Ashly Power Amplifiers FET-200 User manual

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ASHLY

MOS-FET

POWER

AMPLIFIERS

OPERATING

INSTRUCTIONS

ASHLY

AUDIO

INC

TABLE

OF

CONTENTS

Page

!•

Introduction

2

2.

Unpacking,

Installation

3.

Input

&

Output

Connections,

Stereo

Operation

5

4.

Mono

Operation

7

5.

Bridging

Operation

7

6.

Meter

Display

g

7.

Thermal

Status

Indicator

g

3.

Specifications/Block

Diagram

g

9.

Definition

of

Terms

9

1

INTRODUCTION

The

Ashiy

tEX-200

and

FET-500

represent

an

entirely

new

breed

of

power

amplifiers

which

are

destined

to

replace

conventional

amps

in

virtually

every

application.

Far

from

being

just'another

variation

on

well

worn

designs,

these

amplifiers

have

been

engineered

from

the

ground

up

to

take

full

advantage

of

au

exciting

new

semiconductor

technology

which

has

recently

become

availabie_the

Power

MOS-FET

(metal-oxide-semiconductor,

field-effect-

ttausistor).

Combining

many

of

the

desireable

operating

characteristics

of

vacuum

tubes

with

the

efficiency

of

transistors,

the

MOS-FET

offers

superior

audio

fidelity

and

introduces

an

entirely

new

level

of

field

reliability.

Ashiy

power

amplifiers

put

all

of

these

features

together

into

a

carefully

thought

out,

roadworthy,

user-oriented

package

which

will

provide

years

of

maintenance—free

service.

WHY

MOS-FET’3?

coavtntiouai

power

amplifier

design

as

typically

produced

a

circuit

which

consists

of

two

parts;

1)

the

amplifier

itself,

and

2)

a

collection

of

protective

circuits

which

keep

the

amplifier

from

destroying

itself

and

the

speakers

it

is

driving.

Some

of

the

more

common

protective

circuits

include

VI

iimitiug,

ciiermai

feedback,

detectors

that

monitor

DC

at

the

output

terminals,

short

circuit

protection

and

turn-on

delay

circuits

that

keep

the

speatcers

from

jumping

out

of

their

cabinets

when

power

is

applied.

The

result

has

typically

been

a

compromise

in

audio

performance,

greatly

compounded

electronic

and

mechanical

complexity,

and

amplifiers

which

are

intolerant

of

less

than

ideal

operating

environments.

The

basic

weakness

of

these

amplifiers

has

always

been

the

power

output

transistors

themselves,

which

are

prone

to

failure

as

a

result

of

"thermal

runaway

.

This

breakdown

occurs

when

the

amplifier

is

delivering

a

lot

of

power

and

begins

to

heat

up.

Increasing

temperature

produces

an

increase

in

coiltator

current

in

the

output

transistors,

which

in

turn

produces

more

heat.

If

this

cycle

is

unchecked,

the

transistor

will

be

destroyed.

ProDaoiy

tiic

greatest

advantage

of

power

MOS-FET's

for

professional

audio

use

is

their

complete

immunity

to

thermal

runaway.

Not

only

does

this

remove

the

primary

failure

mechanism

of

the

conventional

amplifier

and

eliminate

the

need

for

elaborate

thermal

protection

circuits,

it

also

allows

the

design

engineer

to

use

a

mucii

nigher

quiescent

current

in

the

amplifier's

output

stage,

thereby

insuring

that

the

output

devices

are

always

operating

in

their

most

lineal

region.

This

results

in

consistently

lower

distortion.

In

addition,

the

simpler

input

drive

requirements

of

the

MOS-FET

devices

makes

possible

a

clean,

concise

amplifier

design.

The

resulting

reduction

in

component

count

and

internal

wiring

provides

for

a

compact

design

and

enhanced

reliability.

THE

ASHLY

DESIGN

Our

goal

in

designing

the

FET—200

and

FET—500

was

to

produce

amplifiers

that

combine

the

sonic

excellence

of

a

high-end

stereo

amp

with

the

ruggedness

and

stamina

necessary

in

pro

audio.

2

ELECTRONIC

Both

amplifiers

are

fully

complementary,

push-pull

type

with

totally

discreet,

high

voltage,

wide

bandwidth

electronics.

This

approach

inherently

assures

low

noise,

low

distortion,

and

excellent

transient

response.

Inputs

are

bringing,

active

balanced

(transformerless),

equipped

with

both

1/4"

jacks

and

XLii-type

connectors

of

both

sexes

to

facilitate

linking

several

amplifiers

together.

All

input

connections

can,

however,

operate

as

balanced

or

unbalanced.

This

is

determined

by

the

connector

used

in

conjunction

with

the

input.

Stereo,

mono

and

bridging

modes

are

user

selectable

by

means

of

rear

panel

switches,

requiring

no

internal

modifications

or

additional

components.

All

electronic

components

are

conservatively

rated

and

are

mounted

on

a

rugged

glass-epoxy

circuit

board.

An

efficient

U-I

laminated

power

transformer

saves

space

and

minimizes

magnetic

flux

leakage,

permitting

other

low-level

equipment

to

be

mounted

above

or

below

the

amplifier

with

no

danger

of

induced

hum.

Large

value,

computer

grade

electrolytic

capacitors

assure

long

service.

Two

lU-segment,

27

dB

range

LED

meter

displays

provide

an

easily

viewed

indication

of

power

levels,

and

a

separate

LED

indicates

thermal

overload.

HECiL\NICAL

ihe

Ashly

MOb-EST

power

amplifiers

are

packaged

in

a

rugged,

one-piece

welded

16

gauge

steel

chassis

with

an

anodized

aluminum

front

panel

and

an

easily

removed

steel

top

cover.

The

chassis

and

ail

internal

components

are

integrated

into

a

single,

rigid

unit.

The

FET-500

requires

5

1/4"

of

rack

space

and

ttie

FET-200

requires

only

3

1/2".

The

power

transformer

is

located

near

the

front

of

each

amplifier,

reducing

mechanical

stress

on

the

chassis.

Each

channel's

electronics

and

heat

sink

are

combined

into

a

compact,

plug

in

module

which

can

be

removed

from

the

amplifier

in

seconds.

Hard

wiring

is

at

an

absolute

minimum.

Large

heat

sinks

and

an

aerodynamic

internal

design

permit

the

use

of

an

ultra-quiet,

slow

speed

fan

which

pulls

air

in

through

the

front

panel

directly

across

the

heat

sinks

and

power

transformer,

and

out

through

the

rear

panel.

It

is

unnecessary

to

provide

space

or

ventilation

above

or

below

the

amplifier,

allowing

for

economical

use

of

rack

space.

The

amplifier's

output

connectors

are

conveniently

arranged

on

standard

3/4"

spacing

tor

quick

interconnect

via

banana

plugs,

delecting

the

bridging

output

involves

only

moving

the

banana

plug

to

the

two

center

(RED)

connectors.

Both

the

AC

line

and

the

speaker

terminals

are

fused

protected.

Fuses

can

be

removed

instantly

without

tools.

There

are

no

internal

fuses.

IN

USE

The

result:

better

sounding

amplifiers,

remarkably

un—fussy

about

how

you

use

them.

They

will

tolerate

low

impedance,

highly

reactive

loads

and

hot,

crowded

racks.

They

are

highly

immune

to

RF

interference

and

will

not

be

damaged

by

intermittent

short

circuits—sustained

shorts

will

simply

blow

the

output

fuse.

Due

to

their

balanced

circuit

design,

the

use

of

delay

circuits

and

output

relays

are

unnecessary.

There

is

no

turn-on

thump

and

the

volume

controls

can

remain

up

when

power

is

applied

and

removed.

Both

amps

will

keep

on

running

right

through

a

brown-out,

even

when

line

voltages

fall

to

as

low

as

20

volts!

3

This

manual

will

explain

the

proper

installation

and

use

of

Ashly

amplifiers

and

their

controls.

Please

read

it

carefully

and

refer

to

it

in

case

of

difficulty.

UNPACKING

As

part

of

our

system

of

quality

control,

every

Ashly

product

is

carefully

inspected

before

leaving

the

factory

to

ensure

flawless

appearance.

After

un¬

packing

please

inspect

for

any

physical

damage.

iave

the

shipping

carton

and

all

packing

materials,

as

they

were

carefully

designed

to

reduce

to

a

minimuiu

the

possibility

of

transportation

damage

suould

the

unit

again

require

packiu,;

and

shipping.

In

the

event

that

damage

has

occurred,

immediately

notify

your

dealer

so

chat

a

written

claim

to

cover

the

aamages

can

be

initiated.

THE

RIGHT

TO

ANY

CLAIM

AGAINST

A

PUBLIC

CARRIER

CAN

BE

FORFEITED

IF

THE

CARRIER

IS

NOT

NOTIFIED

PROMPTLY

AND

IF

THE

SHIPPING

CARTON

AND

PACKING

MATERIALS

ARE

NOT

AVAILABLE

FOR

INSPECTION

BY

THE

CARRIER.

SAVE

ALL

PACKING

MATERIALS

UNTIL

THE

CLAIM

HAS

BEEN

SETTLED.

INSTALLATION

Ashly

MOS-FET

amplifiers

are

designed

to

mount

in

a

standard

ly"

equipiacnf

rack.

Since

forced-air

cooling

is

employed,

it

is

not

necessary

to

leave

any

ventilation

space

above

or

below

the

amplifier.

This

permits

efficient

use

of

rack

space

and

multiple

stacking

of

amplifiers.

The

only

precaution

to

observe

is

to

leave

the

front

panel

air

inlets

and

rear

panel

fan

outlet

unobstructed.

The

use

of

four

front

panel

screws

is

recommended

to

evenly

distribute

the

stress

on

the

panel.

The

amplifier

chassis

is

sufficiently

strong

to

support

itself

by

the

front

panel

alone

in

permanent

installations

or

where

the

rack

is

moved

only

occasionally.

For

amplifiers

which

will

spend

much

of

their

time

in

transit,

it

is

suggested

that

some

method

of

rear

support

be

used.

Connect

all

amplifiers

to

a

3-wire

grounded

outlet

supplying

120

Volts

50-60Hz

Maximum

power

consumption

is

600

watts.

Maximum

current

required

is

5

amps.

4

INPUT

AND

OUTPUT

CONNECTIONS

STEREO

OPERATION

Connections

for

stereo

operation

are

shown

in

figure

4

below.

R

L

V-

OUTPUTS

^

MIXING

CONSOLE

+

+

Figure

4

Stereo

Operation

INPUTS

The

input

of

Asnly

amplifiers

is

a

balanced

bridging

type,

with

an

input

impedance

of

lOk

ohms.

Use

of

the

balanced

input

provides

superior

hum

and

noise

rejection

while

eliminating

ground

loops.

The

input

may

also

be

used

in

a

single-ended,

unbalanced

mode

by

simply

using

unbalanced

input

connectors.

Each

channel

provides

a

choice

of

either

1/4"

jacks

or

XLR

input

connectors.

All

four

connectors

are

in

parallel.

Since

only

one

of

the

four

connectors

is

used

as

an

input

at

any

one

time,

the

others

may

be

used

to

jumper

other

amplifiers

to

the

same

source.

Signal

connections

are

as

follows:

The

(+)

or

in-phase

connection

is

on

the

tip

of

the

1/4"

stereo

phone

jacks,

and

is

on

pin

3

of

the

XLR

connectors.

The

(-)

or

out-of-phase

connection

is

on

the

ring

of

the

phone

jacks

and

on

pin

2

of

the

XLR's.

Chassis

ground

and

shield

is

on

the

sleeve

of

the

1/4”

jacks

and

pin

1

of

the

XLR's.

5

When

feeding

the

amplifier

from

an

unbalanced

source,

use

either

an

XLk

connector

or

a

standard

stereo

1/4"

phone

plug

and

connect

the

signal

"hot"

connection

to

XLR

pin

3

or

to

the

phone

plug

tip.

Connect

signal

ground

to

the

XLR's

pins

1

and

2

or

to

the

phone

plug’s

ring

and

sleeve.

The

latter

uiay

also

be

accomplished

by

simply

inserting

a

standard

1/4"

mono

phone

plug,

which

automatically

connects

ring

and

sleeve

together.

In

the

special

case

where

the

amplifier

is

physically

mounted

in

the

same

rack

with

the

signal

source

that

is

feeding

it,

you

may

wish

to

use

an

alternate

connection

system

to

avoid

ground

loops;

connect

the

signal

hot

to

XLR

pin

3

or

to

the

phone

plug

tip.

Connect

signal

ground

to

XLR

pin

2

or

to

the

phone

plug

ring.

Leave

the

XLR’s

pin

1

and

the

jack

sleeve

unconnected.

SPEAKER

OUTPUTS

The

speaker

output

connections

are

combination

banana

jacks/binding

posts

spaced

on

standard

3/4"

centers.

Speaker

connections

may

be

accomplished

either

by

inserting

banana

plugs

or

by

feeding

bare

stranded

wire

into

tho

binding

posts.

Figure

6

MONO

OPERATION

With

the

MONO

switch

depressed,

the

Channel

1

input

will

feed

both

sides

of

the

amp.

Volume

for

both

sides

is

controlled

with

the

channel

1

LEVEL

control.

IN

BRIDGING

OPERATION

Ashly

amplifiers

are

in

ttie

bridging

mode

when

both

the

MONO

switch

and

BRIDGING

switch

are

depressed.

In

this

mode,

the

channel

one

input

feeds

both

sides

of

the

amp,

but

the

phase

of

the

channel

two

amplifier

is

inverted

180

degrees,

so

that

the

two

amplifiers'

outputs

are

out

of

phase.

The

speaker

connection

is

then

made

to

the

two

RED

output

Jacks,

as

shown

in

Figure

8.

The

black

output

jacks

are

not

used.

7

METERS

The

meters

on

the

front

panel

respond

to

the

peak

output

voltage

of

the

amplifier

as

measured

at

the

speaker

terminals.

A

ten

segment,

three

color

LED

display

covers

a

twenty-seven

decibel

range.

the

LED’s

on

one

channel

light

up

and

stay

on

with

only

a

small

input

signal,

a

blown

speaker

fuse

or

faulty

speaker

wiring

is

indicated.

THERMAL

STATUS

INDICATOR

In

the

event

that

the

amplifier

overneats,

it

will

automatically

shut

down

and

the

green

THERMAL

STATUS

LED

will

turn

off.

The

fan

will

continue

to

run,

and^

vdien

the

heat

sink

temperature

returns

to

normal

the

green

THERMAL

STATUS

LED

will

come

back

on

and

the

amplifier

will

turn

itself

back

on.

It

is

extremely

unlikely

that

any

combination

of

musical

program

material

and

load

conditions

will

activate

the

thermal

shutoff

mechanism

in

normal

use.

Should

overheating

occur,

check

to

be

sure

that

the

air

flow

in

front

of

and

behind

the

amplifier

has

not

been

blocked.

Note^

that

there

is

a

very

generous

safety

margin

between

the

temperature

required

to

activate

the

thermal

cutouts

and

temperatures

which

could

damage

components

in

the

amplifier.

SPECIFICATIONS:

FET-200

RATED

POWER

100

Wotts/channel

Both

channels

driven

into

8

ohms

160

Wofts/chonnel

Both

channels

driven

into

4

ohms

320

Watts

into

8

ohms

bridged

mono

FET-500

RATED

POWER

250Wcitts/channel

Both

chonneis

driven

into

8

ohms

400Watts/channel

Both

channels

driven

into

4

ohms

SOOWotts

into

8

ohms

bridged

mono

FREQUENCY

RESPONSE

HARMONIC

DISTORTION

IM

DISTORTION

(SMPTE)

DAMPING

FACTOR

±.5db

lOHz-SOKHz

<

.05%

20Hz-20kHz.

100

watts,

8

Ohms

<

.01%

100

watts,

8

ohms

>

100

20Hz-20kHz

SLEW

RATE:

50V/

fisec

RISE

TIME

2

fisec

10%-90%

FREQUENCY

RESPONSE

±.5db

10Hz-50kHz

HARMONIC

DISTORTION

IM

DISTORTION

(SMPTE)

DAMPING

FACTOR

SLEW

RATE:

RISE

TIME

<

.05%

20Hz-20kHz,

100

watts,

8

Ohms

<

.01%

100

watts,

6

ohms

>

100

20Hz-20kHz

50V/

fisec

2

fisec

10%-90%

8

DEFINITION

OF

TERMS

AS

USED

IN

THIS

MANUAL

ACTIVE

ectronic

circuits

which

use

devices

such

as

transistors

and

c

rcuits,

and

which

are

capable

of

voltage

and

power

gain

as

OSS.

xrcuits

using

only

resistors,

capacitors,

transformers,

referred

to

as

passive.

integrated

well

as

etc.,

are

AMPLITUDE

voltage

level

of

a

signal.

May

be

measured

in

volts

or

decibels,

era

y

corresponds

to

the

volume

or

intensity

of

an

audio

signal.

BALAfJCED

^

circuit

arrangement

in

which

two

conductors

are

designated

as

signa

~)»

and

the

third

is

a

shield

and

chassis

ground.

The

sigua

ines

are

of

opposite

polarity

at

any

given

moment,

and

are

of

equal

potential

with

respect

to

ground,

balanced

input

amplifiers

are

use

on

a

Ashly

SC

series

products^to

improve

hum

and

noise

rejection,

umpering

signal

minus

(—)

to

ground

provides

an

unbalanced

input.

BREATHING

A

usually

undesirable

fluctuation

of

background

noise

compressor

action.

(Also

called

"Pumping.”)

resulting

from

BUTTERWORTH

f

particular

filter

response

shape.

The

response

is

ssentially

flat

within

the

pass-band,

is

3dB

down

at

the

cutoff

frequency,

and

continues

to

attenuate

at

a

constant

slope.

Also

called

a

maxima

y

t

at

or

critically

damped”

filter

shape,

it

is

very

popular

for

crossovers

and

shelving

filters.

CENTER

FREQUENCY

The

frequency

(or

parametric

equalizer

boost/cut

control

has

pitch)

at

which

a

filter

is

most

effective.

In

a

»

it

refers

to

the

frequency

where

a

particular

maximum

effect.

COMPRESSOR

An

amplifier

wliich

reduces

predetermined

"threshold."

its

gain

as

its

input

is

increased

beyond

a

DAMPING

A

force

which

opposes

the

tendency

of

a

system

to

oscillate,

dB

A

unit

by

wnich

audio

levels

can

be

COMPARED.

Often

thoroughly

misun

erstood

are

the

concepts

that

decibels

represent

the

level

of

a

signal

compared

to

some

reference

level

(15

dB

cut

means

a

certain

level

ess

an

a

previous

level

the

absolute

level

of

the

signal

need

not

decibels

are

a

logarithmic

unit.

Some

handy

numbers

to

remember

when

dealing

with

decibels;

+3

dB

-

Double

Power

+10

dB

=

lOX

Power

+6

dB

-

Double

Amplitude,

+20

dB

=

lOX

Amplitude,

lOOX

Power

Quadruple

Power

9