rd

max

midband

power:

1,068

watts/2.702

kBTU/h

Rated

output

power:

Max

midband

power:

1,464

watts/2.938

kBTU/h

1,680

watts/2.873

kBTU/h

Operating

Temperature

Range;

Up

to

60

°C

(140

°F)

ambient

Dimensions

(Rear

of

rack

ears

to

max

depth):

5.25

in

H

X

19

in

W

X

13

in

D

(13.3

cm

H

X

48.3

cm

W

X

33

cm

D)

Electro-Voice

®

a

Mark

IV

Company

9

operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

Shipping

Weight!

Net

Weight:

Color:

42

lbs

(19.1

kg)

34

lbs

(15.5

kg)

Black

Enclosure:

Rack

mount

chassis,

16

GA

steel,

3/16

in

5052

aluminum

alloy

front

panel

Standard

Accessories:

Optional

Accessories:

4

-

“U“

jumper

plugs

for

octal

sockets

(2

per

socket,

installed)

1

-

Operating

Instruct¬

ions

and

Service

Manual

1

-

5

A/250

V

fuse

(for

220/240

V

ac

use)

APX

24

dB/oct

Linkwitz-

Riley

Crossover

APX-2

24

dB/oct

Link-

witz-Riley

Crossover

with

External

High

Frequency

Output

APX-200

Equalizer

module

for

S200

and

FR200

speakers

Electro-Voice

continually

strives

to

improve

products

and

performance.

Therefore,

the

specifi¬

cations

are

subject

to

change

without

notice.

Slo-Blo®

is

a

registered

trademark

of

Litteifuse,

Inc.

10

Electro-Voice

@

a

Mark

W

Company

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

ELECTRO-VOICE

UNIFORM

LIMITED

WARRANTT'

STATEMENT

Electro-Voice

products

are

guaranteed

against

malfunction

due

to

defects

in

materials

or

workmanship

for

a

specified

period,

as

noted

in

the

individual

product-line

statement(s)

below,

or

in

the

individual

product

data

sheet

or

owner’s

manual,

beginning

with

the

date

of

original

purchase.

If

such

malfunction

occurs

during

the

specified

period,

the

product

will

be

repaired

or

replaced

(at

our

option)

without

charge.

The

product

will

be

returned

to

the

customer

prepaid.

Exclusions

and

Limitations?

The

Limited

Warranty

does

not

apply

to:

(a)

exterior

finish

or

appearance;

(b)

certain

specific

items

described

in

the

individual

product-line

statement(s)

below,

or

in

the

individual

product

data

sheet

or

owner’s

manual;

(c)

malfunction

resulting

from

use

or

operation

of

the

product

other

than

as

specified

in

the

product

data

sheet

or

owner’s

manual;

(d)

malfunction

resulting

from

misuse

or

abuse

of

the

product;

or

(e)

malfunction

occurring

at

any

time

after

repairs

have

been

made

to

the

product

by

anyone

other

than

Electro-Voice

or

any

of

its

authorized

service

representatives.

Obtaining

Warranty

Service?

To

obtain

warranty

service,

a

customer

must

deliver

the

product,

prepaid,

to

Electro-Voice

or

any

of

its

authorized

service

representatives

together

with

proof

of

purchase

of

the

product

in

the

form

of

a

bill

of

sale

or

receipted

invoice.

A

list

of

authorized

service

representatives

is

available

from

Electro-Voice

at

600

Cecil

Street,

Buchanan,

MI

49107

(616/695-6831)

and/or

Electro-Voice

West

at

8234

Doe

Avenue,

Visalia,

CA

93291

(209/651-7777).

Incidental

and

Consequential

Damages

Excluded?

Product

repair

or

replacement

and

return

to

the

customer

are

only

remedies

provided

to

the

customer.

Electro-Voice

shall

not

be

liable

for

any

incidental

or

consequential

damages

including,

without

limitation,

injury

to

persons

or

property

or

loss

of

use.

Some

states

do

not

allow

the

exclusion

or

limitation

of

incidental

or

consequential

damages

so

the

above

limitation

or

exclusion

may

not

apply

to

you.

Other

Rights?

This

warranty

gives

you

specific

legal

rights,

and

you

may

also

have

other

rights

which

vary

from

state

to

state.

Electro-Voice

Electronics

are

guaranteed

against

malfunction

due

to

defects

in

materials

or

workmanship

for

a

period

of

three

(3)

years

from

the

date

of

original

purchase.

Additional

details

are

included

in

the

Uniform

Limited

Warranty

statement.

Electro-Voice

®

a

Mark

IV

Company

11

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

7300A

Power

Amplifier

SERVICE

INSTRUCTIONS

*

CAUTION

*

NO

USER

SERVICEABLE

PARTS

INSIDE.

EXTREMELY

HAZARDOUS

VOLTAGES

AND

CURRENTS

MAY

BE

ENCOUNTERED

WITHIN

THE

CHASSIS.

THE

SERVICING

INFORMATION

CONTAINED

WITHIN

THIS

DOCUMENT

IS

ONLY

FOR

USE

BY

ELECTRO-VOICE

AUTHORIZED

WARRANTY

REPAIR

STATIONS

AND

QUALIFIED

SERVICE

PERSONNEL.

TO

AVOID

ELECTRIC

SHOCK,

DO

NO

PERFORM

ANY

SERVICING

OTHER

THAN

THAT

CONTAINED

IN

THE

OIM

k

ATING

INSTRUCIONS

UNLESS

YOU

ARE

QUALIFIED

TO

DO

SO.

OTHERV't

!

REFER

ALL

SERVICING

TO

QUALIFIED

SERVICE

PERSONNEL.

12

Electro-Voice

®

a

Mark

IV

Company

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

9

SERVICE

INFORM¬

ATION

WARNING!

No

user

servicahle

parts

inside.

Extremely

hazardous

voltages

and

currents

may

be

en¬

countered

within

the

chassis.

The

servicing

information

contained

within

this

document

is

only

for

use

by

Electro-Voice

authorized

warranty

repair

stations

and

qual¬

ified

service

personnel.

To

avoid

electric

shock

DO

NOT

perform

any

servicing

other

than

that

contained

in

the

Operating

In¬

structions

unless

you

are

qualified

to

do

so.

Otherwise,

refer

all

ser¬

vicing

to

qualified

service

per¬

sonnel.

NOTICES

Modifications

to

Electro-Voice

products

are

not

recommended.

Such

modifications

shall

be

at

the

sole

expense

of

the

person(s)

or

company

responsible,

and

any

damage

resulting

there¬

from

shall

not

be

covered

under

warranty

or

otherwise.

9.1

Trimpot

Adjustments

Figure

12

is

a

component

layout

of

the

main

circuit

board

for

one

channel

(both

channels

use

the

same

board).

The

sche¬

matic

of

the

amplifier

is

shown

in

Figure

13.

Several

trimpots

are

provided

for

adjustment.

Resistor

R26

adjusts

the

bias.

Resistor

R23

sets

the

negative

current

limit

and

resistor

R24

sets

the

positive

current

limit.

These

two

resistors

also

affect

the

symmetry

of

clip¬

ping.

The

LF

Cancel

trimpot,

R39,

minimizes

distortion

caused

by

ripple

on

the

power

supply

lines.

9.2

Equipment

Needed

To

precisely

adjust

the

trimpots,

you

must

have

the

fol¬

lowing

equipment:

®

1

—

Oscilloscope

(Tek¬

tronix

2445

or

equivalent)

®

1

—

Distortion

analyzer

(Sound

Technology

1700B

or

equivalent)

®

1

—

16

amp

ac

ammeter

®

1

—

4

0

load

rated

at

600

watts

©

1

—

8

0

load

rated

at

300

watts

@

1

—

Small

non-conducting

flat-blade

screwdriver

or

set

of

plastic

TV

alignment

tools

©

1

—

12

in

jumper

cable

with

alligator

clips

on

each

end

®

Miscellaneous

handtools

(to

remove

the

top

cover)

NOTE:

If

you

need

to

verify

the

amplifier’s

performance

against

the

rated

specifications,

you

must

be

able

to

maintain

the

ac

line

voltage

constant

at

120

V

ac

(or

240

V

ac

if

wired

according

to

Figure

2b).

Therefore,

we

recom¬

mend

a

suitably

rated

variac

(50

ampere

rating

at

120

V

ac).

9.3

A

djusting

R39,

the

LF

Cancel

Trimpot

Shown

in

Figure

6

is

a

distortion

waveform

resulting

from

an

improperly

adjusted

R39.

Notice

the

near

sawtooth

appear¬

ance

of

the

waveform.

The

trace

in

Figure

7

shows

the

resulting

waveform

after

R39

is

properly

adjusted.

Notice

the

reduction

in

ripple.

To

adjust

R39

for

minimum

rip¬

ple,

follow

the

procedures

below:

1.

Turn

power

off

and

dis¬

connect

the

unit

from

its

power

source.

Make

sure

the

unit

is

in

the

Dual

mode

with

8

D

loads

con¬

nected

to

each

channel.

2.

Remove

the

eleven

screws

securing

the

top

cover.

Refer

to

Figure

1

for

the

screw

locations.

3.

Connect

the

sinewave

generator

output

of

the

analyzer

to

the

input

of

Channel

1.

Rotate

the

in¬

put

level

control

of

Chan¬

nel

1

to

its

full

clockwise

position.

Rotate

the

input

level

control

of

Channel

2

to

its

full

counter-clock¬

wise

position.

4.

Apply

power

to

the

amp¬

lifier

and

adjust

the

sine-

wave

generator

for

a

60

Hz,

0

dBu

(0.775

V

rms)

output

level.

For

this

ad¬

justment,

it

is

not

nec¬

essary

to

maintain

a

con¬

stant

120

V

ac

line

input

voltage

under

load.

5.

Find

R39

on

the

compon¬

ent

layout

in

Figure

12.

With

a

non-conducting

or

plastic-shaft

screwdriver,

adjust

R39

for

least

amount

of

ripple

as

shown

in

Figure

7.

6

.

Repeat

steps

3

through

5

for

Channel

2.

7.

Turn

off

the

generator’s

output

signal.

If

you

have

concluded

with

the

test

and

alignment

procedures,

disconnect

the

amplifier

from

its

power

source

and

re-install

the

top

cover

with

the

eleven

screws

pre¬

viously

removed.

9.4

Adjusting

R26,

the

BIAS

Trimpot

Shown

in

Figure

8

is

a

distortion

waveform

resulting

from

an

improperly

adjusted

R26.

Notice

the

pronounced

spikes

at

the

crossover

point

in

the

wave¬

form.

The

trace

in

Figure

9

shows

the

waveform

with

less

pronoun¬

ced

spikes

after

R39

is

properly

adjusted.

To

adjust

R26

for

the

proper

bias,

follow

the

procedures

below:

1

.

Turn

power

off

and

dis¬

connect

the

unit

from

its

power

source.

Make

sure

Electro-Voice

®

a

Mark

W

Company

13

operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

the

unit

is

in

the

Dual

mcxie

with

8

fl

loads

con¬

nected

to

each

channel.

their

full

clockwise

posi¬

tions.

2.

Remove

the

eleven

screws

securing

the

top

cover.

Refer

to

Figure

1

for

the

screw

locations.

3.

Connect

the

sinewave

generator

output

of

the

analyzer

to

the

input

of

Channel

1.

Rotate

the

input

level

control

of

Channel

1

to

its

full

clockwise

position.

Rotate

the

input

level

control

of

Channel

2

to

its

full

coun¬

ter-clockwise

position.

4.

Apply

power

to

the

amp¬

lifier

and

adjust

the

sinewave

generator

for

a

1

kHz,

0

dBu

(0.775

V

rms)

output

level.

For

this

ad¬

justment,

it

is

not

nec¬

essary

to

maintain

a

con¬

stant

120

V

ac

line

input

voltage

under

load.

5.

Find

R26

on

the

compon¬

ent

layout

in

Figure

12.

Rotate

the

shaft

of

R26

slowly

clockwise

until

the

spikes

are

minimized

in

the

distortion

waveform

as

shown

in

Figure

9.

6

.

Repeat

steps

3

through

5

for

Channel

2.

7.

Check

the

ac

idle

current

draw.

With

both

channels

at

idle,

the

ac

line

current

should

be

approximately

0.6

amps

rms.

If

the

idle

current

draw

is

signifi¬

cantly

greater,

rotate

R26

counter-clockwise

slightly

on

both

channels

until

the

idle

current

is

approx¬

imately

0.6

amps

rms.

8

.

Turn

off

the

generator’s

output

signal.

If

you

have

concluded

with

the

test

and

alignment

procedures,

disconnect

the

amplifier

from

its

power

source

and

re-install

the

top

cover

with

the

eleven

screws

previously

removed.

9.5

Adjusting

R23

and

R24,

the

Negative

and

Positive

Current

Limit

Trimpots

Shown

in

Figure

11

is

an

asymmetrically

clipped

waveform

caused

by

an

improperly

adjusted

positive

current

limit

as

deter¬

mined

by

R24.

Had

R23

been

im¬

properly

adjusted,

the

negative

half

of

the

waveform

would

be

clip¬

ped

as

well,

but

its

degree

of

clipping

is

a

function

of

R23

only

and

is

independent

of

R24.

In

the

following

procedures,

you

will

be

adjusting

the

current

limit

thresholds

by

varying

R23

and

R24

in

such

a

way

so

as

to

insure

symmetrical

clipping.

1.

Turn

power

off

and

dis¬

connect

unit

from

power

source.

Make

sure

the

unit

is

in

the

Dual

mode

with

a

4

n

load

connected

to

the

channel

under

test.

2.

Remove

the

eleven

screws

securing

the

top

cover.

Refer

to

Figure

1

for

the

screw

locations.

3.

Connect

the

sinewave

gen¬

erator

output

of

the

anal¬

yzer

to

the

input

of

Cha¬

nnel

1.

Rotate

the

input

level

control

of

Channel

1

to

its

full

clockwise

posi¬

tion.

Rotate

the

input

level

control

of

Channel

2

to

its

full

counter-clock¬

wise

position.

4.

Find

R23

and

R24

on

the

component

layout

in

Fig¬

ure

12.

With

a

small

non¬

conducting

screwdriver,

rotate

R23

and

R24

to

5.

Apply

power

to

the

amp¬

lifier

and

adjust

the

sine¬

wave

generator

for

a

1

kHz,

-10

dBu

(0.245

V

rms)

output

level.

For

this

adjustment,

it

is

not

nec¬

essary

to

maintain

a

con¬

stant

120

V

ac

line

input

under

load.

6

.

Increase

the

level

of

the

generator

until

the

output

of

the

amplifier

reaches

34.6

V

rms

(which

corre¬

sponds

to

300

watts

out¬

put

into

the

4

O

load).

7.

While

monitoring

the

dis¬

tortion

waveform

on

the

oscilloscope,

rotate

R23

counter-clockwise

until

the

negative

half

of

the

waveform

just

begins

to

visibly

clip

(more

pro¬

nounced

spikes

will

ap¬

pear

on

the

distortion

waveform).

Then,

rotate

slightly

clockwise

just

until

the

visible

clipping

disappears

and

the

spikes

in

the

distortion

waveform

reduce

to

their

pre-clip

level.

8

.

Repeat

Step

7

for

the

posi¬

tive

current

limit

pot

R24.

You

may

have

to

slightly

re-adjust

R23.

9.

If

R23

and

R24

are

pro¬

perly

adjusted,

the

cha¬

nnel

should

clip

symmet¬

rically

(@

1%

THD)

at

ap¬

proximately

450

watts

as

shown

in

Figure

11.

10

.

Repeat

Steps

3

through

9

for

Channel

2.

11.

Turn

off

the

generator’s

output

signal.

If

you

have

concluded

with

the

test

and

alignment

procedures,

14

Electro-Voice

®

a

Mark

IV

Company

operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

disconnect

the

amplifier

from

its

power

source

and

re-install

the

top

cover

with

the

eleven

screws

previously

removed.

5.6

Checking

the

Short

Circuit

Current

With

one

channel

oper¬

ating

at

full

rated

power

into

an

4

Cl

load,

carefully

short

the

output

terminals

using

the

12

inch

jump¬

er

cable

while

monitoring

the

ac

line

current.

The

ac

line

current

draw

under

a

short

circuit

con¬

dition

should

be

at

least

3.5

amps,

but

no

more

than

4

amps

rms).

If

it

exceeds

4

amps,

re-adjust

R23

and

R24

by

rotating

them

slightly

counter-clockwise,

both

by

ap¬

proximately

the

same

amount,

un¬

til

the

ac

line

current

is

typically

3.5

amps.

Repeat

this

procedure

for

Channel

2.

9.7

Ordering

Replacement

Parts

To

order

replacement

parts,

look

up

the

ordering

number

from

the

component

parts

listing

and

call

(405)

324-5311,

FAX

(405)

324-8981,

or

write:

Electro-Voice

Replacement

Parts

Sales

600

Cecil

Street

Buchanan,

MI

49107

U.S.A.

9.8

Factory

Service

If

factory

service

is

required,

ship

the

unit

in

its

original

packing

prepaid

to:

Electro-Voice

Customer

Service/Repair

600

Cecil

Street

Buchanan,

MI

49107

U.S.A.

Tel:

(616)

695-6831

FAX:

(616)

695-1304

Electro-Voice

Customer

Service/Repair

8324

Doe

Avenue

Visalia,

CA

93219

U.S.A.

Tel:

(209)

651-7777

FAX:

(209)

651-0164

Enclose

a

note

describing

the

pro¬

blem

in

as

much

detail

as

possible.

Include

any

additional

helpful

in¬

formation

such

as

test

conditions,

where

used,

how

used,

etc.

9.9

T

echnical

Assistance

For

applications

assistance

or

other

technical

information,

contact

the

Technical

Services

Manager.

You

can

call

(616)

695-

6831,

TWX

810-270-31353,

FAX

(616)

695-1304,

or

write:

Electro-Voice

Technical

Services

Manager

600

Cecil

Street

Buchanan,

MI

49107

U.S.A.

Electro-Voice

®

a

Mark

TV

Company

15

Figure

lH

Improperly

Adjusted

Positive

Current

Limit

Figure

11

Properly

Adjusted

Pos

and

Neg

Current

Limit

1'

Electro-Voice

®

a

Mark

TV

Company

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

Electro-Voice

®

a

Mark

IV

Company

Operating

and

Service

Instructions

for

the

Electro-Voice

7300A

Power

Amplifier

SCHEflATIC

CHl(X)

CH2(10X)

Electro-Voice 7300A Operation manual

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