Adcom GFP-345 User manual

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1

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HIGH

DEFINITION

PREAMPLIFIER

INTRODUCTION

Please

read

thoroughly

these

operating

instructions

for

the

GFP-345

before

connecting

or

attempting

to

operate

this

unit

For

your

own

benefit,

follow

all

the

instructions

in

this

manual

and

save

it

for

future

reference.

The

ADCOM

GFP-345

is

a

result

of

a

thorough

examination

and

reevaluation

of

all

factors

affecting

the

sonic

performance

of

preamplifiers.

A

great

deal

of

care

was

taken

to

insure

that

the

audio

performance

of

the

GFP-345

could

be

maintained

for

years

to

come

by

the

selection

of

top-quality

components

and

circuit

topologies.

The

result

is

a

preamplifier

which

is

as

musical-sounding

as,

and

which

preserves

the

dynamic

contrasts

of,

an

original

performance.

I^

in

fh

3

at

'°

n

i

nd

°

per

‘*

,,onof

the

GFP-345

are

described

in

the

following

pages.

We

sincerely

hope

you

will

value

and

enjoy

the

considerable

attention

we

have

given

its

design

and

construction.

This

manual

has

been

written

to

help

you

understand

the

correct

operation

of

the

GFP-345.

Please

read

it

carefully

to

fully

comprehend

all

its

features

and

functions

and

thereby

derive

the

maximum

performance

from

its

use

in

your

system.

FEATURES

GFP-345

I!*®^

3

S?«

t

0dei

!

d

L

a

J!f

r

c

«

e

h

'

9hly

innovative

internal

designs

and

circuit

topologies

of

both

the

"Reference

Standard

GFP-565

and

GFP-555H

preamplifiers

-

accordingly,

it

is

setting

new

standards

for

products

in

its

price

category.

Many

of

the

most

significant

performance

characteristics

of

the

GFP-565

and

GFP-555II

have

been

built

into

the

GFP-345.

The

power

supply

and

low

impedance

outputs

were

designed

to

preserve

music

dynamics.

The

amplification

staqes

employ

direct-coupled,

custom-designed,

linear-gain

amplifiers

operating

in

full

Class

A

to

insure

the

minimum

distortion

and

low-noise

required

for

digital-source

material.

Buffered

tape

outputs

insure

input-signal

integrity,

and

precl

ude

interference

with

the

main-source

signal

in

the

preamplifier's

circuits

when

digital

or

cassette

tape

recorders

are

connected

(even

when

these

are

not

operating).

The

optional

phono

preamplifier

(available

as

a

plug-in

board:

the

PHO-802A)

delivers

the

quietest

obtainable

performance

with

unmatched

record-equalization

accuracy

and

lowest

distortion.

Operating

in

full

class

A

its

unrestricted

dynamics

and

musical

accuracy

are

delivered

at

surprisingly

modest

cost.

The

GFP-345

contains

the

highest-quality

components;

never

before

available

in

a

component

of

such

This

should

insure

stable,

dependable

operation

and

long,

trouble-free

life.

moderate

cost.

Low-impedance

power

supply

for

best

regulation

and

optimal

circuit

performance.

This

type

of

design

insures

that

music

dynamics

are

delivered

through

the

preamplifier

without

compression.

•

Thick

power-supply

traces

on

printed

circuit

board

for

minimal

losses

and

improved

voltage

stability.

This

technique

insures

constant

voltage

to

all

the

circuitry,

regardless

of

volume

or

dynamic

demands

of

the

music.

•

AM

capacitors

are

state-of-the-art

electrolytics

and

film

capacitors

with

very

low

ESR

and

unsurpassed

sonic

purity

This

design

feature

provides

an

audible

benefit,

the

lowest

possible

distortion

of

music

signals.

•

Overdesigned

mu-metal-shielded

power

transformer

for

better

regulation.

This

transformer

design

eliminates

stray

hum

fie

ds

for

lowest

noise

and

provides

undiminished

voltage

to

circuits

for

best

performance

under

any

demands

•

Precision

programmable

regulators

for

stabilized,

constant

DC

voltages,

regardless

of

load.

This

type

of

requlator

insures

stable

operation

of

all

circuits

regardless

of

the

dynamic

demands

of

the

music

being

played.

•

Amplifier

stages

use

ADCOM

premium-grade

ICs

selected

for

their

linear

operation

and

sonic

quality.

These

linear

amplifiers

insure

extremely

low

noise,

low

distortion

and

low

DC

offset

for

best

performance

with

either

set

of

hrOOmn

At

ifmirn

•

Amplifiers

are

operated

in

pure

Class-A

mode

to

insure

lowest

distortion

the

level

control.

regardless

of

the

signal

level

or

setting

of

•

Entire

signal

path

is

direct-coupled

from

input

to

output.

Direct

coupling

minimizes

the

number

of

components

signal

must

go

through,

preventing

degradation

of

the

music.

*

I

W

th

Se

,

,

f°'?^

t

"2^

TPUTS

LAB

ar

®

direct

‘

coupled

-

The

V

Provide

a

signal

in

the

most

straightforward,

simplest

patn.

OUTPUTS

NORM

are

capacitor-coupled

using

precision,

high-grade

film

capacitors

for

power

amps

which

can

not

accept

ultra-wide

bandwidth

inputs.

1

•

Low-output-impedance

(100

ohms)

from

both

sets

of

outputs

to

reduce

interaction

of

connecting

cables

and

other

equipment

and

preserve

music

dynamic

contrasts.

•

Five

sets

of

inputs,

front

panel

controlled,

including

TAPE

IN;

six

sets

if

the

EXTERNAL

PROCESSOR

IN

jacks

are

used

also

as

an

auxiliary

input.

•

*f

Pe

°^

tpu,s

{10

°

ohms)

to

P

erf

ectly

interface

with

any

type

of

tape

recorder.

This

technique

allows

^

recorder

-

including

DAT

and

DCC.

and

insures

the

best

recording

characteristics

independently

of

the

cable

used

and

the

load

impedance

of

the

tape

recorder

inputs.

•

Buffered

tape

outputs

to

preserve

input-source-signal

integrity

and

preclude

"loading”

of

the

signal-source

components

and

distortion.

Buffering

prevents

the

degradation

of

the

source

signal

caused

by

most

tape

recorders

when

they

are

connected

to

the

tape

outputs.

The

buffers

insure

that

the

integrity

of

the

internal

signal

path

will

not

be

affected

by

the

tape

recorder

used.

•

H.

r

°

n

,H

Pa

:

e,

.;

SWitChab,e

proc

l

essor

l0

°P'

Sh

ortens

the

signal

path

by

switching

the

processor

in

and

out

of

the

circuit

directly

on

the

main

circuit

board.

Allows

the

processor

to

be

removed

totally

from

the

circuit

when

not

needed.

•

All

high-grade

construction

parts

including

1%.

Roederstein

metal-film

resistors

and

all

metallized-film.

precision

capacitors

throughout.

These

components

helps

the

GFP-345

achieve

lower

noise

levels

and

lower

signal

degradation

than

preamps

selling

for

many

times

its

price.

•

Extremely-low-noise,

optional

phono

preamplifier

board

(PHO-802A)

with

virtually

zero

RIAA

error,

optimized

for

high-output

mov.ng-co.l

and

moving-magnet

cartridges

plus

direct-coupled

signal

output

for

maximum

bass

impact

and

dynamic

response.

These

features

will

provide

the

flattest,

lowest-noise.

lowest-distortion

response

from

a

phono

cartridge

and

musically

satisfying

reproduction

from

any

vinyl

record.

•

J-°^‘

,mpedance

-

RIAA-equalization

network.

This

unique

network

insures

the

lowest

achievable

noise

level

in

a

pnono

preamp.

UNPACKING

THE

GFP-345

ariu

r

wn^rr:nnni

the

'T^

it

^

as

1

car

«

,ul|

y

inspected

'or

physical

imperfections

and

electrical

performance

as

fnsure

a

orolct

fS2S«

«

VCo

"

tro,

-

™

S-

al

°"9

with

full

operational

and

mechanical

testing,

should

insure

a

product

flawless

in

both

appearance

and

performance.

After

you

have

unpacked

the

GFP-345

inspect

it

for

poss

i

b

Hty

oTt^a

n

s

do

rtet

km

damn

no

TZT

al

!

p

acking

materials

as

the

Y

are

intended

to

reduce

to

a

minimum

the

^

a

^

.

6

pr0dUC

'

ever

need

t0

^

shipped

again.

In

the

unlikely

event

damage

has

damage

<UnbeiJSiat^

*

^

'

m

y

and

request

the

name

of

,he

carrier

so

tha

»

a

written

claim

to

cover

shipping

RIGHT

TO

A

CLAIM

AGAINST

A

PUBLIC

CARRIER

CAN

BE

FORFEITED

IF

THE

CARRIER

IS

NOT

NOTIFIPn

^cdc^i!

IN

WRITING

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.^

INSTALLING

THE

GFP-345

Although

the

GFP-345

does

not

generate

much

heat,

you

will

help

insure

its

long-term,

trouble-free

operation

if

vou

keen

should

SrbeSS?

9

?

T

h

radiators

or

h

ot-airducts,

and

provide

reasonable

ventilation.

The

GFP-345

p

'

acad

w,t

.

h

0,her

heat-producing

components

in

a

cabinet

or

enclosure

lacking

free

air

flow.

If

placed

the

component

hea,

'

producmg

component

’

such

33

a

power

amplifier,

please

allow

a

minimum

of

three

Inches

between

For

use

in

professional

installations,

the

GFP-345

may

be

mounted

in

a

standard

19-inch

rack-mount

adaptors

available

through

ADCOM

dealers.

rack

using

the

optional

RM-3

CONNECTING

THE

GFP-345

7

m

d

S

pe

"

d

°

n

the

quality

of

the

'

nterc

onnection

of

both

the

preamplifier

and

its

associated

equ£ment.

All

the

input-

and

output-signal

connections

should

be

made

only

with

hiqh-aualitv

low-loss

audio

cables.

LEFT

CHANNEL

and

RIGHT

CHANNEL

inputs

and

outputs

are

cleaHy

labelled

on

the

r2r

panel

2

NOTE

WHENEVER

CONNECTIONS

TO

OR

FROM

THE

GFP-345

ARE

BEING

MADE,

BE

CERTAIN

ALL

ASSOCIATED

COMPONENTS

ARE

TURNED

OFF.

GND

O

Ground

connection

to

chassis

is

provided

primarily

to

connect

phonograph

(turntable)

ground

terminals.

Most

turntables

are

supplied

with

a

separate

ground

wire

to

help

eliminate

hum.

Connect

the

separate

ground

wire,

if

supplied

with

your

turntable,

to

the

GND

Q

terminal.

The

GND

Q

terminal

can

also

be

used

to

connect

the

chassis

of

the

GFP-345

directly

to

the

center

screw

of

your

AC

wall

outlet

or

other

good

“earth”

connection

such

as

a

water

pipe

or

radiator.

This

earth

connection

may

be

useful

in

areas

of

high

RF

interference,

and

may

help

to

minimize

noise

particularly

when

playing

low-

output-level

phonograph

cartridges

(see

section

PHONO

(PHO-8Q2A

OPTION)

©

following).

NOTE

Although

the

GNO

Q

connection

is

probably

the

best

place

at

which

to

connect

your

system

to

a

good

earth

ground,

it

should

be

pointed

out

that

only

one

connection

to

an

earth

ground

is

to

be

made

in

any

system.

Otherwise

what

is

commonly

known

as

a

“ground-loop”

will

be

caused

and

hum

and

noise

may

increase

sufficiently

to

become

a

nuisance.

In

any

system,

only

one

ground

connection

can

be

made

to

earth.

If

one

of

your

components

is

supplied

with

a

three-prong

AC

connector

which

is

plugged

into

the

AC

wall

outlet,

earth

connection

will

be

made

through

this

plug

and

additional

ground

connections

are

not

recommended.

Similarly,

if

the

system's

units

are

mounted

in

a

rack

and

ground

connection

between

chassis

is

made

through

the

rack

mounting,

special

techniques

must

be

undertaken

to

minimize

ground-loops

and

subsequent

noise.

A

detailed

discussion

of

ground-loops

with

methods

for

their

elimination

is

beyond

the

scope

of

this

manual.

AUX

1

©

This

set

of

input

jacks

is

for

use

with

a

high-level

signal

source,

such

as

a

tape

player,

the

audio

signal

from

a

video-disc

player,

or

video-cassette

recorder

(VCR).

The

load

impedance

of

this

input

is

approximately

22,000

ohms.

This

input

can

also

be

converted

for

use

with

an

analog

disc

turntable

if

the

optional

PHO-802A

board

is

installed

onto

the

main

PCB

of

the

GFP-345.

This

is

a

procedure

best

left

to

your

dealer,

or

ADCOM

authorized

service

personnel.

It

is

not

recommended

you

undertake

the

installation

of

the

PHO-802A

board

within

the

GFP-345

yourself.

PHONO

(PHO-802A

OPTION)

©

To

use

an

analog

disc

turntable

with

the

GFP-345

requires

installation

of

the

optional

PHO-802A

phono

preamp

board

onto

the

main

PCB

of

the

GFP-345.

Once

the

PHO-802A

board

is

installed,

the

input

jacks

marked

AUX

1

©

are

then

usable

with

any

high-output

moving-coil

or

moving-magnet

phono

cartridge.

These

two

standard

RCA

jacks

will

accept

all

common

RCA

plugs,

one

for

each

channel,

left

and

the

right,

usually

supplied

at

the

ends

of

the

turntable's

cables.

LEFT

CHANNEL

and

RIGHT

CHANNEL

inputs

are

clearly

labelled

and

their

routing,

even

when

the

PHO-802A

board

is

installed,

will

remain

left

and

right

as

indicated.

Determine

the

exact

color

coding

or

markings

on

your

turntable’s

cables

for

left

and

right

channels

in

order

to

insure

the

correct

connections.

The

PHO-802A

circuit

is

designed

to

accept

the

signal

from

any

high-output

moving-coil,

moving-magnet,

induced-magnet,

moving-iron

or

variable-reluctance

car¬

tridge,

the

output

from

which

is

rated

at

2.2

mV/cm

or

higher.

The

PHO-802A-input

electrical

impedance

characteristics

are

the

standard

47,000

ohms

with

lOOpF

shunt

capacitance.

ADCOM

high-output

moving-coil

cartridges,

for

example,

are

ideally

suited

for

use

with

this

phono

preamplifier.

Low-output

moving-coil

cartridges

which

normally

require

a

pre^

preamplifier

(sometimes

referred

to

as

a

"head-amp''),

or

step-up

transformer

must

have

these

auxiliary

devices

connected

before

the

RCA

jacks

feeding

the

input

to

the

PHO-802A

board.

A

pre-preamplifier,

or

step-up

transformer

provides

the

additional

gain

required

by

very-low-output

moving-

coil

cartridges

to

operate

with

a

standard

preamplifier

circuit.

A

pre-amplifier,

or

step-up

transformer,

is

not

necessary

and

must

not

be

used

with

high-output

moving-coil

cartridges

or

moving-magnet,

induced-magnet,

etc.

cartridges.

If

you

are

uncertain

as

to

which

type

of

cartridge

you

will

be

using,

please

consult

the

instruction

manual

or

specification

sheet

which

was

included

with

your

cartridge,

or

contact

the

dealer

from

whom

you

purchased

the

cartridge,

or

the

cartridge

manufacturer.

Some

turntables

are

supplied

with

a

separate

ground

wire,

which

must

be

connected

to

ground,

to

reduce

hum.

If

the

turntable

is

provided

with

this

separate

ground

wire

simply

connect

it

to

the

GND

©

screw

on

the

rear

panel

of

the

GFP-345

directly

to

the

left

of

the

AUX

1

inputs

(now

converted

to

PHONO).

There

are

simplified

instructions

on

the

main

PCB

of

the

GFP-345

to

facilitate

installation

of

the

PHO-802A

board.

Detailed

instructions

are

also

supplied

in

the

section

INSTALLING

THE

PHO-802A

BOARD

IN

THE

GFP-345

at

the

end

of

this

manual.

3

CD

Q

Iia!»r

et

.hl

SK

iaCkS

'?l

0r

USe

W

j

th

a

Com

P

act

Disc

(

CD

>

P'ayer

Or

other

similar

high-level

signal

source,

such

as

a

tape

approximatet/

22

OOOohrlT

3

P

'

ayer

’

°

r

vide

°-

cassette

record

e

r

(^R).

The

load

impedance

of

this

input

is

TUNER

O

Although

this

pair

of

inputs

is

provided

for

your

tuner,

they

may

be

used

with

any

other

high-level

source

such

as

a

taoe

Playe

'

0rO,herSiml,ar

signal

source.

The

load

impedance

of,his

input

AUX2

0

T

Vided

f

?:

any

°

thef

high-level

source

you

may

have

available

such

as

a

tape

player,

an

additional

CD

&

Sp°ut

C

°

P

3yer

°

r

h6r

S

'

m

'

3r

h

'

9h

'

level

source

-

The

load

impedance

of

this

input

is

identical

to

that

of

the

TAPE

IN

O

Ibolfthe

c

a

nO

inmi

ann!

iC

Xh

n

Sensitiv

‘

,y

and

electd

cal

characteristics

to

the

CD

O

inputs

and

the

comments

made

tbe

,

C

?

®

,"

puts

app

'

y

;

These

may

be

used

not

on|

y

,or

cassette

or

other

audio

tape

recorders

(such

as

DAT

or

DCC),

but

also

with

any

high-level

signal

source

such

as

a

VCR's

audio

outputs,

etc.

If

you

desire

simple

Payback

ofprerecorded

tapes,

plug

the

left

and

right

outputs

of

your

tape

machine

labelled

“tape

nulh

In

hP

TA

U

pFMn2

e

ffi

.

k

G

|aCk

f

USin9

3

S6t

°

f

Sood-q^ty,

low-loss

audio

cables.

To

select

playback

of

tape

pd

®

b

"

f

P

M

S

N

P

s

*'

,ch

on

the

,ront

P

anel

of

,he

GFP-345.

Whenever

the

TAPE

MON

©

is

activated

the

LED

directly

above

it

will

glow.

Also,

whenever

the

TAPE

MON

©

switch

is

pushed

in

the

INPUT

©

selector

will

be

disconnected

from

the

circuit.

That

is,

whatever

source

has

been

selected

through

the

INPUT

©

selector

will

be

SKTSF

frdm

th

®

c,rcu,,s

of

the

GFP

*

345

and

will

be

supplanted

by

the

source,

or

tape

recorder,

plugged

into

the

TAPE

IN

Q

jacks

on

the

rear

panel

of

the

preamplifier.

TAPE

OUT

O

'^

biph

®

v

®^

i

"

pdt

is

3

®'®

cted

via

,h

«

INPUT

©

selector

knob

will

appear

at

the

TAPE

OUT

O

jacks.

It

should

be

pointed

ou

,

that

re

9

ard|

ess

of

the

positionthe

TAPE

MON

©

switch

is

in,

whatever

source

is

selected

via

the

INPUT

©

selector

All

8

T

X

PE

OUT

°

iaCkS

-

TheTAPE

M0N

°

SWitCh

only

CO

"

trols

the

P^y^ckcircuitsof

theGFP-345^

tapp

unSffifc?

h

.•

If

y

°

U

are

rn

°7

,0nn9

3

recordin

2

which

is

being

made

on

a

tape

or

cassette

machine,

by

using

the

TAPE

MON

©

function,

you

must

leave

the

INPUT

©

selector

on

the

source

selected

for

recording

or

the

recording

thr^nLT^nnT

P

e

H

r

,n

P

.h

e

;

'

S

’

,

he

changing

of

SOurce

selection

through

the

INPUT

©

selector

switch

will

interrupt

T

9

,ed

tP

the

tape

or

cassette

recorder

via

the

TAPE

OUT

O

jacks.

To

hook-up

the

TAPE

OUT

Q

to

your

cassette

or

tape

recorder,

connect

the

right

and

left

jacks

on

the

cassette

or

tape

recorder

labelled

“line

in"

or

“record

in"

L6FT

CHA

,T

EL

and

RIGHT

CHANNEL

TAPE

OUT

o

jacks

on

the

rear

panel

on

the

GF^is

It

recording

P

°

r,ant

^

Y

°

U

^

°

n

Y

high

"

quallty

’

low

*

loss

interconnecting

cables

in

order

not

to

degrade

the

quality

of

the

NOTE

T

^|

PE

?!^

T

®

circuds

are

actively

“buffered"

in

order

to

insure

that

the

signal

within

the

circuitry

of

the

GFP-

345

will

not

be

compromised

regardless

of

whether

the

tape

recorder

is

in

use

or

not.

Therefore,

you

can

listen

‘J®

source

which,

yot.are

recording

without

fear

of

deg

rading

the

signal

either

in

the

recording

or

the

listening

mode.

In

addition,

the

buffered

outputs

will

prevent

the

normal

degradation

that

tape

recorder

inputs

cause

an

audio

signal

in

a

preamplifier

when

the

tape

recorder

circuits

are

turned

off

and

not

in

operation.

EXTERNAL

PROCESSOR

IN

©/

EXTERNAL

PROCESSOR

OUT

©

J,

h

'®

-"Puts

and

outputs

is

provided

for

use

with

any

"signalprocessor"

such

as

an

equalizer,

time-delay

unit.

EEfTT*

d6

^

er

:

®

T

he

^^NAL

PROCESSOR

IN

0

/

EXTERNAL

PROCESSOR

OUT

©

jacks

are

selected

and

controlled

by

the

front-panel

button

labelled

EXT

PROC

©.

Pushina

in

the

EXT

PROC

©

button

will

connect

whatever

processor

is

plugged

into

the

EXTERNAL

PROCESSOR

IN

©/EXTERNAL

PROCESSOR

OUT

to

C

TCU'try

of

the

GFP-345.

Whenever

the

EXT

PROC

©

button

is

pushed

In.

activating

this

circuit,

the

red

li^F^FRNAi

1

ppnr

r

Ji*

as,

"

B

]

h

®

0(7

PROC

®

button

will

disconnect

the

EXTERNAL

PROCESSOR

IN

St

PROr®

L

hMn°

CES

^

OR

^

U

h

T

®

jacks

from

the

circuitry

of

the

preamplifier

It

is

important

to

note

that

when

the

EXT

PROC

©

button

is

released,

both

sets

of

jacks

(EXTERNAL

PROCESSOR

IN

©/EXTERNAL

PROCESSOR

OUT

©)

E*?"

0

?*

removed

,rom

,he

circui,r

V

of

Preamplifier

(and,

so,

consequently

whatever

processor

is

plugged

into

these

jacks)

to

prevent

any

possible

degradation

of

the

signal

selected

through

the

INPUT

©

selector

switch.

4

To

connect

the

processor,

equalizer

or

surround-sound

decoder,

etc.,

to

the

GFP-345

always

use

high-quality

low-loss

PROCESSOR

OUT

©

£2?

°V^

***

P

[°f

SSO

I

,

ab

*"

ed

"‘"P*"

Hn*n".

or

"source-

into

the

EXTERNAL

Ph

°

UT

®

k

,

th

®

r

ear

pane

0f

lhe

GFP

‘

345

'

observing

the

left

and

right

labelling

on

both

sets

of

jacks

PRnrpstqnR

iw

rfi

h

n

S,9n

.t

processor

marked

“output,

"out"

or

"line-out"

to

the

GFP-345

jacks

labelled

EXTERNAL

Fp^°"-M

e

K^hese

connections

have

been

effected

simply

pushing

in

the

EXT

PROC

©

button

on

the

front

panel

of

the

GFP-345

will

bring

the

processor

into

the

circuit.

NOTE

11

n0

processor

is

plugged

into

the

EXTERNAL

PROCESSOR

IN

©

and

EXTERNAL

PROCESSOR

OUT

©

jacks,

and

the

EXT

PROC

©

button

is

pushed

in,

all

the

inputs

of

the

GFP-345

will

be

disconnected

and

no

output

signal

will

be

present

at

either

the

OUTPUTS

NORM

©

or

the

OUTPUTS

LAB

®

*

n

£

SOund

wil1

be

heard

throu

9h

the

s

y

s,em

-

Whenever

a

signal

processor

is

not

being

used,

the

EXT

PROC

©

button

should

always

be

in

the

out

position.

!

v

^r,

r

'

n

°

P

rocessor

is

connected

to

the

EXTERNAL

PROCESSOR

IN

©and

Kt

PRnr

L

flft

R

?

C

.f

SS

.?

R

OUT

0

jacks,

to

use

the

EXT

PROC

©

button

as

a

mute

function.

By

pressing

in

the

relMMd

°

®

bU

*

®

S

'

9

W

66

m,errupted

until

,he

EXT

PROC

©

button

once

again,

pushed

in

and

3.

Normally,

the

GFP-345

does

not

invert

polarity;

that

is,

if

a

positive-going

signal

is

present

at

any

of

its

inputs,

or^^^

8

i

t

i

V

f^Sl

n9

signal

at

the

ou,puts

-

However,

if

a

signal

processor

is

connected

to

the

EXTERNAL

PROCESSOR

IN

©

and

EXTERNAL

PROCESSOR

OUT

©

jacks,

and

its

circuitry

inverts

polarity

the

signals

present

at

the

OUTPUTS

NORM

©

and

OUTPUTS

LAB

©

will

also

be

inverted

in

polarity

(check

the

Instruction

Manual

of

your

signal

processor

to

determine

if

it

does

or

does

not

invert

polarity).

4.

Usually,

there

should

be

no

appreciable

level

difference

whenever

a

signal

processor

is

connected

into

or

out

of

the

circuitry

of

the

GFP-345

(through

the

use

of

the

EXT

PROC

©

button),

so

long

as

the

processor

was

designed

with

an

absolute

gam

of

1

and

adequate

input

and

output

impedances

to

fulfill

this

function.

If

a

level

difference

can

be

detected

when

switching

a

processor

in

and

out

of

the

circuit,

and

this

is

disturbing

to

you

please

contact

the

manufacturer

of

the

processor

you

are

using

to

see

if

a

correction

of

this

level

difference

carl

d©

enectea.

5

It

is

also

possible

to

employ

the

EXTERNAL

PROCESSOR

IN

©

jacks

as

an

additional

set

of

inputs,

since

Sf5£55'

a

pRn

t

^2S

,

rl^f«-

U,

l

ry

*

before

j

beLEVEL

©

and

BALANCE

©

controls.

If

you

wish

to

use

the

S

^

R

N

®

,acks

88

an

add,tional

lf1

P

ut

.

simply

plug

the

signal

source

into

the

EXTERNAL

PROCESSOR

IN

©jacks

as

you

would

any

of

the

other

inputs

(CD

©,

TUNER

©.

etc.)

and

select

that

source

by

pushing

In

the

EXT

PROC

©

button.

Whatever

other

selection

of

sources

has

been

made

through

the

INPUT

p

selector

wiM

be

disconnected

and

the

source

plugged

into

the

EXTERNAL

PROCESSOR

IN

©

jacks

will

then

be

fed

through

the

circuits

of

the

GFP-345

and

out

of

the

OUTPUTS

NORM

©

and

OUTPUTS

LAB

©

5

Whatever

processor

is

connected

to

the

EXTERNAL

PROCESSOR

IN

O

and

EXTERNAL

PROCESSOR

OUT

O

jacks

ro'Tnhfh!

i

acks

-

l

f

V

ou

wj

sh

to

insert

an

equalizer

into

the

tape

recorder

circuits

this

must

be

done

through

the

specific

TAPE

IN

©

and

TAPE

OUT

©

jacks

along

with

the

particular

recorder

In

such

an

instance

this

processor

will

not

operate

on

any

other

source

selected

through

the

INPUT

©

selector

but

will

operate

only

on

the

FXTFRNAI

°pinr^nSl^n

n

n

T

te(i

'

simi,arly

'

because

of

the

design

of

the

circuitry

in

the

GFP-345.

and

when

the

TA

QC

,

S

S0R

IN

®

)acks

are

used

an

additional

high-level

input,

this

individual

signal

will

not

appear

at

the

TAPE

OUT

©

jacks,

nor

can

it

be

selected

through

the

INPUT

©

selector

Therefore,

tape

recordings

cannot

be

made

of

the

signa

source

Pegged

into

the

EXTERNAL

PROCESSOR

©

jacks.

To

return

to

usual

operation

of

the

preamplifier

push

and

release

the

EXT

PROC

©

button

and

the

operation

of

all

the

switches

and

selectors

will

return

to

normal

and

the

source

plugged

into

the

EXTERNAL

PROCESSOR

IN

©

jacks

will

be

disconnected

from

the

circuitry

of

the

GFP-345.

OUTPUTS

NORM

©

The

OUTPUTS

NORM

©

are

capacitively

coupled

using

very-high-grade

metallized

film

capacitors.

It

is

ideal

for

use

with

power

amplifiers

which

require

a

bandwith-limited

signal

which

does

not

extend

to

DC.

Although

these

capacitivelv-

coupled

outputs

do

restrict,

somewhat,

the

extremely

low

frequencies,

around

5

Hz

or

10

Hz,

it

does

not,

in

any

way

sonic

detedoration

°

f

^

S

'

9nal

fr

°

m

,he

preampli,ier

Great

care

was

taken

in

the

selection

of

capacitors

to

preclude

any

™

£

tpUtS

,0

V

°

Ur

POWer

arnplifier

'

sim

P'y

interconnect

the

LEFT

CHANNEL

and

RIGHT

CHANNEL

OUTPUTS

NORM

©

jacks

to

the

corresponding

left

and

right

input

jacks

on

the

amplifier.

To

preserve

the

extremely

hiqh

quality

of

the

circuitry

in

the

GFP-345,

it

is

recommended

that

you

use

as

high

a

quality

cable

as

possible

to

make

this

interconnection.

NOTE

Both

the

OUTPUTS

NORM

©

and

the

OUTPUTS

LAB

©

may

be

used

simultaneously

should

you

wish

to

bi-amp

your

speakers,

or

drive

more

than

one

amplifier.

When

using

both

of

these

outputs

simultaneously

there

will

be

no

loading

effects

on

the

preamplifier.

y

OUTPUTS

LAB

©

Tha

?

U

J«

PUTS

L

^

B

®

.

,s

direct-coupled,

with

no

capacitors,

and

was

designed

to

provide

an

output

voltaqe

ideally

ma

c

ed

for

operation

with

the

ADCOM

brand

of

amplifiers.

!t

can

be

used,

however,

to

drive

almost

any

power

amplifier

presently

available

with

input

sensitivities

ranging

from

below

500mV

(0.5V)

to

well

above

2.0V.

To

connect

this

output

to

your

power

amplifier,

please

follow

the

instructions

in

the

section

above

OUTPUTS

NORM

©.

It

should

be

pointed

out

that,

since

the

OUTPUT

LABS

©

is

direct-coupled,

it

is

an

extremely

broadband

circuit

which

l

™

uwii°

W

h|

t0

.

D

?

(d

J[’

e

?’

C

Urren,)

'

There,ore

'

'*

requires

that

your

power

amplifier

(if

it

is

not

an

ADCOM-brand

amplifier)

be

able

to

handle

this

extremely

broadband

signal.

NOTE

Although

the

GFP-345

was

designed

primarily

for

use

with

stereo

power

amplifiers,

it

can

operate

just

as

well

with

wo

mono

power

amplifiers.

When

two

mono

amplifiers

are

used

for

stereophonic

reproduction,

it

is

strongly

suggested

that

they

be

a

matched

pair

with

respect

to

brand,

model,

input

sensitivity

and

power

output.

SWITCHED

©

OUTLET

The

SWITCHED

©

outlet

is

controlled

by

the

power

switch

©

on

the

front

panel

of

the

GFP-345.

You

may

plug

the

AC

line

cord

of

your

power

amplifier,

or

any

other

accessory,

which

you

want

to

turn

on

and

off

with

the

power

switch

©

of

the

GFP-345

into

these

outlets.

The

current-carrying

capacity

of

the

switch

©

Is

sufficient

to

handle

the

inrush

current

°J

P

?

™

er

am

P

|lfiers

up

to

the

200-watt-per-channel

class.

It

is

not

recommended

that

very-large-power

amplifiers,

above

the

200-watt

class,

be

plugged

into

these

outlets

(see

NOTE

below

following

UNSWITCHED

©

outlet).

UNSWITCHED

©

OUTLET

The

UNSWITCHED

©

outlet

can

supply

the

AC

power

requirements

of

any

accessory

source

used

with

the

GFP-345,

f^

a

S

r

a

?

P

P

^

yer

anal

°9

The

AC

line

cord

of

the

accessory

may

be

plugged

into

this

outlet.

The

UNSWITCHED

©

outlet

is

not

controlled

by

the

power

switch

©

on

the

front

panel

of

the

GFP-345,

and

power

will

always

be

available

at

this

outlet

so

long

as

the

GFP-345

is

plugged

into

an

energized

wall

outlet,

regardless

of

the

position

of

the

mam

power

switch

©.

The

total

power

drawn

through

the

UNSWITCHED

©

outlet

must

never

exceed

800

watts.

6

NOTE

Most

electronic

or

electrical

devices

state

the

maximum

power

drawn

by

the

device

on

a

plate,

or

label,

on

the

rear

panel

of

the

unit,

near

the

AC

line

cord

which

supplies

power

to

the

unit.

It

is

a

good

idea

to

check

these

requirements

before

plugging

an

amplifier

into

either

the

UNSWITCHED

©

outlet

or

the

SWITCHED

©

outlet.

Most

large-power

amplifiers

should

be

plugged

directly

into

an

AC

wall

outlet.

AC

FUSE

©

The

AC

line

fuse

protects

the

circuits

of

the

GFP-345.

This

fuse

should

be

replaced

only

with

a

fuse

of

the

same

current

value,

type

and

rating

as

thatsupplied

with

the

preamplifier.

The

correct

fuse

type,

current

value

and

rating

is

printed

directly

above

the

AC

FUSE

©

socket

on

the

rear

panel

of

the

GFP-345.

Replacements

with

fuses

of

higher

value

and/

or

different

rating

and/or

type

will

not

protect

the

GFP-345

circuits,

may

void

the

Warranty

and

may

cause

a

fire

hazard.

NOTE

Before

checking

or

replacing

a

blown

fuse,

make

certain

you

UNPLUG

THE

POWER

COR

D

FROM

THE

AC

WALL

OUTLET

TO

PREVENT

POSSIBLE

ELECTRICAL

SHOCK.

POWER

©

SOCKET

The

POWER

©

socket

permits

connection

of

an

ACcord

and

plug,

suitable

to

your

particular

area

or

country,

to

provide

AC

power

to

operate

the

GFP-345

circuits

and

energize

the

SWITCHED

©

and

UNSWITCHED

©

outlets.

The

AC

line

cord

should

be

plugged

into

any

standard

wall

outlet

providing

the

correct

operating

voltage.

To

determine

the

voltage

for

which

the

GFP-345

has

been

set.

check

the

voltage

listing

on

the

upper

right-hand

corner

of

the

GFP-345's

rear

panel.

NOTE

The

GFP-345's

POWER

©

socket

is

“polarized"

and

its

lower,

center

pin

is

grounded

as

required

by

many

standards

and

safety

organizations.

If

at

all

possible,

make

certain

that

there

is

a

matching,

3-prong

plug

on

the

end

of

the

AC

cord

so

that

the

chassis

of

the

GFP-345

will

be

grounded

to

“earth”.

If

a

3-prong

plug

is

not

available

m

your

area,

or

in

your

specific

circumstances,

experiment

with

the

“phasing”,

or

reversing,

of

the

AC

plug

to

achieve

minimal

hum

in

your

system

and

minimal

noise

as

well.

CONTROLLING

THE

GFP-345

Please

refer

to

the

diagram

of

the

front

panel

of

the

GFP-345

to

identify

all

the

controls

and

their

functions.

AC

POWER

SWITCH

©

©

The

"rocker"

AC

power

switch

©

controls

power

to

the

circuits

of

the

GFP-345

and

to

the

SWITCHED

©

outlet

on

the

rear

panel

of

the

GFP-345.

Whenever

the

GFP-345

is

energized,

the

red

LED

©

will

glow.

Push

the

top

of

the

rocker

switch

to

energize

the

GFP-345.

Push

the

bottom

of

the

rocker

switch

to

turn

the

unit

off.

7

INPUT

©

SELECTOR

This

rotary

selector

lets

you

choose

any

input

connected

to

the

GFP-345

and

feed

it.

through

the

circuitry

of

the

GFP-345,

to

both

the

OUTPUTS

NORM

©

and

OUTPUTS

LAB

©

jacks

and,

then,

through

your

amplifier

and

loudspeakers

The

INPUT

©

selector

will

also

feed

the

signal

you

choose

to

the

TAPE

OUT

O

jacks

on

the

rear

panel

of

the

preamplifier.

AI1

on

the

front

panel

of

the

GFP-345

will

affect

the

signal

present

at

the

OUTPUTS

NORM

©

and

OUTPUTS

LAB

©

jacks.

Please

note

that

some

of

these

controls

will

not

affect

the

signal

present

at

the

TAPE

OUT

©

jacks.

TAPE

MON

©

The

TAPE

MON

©

switch

selects

the

TAPE

IN

©

jacks

on

the

rear

panel

of

the

GFP-345.

This

switch

is

meant

to

provide

you

with

the

capability

of

"monitoring"

a

recording

you

are

making

on

a

tape

machine

which

is

provided

with

3-heads

(that

is,

an

erase

head,

record

head

and

separate

playback

head).

With

2-head

machines,

DAT

recorders

and

DCC

machines,

itwill

permit

you

to

verify

that

thereis

a

signal

being

fed

to

the

tape

recorder

and

through

its

circuits

into

the

TAPE

IN

©

jacks.

Whenever

the

TAPE

MON

©

switch

is

pushed

in,

the

red

LED

above

this

switch

will

glow

and

the

signal

selected

by

the

INPUT

©

selector

will

be

disconnected

from

the

amplification

circuits

of

the

GFP-345.

Please

note

that

whatever

source

is

selected

via

the

INPUT

©

selector

will

still

appear

at

the

TAPE

OUT

Q

jacks.

EXTPROC©

Pushing

in

this

switch

connects

the

EXTERNAL

PROCESSOR

IN

©

and

EXTERNAL

PROCESSOR

OUT

©

jacks

on

the

rear

panel

of

the

GFP-345.

Please

refer

to

the

section

EXTERNAL

PROCESSOR

IN

©

/EXTERNAL

PROCESSOR

OUT

©

above

for

a

complete

explanation

of

the

function

of

this

circuit.

Whenever

the

EXT

PROC

©

switch

is

in

the

red

LED

above

this

switch

will

glow.

Please

note

that

whenever

the

EXT

PROC

©

switch

is

in

the

out

position,

whatever

processor

is

connected

to

the

EXTERNAL

PROCESSOR

IN

©

/EXTERNAL

PROCESSOR

OUT

©

jacks

will

be

completely

disconnected

from

the

circuit

to

prevent

any

possible

degradation

of

the

signal

being

amplified

by

the

GFP-345.

MONO

©

Pushingin

this

switch

mixes

the

left-

and

right-channel

signals.

This

combined

signal

is

then

fed

to

both

OUTPUTS

NORM

©

and

OUTPUTS

LAB

©

jacks.

The

mono

switch

does

not

insert

switch

contacts

in

series

with

the

signal

path

but

simply

parallels

the

left

and

right

channels.

The

MONO

©

switch

is

useful

in

reducing

FM

noise

and

distortion

on

weak

stations,

or

when

playing

older

analog

mono

recordings,

or

in

checking

relative

phasing

of

your

loudspeakers

It

is

also

useful

when

setting

the

channel

balance

of

your

loudspeakers

using

the

BALANCE

©'

control.

CONTOUR

©

The

CONTOUR

circuit

in

the

GFP-345

differs

markedly

from

conventional

loudness

compensation

circuits.

Recent

studies

show

that

conventional

circuits

overcompensate

for

natural

low-

and

high-frequency

hearing

reduction

at

low

signal

levels.

The

studies

of

Robinson

and

Dadson

of

Harvard

University

have

provided

guidelines

for

a

newer

and

more

accurate

curve

for

loudness

compensation.

In

our

judgement,

a

subtle

boost

of

low

frequencies

(in

the

20-100Hz

range)

and

no

boost

at

high

frequencies,

provides

the

ideal

musical

balance

for

listening

at

low

to

moderate

levels.

The

effects

of

the

circuit

gradually

diminish

as

the

volume

level

is

increased

(that

is,

when

the

LEVEL

©

control

is

turned

clockwise)

Pushing

in

the

CONTOUR

©

switch

activates

this

function.

Whenever

the

CONTOUR

©

switch

is

in

the

out

position

the

CONTOUR

circuit

will

be

disconnected

from

the

circuitry

of

the

GFP-345.

BALANCE

©

The

BALANCE

©

control

permits

you

to

adjust

the

level

of

the

left

channel

versus

the

right

channel

and

vice-versa.

Turning

the

control

counterclockwise

will

reduce

the

level

of

the

right

channel.

Turning

it

clockwise

will

reduce

the

level

of

the

left

channel.

At

the

maximum

counterclockwise

position,

only

the

left

channel

will

operate.

Conversely,

at

the

maximum

clockwise

position,

only

the

right

channel

will

operate.

In

most

cases

the

proper

setting

of

the

BALANCE

©

control

will

be

at

or

near

its

12

o’clock

position.

To

adjust

for

optimum

balance

between

channels,

it

is

easiest

to

use

a

tuber

tuned

to

a

station

in

which

the

announcer

is

speaking.

This

will

almost

alwaysbe

a

mono

signal.

Place

yourself

in

your

normal

listening

position

and

adjust,

or

have

someone

adjust,

the

BALANCE

©

control

until

the

announcer

appears

to

be

centered

between

the

two

speakers.

This

method

will

compensate

for

almost

all

the

variations

within

your

system,

and

the

room,

and

is

the

easiest

of

all

methods

to

use.

Ifvour

system

does

not

include

a

tuner,

the

nextbest

way

is

to

select

a

CD,

push

in

the

MONO

©

button,

place

the

INPUT

©

selector

on

CD

and

adjust

the

BALANCE

©

control

as

described

above.

Once

the

correct

setting

is

chosen,

it

will

need

to

be

changed

only

to

compensate

for

unequal

signal

levels

from

an

outside

music

source,

such

as

a

cassette,

disc,

etc.

LEVEL

©

This

rotary

control

sets

the

level

at

the

OUTPUTS

NORM

©

and

OUTPUTS

LAB

©

and,

consequently,

the

level

heard

through

the

amplifier

and

loudspeakers.

Turning

this

control

clockwise

will

raise

the

level

of

the

signal

chosen

via

the

INPUT

©

selector.

Turning

the

control

counterclockwise

will

reduce

the

level

of

the

signal.

Normally,

when

used

with

8

f“

d

r

P

"

f,erS

.!

ndSP

°

akerS

hav

'

ng

med,ljrn

-to-low

sensitivities,

the

position

o<

this

control

will

beat

its

normal

1230

to

-I

.

30

O

clock

position.

There

are

many

factors

which

will

affect

the

position

of

the

LEVEL

©

control

for

any

qiven

listening

level.

Among

these

are:

the

specific

sensitivity

of

the

power

amplifier

for

maximum

output;

the

sensitivity

(or

efficiency

)

of

the

speakers

being

used;

the

size

of

the

room

in

which

the

speakers

are

located;

the

output

levels

of

the

USe

i?

3nd

plu

"

ed

'

n,

°

the

GFP-345

(cassette

machines,

tape

recorder.

CD

player,

etc.);

the

modulation

,

9

7*7*

J.

y

yourtuner;

etc

-

The

Position

of

the

LEVEL

©

control

is

a

relative

indication

to

permit

/

l

evel

^

ttmg

agam

and

a

9

ain

-

1

1

is

n

°>

an

absolute

indication

of

how

much

power

the

amplifier

9

*

th

f

peakers

or

how

Powerful”

a

system

is.

It

is

quite

possible,

with

different

component

systems,

to

have

°

utpi

f

,rom

an

am

P

|d|

ef,

and

sound

level

from

the

speakers,

but

with

different

LEVEL

©

control

settings

nnjrnu

50

qu

:l

e

C

?

mm

l

°

n

t0

have

t0

set

the

LEVEL

©

contro1

to

a

different

position,

when

switching

from

“

i-

{

%

CD

}

X

°

a

"°’

her

(SUCh

as

a

cassette

machine),

to

achieve

the

same,

or

approximate

volume

level

from

the

'

h'

ar

y

'

‘flT®'’

6

"'

FM

and

AM

stat

'ons

received

by

your

tuner

may

require

adjustment

of

the

LEVEL

of

music

it

broadcasts

°"

^

am

°

Unt

°

f

aud

'°

“

l,m,,,n

9"

and

“compression"

used

by

the

particular

station

and/or

the

type

NOTE

For

the

reasons

described

above,

it

is

good

practice

to

lower

the

LEVEL

©

control

before

changing

the

INPUT

selector

to

a

different

source.

The

design

of

the

GFP-345

makes

it

usable

with

the

gamut

of

power

amplifiers

presently

available,

as

well

with

all

loudspeakers

presently

in

use.

The

LEVEL

©

control

was

designed

to

be

fully

operable

throughout

its

complete

rotation.

CARING

FOR

YOUR

GFR-345

I

5660

l

aken

by

ADC(

?

M

t0

assure

thal

y°

ur

preamplifier

is

as

flawless

in

appearance

as

it

is

electronically.

pane

'

ls

a

heavy-gauge,

high-grade,

anodized-aluminum

extrusion,

bead-blasted

for

durability.

The

bottom

Should

Iprlm

H

P

C

.°

ver

and

rear

panel

are

of

heavy-gauge

steel,

both

painted

and

baked.

If

the

front

panel,

top

or

sides

detergent

solution

V

°

rf,n9erprmted

'

,he

y

can

be

cleaned

with

a

soft,

lintless

cloth,

slightly

dampened

with

a

very

mild

NOTE

DO

NOT

SPRAY

OR

USE

LIQUIDS

OF

ANY

KIND

ON

THE

SURFACES

OF

THE

GFPv345.

SERVICING

3

"'‘if

Service

Department

to

answer

questions

pertinent

to

any

difficulties

you

encounter

in

the

ZT

Ztir

Un,t

f

y

?

U

encounter

Problems

obtaining

advice

or

resolving

your

problems

locally,

please

contact

us

we

mai

rofervm,

.

r

®

co

"\

mendat

'

on

;

lf

y°

ur

problem

cannot

be

resolved

directly

through

instructions

from

us,

we

may

refer

you

to

an

authorized

representative

near

you

for

resolution.

Please

address

mail

inquiries

to:

ADCOM

Service

Corp.

11

Elkins

Road

East

Brunswick,

NJ

08816

U.S.A.

^»n

d

rlT,°

re

6Xped

'

ent

*°

C

°

ntaCt

US

Via

f3X

'

,he

numb€r

is

(908-390-9152).

Please

include

a

return

fax

number

9