Audio Research SP4 User manual

audio

research

H I G H D E F I N I T I O N®

3900

ANNAPOLIS

LANE

NORTH/

PLYMOUTH,

MINNESOTA

55447-5447

PHONE:

763-577

9700

FAX

763-577

0323

August

1977

SP4,

SP4A

MANUAL

SP4,

SP4A

SCHEMATIC

AND

PARTS

LIST

INTRODUCTION

Congratulations

your purchase.

The

-4 stereo preamplifier

was

conceived

and

designed for audio

perfectionists

Analog

Module

circuitry

provides unequaled performance under actual

dynamic

listening

conditions.

addition to the

normal

complement

features,

the

SP-4

has:

provisions for

optional

(*)

low

level

head

amp,

alternate

compensation

of magnetic

(mag

phono

section,

1600

watt relay controlled

power

outlets,

main

output

turn-

delay,

high

quality

anodized

aluminum

panels, knobs,

and

handles,

and

scuff-resistant

chassis

finish.

Conservative design

and

extensive use of high

quality

industrial

grade

components

insure

many

years of

trouble-free

performance.

WARRANTY

A limited

Day

Warranty

(from

the date of purchase

the original purchaser)

provided

Audio

Research Corporation. This warranty

subject to the

conditions

and

limitations

stated within the

documents

attached to the outer

shipping carton.

LIMITED

YEAR

WARRANTY

A 3-Year Limited Warranty Application

included with the

documents

attached to

the outer shipping carton.

THIS

LIMITED

3-YEAR

WARRANTY

WILL

NOT

ISSUED

EFFECTIVE

UNLESS

WITHIN

THIRTY

DAYS

AFTER

THE

DATE

SALE

THE

PURCHASER

MAILS

AUDIO

RESEARCH

LIMITED

YEAR

WARRANTY

APPLICATION

FORM

WHICH

HAS

BEEN

COMPLETED,

DATED

AND

SIGNED

BOTH

THE

SELLING

DEALER

AND

THE

PURCHASER

AND

COPY

THE

BILL

SALE

OTHER

PROOF

PURCHASE

THE

PRODUCT

WARNING

FAILURE

COMPLY

WITH

THE

ABOVE

CONDITIONS

WILL

RESULT

THE

WARRANTY

BEING

RESTRICTED

THE

LIMITED

90-DAY

WARRANTY

PACKAGING

Save

All

The

Packaging -

Your

Audio

Research

component

a precision

electronic

instrument

and

should

properly cartoned

any

time shipment

made

You

may

never

have

occasion to return

to the factory for

service,

but

such

should

necessary, or other occasion to ship

occurs, the original packaging

may

save your investment

from

unnecessary

damage

or delay.

- 1-

ACCESSORIES

The

following optional

(*)

accessories

for

your

-4

preamplifier

will

made

available

through your

Audio

Research

dealer

* Walnut veneered

oiled

finish

cabinet

* Programable

low

level

head

amp

electronics

LINE

VOLTAGE

CONVERSION

This equipment

can

operated

from

either

120

Volts or

240

Volts A.

50/60

Hz.

Check

the

position

the

line

voltage

selector

switch

the

rear

panel.

necessary,

remove

the switch

safety

cover

and

set

the

switch to the proper voltage as

indicated

below

the switch. Secure the

switch

position

with the

safety

cover

and

screws with the

word

"fuse"

showing.

Install

the

appropriate

fuse as

indicated

below

the

line

voltage

different

than

that

set

for

the

factory

WARNING

Voltage

120

240

Fuse

1/4

Amp

Type

3AG

MDL

Slo-Blo

1/8

Amp

Type

3AG

MDL

Slo-

Blo

prevent

fire

or shock hazard,

not expose

this

equipment to

rain

moisture.

This

unit

contains

voltages

which

may

lethal

not

operate

this

unit

with covers

removed

. Refer

servicing

qualified

personnel .

CAUTION

For continued

protection

against

fire

hazard ,

replace

only with

same

type

and

rating

fuse.

-2-

J11

JlJ

JlS

J17

J19

J21

OT2 OTJ

OT4

I l= l= l= l= l- 1- 1= 1 I j j I

RIGHT

PUTS

r--

AIGHT OUTPUTS

-----,

audio

research

ITCH

SWITCHED

CHED

SWITCHEO @

~~~~

I @ @ @ @ @ @ @ @ @ @ @

PREA

MPLIFI

MODEL

I 50-60 Hr

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120 VAC 1600 WATTS MAX

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flAEHAZARD

REPlA

INPUTS

L.__

LEFT OUTPUTS

_.J

SERIALNUr.lBER~

0'1Jow~~~1~~Mf'u~~P

E SLO·OLO

I 17

1-1

1- 1- 1- 1- 1- 1 1

J4 J6

JlO

J12

J14 J16

J18

J20 J22

S10

REAR

PANEL

LAYOUT

REAR

PANEL

FUNCTIONS

Refer to the "Rear

Panel

Layout" diagram above.

Audio

Inputs:

Head

Amp*

(optional),

Right

Channel

Head

Amp*

(optional ), Left

Channel

Provision for "optional "

Head

Amp

electronics

have

been

made

within the

-4

directly

behind the

Head

Amp

input connectors.

These

input

and

associated

electronics

will

required only

for

low

output

moving

coil transducers. Consult your dealer for information

and

use

this

special input

feature.

These

inputs are not connected

internally

the factory

and

are not

used

in systems employing moderate or high

output

moving

coil magnetic

cartridges.

-Magnetic 1, Right

Channel

-Magnetic 1, Left

Channel

Connect to tone arm/cartridge

record player.

Nominal

input

impedance

ohms

(200

shunt).

Use

with magnetic type

cartridges

requiring

RIAA

playback compensation. Note:

Normally

connect grounding wire

from

record

ayer

arm

to the

"Ground

Terminal 11 screw 1ocated

xt to

and

between

and

J2.

With

certain

systems

this

may

add

hum

which

case

ground wire

required.

-Magnetic 2, Right

Channel

-Magnetic 2, Left

Channel

Same

above

Allows

use

of a second record player

when

selected

from

the

front

pane

Note:

The

input

characteristics

and

gain of the

-4

have

been

factory

set

accommodate

most

the high

quality

magnetic

phono

cartridges

the market today.

However,

the

-4

low

level

mag

sections

can

programmed

a technician for

different

gain, input

resistance

and

capacitance. This

feature

allows

matching

of various

cartridges

the

magnetic

preamp

section for

optimum

performance . Consult your

dealer

for

further

information

and

use

this

special input

feature

-3-

-Tuner, Right

Channel

-Tuner, Left

Channel

High

level inputs. Connect to the output of

and

/or

tuner

component.

Nominal

input

impedance

Kin

the

stereo

reverse

mode,

Kin

the

left

right

mode,

and

Kin

the

"mono"

mode.

-Spare, Right

Channel

JlO

-Spare, Left

Channel

Provides high level inputs

for

any

auxiliary

system

component

Nomi

1 input

impedance

the

same

as the

tuner

inputs

and

above

Jll

Tape

1, Right

Channel

J12

Tape

1, Left

Channel

High

level inputs. Connect to tape recorder

line

outputs.

input

impedance

the

same

as for the tuner inputs

above

any

load(s) connected to the tape outputs

when

the

front

tape dubbing switch

(S4)

in the

copy"

position.

Jl3

Tape

2, Right

Channel

J14

Tape

2, Left

Channel

Nominal

shunted

panel

Same

as above.

Allows

use

of a second tape recorder

when

elected

from

the

front

panel .

Audio

Outputs:

J15

Tape

1, Right

Channel

J16

Tape

1, Left

Channel

Connect to tape recorder

line

inputs. Provides a

program

source

for

tape

recording. Output signal

independent of "

volume

control

setting

and

equal to the source input

level,

i .e. "tuner" ,

spare

, "tape l" ,

tape

or magnetic

phono

preamplifier output.

Nominal

output

impedance

ohms

plus the output

impedance

of the selected source .

general, the load

impedance

should

greater

than

Kfor

optimum

performance .

J17

Tape

2, Right

Channel

J18

Tape

2, Left

Channel

Connect to the

line

inputs of a second tape recorder

when

used. Function

and

characteristics

are

same

above.

-4-

J19

Main

1, Right

Channel

J20

Main

1, Left

Channel

Connect to

power

amplifier

(or

electronic

crossover) inputs.

Nominal

output

impedance

ohms.

general, the load

impedance

should

greater

than

Kfor

optimum

performance.

The

outputs are

coupled through a 5

capacitor.

J21

Main

2, Right

Channel

J22

Main

2, Left

Channel

Same

(in

parallel

with) outputs above.

to drive a second

power

amplifier.

Combined

load

impedance

Main

and

Main

2 should

minimum

for

optimum

performance.

Power

Circuits:

OTl

-Switched

Convenience Outlet

OT2

-Switched

Convenience Outlet

OT3

-Switc

hed

Convenience Outlet

Connect to system

components

(power

amplifier(s)

tuner(s)

electronic

crossover,

etc.)

that

are to

turned

the

front

panel

power

switch (Sl) .

Will

accept 2 or 3

prong

line

plugs . Outlets are

switched

internal

power

relay.

Cap

acity

1600

watts

total

including the unswitched

outlet

(OT4).

The

outlets

are not fuse

protected.

Note:

internal

.01

MF/1600

capacitor

connected (

for

arc

suppression) across the

internal

power

relay

contacts.

Audio

Research

RPR-1

(Remote

Power

Receptacle)

used

in the system to

remotely turn

the

power

amplifier(s),

the

.01

capacitor

must

removed.

The

small

current

passed

the

capacitor

sufficient

to turn-on the

RPR

-1

transmitter

electronics

continuously

even

with

the

SP-4

power

switch (Sl)

off.

Since

relay

contact arcing

not a problem

when

using the

RPR-1

(power

amplifiers are instead connected to the

RPR

-1

outlets),

this

capacitor

can

safely

removed.

accomplish

this,

remove

the

-4 top cover

and

8 holding screws.

CAUTION:

UNPLUG

SP-4

POWER

CORD

BEFORE

REMOVING

TOP

COVER

AND

CAPACITOR.

Locate the .01

MF/1600

capacitor

nested

between

the

power

relay

contacts -towards the

rear

panel next to the

power

transformer. Clip the leads

off

close to the solder

joints,

remove

the

capacitor,

and

replace the top cover.

The

SP-4

now

ready for

use

with

RPR-1

-5-

OT4

-Unswitched

Convenience

Outlet

Connect to record

player,

turntable,

tape recorder

where

power

should

controlled

the component

off

switch only. This unsures proper

"cycling"

and

mechanism

disengagement.

Note:

The

"grounding" type convenience

outlets

are provided to

accommodate

power

amplifiers

with 3 prong (grounded)

line

plugs.

avoid "system" ground loops, the ground

circuits

the

rear

panel

are connected to the ground conductor

the

-4

line

cord only.

preamplifier

chassis

not connected to the convenience

outlet

cord/plug ground

circuTt

-. -

Preamplifier

Line

Fuse

Receptacle

outlets

The

Provides

protection

for

preamplifier

electronics

only. Refer to

page

for

fuse replacement information.

SlO

-Line Voltage

Selector

Switch

Selects

for

120

240

volt

input

power

. Refer to

page

for

"Line

Voltage Conversion" procedure.

SYSTEM

CONNECTION

Before connecting the

-4

into

your system,

familiarize

yourself

with

the

rear

panel functions

referring

to the diagram

and

description

the

rear

panel in

the previous

section.

Use

only high

quality

shielded

phono

cables

when

interconnecting

the

-4 with

any

signal

sources,

power

amplifiers,

electronic

crossovers.

Avoid

inexpensive

cables

which

use

"weak

soft

metal grounding

shells

as they

may

introduce

hum

and/or noise

into

the

system.

Keep

audio cables

neatly

dressed

and

away

from

all

power

cords

for

minimum

hum

and

noise

interference

When

connecting

the magnetic

and

tape

inputs,

use the

number

l 11 connectors

single

turntable

and/or tape deck

employed. This

will

result

easier

and

convenient

front

panel control switching.

should

noted

that

the

-4

line

cord grounds the convenience

outlet

grounds

only.

The

preamplifier

chassis

not connected to the

line

cord ground in order

to minimize system ground loops.

-6-

0 l

r-"OWEn--i

audio

research

BASS

l l

IGH

0€F

ITI

•~

•4

PAEA

MPt..l F l E A

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---+---

f--+-j

- j- j- /- j- j

LED

FRONT

PANEL

LAYOUT

FRONT

PANEL

FUNCTIONS

Refer to the "Front Panel Layout" diagram

above

Rotary Controls:

Volume

(Rl) -Controls preamplifier

"main

output"

level.

Power

amplifier

or source gain

controls

(if

available)

should

set

such

that

normal

listening

levels

occur

approximately a 1 or

o'clock

setting.

This will provide ideal

volume

control

"range

•

Balance

(R2)

-Controls the

relative

volume

of each channel .

Equal

channel

volume

occurs

when

the control

centered

the

indicator

mark.

Clockwise

rotation

from

center

position

increases

right

channel

"main

output" level while decreasing

left

channel output. Counter-clockwise

rotation

increases

left

channel output

and

decreases

right

channel output.

Bass

(R3)

Bass

tone control

circuitry

activated

when

switch (S3)

moved

the

tone

position.

Response

flat

when

control

centered

indicator

mark.

Clockwise

rotation

increases

bass response while counter-clockwise

rotation

decreases response.

Treble

(R4)

-Treble tone control

circuitry

activated

when

switch

(S3)

moved

to the

tone

position. Response

flat

when

control

centered

indicator

mark.

Clockwise

rotation

increases

treble

response while counter-clockwise

rotation

decreases

response .

Rotary Switches :

Mode

(SB)

-Switch

selects

one

of five

"main

output"

modes

Mono

Combines

the

left

and

right

input channels

internally

to provide a

monaural

output

(common

output for both

left

and

right

main

outputs).

"Reverse" -Provides stereophonic operation except channels are

reversed,

i.e

left

input to

right

output ,

right

input to

left

output.

-7-

Stereo

-Provides

normal

stereophonic operation without

channel revers

al,

i .

left

input to

left

output,

right

input

right

output.

Left

-Left channel input sources are coupled to both the

left

and

right

"main

outputs" simultaneously.

The

balance

control functions as

normal

Right

Same

above

except

right

channel input sources

are coupled to both the

left

and

right

"main

outputs"

simultaneously.

Note

The

"tape outputs" are unaffected

the

position

the

"mode

switch.

Source

(S9)

-Switch

selects

one

of five

rear

panel inputs (program sources)

as marked.

The

selected

source

also switched to the "tape

outputs"

when

switch

(S4)

in the

norm

position.

Note:

The

"Head

Amp*"

position

not normally used .

Toggle Switches :

Provisions for optional (*)

Head

Amp

electronics

have

been

made

within the

SP-4

directly

behind the

Amp

input connectors.

These

inputs

and

associated

electronics

will

required only

for

low

output

moving

coil

transducers.

Consult your dealer for information

and

use

this

special

input

feature.

These

inputs are not connected

internally

the factory

and

are not used in systems employing

moderate or high output

moving

coil magnetic

cartridges.

Power

(Sl) -Preamplifier

off

switch.

Move

handle

for

power

• Also

turns

the

switched

rear

panel

outlets

Green

indicator

(LED)

illuminates

when

preamplifier

on.

Filter

(S2)

-Active

low

frequency (subsonic)

filter

. Enabled

when

handle

moved

filter

position. Switch

normally

left

in the

full

range

out

position

for

optimum

response .

Use

only

for

removal

of excessive

low

frequency noise

(turntable

rumble ,

etc

. ).

Tone

(S3)

Moving

handle to

tone

position

activates

bass

and

treble

tone

control

circuitry.

Unless needed, switch should

left

in the

out

position

for

optimum

performance

and

flat

response.

-8-

Tape

Copy

&Monitor Switches (S4, S5,

S6,

S7)

-Controls output signal

tape output" connectors

(Jl5,

Jl6

Jl7

Jl8).

the

normal

norm

position,

the signal source selected

the source

switch

(S9)

also

switched to the tape outputs

Jl5,

Jl6

Jl7,

Jl8.

When

two

tape recorders are

used

in the system

and

tape copying or

dubbing

desired,

the switch

moved

to the

copy

position.

This allows

you

to tape

from

one

deck to another

and

at the

same

time

listen

to another

program

source

selected

(S9).

When

the

copy

position,

the "tape outputs"

are

connected to the

tape 1

or "tape 2

inputs as

selected

(S5).

Used

in conjunction with

(S4)

above. Selects

either

tape 1

tape 2

inputs

and

connects

them

to the tape outputs

Jl5,

Jl6

Jl7,

and

Jl8

when

(S4)

in the "copy"

position

. Position

connects the outputs of

tape recorder

to the inputs of tape recorder

and

position

•

connects the outputs of tape recorder

to the inputs of tape recorder

#1).

Used

in conjunction with monitor switch

(S7)

described

below

. Selects

either

"tape l

tape 2

inputs

for

monitoring of tape recordings

when

(S7)

in the

monitor

position.

This switch also functions

asa

program

or tape input

selector

when

using tapes as a

program

source.

Allows

monitoring

tape recordings

selection of a

program

(tape) source

when

used

in conjunction with

(S6)

above

and

in the 1'monitor

position.

the "source"

position,

selector

switch

(S9)

controls the

program

source

allowing

selection

all

"magnetic",

"tuner",

spare

inputs. Source

switch

(S9)

bypassed

when

in the

moni

tor

position.

Indicator:

LED

-Green

light

emitting diode. Illuminates

when

preamplifier

power

switch,

Sl,

•

-9-

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