Cetec broadcast group Tep3s User manual

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.c

0

s

Models

TEP3S

and

TEP3M

Turntable

Preamplifiers

www.SteamPoweredRadio.Com

I

Models

TEP3S

and

TEP3M

I

Turntable

Preamplifiers

1-

I

I @1969

098-2260

I

www.SteamPoweredRadio.Com

I

·I

I

TEP

3S,

TEP

3M

PHONO

EQUALIZED PREAMPLIFIERS

SPECIFICATIONS

FREQ. RESPONSE:

RIAA

(NAB)

within

typical

+

0.

5

db

(+ 1

db

max).

OUTPUT LEVEL, PROGRAM:

J5

dbm

into

600

ohms

balanced,

adjustable

to

below

-20

dbm.

OUTPUT LEVEL,

MAX:

+10

dbm

(12

to

14

dbm

typical)

DISTORTION:

Less

than

O

.1

%

(0.

03 %

typical)

THD.

INPUT

IM

PE

DANCE:

4

7K

ohms.

Can

be

changed.

SENSITIVITY: 5

millivolts

for

%

dbm

output

at

1

KHz.

NOISE: 70

db

below

Program

Level.

More

than

80

db

below

max.

output.

HUM:

Inaudible

and

virtually

un-measureable.

(Below

noise)

SEPARATION:

Stereo:

70

db

typical

(65

db

min.)

SIZE:

Width,

4.5".

Height

2 .

6"

,

Depth

6

.5

11

WEIGHT: 1

lb.

6

oz.

POWER:

110

to

125

VAC,

50-60

Hz.,

0.25A

MOUNTING:

Rubber

feet

plus

two

single-hole

"Z

11

clamps.

A.

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INSTALLATION:

Please

Read

Carefully!

As

with

all

electronic

instruments

,

best

performance

will

be

assured

by

following

good

wiring

practices

and

proper

installation

procedures

.

RCA

type

phono

input

connectors

are

provided

plug

a

ground

terminal

for

the

turntable

frame

lead

and

tone-arm

shell

ground

,

if

part

of

the

tone-arm

cable

.

The

tone-arm

cable

length

should

not

exceed

30

inches

,

to

avoid

excessive

shunt

capacitance

which

could

result

in

losses

of

the

higher

audio

frequencies

.

Output

connections

are

via

an

Amphenol 91

series

connector

.

When

soldering

the

output

cables

,

be

certain

not

to

leave

excess

solder

on

the

pins

which

might

distort

the

mating

socket,

and

carefully

remove

any

remaining

flux

or

rosin

before

engaging

the

connector

.

Additional

information

will

be

found

in

the

following

1

DESCRIPTION

section

under

"output"

.

A

common

cause

of

RFI

in

low-level

audio

equipment

occurs

when

a

connecting

cable

length

represents

a

multiple

of

an

electrical

quarter-wave

at

the

frequency

of

a

nearby

transmitter,

and

thereby

acts

as

an

antenna

.

Connecting

cable

lengths

should

be

chosen

slightly

longer

than

required

so

they

can

be

re-routed

or

shortened

electrically

by

folding-over

arid

tying

the

excess

length.

Always

avoid

excess

cable

lengths

and

never

coil

audio

connecting

cables.

In

strong

RF

fields

,

these

same

conditions

may

apply

to

the

AC

power-cords

in

a

system;

excess

or

critical

lengths

should

be

avoided

.

In

extreme

circumitances

it

may

be

necessary

to

experiment

by

adding

or

removing

various

system

grounds

B.

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1·

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1·

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INSTALLATION

(cont'd)

to

find

the

best

combination.

The

output

circuit

of

the

TEP-3

series

is

a

transformerless

para-phase

inverter

which

avoids

the

problems

associated

with

cascaded

output

and

input

transformers.

This

contributes

significantly

to

the

excellent

equalization

and

freedom

from

ex-

traneous

hum

pickup

of

the

TEP-38.

Please

read

the

following

description

thoroughly

to

obtain

the

maximum

benefit

from

this

feature

.

.,

C.

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I

DESCRI

PrION

:

The

SPARTA

TEP 3S (

Stereo

)

and

TEP

3M

(

mono

)

preamplifiers

are

completely

self-contained

and

equalized

for

use

with

any

modern

variable-reluctance

or

magnetic

cartridge

.

They

offer

a

combination

of

capabilities

and

performance

features

rarely

,

if

ever

,

found

in

other

phono-equalized

preamplifiers

for

broadcast

use

.

Most

significant

is

the

use

of

a

dual

(stereo)

integrated-circuit

(IC)

in

the

amplifier

proper

.

The

extremely

high

open-loop

gain

(typ

. 20 ,000)

allows

both

the

operating

gain

and

equalization

to

depend

solely

on

the

characteristics

of

simple

passive

components,

which

provides

inherent

long-term

stability

and

reliability

.

In

addition

,

the

s/n

ratio

of

the

IC

is

equal

to

or

better

than

can

be

obtained

in

discrete

designs,

which

leaves

the

noise

performance

primarily

dependent

upon

the

resistors

used

in

...

the

external

circuitry

.

Other

preamplifiers

are

specified

at

10

or

12 mv .

input

for

rated

output.

But

most

modern,

high-performance

cart.ridges

provide

less

than

10 mv .

output

at

normal

program

level,

with

some

as

low

as

5 mv .

So

the

SPARTA

TEP 3S

and

TEP

3M

preamplifi

e

rs

we

re

designed

with

added

gain

for

the

newer

low-output

cartridges

without

compromising

any

other

performance

feature

. An

interesting

side

benefit

comes

about

when

gain

is

adjusted

lower

to

accommodate

high-output

cartridges;

The

gain

reduction

also

reduces

the

noise

,

resulting

in

further

improvement

of

the

already-excellent

noise

figure.

The

input

impedance

of

each

channel

is

set

at

47K

ohms

by

an

internal

1.

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DESCRIPTION:

(cont'd)

resistor.

This

is

the

proper

value

for

virtually

all

monaural

and

stereo

cartridges,

but

can

easily

be

changed,

if

need

be,

by

referring

to

the

schematic

diagram.

Care

should

be

taken

to

use

only

deposited-film,

low-noise

resistors.

The

self-contained

power

-supply

is

extremely

well

regulated

and

will

)

maintain

proper

performance

below

llOV

AC

input.

This

results

in

an

output

hum-level

that

is

virtually

un-detectable

and

completely

masked

by

normal

"white"

noise

produced

by

various

circuit

resistances

.

OPERATION:

Gain

Adjustment:

During

final

test

at

SPARTA,

the

gain

(sensitivity)

of

the

TEP 3S

or

TEP

3M

is

set

for

J5

dbm

output

with

10

mv .

input.

If

they

were

set

for

higher

sensitivity,

then

operation

with

a

high

output

cartridge

would

provide

more

than%

dbm

output

and

seriously

decrease

the

available

headroom

for

program

peaks.

If

the

output

level

of

your

cartridge

is

unknown

and

you

do

not

have

an

NAB

test

record

plus

the

means

to

accurately

measure

the

preamp

output

level,

it

is

suggested

that

the

gain

controls

be

left

at

the

factory

setting.

With

a

test

record

and

a

suitable

meter,

the

1 KHz

reference

tone

at

7

cm/sec

velocity

(lateral)

can

be

played

and

the

gain

controls

set

for

J5

dbm

output

across

600

ohms

(774

mv

.)

or

for

-6

dbm

(387

mv

.)

from

either

plus

or

minus

output

to

ground

(shield).

This

will

assure

the

maximum

program

output

level

while

maintaining

a

minimum

of

10

db

head

room.

Note

that

the

7cm/sec.

lateral

test

tone

will

produce

the

same

level

in

each

channel

of

a

stereo

unit

as

a

Scm/sec

left

or

right

channel

only

tone

will.

2•

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I

OPERATION

(Cont'd)

Balance.

Since

a

lateral

test-tone

should

produce

equal

outputs

from

each

half

of

a

stereo

cartridge,

the

method

described

automatically

assures

a

balanced

output

from

the

preamp

system,

for

the

gains

are

being

set

also

to

compensate

for

any

cartridge

unbalance.

Further

tests

may

be

made

at

other

frequencies

to

determine

if

the

system

is

retaining

proper

balance

throughout

the

audio

range.

Balance

may

also

be

set

by

playing

a

mono

record

and

noting

the

console

VU

meters.

Balance

should

be

accomplished

by

reducing

9ain

of

the

channel

which

is

too

high,

which

again

insures

that

gains

have

not

been

increased

to

the

detriment

of

the

adequate

headroom.

Input

is

made

via

a

standard

phone

jack

plus

a

separate

front-panel

ground

stud.

The

stud

is

provided

for

the

separate

tone-arm-shell

ground

lead

which

is

often

provided

and

is

also

the

proper

place

to

connect

the

turntable

frame

ground.

Tone-arm

to

preamp

cables

should

not

be

much

longer

than

30

inches

since

excessive

capacitive

loading

will

affect

the

cartridge

high-frequency

response.

Output

is

taken

from

the

six-pin

panel

socket

using

the

plug-in

connector

provided.

Refer

to

the

schematic

diagram

for

proper

connections,

noting

that

pins

'1

and

2

are

not

used

on

the

TEP

3M

(monaural)

and

taking

care

to

note

proper

output

phasing

on

the

TEP 3S

(stereo)

as

indicated

by

the

polarity

indications.

It

should

also

be

noted

that

outputs

are

true

differential

balanced-to-ground

in

the

standard

versions,

and

care

must

be

taken

tra

t

neither

output

is

.....,.

shorted

to

ground.

If

single-ended

output

is

needed

for

testing

purposes,

it

can

be

taken

from

either

plus

or

minus

output

and

ground,

with

the

attendant

6db

3.

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OPERATION

(Cont'd)

Output

(cont'd)

reduction

in

overall

output

level.

Output

connections

are

normally

made

with

standard,

twisted-pair

shielded

audio

cable,

although

separate

single

shielded

cables

will

work

equally

well.

The

source

impedance

of

the

TEP

3S/M

is

quite

low,

so

cables

of

any

reasonable

length

may

be

used.

In

the

interest

of

RFI

reduction,

however,

the

cables

should

be

no

longer

than

required

and

the

shields

may

be

left

floating

at

one

end

only,

usually

the

source

end,

to

prevent

magnetic

field

pickup.

The

best

arrangement

can

be

determined

experimentally

for

the

individual

installation.

As

stated

earlier,

hum

is

virtually

non-existent

in

the

TEP

3S/M.

If

hum

is

experienced

in

a

final

installation,

it

will

most

likely

be

due

to

pickup

in

the

cartridge

or

tone-arm

leads.

This

can

be

determined

by

shorting

the

preamp

inputs

with

shorting-plugs.

If

the

hum

disappears,

it

was

iptroduced

before

the

preamp.

Similarly,

disconnecting

the

preamp

output

plug

will

determine

if

hum

is

coming

through

or

from

the

preamp.

If

the

output

cable

shield

was

originally

connected

to

the

preamp

output

shield

terminal

(3),

it

should

be

disconnected

and

the

plug

then

reinserted

to

eliminate

any

ground-loops

through

the

shield.

Also,

it

is

worthwhile

to

determine

if

the

load

(console)

has

a

grounded

center-tap

on

the

primary

of

the

input

transformer.

If

so,

this

ground

should

be

broken,

so

the

input

is

isolated

from

any

possible

ground-loops.

Rumble

filter.

Both

the

TEP 3S

and

TEP3M

preamps

incorporate

rumble

suppression

in

the

form

of

a

controlled

low-frequency

characteristic

as

described

in

the

Circuit

Theory

section.

Response

is

shaped

so

as

to

be

nearly

2

db

down

at

30

Hz

and

3

db

down

at

20Hz.,

approaching

a

12db-per-octave

slope

_

at

the

usual

rumble

frequencies.

The

suppression

thus

obtained

is

more

than

4.

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OPERATION

(Cont'd)

Rumble

filter

(cont'd)

adequate

for

essentially

rumble-free

operation

with

any

reasonable

turntable,

without

restricting

low-frequency

reproductim

of

program

material.

High

frequency

filtering

.

As

indicated

earlier,

the

input

impedance

of

the

TEP 3S

and

TEP

3M

preamplifiers

is

47 K

ohms.

If

a

cartridge

is

terminated

in

a

higher-than-optimum

impedance,

undesirable

high-frequency

peaking

will

result

.

If

a

lower

value

is

used,

however,

the

terminating

resistor

with

the

cartridge

inductance

will

result

in

a

rolloff

of

the

higher

frequencies.

Filtering,

then,

can

be

obtained

simply

by

providing

a

lower

terminating

resistance.

The

proper

value

is

best

determined

by

trial-and-error

until

the

desired

rolloff

is

obtained.

A

resistor

may

then

be

added

directly

across

the

input

phone

jack(s)

without

altering

components

on

the

circuit

board.

5.

Cetec Broadcast Group TEP3S User manual

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