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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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.

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MAINTENANCE -

Circuit

Theory:

Power

Supply

:

The

TEP

3S/M

power

supply

is

a

hard-regulated

design

capable

of

supplying

30

to

33 VDC

at

40

ma

continuous.

The

output

voltage

is

determined

by

the

values

and

tolerances

of

D3

,

RS

and

R6.

Since

these

are

5%

tolerance

cc;>mponents,

it

would

theoretically

be

possible

for

the

output

voltage

to

fall

between

29

.1

and

33.

9

volts

.

In

fina

l

test

,

however

,

one

of

those

components

is

changed,

if

required

,

to

hold

the

voltage

within

proper

limits

.

The

maximum

load

current

is

determined

primarily

by

the

limits

of

the

power

transformer,

Tl.

Normal

operation

is

as

follows:

The

rectified

DC

supplied

by

Tl

and

diodes

Dl

and

D2

provide

·a

nominal

40

V DC

across

filter

capacitor

C2

.

This

voltage

will

vary

between

mono

and

stereo

units

and

also

vary

with

input

line

voltage

.

Proper

operation

can

be

expected

with

as

low

as

34

to

36

volts,

however

,

so

long

as

this

voltage

is

4

or

5

volts

higher

than

the

expected

output

voltage.

When

first

turned

on

,

the

voltage

from

C2

causes

current-flow

through

R2

,

R3

and

the

emitter-to-base

junctions

of

Q2

and

Ql

.

Q2

is

a

Darlington

driver

,

or

current-multiplier,

so

Ql

and

Q2

may

be

considered

as

a

single

transistor

with

very

high

current-gain

(hfe

).

Ql

will

conduct

very

heav-ily,

delivering

current

through

the

load

until

the

QUtput

voltage

rises

to

rated

le

vel.

During

this

rise,

Q3

has

not

been

able

to

conduct

because

the

emitter

has

been

rising

with

the

output

voltage,

but

the

base

voltage

has

been

lower

than

the

emitter

due

to

divider

RS/R6

.

With

Q3

not

conducting

,

all

of

the

current

through

R2

and

R3

is

being

used

to

turn

on

Ql/Q2.

6.

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I

MAINTENANCE -

Circuit

Theory

:

Power

Supply

(cont'd)

When

the

output

reaches

22

volts,

zener

diode

D3

begins

to

conduct

and

prevents

the

emitter

of

Q3

from

rising

further.

But

Q3

still

cannot

conduct

until

its

base

voltage

has

risen

0.

6

volts

higher

than

its

emitter

.

This

cannot

occur,

due

to

divider

RS/R6,

until

the

output

voltage

reaches

the

proper

level

.

As

the

output

voltage

attempts

to

rise

above

normal

,

Q3

comes

into

conduction

and

draws

current

from

R2/R3,

which

in

turn

decreases

the

drive

current

to

Q2.

Thus,

a

state

of

equilibrium

is

reached

wherein

any

tendency

of

the

output

voltage

to

change

will

signal

Q2

to

cause

an

increase

or

decrease

in

base

drive

to

Q2

.

Cl

protects

diodes

Dl

and

D2

from

line

transients.

C3

prevents

de

pulses

from

~

r

power

supply

from

reaching

Q2

and

appearing

in

the

output

and

also

causes

a

slow

turn-on

characteristic

.

Rl

limits

the

peak

current

through

the

diodes

at

turn-on

and

also

limits

the

power

dissipation

in

Ql.

C4

filters

the

zene

r

noise

and

CS

improves

the

ac

regulation

by

bypassing

the

attentuator

RS/R6.

There

is

a

frequency

in

the

several-hundred

KiloHertz

region

where

phase-shift

through

Q3,

Q2

and

Q1

would

exceed

180

degrees

.

C6

reduces

the

loop

gain

of

the

regulator

circuit

to

less

than

unity

to

prevent

oscillation.

Troubleshooting.

When

servicing

solid-state

circuits,

a

knowledge

of

only

a

few

characteristics

of

transistors

plus

the

application

of

a

little

thought

is

usually

all

that

is

needed.

For

example

(1)

a

normally-operating

silicon

transistor

will

always

have

a

base

voltage

that

is

about

0.

6

volts

different

than

the

emitter

,

i.e.

the

emitter-to-base

junction

must

be

forward-biased

(0.

25v

for

germanium)

.

(2)

The

collector

voltage

will

always

lie

between

7.

www.SteamPoweredRadio.Com

MAINTENANCE -

Circuit

Theory:

Troublesh

o

oting

(cont'd)

the

emitter

voltage

and

the

collector

supply

voltage

. (

3)

If

we

short

the

emitter

to

the

base,

the

transistor

should

turn

off

,

so

the

collector

will

look

like

an

open

circuit

and

the

collector

voltage

will

rise

towards

the

supply

voltage

.

Considering

these

factors

,

let

us

now

apply

them

to

several

possible

power

supply

malfunctions:

1 .

No

output

voltage

.

a)

Voltage

across

C2

higher

than

normal

would

indicate

that

Ql/Q2

is

not

conducting

.

If

the

voltage

at

Q2's

base

indicates

that

both

Ql

and

Q2

have

normal

forward

bias,

then

collectors

of

Ql

and

Q2

must

be

open.

If

the

bias

voltage

of

Ql

or

Q2

is

much

more

than

O.

6v

each

,

then

either

a

base

or

an

emitter

must

be

open

.

b)

Voltage

across

C2

lower

than

normal

would

indicate

excessive

load

current

and

suggest

a

shorted

C6,

in

which

case

Ql

and

Rl

would

be

very

hot

.

In

this

event

,

either

Q

l,

Q2

or

Rl

would

probably

burn

open

and

result

in

(a)

above

.

2 .

Output

voltage

high

. -

This

would

indicate

that

Q3

is

not

diverting

current

from

R2/R3,

allowing

Q2/Ql

to

turn

on

full

.

Check

for

normal

zener

voltage

at

the

emitter

of

Q3

and

then

for

normal

base

voltage

at

Q3

. An

open

zener

will

raise

the

Q3

emitter,

or

an

open

RS

will

lower

the

Q3

base

--

either

one

will

turn

off

Q3

.

If

the

emitter-to-base

voltage

of

Q3

is

normal

,

then

Q3

must have

an

open

collector

.

3 .

Output

Volt:ige

low

.

In

all

such

cases

,

the

first

step

is

to

determine

the

status

of

Q3

by

8 .

I

www.SteamPoweredRadio.Com

I

MAINTENANCE -

Circuit

Theory

:

3 .

Output

Voltage

low;

(cont'd)

measuring

emitter

and

base

voltages.

Next,

determine

that

Q3

is

responding

to

the

base

voltage

by

shorting

Q3

emitter

to

base

--

the

output

voltage

should

rise

.

If

it

does

rise,

it

almost

certainly

indicates

a

failure

in

the

base

divider

such

as

an

open

R6

or

shorted

CS .

If

it

does

not

rise

it

is

very

likely

that

Q3

has

an

emitter

to

collector

short

.

It

can

be

seen

by

the

examples

given

that

the

basic

approach

in

transistor

servicing

is

one

of

determining

if

the

transistor

has

normal

emitter-to-base

bias,

and

then

noting

if

the

collector

responds

normally

to

a

change

of

this

bias,

such

as

complete

removal.

This

explains

in

part

why

most

companies

including

SPARTA

do

not

provide

transistor

sockets

--

it

is

much

too

easy

to

determine

if

a

transistor

is

operable

without

introducing

the

liklihood

of

intermittent

socket

contacts,

quite

aside

from

the

added

cost

factor

.

9 .

www.SteamPoweredRadio.Com

Preamplifier.

The

TEP 3S

and

TEP

3M

preamplifiers

utilize

an

integrated-circuit

operational

amplifier;

a

term

which

aptly

describes

its

common

useage

in

performing

mathematical

operations.

And

the

characteristics

which

make

it

valuable

in

computers

also

make

it

ideal

for

use

as

an

equalized

preamp.

An

"op-amp"

is

characterized

by

having

differential

.

input

terminals;

that

is,

a

plus

or

non-inverting

input

and

a

minus

or

inverting

input,

and

also

by

having

extremely

high

open-loop

gain

capability

as

compared

to

its

normal

operating-level

gain.

A

signal

applied

to

the

plus,

or

non-inverting

input,

will

appear

amplified

at

the

output

terminal

and

in-phase

with

the

input

signal.

The

IC

op-amp

.

used

in

the

TEP 3

series

has

a

typical

open-loop

gain

of

20,000,

so

the

output

will

try

to

be

20,000

times

larger

than

the

input

signal.

If

the

output

signal

is

now

connected

back

to

the

minus,

or

inverting

input,

the

fed

-back

signal

will

act

to

cancel

the

input

signal.

Cancellation

will

only

take

place

when

the

two

input

signals

are

equal

in

amplitude

and

phase

(th

e

necessary

phase-inversion

takes

place

at

the

minus,

or

inverting

input),

and

so,

if

all

the

output

also

appears

at

the

minus

input,

the

output

is

forced

to

follow

the

original

signal

input

and

we

have

a

unity-gain,

voltage-follower.

Maintenance

of

the

TEP 3

series

preamps

is

made

very

easy

by

applying

the

principle

just

described

to

set

the

DC

operating

point

of

the

IC

amplifier,

so

that

two

simple

DC

voltage

measurements

are

all

that

is

required

to

10.

I

.I.

I

www.SteamPoweredRadio.Com

I

Maintenance

(Cont'd)

assure

the

IC

is

operating

properly

and

is

capable

of

responding

to

the

input

signal.

Transistors

and

!Cs

do,

of

course,

have

frequency

limitations,

but

these

are

included

in

the

original

circuit

design.

And

any

subsequent

failure

of

a

solid-state

device

will

invariably

aff~ct

both

the

AC

and

DC

operation

of

the

device.

So

again,

if

the

IC

will

respond

properly

to

the

DC

voltages

used

to

set

the

operating-point,

it

will

also

respond

properly

to

normal

signal

inputs.

Referring

to

the

schematic

diagram,

when

the

circuit

is

first

turned

ON,

capacitor

C2

charges

very

rapidly

to

8

volts

or

so,

or

one-half

of

the

voltage

at

14

of

the

IC,

through

divider

R3/R2.

This

voltage

also

appears

through

Rl

as

an

input

voltage

to

the

IC,

so

the

output

at

1

swings

towards

the

supply

as

fast

as

it

can

charge

C9.

At

the

same

time,

the

output

voltage

begins

to

charge

C3

through

R4,

R6

and

R7

(We

will

ignore

Dl

for

the

moment).

Because

of

the

high

value

of

R7,

C3

will

require

nearly

40

seconds

to

charge

to

8

volts,

but

once

it

does

it

will

cancel

the

input

voltage

at·

5,

since

the

voltage

of

C3

is

also

present

at

the

inverting

input,

6

of

the

IC.

The

output

voltage

will

now

fall

until

it

is

equal

to

the

voltage

at

.

:

5

and

a

state

of

equilibrium

is

reached.

Any

attempt

at

deviation

appears

as

an

error-voltage

at

6,

and

the

full

open-loop

gain

of

the

IC

is

used

to

hold

the

output

in

agreement

with

the

plus

input.

11.

www.SteamPoweredRadio.Com

;

Maintenance

(Cont'd)

Since

the

time-constao.t

·--

0f

C3/R7

is

quite

long,

the

voltage

across

G3

can

only

res

pond

to

the

average,

or

very

low

frequencies

in

the

output.

At

frequencies

in

the

audio

range,

C3

appears

as

a

near

short-circuit

so

gain

is

no

longer

limited

to

one,

or

unity.

Diode

Dl

is

added

so

that

at

turn-on

capacitor

C3

can

charge

more

rapidly

through

R4

up

to

7

.4

volts

(the

8

volt

reference

less

th~

0.

6

volt

diode

drop).

As

C3

continues

to

charge

the

·

aiode

drops

out

of

conduction

and

plays

no

further

part.

This

allows

the

circuit

to

turn

on

and

stabilize

in

10

seconds

or

less.

To

assure

that

the

IC

is

operating

normally,

it

is

only

necessary

to

measure

the

voltage

at

:

5

and

then

check

to

see

that

1

has

the

same

voltage.

If

the

output

voltage

is

high,

the

is

to

see

if

this

voltage

is

getting

back

to

6.

Incidentally,

these

measurements

must

be

made

with

a

high-impedance

VTVM

or

FETVM.

If

the

voltage

at

6

is

also

higher

than

5,

the

IC

is

defective.

Conversely,

if

the

output

is

low,

it

can

only

be

due

to

an

external

short

or

defective

IC.

In

the

stereo

TEP 3S

these

measurements

must

of

course

be

made

for

both

halves

of

the

IC,

using

the

9ppropriate

numbers

as

indicated

on

the

schematic

.

It

should

be

noted

that

IC

failures

are

quite

rare,

and

it

is

worthwhile

to

be

very

sure

before

going

to

the

expense

and

trouble

of

re-

placing

one.

If

it

does

become

necessary

it

should

be

removed

very

caref.

fully

to

avoid

damaging

the

PC

board.

Use

of

a

solder-removing

tool

or

wick

is

strongly

recommended.

12.

I

www.SteamPoweredRadio.Com

I

Audio

operation

of

the

IC

amplifier

is

identical

to

the

DC

and

low-frequency

operation

described

with

the

exception

of

the

gain

changes

allowed

by

the

components

in

the

external

feedback

network.

For

all

frequencies

in

the

audio

range,

capacitor

C3

is

essentially

a

short-circuit

so

that

R4

now

becomes

part

of

a

voltage-divider

in

the

feedback

path.

At

the

lowest

audio

frequencies,

the

gain

is

the

highest,

more

than

60db,

since

the

capacitors

C6

and

C7

have

very

little

effect

and

the

output

signal

must

now

be

quite

high

in

order

to

produce

a

cancelling

signal

through

the

feed-back

network

.

As

the

input

frequencies

increase,

however,

more

feedback

occurs

through

C6

and

C7

and

the

closed-loop

gain

decreases

accordingly.

So

it

is

apparent

that

the

gain

and

frequency

response

are

determined

strictly

by

the

values

and

tolerances

in

the

feedback

network,

primarily

R6, R7,

C6

and

C7.

If

it

is

suspected

that

the

amplifier

is

not

within

the

nominal

0.

5

db

of

the

RIAA/NAB

curve,

this

should

be

carefully

verified

with

an

audio

generator

and

output

meter

known

to

be

accurate

within

0

.1

db

over

the

audio

range.

It

is

not

sufficient

to

rely

upon

a

test

record

and

playback

cartridge,

since

even

the

best

of

these

are

subject

to

variations

of

plus

or

minus

a

db

or

more.

Rumble

filtering

is

provided

by

capacitors

C9

and

Cl0

plus

resistors

R9

through

Rl3.

These

components

allow

a

rolloff

of

nearly

2

db

at

30

Hz

and

3

db

at

20

Hz,

with

a

curve

approaching

12

db/octave

below

20

Hz.

In

addition,

C3

becomes

ineffective

at

12

to

15

Hz,

allowing

an

even

more

rapid

rolloff

towards

unity

gain.

13.

www.SteamPoweredRadio.Com

The

output

amplifier,

Q4,

is

a

paraphase

inverter

which

supplies

a

balanced,

differential

output

to

the

external

600

ohm

load.

The

emitter

signal

is

a

replica

of

the

base

signal,

but

the

collector

signal

is

equal

in

amplitude

and

out

of

phase

with

the

emitter.

Therefore,

the

output

amplifier

provides

a

transformerless

output

with

6

db

of

added

gain,

without

the

weight,

bulk,

hum-pickup

or

frequency

limitations

associated

with

transformers.

Several

side

....

benefits

of

operational

amplifiers

are

of

incidental

interest:

If

the

open-loop

gain

were

infinite,

rather

than

just

high,

the

application

·

of

negative

feedback

would

reduce

distortion

to

zero

because

the

output

would

be

forced

to

follow

the

input

exactly.

In

the

TEP 3

s,

the

nominal

open-loop

gain

is

86

db

whereas

the

maximum

closed-loop

gain

is

slightly

over

60

db.

This

assures

a

minimum

of

more

than

20

db

of

feedback,

which

accounts

for

the

extremely

low

distortion,

typically

0.

03%.

The

same

negative

feedback

has

the

effect

of

raising

the

input

impedance

in

direct

prop

:

xtion,

so

that

the

actual

input

impedance

of

the

preamplifier

becomes

that

of

the

input

terminating

resistor,

Rl.

This

assures

perfect

termination

for

the

cartridge

simply

by

selecting

the

correct.resistor

.

Negative

feedback

also

lowers

the

output

impedance

which

provide

·s a

pure

voltage

drive

for

the

equalizing

components

-in

the

feedback

network.

This

further

assures

that

performance

depends

solely

on

the

feedback

components

.

The

end

result

is

a

preamplifier

which

is

hum-free,

and

represents

state

-

of-the-art

performance

in

regards

to

noise,

distortion

and

faithful

reproduction.

14.

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www.SteamPoweredRadio.Com

I

Pin 1

Pin 2

3

Pin 4

Pin 5

Note:

Pin 1

Pin 2

3

Pin 4

Pin 5

Note:

TEP-3

OUTPUT CONNECTIONS

BALANCED

Right

output

(+)

Right

output (-)

Common

(See Note)

Left

output

(-)

Left

output

(+)

In

balanced

lines

the

shield

is

normally

left

floating

at

the

audio

source

and

is

connected

to

ground

at

the

audio

console.

But,

if

RF!

is

experienced,

it

may

be

necessary

to

ground

the

shield

at

the

TEP-3

also.

UNBALANCED

(Not

used)

Right

output

Common

Shield

Left

Output

(not

used)

Pins 1

&

2

not

used

on

TEP-3M

15.

Cetec Broadcast Group TEP3S User manual

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