Inovonics 375 Instruction Manual

INSTRUCTION

MANUAL

MODEL

375

TAPE

RECORDING

ELECTRONICS

August,

1975

0-

INOVONICS

1630

DELL

AVE

.,

CAMPBELL,

CALIF

95008

INCORPORATEO

(408)

374·8300

TABLE

OF

CONTENTS

SECTION

1.0

2.0

3.0

4.0

GENERAL

INSTALLATION
OPERATIJN
ALIGNMENT
PARTS
SCHEMATICS.

INFORMATION

AND

USE

AND

FUNCTIONAL

AND

MAINTENANCE

LIST.

........

. . . . . . . .

DESCRIPTION

PAGE

.

2

7

9

·

17

·

23

•

28

SECTION

1.0

GENERAL

INFORMATION

The

lnovonics

375

is

a compact, up-to-date magnetic recording

elec-

tronicspackage, completely self-contained with

integral

power

supply.

Available in several versions, the

375

is

equally well suited to

new

installations,

or to

improve

the performance

and

reliability

of

older

professional tape recorders.

The

375

is

delivered with proper interconnect cabling for whatever

tape

transport

is

specified

for

use

with

it.

When

no

specification

is

made,

the unit

is

supplied with cabling for

Ampex

350/351

series

mqchines.

Among

the features incorporated are:

Calibrated positions

on

Record

and

Reproduce

gain

controls.

Provision for remote switching

of

all

monitor

and

equalization

functions,

and

solid-state

switching to eliminate contact noise

problems.

3-speed equalization to

accommodate

any

combination of

NAB

and

IEC

characteristics.

Harmonic

and

phase

distortion

nulling

circuits.

Able

to

accommodate a wide

variety

of

original-equipment

and

replacement heads.

Optional

SYNC

Reproduce

Amplifier with independent equalization

and

automatic

SYNC-INPUT

monitor

transfer

switching (-03 version

only).

-2-

1.1

SPECIFICATIONS

NOTE:
by

for upgrading older recorders in broadcast
as well
cations are given, each with respect to the heads, tape

generally in use in each

tains

1.1.1 Specifications derived using

replacement

Frequency

Signal-to-Noise

Performance

the

heads

as

those

of

and

tape employed. ihe Inovonics

for

new

studio

specifications

head

Response

3.75

assembly

;

ps

15

ips

7.5
ips

Ratio (in

(in

a magnetic recording system

375

and

similar

installations.

installation

which

on

an

Ampex

Hz)

+2dB
+2dB
+3dB

dB,

referred

are not

3M

Hence

situation.

application

206

tape

351

t , ansport.

a "peak"

to

two

and

20
20
20

is

limited in

is

sets

A

third

oriented.

a Taber

20k
15k

8k

-

record 1evel

part

intended both

applications,

of

specifi-

and

standards

group con-

full

track

6dB

above

3.75 ips

Erase/Bias Frequency

100kHz

Erasure

70dB
saturation.

200nW/m,

15

ips

7.5 ips

erasure

or

approx.

OVERALL

u'wtd.

-67 -76 -76

-69 -77

-66 -74

of

500Hz

3dB

below

NAB

wtd.

signal recorded

3%

THO;

STANDBY

u'wtd.

-76

-72 -83

3dB

below

20Hz -20kHz)

NAB

wtd.

-87

-86

tape

--

-3-

Recorded

Distortion

(at

15-mil

wavelength bias

LIN

out

peak -typical)

LIN

in

1.1.2

of

320nW/m

duce)

Operating
6dB

above

8dB

above

10dB

above

Specifications derived using

and

heads

- 70-mil

Level
Op

Level

Op

Level

Op

Level

Nortronics

track

cations.

Frequency

Response

30

ips
ips

15

(i n

Hz)

7.5 ips

Signal-to-Noise Ratio (in

20Hz -20kHz)

u 'wtd. wtd. u 'wtd. wtd.

.45%

2%
3%

5.5%

3M

250

tape,

9227

(erase),

9203

(record)

width format, typical

+2dB
+2dB

+2dB

dB,

referred

OVERALL

60 -22k

30 -22k
20 ~ 16k

to approx.

SYNC

.02%

.015%

.02%

2.2%

an

Operatinq

and

of

multi-track

(SYNC

640nW/m

Level

9213

(repro-

appli-

reproduce
response essen­tially
to

or

identical

normal

3%

THO;

overall)

STANDBY

u'wtd. wtd.

30

ips

15

ips

7.5 ips

Erase/Bias Frequency

250kHz

Erasure

lOdB

level,

erasure

or approximately

-71

-67

-67 -76

of

500Hz

-78 -71 -80 -80 -87

-77

signal recorded

3dB

-4-

-67

-67 -77

below

-77

12dB

tape

above

saturation.

-75 -86

-74 -85

Operating

Recorded

Distortion

(at

IS-mil wavelenth bias

LIN

out

peak -typical)

LIN

,in
Operating
3dB

above

6dB·above

Level
Op

Level

Op

Level

.5%

1%

2.5%

1.1.3 Specifications Independent of Application

Equalization

3 speed with pushbutton
tween

modates

30

INTER

and

NAB,

LOW

lEe

ips operation.

(or

when

mixed)

selection,

transport

characteristics

automatic switching be­provides closure.

Amplifier Distortion

Record:

~.1%

<:.25%

THO
THO

at

Op

25dB

Level

above

Op

Level

.15%

.3%
.8%

for

Accom-

3.75 through

Input '

Outputs

Reproduce:

<:.1%

~.5%

THO
THD

Sensitivity:

Impedance:

Line

Out~ut:

Headphones:

at

Op

Level

at

+24dBm

-20 to

Line Output (clipping level

+8dBm
input transformer)
10K

bridging

feeds

terminated

600

line,

or

Front panel jack

(-8

to ,-f:8dBm

balanced

not,

at

+4

with

or
or

-01

unbalanced,
+8dBm

+25dBm)

option

for

Zero-VU.

-5-

Panel

Controls

RECORD

GAIN

(with

pre-set

CAL

position)

REPRO

LEVEL

(with

pre-set

CAL

position)

MONITOR:

selects

between

INPUT,

REPRO

and

SYNC

(-03 versions)

SAFE/READY

RECORD
EQUALIZATION:

manual

selection of

HIGH,

INTER

or

LOW.

POWER

Power

Requirement

105-130

VAC

(230V

available)

SO/60Hz,

.3A

(plus transport)

Size

and

Shipping

Weight

x

19

11

3~1I

X

10"

15 1bs

-6-

SECTION

2.0

INSTALLATION

AND

USE

2.1

Upon

receipt

of

the equipment, inspect for shipping

damage.

Should

any

be

observed, notify the

carrier

immediately;

if

not,

proceed

as

outlined

below.

It

is

suggested

that

the

original

ship-

ping carton

and

materials

be

saved for possible future reshipment.

2.2

The

375

is

packaged to

mount

in a standard 19-inch equipment

rack, requiring

3~-inches

of

panel space.

When

replacing

original

electronics

in

an

overbridge

above

the

transport,

it

may

be

necess-

ary to

drill

and

tap

an

additional

two

holes to

accommodate

the

375

panel.

2.3

The

signal,

head

and

transport

connectors are

directly

compati-

b'~

with

Ampex

350,

351

and

354

equipment. Units ordered

for

use

with

other

transports-

or for use in

stereo

pairs are supplied with

appropriate interconnect cabling.

2.4 Unless supplied otherwise to special order,

units

intended for

mono

or

stereo

installations

are delivered properly aligned for

use

with

3M

206

tape

at

an

operating level

of

200nW/m,

with

Ampex

351-

type

heads

(1.

5mHy

erase,

5-10mHy

record

,and

·lHy reprod'lce)

and

100kHz

bias. Units for

multi-track

use

normally operate with lower

inductance

heads

(O.5mHy

erase,

4-5mHy

record,

and

400mHy

reproduce),

utilize

250kHz

bias,

and

incorporate the optional

SYNC

reproduce

amp-

lifier:

Heads

with inductances other than those suggested

above

can

be

accommodated.

Section

4.1.4.2

outlines

the necessary changes.

2.5

As

delivered, the

375

is

calibrated

to operate

at a +4dBm

signal

level.

Should

operation

at

+8dBm

be

necessary,

clip

the jumper

shun-

tingthe

4.7K

resistor

near the

line

output connector

and

recalibrate

as described in paragraph

4.1.2.8.

2.6

The

low

source

impedance

of

the

375

line

output

results

in only

about

~dB

level

change

from

an

unloaded to

600

ohm

loaded condition .

._.

-7-

The

375

should,

nevertheless,

be

connected to

its

intended load

prior

to final

calibration.

2.7

Even

with the optional input

isolation

transformer option sup-

plied (-01 version

only),

the

375

input impedance

is

10K

ohms

or

greater.

Should the equipment feeding the

375

require

a terminating

load, a

600-ohm

resistor

should

be

placed in

parallel

with the

375

input.

2.8

No

provision for meter

indication

of

bias

or

erase

current

is

made,

as

the inherent

stability

of

the

circuitry

is

greater

than

that

of

the

heads

and

meter

at

bias frequencies.

2.9

When

two

Ot'

more

375's are

employed

in dual

or

multi-track

ap-

plications,

the interconnecting cablinq supplied

delivers

AC

power

to

all

units

and

to the

transport,

if

it

derives

power

from

the

elect-

ronics.

The

cabling also "slaves"

all

erase/bias

amplifiers

to a

single

oscillator,

thereby avoid-ing bias "beats"

or

the

necessity

of

synchronizing

two

or

more

oscillators.

-8-

SECTION

3.0

OPERATION

AND

FUNCTIONAL

DESCRIPTION

3.1

OPERATION

3.1.1

The

RECORD

GAIN

and

REPRO

LEVEL

controls are provided with a

detented

CAL

position

at

full

CCW

rotation.

They

are normally

left

in these positions except for temporary correction

for

an

improperly

recorded tape

or

abnormal

line

level.

Range

is

adequate to record

from a -20dBm

line

level

(-8dBm

with optional input transformer)

and

to produce

normal

line

output

from

a tape under-recorded

by

10dB.

3.1.2

The

MONITOR

buttons determine whether the

line

amplifier will

derive

its

si9~al

from

the incoming

program

(INPUT),

the reproduce

head

(REPRO),

or in versions with

-03

option, the record

head

(SYNC).

When

any

button

is

only

slightly

depressed to

release

all

three to

their

"out"

position,

the monitor

selection

is

transferred

to the

rear

panel

REMOTE

connector.

On

versions with the -03 option,

mon-

itor

is

automatically switched

from

SYNC

to

INPUT

when

entering the

record

mode.

3.1.3

The

alternate-action

SAFE/READY

switch,

when

depressed, per-

mits the

375

to

enter

the record

mode

when

the

transport

is

in "record".

When

this

button

is

"out", the

375

will not

enter

the

recoY'd

mode,

thereby preventing accidental

erasure

of a tape or

that

track

of a dual

or

mult-track recording.

3.1.4

The

RECORD

button places the

transport

in the record

mode.

The

button will not illuminate, though,

nor

will

~he

375

go

into "record"

unless the

SAFE/READY

button

is

depressed.

In

dual

or

multi-track

in-

stallations,

depressing

any

RECORD

button will place the

transport

in

the record

mode;

only those

375 1 s in "ready" wi.l record,

however.

3.1.5

The

EQUALIZATION

buttons

select

record

and

reproduce equal-

lizationappropriate

to the

transport

speed

employed.

Three independ-

ent

sets

of

equalizers are provided, although

most

transports

are only

-9-

dual
a

European

speed

units.

or

other non-standard curve.

In

these cases the

third

In

position

may

be

used for

the event of use with a

transport providing

an

switch, the equalization
matically
wired)

between

by

depressing

INTER

an

three buttons are "out".

3.1.6
375

3.1.7
through a

or

3.1.8

and

as

The

alternate

to the

The

470

an

unbalanced, uncalibrated

The

transport,

PHONES

ohm

recessed

action

jack
resistor.

slide

enables or defeats the

equalization-switching pole

selection

and

LOW

EQUALIZATION

POWER

if

it

is

connected

It

can

be

transferred

(if

the

transport

button

slightly

switch controls

is

powered

ahead

is

suitable

line

by

of

for

output for servicing.

the

the output transformer

on

the speed
to change auto-

is

appropriately
so

that

AC

power

electronics.

headphone

monitoring

switch behind the adjustment cover panel

linearization

circuit,

(see paragraph

all

to the

4.2.1).

-10-

3.2

CIRCUIT

DESCRIPTIONS

3.2.1 General

Electronic

circuitry

for the Recording, Reproducing

and

Erasing

Amplifiers

iS

,contained

on a single

"piggy-backed" plug-in assembly.

The

lower board (Reproduce)

carries

the Reproduce, optional

SYNC

and

Line Amplifiers; the upper board (Record), the Erase/Bias

and

Record

Amplifiers. Another

single

PC

assembly within the chassis contains

the

power

supply

and

bias

oscillator

circuits.

3.2.2

Reproduce

Amplifier

(sche~atic

129000).

Signals

from

the reproduce

head

enter

on

pins

13

and

14.

An

option-

al

head

input transformer (-04 version only)

can

be

strapped in to

permit

use

of

low

(4-5mHy)

inductance heads. Resistor

Rl

is

selected

to

dampen

head

resonance

and

yield

smoothest playback response (see

paragraph

4.1.2.4).

Transistors

Ql

and

Q2

form

a complementary feedback-pair input stage,

Q3

serving primarily as

an

emitter-follower buffer.

DC

feedback

is

maintained through

RIg

and

Rll, bypassed

at

audio frequencies

by

C2.

AC

feedback .

is

routed througli

an

appropri

ate

equa

1i

zat ion

network

by

FET

switches

Q4,

Q5

or

Q6.

A secondary function

of

Q3

is

to provide

a phase-inverted reproduce signal

(at

the

collector)

for the repro-

duce

phase compensation

circuit.

This

signal,

coupled through

C7,

'

interacts

with the in-phase

emitter

signal fed through

R25

to provide

an

adjustment

of

reproduce phase

shift

to

complement

and

cancel the

phase

shift

which

normally occurs during the recording process.

FET

switch

Q7,

normally on, defeats

this

compensation, except

at

the

one

speed for

which

the adjustment

is

made

(see paragraph

4.2.2.2).

IC2

imparts voltage gain to the reproduce

signal,

with

R28,

the

REPRO

CAL

adjustment, providing a controi over the gain

and a means

of

obtain-

ing a given signal level for a

variety

of

head

outputs. This amplified

signal

is

fed through

R29,

bridged

by

the front panel

REPRO

LEVEL

con-

-11-

trol,

to the L ineAmpl

ifier.

3.2.3

The
tially

that

R53

gain. This

has

3.2.4

FET's

SYNC

Amplifier

optional

identi~al

the

is

increased over

head

SYNC

input transformer

is

greater

output than a

Line Amplifier

Q8,

Q9

and

required

Q28
Amplifier, passing
and

SYNC

Amplifier,

sistors
circuit
ground

are normally held
between

potential

the source

either

reproduce

to the

Reproduce

that

as

perform

signals

respectively.

at

by

amplifier

Amplifier

is

always used,

of

its

counterpart
the record
true

from

reproduce

an

input switching function for the Line
the

The

-20

volts,

and

drain.

the

front

(-03 version only)

head

used

head

Reproduce

just

discussed, except

and

the value

R3

to reduce overall

as

a reproduce

of

similar

Amplifier, input source,

gates of these switching

introducing

When

panel

MONITOR

the gate

an

effective

is

brought to

switch or through

is

essen-

of

head

inductance.

tran-

open

REMOTE

the
selected

Transistor
option (-03 version

INPUT

R34,

monitor

36,
beginning
might appear

IC1

performs the vcltage gain function
gain
Ql1

established

and
driving
short

circuits

connector, the source-drain

signal.

Q29

and

associated

when

C10

and

12

at

about
at

the

by
associated
low

impedance

is

only),

the

are

30kHz.

line

feedback

components

afforded

switching the

375

enters

part

This aids in reducing whatever bias signal

output, primarily in the

loads

and

by

resistance

circuitry

the record

of

an

resistors

is

active

of
R35

part

of

line

amplifier

mode.

low-pass

the Line Amplifier, with

and

37.

provide the output

long cables. Protection

diodes

CR3

and

4.

drops, passing the

the

SYNC

filter

SYNC

reproduce

Transistors

current

reproduce

from

SYNC

with

cutoff

mode.

Q10,
required for
from

output

to

-12-

3.2.5

Reproduce Line Amplifier

Although not

available

included in the
dedicated
option

3.2.6

Input
attenuated

R2

and
active
removes

mi

ght otherwi se cause
portion
ier

through

C4

imparts a 6dB/octave

to

is

relegated

Record

signals

by

R3,

capacitors

low-pass

RF

and

of

the mplified input signal

the reproduce function.

Amplifier (Schematic 129100)

from
the

other

RECORD

as a factory-installed

PC

artwork to incorporate a second Line Amplifier

Use

to

the

RECORD

filter

spurious

CAL

special

front

LEVEL

Cl

and 2 and

with

hi

gh

control

rising

applications

panel

RECORD-GAIN

calibration

first

cutoff

signals

beginning about

outside

frequency ollerl

is

R7

for

spurce monitoring.

characteristic

gain

directed

option,

of

this

or

user-installed

effects

control are

control,

stage

Rl. Resistors
ICI

30kHz.

the audible range

oad-j

ng

duri

ng

to the Line Amplif-

to

the

imput signal as

provision

generation.

form

recordi

is

further

an

The

filter

which

ng.

A

for

required

and

equalization

recording pre-emphasis. Depending

high frequencies

ted

in the feedback path
falling
zation

loop

falling

point

network

Rll

characteristic

trimmers

when

the

appropriate

characterisitc.

of

the

effective

characteristics.

and

C5

modify the pre-emphasis curve

characterisitc
or

no

increase

of

which

R34,

35

and

FET

This

pre-emprasis curve provided

used, however, only a

at

all

may

be

IC2,

therefore

cancels the

36

are introduced

switch

affords

is

control over

provides a complementary

effect

activated,

slightly,

upon

required.

of

C4.

into

the
and
the
by

causing a droop

in the 5kHz-and-above region. These component values

for

smoothest overall response, but
promise

for

heads typical

of

the

are

supplied as

application

for

the version

ed.

the tape speed

rise

at

very

C7,

connec-

Record
lC2
"shelf"

equali-

feedback

the

inflection

the

combined

can

be

changed

the

best

com­order-

-13-

0

---

A

3dB

boost

at

50Hz

(required

for

the

NAB

record

characteristic)

is

effected

by

shunting

C4

by

RIO.

FET

Q5

is

normally

off,

but

can

be

turned

on

for

one

or

more

equalization

positions

if

IEC

or

other

IIflat-low-end

ll

record curves are desired. This

is

accomplished

on

the

Power

Supply

PCB

(see paragraph

3.2.9).

CR3

and

4,

IC3,

and

associated

circuitry

forms

the

IIlinearizer

ll

net-

work.

When

Q9

is

turned

on

by

activating

the

LINEARITY

switch under

the adjustment cover panel, a

variable

non-linear

characteristic

can

be

imparted to the record signal

that

when

properly adjusted cancels

a major portion

of

the

tape-gener~ted

third

harmonic

distortion

(see

section

4.2.1).

1C4

and

associated

components

form

the

constant-current

head

driver

stage.

Relay

Kl

connects the record

head

to the output

of

IC4

in '

the record

mode,

and

to the input

of

the

SYNC

amplifier

for

SYNC

re-

produce (-03 version only). A bias

trap

composed

of

L2/C22,

C24

and

L3/C23

keeps bias

from

disturbing

the

head

driver

stage

or

overloading

the

SYNC

amplifier.

FET

switch

QI0

opens

the input to

IC4,

except

when

the

375

is

in the record

mode.

3.2.7

Erase/Bias Amplifier

The

bias signal generated

on

the

Power

Supply

PC

assembly

is

raised

to the required

power

level

for

erasure

and

bias

by

Ql, 2, 3

and

4.

Q1

arid 2 raise

the

1Vrms

signal to a proper level

to

just

saturate

the

class

lie'

output

stages,

Q3

and

4. · R23

and

25

control drive

and

symmetry,

respectively,

and

are

factory-adjusted.

Transformer

T1

raises

the

amplifier

output

vol~age

to

approximately

the

150

volts

P-P

required

for

erase

head

driving requirements.

Capacitor

C16

resonates the erase

head

at

the operating frequency.

C25

and

BIAS

ADJUST

control

R50

couple the required bias signal to the

record head.

In

the case

of

erase heads

of

lower than

nominal

induct-

ance,

an

inductor,

L4,

is

inserted

in

series

to

bring erase

head

-14-

inductance

up

to the

nominal

value (see paragraph

4.1.4.2).

3.2.8

In

375

IC5,
ramp
the

(-03 version only).
head

duced
stage concurrent with the relay closure.
and

Record

Logic

Timing

order to insure inaudible "punch-inls"

must

C26
when

Line

enter

and

the

Amplifier

the record

R58

form

unit

goes

is

mode

a Miller

-into

first

Next

K1

with the proper sequence of events.

Integrator

"record.

switched

is

energized,

II

At

from

to the output of the record amplifier. A

by

R45

and

C19

applies the input signal to the

erase

field

begins to build.

UpOh

leaving the record

and

which

SYNC

transferring

At

opposite chain of events occurs. "Punch-in"

is

symmetrical

3.2.9

Power

at

about

100

milliseconds.

Supply (Schematic

129200)

"punch-outls", the

generates a

the

start
to

of

INPUT

the

monitor

the record

short

delay
head

this

and

point the bias

"Punch-out" time

linear

ramp,

intro-

driver

mode,

the

Triac

Y1

operates in conjunction with the front-panel
to control primary
if

deriving

heavy

The
ifier,

surge currents

chassis-mounted

diodes CRl-4. A bipolar

appears across

IC1

is

the

up

to

250mA,
ternal to
short-circuit
the regulated
ial input

power

filter

positive

at

+2~

IC1

limit
protection.
positive

pair

driving the

AC

power

from

and

power

capacitors

supply
volts
the

supply,

the

to the

unit.

375

and

associated tape

This saves the switch contacts

inductive loads.

transforme~~pplies

"raw"

C1

regulator,

supply

and

with

C2.

AC

of

Q1

connected to provide

(nominal). Resistor

available

The

compound

current

negative

and

utilizes

output stage

to

power

Q3

this

source

POWER

to the bridge

about

R3

and

Q5/Q6.

and
value

is

Q4

+30

circuitry

and
referenced to

a

as

CR6,

switch

transport,

from

re~t

volts

in-

establish

di

fferent-

7,

and

-15-

8

and

RI

provide

current

limiting

and .short-circuit

protection.

Transistors
vibrator
established
QI2

amplifies the

QIO

and

II

configuration,

by

the value

oscillator

are connected in

oscillating

of

C7

and

signal

at

trimmed

and

an

emitter-coupled

the

erase/bias
by

applies
resonant network LI/C8, transforming the square
form.
low

Transistor
ization
command

or a

Transistor
versions) phase compensation network, except
the network
tion

Transistor

output

impedance

Q7

and

Q9,

an

for

its

associated

emitter-follower
the

switching system, placing the
is

received,

transport

Q8,

is

speed switch closure.

normally

optimized

either

off,

and

from

4.2.2).

IV

rms

bias

components

the

front

disables

for

which a strap

buffer

oscillator

form

375

i

~

INTER

panel

the reproduce

at

multi-

frequency

FREQ

adjustment

it

to

the

wave

into

stage,

parallel­sine

provides a

signal.

part

EQ

of

the equal-

when

no

EQUALIZATION

(and

the

one

is

connected (see sec-

SYNC,

speed

R33.

wave

other
switch,

on

for

which

-03

Similarly,

low

a
be
shown

frequency boost,

defeated

on

the record

at

the schematic.

SCRI, a silicon

the

Q2

signal

relay

The

front

isolate

from

"record"
transports.
when
the

transport
sistor
logic

amplifier

as

required for

one

or

more

controlled

speeds

rectifier,

usually required

SCR

is

triggered

panel

leaves the

RECORD

button

PLAY

mode.
the ground-referenced
the

transport

pre-emphasis

NAB

by

the

characteristic

equalization,

installation

of

replaces the electro-mechanical

by

Ampex

"on"

is

300-,350-,

in the

depressed,

An

optical

Record

and

transport

and

latches

coupler

and

Erase/Bias Amplifier

PLAY

Al

control function voltages.

includes

which

can

diodes as

440-

series
mode
until

and

tran-

-16-

SECTION

4.0

ALIGNMENT

AND

MAINTENANCE

4.1

4.1.1

4.1.

2

4.1.2.1

4.1.2.2

Routine Calibration

Equipment

Head

Required:

Demagnetizer
Appropriate Reproducer Alignment
Audio
AC

Oscillator

Voltmeter

REPRODUCE

Depress

heads,
heads,
before unplugging

Depress

INPUT
moving
and

withdrawing

REPRO

monitor button. Clean

very slowly while the demagnetizer

it.

monitor button
appropriate for the
switched.

it

about a yard

and

equalization

Tapes

and

thread
to

which

demagnetize

from

the

head

an

alignment tape

the

electronics

all

is

near the

assembly

is

4.1.2.3

4.1.2.4

4.1.2.5

While

reproduce

If
the top
signal-to-noise
served
lifier

whether
H.F.
reference frequency tone
at

reproducing the highest frequency

head

the resonance

of

azimuth

of

for

the reproduce

the passband (as

maximum

performance), a

at

the highest frequencies.

card

control

its

is

provided to

value

so

is

that

damp
correct
5kHz

playback

on

the highest frequencies,

crease, or lower to decrease,

Set

H.F.

control for smoothest response

quency to highest frequency.

on

the tape,

output.

head

with

is

usually the case

peak

this

for the

in response will

R1

on
resonance.
head

is

flat

its

the Reproduce

used,

with
the alignment tape.
and

raise

this

the value

level.

from

reference

adjust

cable

for

best

To

determine

set

High

respect

Note

of

R1

is

near

be

ob-

Amp-

Speed

to the
response
to in-

fre-

-17-

4.1.2.6

If

alignment tape track width

is

the

same

as reproducer

track width,

set

L.F. control for smoothest response

from

reference frequency to lowest frequency.

If

not, as with

full-track

tapes

and

half-track

reproduce heads, wait until

step

4.1.5.4

to trim the

control.

4.1.2.7

Repeat the preceding

two

steps

for

the

other

speeds.

It

is

advisable to

make

final azimuth

setting

at

the lowest speed

to

be

used.

4.1.2.8

Turn

front

panel

REPRO

LEVEL

control

fully

ccw

to

CAL

posi-

tion und

adjust

R34

REPRO

CAL

on

Reproduce

card

for

an

indi-

cation

of

Zero-VU

while reproducing a reference tone recorded

to the desired operating

level.

If

it

is

wished to operate

into a

+8dBm

line,

remove

the jumper across the

4.7K

resistor

near the output connector before

making

this

adjustment.

4.1.3

SYNC

REPRODUCE

(-03 version only)

The

SYNC

reproduce function,

on

375 1 s

so

equipped,

is

aligned

in the

same

manner

as the

normal

reproduce section described

in

4.1.2.1

through

4.1.2.7.

Playback

is

from

the record

head

in

this

case,

and

there

is

no

front

panel level adjustment.

4.1.4

ERASE/BIAS

4.1.4.1

The

Model

375

is

available

with the option

of

100kHz

(-00

version)

or

250kHz

(-02 version)

era~e/bias

frequencies.

The

lower frequency

is

intended

for

operation with

older

metal

heads, as are

found

on

the

earlier

Amrex

vacuum-tube recorders.

Heads

for operation

at

250kHz

must

be

of

lower inductance

and

greater

efficiency.

4.1.4.2

For

100kHz

operation the

375

is

designed to drive

an

erase

head

in the 1.2 to

1.8mHy

range.

At

250kHz,

the requirement

-18-

is

0.4 to 0.

ied

is

ing

strap

6mHy.

intended for

in place

If a head

use

at

of

L4

on

of

either

the

lower inductance than

frequency,

Record

PCB

remove

and

the

install

specif-

short-

a

choke

4.1.4.3

coil,
ductance, will equal
or

version only)

be

the inductance

0.5mH

(for

strapped as

250kHz
head

input transformer

shown

of

which

1.5mH

(in the case

units).

on

the board to

when

added

Similarly,

on

accqmmodate

to the

of

the

erase

100kHz

operation),

optional (-04

the Reproduce

low-Z

head

PCB
{4-5mHy

reproduce heads.

NOTE:
require a biasing procedure
itonal 15-mil wavelength "peak"

Present-day tapes with higher

slight~y

method

coercivity
modified

oxides

from

the

described below. Follow

tape manufacturer's recommendation for best performance.

Depress the
to the
of

record
ating

INPUT

the type

mode

level;

REPRO

of
at

monitor button, connect

connector,

tape to
15

ips

adjust

and

R13

and

be

BIAS

thread

used

adjust

control for

an

audio

transport

with a

subsequently. Place

input to

1kHz

at

maximum

about oper-

reproduced

oscillator

good
machine

in-

can

may

trad-

sample

in

signal.
at

15

4.1.

5

RECORD

4.1.5.1 ' With
cord
+4dBm
duce
not operate

4.1.5.2

Raise the frequency
for
record
be

repeated.

(Use

ips.)

conditions

mode

at

(+8dBm

level

by

at

maximum

head

output.

azimuth

500Hz

as

at

for

7

~

4.1.4.3
highest speed
if

reproduce

about

15

10dB

ips.

to

15kHz

Note:

was

made

ips

on

units

above, place recorder in

and

set

input signal to

was

calibrated

in the case

and

adjust

on

-03

versions,

in

SYNC

which

of

transports

for

do

this

the record

the adjustment

calibration

not operate

re-

700Hz

at

level).

which

head

and

need

do

azimuth

not

Re-

of

-19-

'-

4.1.5.3

Set record pre-emphasis

for

smoothest response

by

adjusting

from

R34

on

the

reference frequency

Record
up.

PCB

4.1.5.4

4.1.5.5

4.1.5.6

4.1.5.7

If

incompatibility

ducer

track

in paragraph

for

flattest

width prevented

4.1.2.6,
over-all

of

alignment tape track width to repro-

adjust

setting

R14

reproduce L.F. controls

on

the Reproduce

response.

Set equalization for lower speeds using
and

LOW

duced

Switch
ccw

to

the

same

used,

speeds,

by

10dB

front
CAL

position.

frequency

set

R1

respectively.

for alignment

panel

RECORD

With

as

the reference tone

on

Record

PCB

of

GAIN

input

for

The

input level should

7~

ips

and

REPRO

of

normal

an

indication

meter.

Depress

for

INPUT

an

indication

monitor button

of

Zero-VU

and

adjust

on

the meter.

R34

and

and

lower speeds.

LEVEL

line

on

the alignment

of

R7

on

PCB

now

R36

for

be

controls

level

and

Zero-VU

the record

INTER

re-

fully

of

t~pe

on

the

PCB

-20-

.'Hol

(

4.2

SPECIALIZED

ADJUSTMENTS

4.2.1

Linearizer

4.2.1.1

The

375

is

equipped with a

"linearizer"

circuit

which,

when

properly adjusted,

can

cause a

significant

reduction in tape-

generated

odd

harmonic

distortion.

This

circuit

is

enabled

or

defeated

by a slide

switch located under the adjustment

cover panel.

4.2.1.2

Precise

calibration

of the

linearizer

requires a low

distor-

tion

sine

wave

oscillator

and a wave

analyzer type

of

dis-

tortion

meter.

The

procedure, in

this

case,

is

to record a

1kHz

tone

at

6dB

above

operating level

and

adjust

R39

on

the

~ecord

PCB

for

the

minimum

3kHz

distortion

component

repro-

duced

from

the tape.

4.2.1.3

An

alternate

method

of adjustment requires only a typical

studio

program

equalizer

which

can

be

peaked

at

3kHz

and

give

at

least

15dB

rejection

at

1kHz.

With

this

method, the out-

put of the

375

is

routed through the

equalizer

to the monitor

speaker system,

and

R39

adjusted

for

minimum

perceived

dis-

tortion.

4.2.2

Phase Compensation

4.2.2.1

The

375

is

equipped with a phase

correction

network in both

. .

the

normal

Reproduce

and

SYNC

reprod~ce

(-03 version only)

Amplifiers.

The

networks,

operative

at

one

selected

speed

only, are adjusted for best reproducerl square

wave

response.

4.2.2.2

The

phase

corrector

is

enabled

at

the

selected

speed

by

strapping a jumper

between

PH

COMP

and

either

H(HIGH),

I(INTER)

or

L(LOW)

on

the

Power

Supply

PCB.

The

only

way

to

adjust

the network(s)

is

to record a

3kHz

square

wave

at

-21-

j

the selected speed,

and

adjust

R25

(and

R75

on

-03 versions)

for

a best-looking square

wave

on

playback as monitored

on

an

oscilloscope.

4.3

SERVICE

NOTES

4.3.1

Meter

Lamps -The

meter

is

iliuminated

by

two

long

life

#388

lamps

which

are considerably under-voltaged.

In

the event

it

eventually

becomes

necessary to replace one,

remove

the

top cover

and

remove

the 3/16"

hex

threaded spacer

retaining

the socket

of

the burned out

lamp.

4.3.2

All

illuminated switch buttons - Squeeze the button

from

top

and

bottom

and

pull

straight

off.

The

#387

lamp

can

be

re-

moved

carefully

with a

pair

of

long-nosed

pliers.

-22-

- -

1

..

(

PART

SCHEMATIC

NUMBER

DESCRIPTION

MFG.

:

REF.

NO.

C1
C2,

22

C3~

14,

23,

34

C4,

5,

6,

24,

25,

26

C7,

27

C8,

13,

28

C9,

11,

29
C10
C12

CR1-

6

reI,

2,

3
Q1,

3,\21,

23

Q2,

11,

22,

29

Q4-9,24-28

:

Q10
R5,

55

R6,

7,

28, .56,

57,

78

R12,

13,

14,

62,

63,

64

R25,

75

T1,

2

I

N

W

I

,

0.28200/

~28201A

0904
0906
0810
0862

0820

D80l

0901
0811
0832

1100
1300
f210

1205
1211
1204

0511
0510

0519
0514

1500

REPRODUCE

PCB

ASSY

(SCHEHATIC

129000)

Capacitor,

25uF,

25V

"

100uF,

3V

"

100pF

"

O.OluF,

100V

'

..

to

680pF
10pF

"

5uF,

25V

"

120pF

"

62pF

Diode,

Silicon

IN4009

Integrated

Cct.

Type

748-C

Transistor,

SE4010

"

2N3645

to

}-IPF111

"

2N3567

~

Resistor,

adjustable20K

"

10K

"

It

"

2meg

" "

lOOK

Transformer,

head

matching

Sprague

"

Elmenco
Sprague

Elmenco

II

Sprague
Elmenco

"

FSC/GE

Signetics

FSC/NSC

"

NSC/Notor.
NSC/FSC

Spectrol

"

. .

"

"

Beyer

MANUFACTURER

PART

NUMBER

TE1207
TE1059.5

mnS-lOlJ

225Pl0391

m-n9-681J
milS-100J
TE1202
mn5-121J

D~H

5-620J

.

43P-203
43P-103

43P-205
43P-I04
145/BV

35704

-----

PART

REF.

NO.

SCHEY.Ii-\TIC

}";1.JMBER

128300/
128301A

0827

C2

C1,

25

0814

C3,

6,

18,

21,

0801

27

C4

0850

C5

0854

C7,

8,

9,

10,

0862

11,

12

C13,

14

1053

C23

(-00)

0834
0828

(-01

)

C16

(-00

)

"

0825

..

0821

C17,

28

(-01)

0901

C19,

26

0867

C20

0810

C22

(-00)

0829
0828

(-01)

C24

(-00)

"

0829
0828

(-01)

"

1100

CRl-

6

1300

ICl-

5

1904

K1

L2,

3 . .

(-00)

·

1403

1401

LS,

6

L2,

3

(-01

)

1409

I

N

.,::,.

I

DESCRIPTION

RECORD

PCB

ASSY

(SCHEMATIC

129100)

Capacitor,

300pF

..

220pF

"

1CpF

..

O.

001uP,

100V

"

0.0022uF,

100V

II

O.

OluF,

100V

..

2.

2uF,

20V

..

2700pF

..

750pF

..

II

1800pF
820pF

5uF,

25V

..

"

..

O.

luF

,100V

.

100pF

..

3000pF

..

7S0pF

..

1000pF

470pF

"

Diode,

Silicon

1N4009

Integrated

Cct.

Type

Relay,

SPDT

Inductor,

1rnHy

748-C

560uHy

shielded

"

to

220uHy

MFG.

Elmenco

..

"

Sprague

..

"

Hatsuo

Elmenco

"
"

"

Sprague

"

Elrnenco

II

"

"

"

FSC/GE
Signetics
Sigma
Delevan
Kytronics

Delevan

MANUFACTuRER

PART

NUMBER

DM15-301J
DH15-221J
DH15-100J

225P1C291

.

225P22291
225Pl0391

DTSAl-2002-225H
DN

19-272J

D~'n

9-751J
DH19-182J
DH19-821J
TE1202

225F10491
mr15-101J
DH19-302J
DN19-751J
DH19-102J

D~·r

19-4

71J

191TEIC1-12G

2500-28
SWD

560

1537-92

.

..

!

~

..

SCHEMATIC

REF.

NO.

Ql

Q2~

11
Q3
Q4
Q5 -10
Q12,

13

'

R1,

7,

34,

35,

37

~

38,

39
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R25

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R50

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NUMBER

1210
1205
1212
1200
1211
1204

0510

0557
0556
0511
0513

127000

129400,.
129401

1307
0910

1053
0850

0827
0857
0852
08

34
0828
08

67

(

DESCRIPTION

Trans

istor

~

SE4010

"

2N3645

"

40319

"

2N2102

"

HPF111

tt

2r\3567

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adjustable

10K

It

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2K

"

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1K

"

"

20K

"

"

50I-<:

Transformer,

Bias

Amplifier

PO

HER SUPPLY

1:92

~

(SCHEY~TIC

129200)

Optical

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500uF,

50V

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2.2uF,

20V

O.OOluF,

100V

"

..

300pF

0.0039uF,

IOOV

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O.OO15:;,

F,

100V

"

"

2700

pF

7S0pF

"

It

O.luF,

lOOV

MFG.

FSC/NSC

"

RCi\

RCi\/NSC
N

SC/Hoto

FSC/

NSC

Spectrol

Helipot

"

Spectrol

..

(

Inovonics

Fairchile

Sprague
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atsuo

Sprague

Elmenco

Sprague

"

Elme nco

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MANUFACTURE]

PART

NUMBEJ

43p-103

91AR2K
91A...-q1K
43P-203
43P-503

FeD

820

TVA1315
DT

SAl-2002-

225!-'!
225P10291
DN15-301J
225P39291
225P15291
D:.fl 9-2 7

2J
Dlv1l9-751J
225P10491

----

-

;

SCHEMATIC

REF.

NO.

CR1 ~ 4
CR6 -

12
IC1
L1

(-OO)

II

(-01)

Q1,

6

02,

5,

9,

10,

11

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4,

7,

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1100

1301

1403
1400

·

1213
1204

1205

0556
0564

1151
1152

0872
2706

2702
2012
0601

DESCRIPTION

Diode,

Silicon

Rectifier

1N4005

..

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2N3567

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adjustable

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Silicon'Controlled

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C1033

Triac,

T2500B

CH.1\SSIS-MOUNTED ELECTRONIC

COXPONENTS

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600V

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3A

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!zA

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Type

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lOOK

w/

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..

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..

GE

RCA

Sprague

CN/Norelco

Allen/Brad.

2500-28
2500-16

91A.R1K
91AH200K

.

6PS-S10

..

70K4l\040S

lO4UA

(

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REF.

NO.

Sl
S2
S3

PART

NUMBER

1820
18

19

1818

DESCRIPTION

Sidtch,

RECORD

"

}fON

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109000

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130100

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WARRANTY

Inovonics, Inc.
workman
will
days and one year
installatio
return
purcha
the user's loca

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his war

1. Warr nty

2. Warran

3. Warr

ship.

be repa

n billed

equipment for warranty

sed

ran

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Any disc

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tion

ty

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ty

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tification

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rates.

with

to damage caused

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service

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the

of

purch

ed

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to

be

with

in

, parts

will

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be

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to

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made

with

conditions

equipment

ase.

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free

from

90

days

for

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be

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responsibility

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at repair

by

from

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dealer

:

must

be

misuse, abuse,

defects in

of

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of

whom

to

inspect

completed

or

modification

or

material

date

of

purchase

of

charge,

the purchaser

it

was

originally

or

repair

and

returned

have been

altered.

or

accident.

and

90

with

to

at

4. Warranty

valid

only to

original purcha ser.