Fairchild 670 User manual
INSTRUCTION
MANUAL
MODEL
6
7
0
STEREO
LIMITER
Serial
No.
Fairchild
Recording
Equipment
Corporation
10-LO
5th
Avenue
Long
Island
City
1,
New
York
December
1959
(Supersedes
all
previous
issues)
FAIRCHILD
STEREO
LIMITER
-
MODEL
670
OUTSTANDING
FEATURES
FIRST
MODERN
LIMITER
A
radical
departure
fram
the
classical
limiter
design
in
the
MODEL
670
is
char~
acterized
by
the
complete
absence
of
audible
thumps,
absence
of
distortion
and
noise,
and
it
is
extremely
stable
over
long
periods
of
time.
,
UNITS
IN
ONE
The
MODEL
670
is
either
2
Independent
Limiters,
or
by
the
flick
of
a
switch
a
Vertical-Lateral
Component
Limiter—all
this
enclosed
within
1
inches
of
rack
space.
INDEPFNDENT
CONTROL
OF
BOTH
VERTICAL
AND
LATERAL
AMPLITUDES
ON
STEREO
DISKS
Large
vertical
amplitudes
on
STEREO
DISKS
often
produce
processing
as
well
as
.
tracking
problems.
Large
vertical
amplitudes
are
produced
by
randan
coincidence
of
out-of-phase
components
in
the
two
STEREO
channels.
The
MODEL
670
is
the
only
wit
presently
in
production
which
can
control
both
components
(vertical
and
lateral)
independently,
and
accomplish
this
with
minimum
loss
of
separation.
EXTREMELY
FAST
ATTACK
TIME
Many
a
short
transient
can
pass
through
conventional
limiters
because
of
their
slowness
in
attack,
The
MODEL
670
can
produce
full
limiting
effect
during
the
first
10,000ths
of
a
secamd.
VARIABLE
RELEASE
TIME
Different
program
materials
require
different
limiting
action.
By
choosing
the
correct
release
time
characteristic,
even
severe
limiting
can
be
made
to
be
practically
imperceptible.
The
MODEL
670
supplies
six
different
timing
curves,
several
of
them
making
the
release
time
an
automatic
function
of
the
amount
of
limiting
used.
LIMITER
OR
COMPRESSOR
The
type
of
program
material
as
well
as
personal
preference
dictate
the
use
of
either
a
limiter
or
a
compressor.
The
MODEL
670
can
be
adjusted
to
work
either
as
a
compressor,
with
a
ratio
of
2
to
1
and
a
threshold
of
5
db
below
normal
program
level;
or
as
a
peak
limiter,
with
a
canpression
ratio
of
30
to
1
and
a
threshold
of
10
db
above
normal
program
level;
or
it
can
be
adjusted
to
operate
anywhere
in-between
these
two
extremes.
RELIABILITY
Highest
grade
commercial
and
military
components
are
used
throughout
working
well
below
their
maximum
ratings
to
insure
long,
trouble-free
operation.
D8~670-659
LATERAL
CHANNEL
A
u
LATERA
METERING
INPUT
GAIN TIME
CONSTANT
ZERO
5
a4
»
&,
Ro
:
es
°'
A
sa
e.
ad
VERTICAL
CHANNEL
8
VERTICAL
METERING
INPUT
GAIN
THRESHOLD
a
ae
:
VERTICA.
eS
Nea
iy
.
TIME
CONSTANT
e
r
FAIRCHILD
MODEL
670
LIMITER-AMPLIFIER
TWO-CHANNEL
FOR
STEREO
MODEL
670
STEREO
LIMITER
GENERAL
DESCRIPTION
The
FAIRCHILD
MODEL
670
incorporates
on
one
chassis
two
independent
limiters
which
can
limit
either
two
independent
signals,
such
as
the
left
and
right
channels
of
a
stereo
signal,
or
the
vertical
and
lateral
components
of
same.
The
latter
is
accomplished
by
first
bringing
the
two
stereo
channels
through
a
matrixing
network,
dividing
them
into
their
vertical
and
lateral
components,
limiting
them
independently,
and
recombining
them
through
a
second
matrixing
network
into left
and
right
channels.
Each
half
of
the
MODEL
670
uses only
a
single
push-pull
stage
of
audio
amplification
and
an
extremely
high
control
voltage,
with
the
result
that
the
Automatic
Gain-Controlled
Amplifier
never
produces
any
audible
or
observable
thumps.
Contrary
to
most
limiting
amplifiers
heretofore
available,
this
unit
has
extremely
low
distortion
and
noise
under
all
conditions,
both
as
a
straight-through
amplifier
and
under
maximum
limiting
conditions.
The
attack
time
of
the
unit
is
made
extremely
fast
in
order
to
catch
short
transients,
and
the
release
time
is
made
adjustable
from
0.3
seconds
to
25
seconds
in
six
steps.
Two
of
these
have
release
times
which
are
automatic
functions
of
the
program
material,
providing
fast
recovery
for
short-duration
peaks
and
an
automatic
reduction
with very
long
recovery
time
of
overall
gain
should
the
program
level
remain
high.
In
the
circuitry
used,
each
half
of
the
amplifier
consists
of
two
separate
amplifiers:
one
is
the
Automatic
Gain
Amplifier,
and
the
other
provides
the
necessary
power
for
producing
the
DC
control
voltage.
Because
of
this,
the
controls
are
somewhat
different
from
those
of
most
other
limiters.
Essentially
there
is
one
control
common
to
both
channels
which
will
switch
between
independent
limiting
and
vertical-lateral
component
limiting,
besides
four
controls
for
each
channel:
a
Switch
for
Metering;
an
Input
Level
Control;
a
Limiting
Threshold
Control;
and
an
Attack
and
Release
Time
Switch,
Owirg
to
the
wide
choice
of
attack
and
release
time,
as
well
as
the
automatic
recovery
feature,
this unit
can
be
used
to
limit
program
material
severely
without
producing
the
audible
thumps
or
pumping
so
often
associated
with
limited
program
material.
A
limiting
meter
is
provided
with
provision
for
connecting
a
remote
meter
to
the
terminals
exposed
at
the
rear
of
the
amplifiers.
The
MODEL
670
is
designed
tobe
placed
into
any
normal
line
level
circuit
and
can
be
set
to
have
a
unity
gain
at
no
limiting.
Since
all
critical
components
are
of
highest
quality,
working
well
below
their
maximum
ratings,
a
dependable
operation
can
be
expected.
2
LIMITING
IN
STFREO
DISK
RECORDING
The
cutting
of
STEREO
DISKS
has
uncovered
a
number
of
new
problems
heretofore
unknown.
The
normally
modulated
STEREO
groove
requires
approximately
twice
the
space
of
lateral
grooves
for
similar
modula-
tion,
yet
the
available
space
is
no
greater.
In
addition,
the
two
STEREO
channels,
depending
on
their
phase
relationship,
may
result
in
either
lateral
or
vertical
modulation,
or
a
combination
of
both.
It
stands
to
reason
that
some
peaks
may
result
in
purely
vertical
modulation
on
the
disk,
others
purely
lateral.
If
this
were
allowed
to
happen
continually,
the
result
would
be
only
15
minutes
on
the
STEREO
LP
side
or
else
it
would
be
necessary
to
reduce
the
recorded
level
radically.
Otherwise,
judicious
use
of
variable
pitch
and
variable
depth
would
have
to
be
exercised.
The
fact
is,
because
of
the
smaller
playback
tip
radii
and
the
response
of
the
playback
pickups
to
vertical
as
well
as
lateral
motions,
the
signal-to-noise
ratio
on
STEREO
DISKS
is
already
reduced
over
the
lateral
counterpart.
Besides,
radical
use
of
automatic
variable
depth
will
further
increase
processing
problems
already
severe
in
STEREO
DISKS.
Another
problem
exists
because
of
the
difficulty
of
tracking
large
vertical
amplitudes.
Most
commercially
available
STEREO
pickups
have
considerably
less
vertical
compliance
and
consequently
are
less
capable
of
tracking
large
vertical
modulations.
Also,
we
should
not
forget
that
the
tip
radius
on
the
STEREO
playback
stylus
is
still
0.7
mil,
which
necessitates
a
minimum
of
1
mil
groove
width,
or
poor
tracking
might
result.
The
one
apparent
solution
to
these
problems
is
to
break
the
STEREO
signal
down
to
its
respective
vertical
and
lateral
components.
Limit
the
vertical
and
lateral
canponents
independently
corresponding
to
the
available
groove
space
and
depth,
then
recombine
these
components
to
regain
the
original
STEREO
signal.
This
can
be
done
with
the
FAIRCHILD
MODEL
670
LIMITER
and
many
thousands
of
STEREO
masters
have been
cut
successfully
with
the
help
of
this
FAIRCHILD
wit.
The
limiting
of
the
vertical
and
lateral
components
instead
of
the
left
and
right
channels
has
additional
merits.
Such
limiting
will
retain
the
spatial
distribution
of
instruments
and
soloists
as
orig-
inally
recorded
without
producing
any
annoying
image
drift.
Of
course
some
program
material
of
the
ping-pong
type
requires
independent
limiting
of
each
channel,
and
this
is
also
available
in
the
MODEL
670
LIMITER.
SPECIFICATIONS
(Each
channel,
unless
otherwise
specified)
INPUT
IMPEDANCE
600
2
OUTPUT
IMPEDANCE
600
2
OUTPUT
LEVEL
+),
or
+8
VU
(+27
dbm
clipping
point)
GAIN
7
db
(no
limiting)
FREQUENCY
RESPONSE
hO
cycles
to
15
ke
+
1
db
NOISE
LEVEL
70
db
below
+)
dbm
LIMITING
NOISES
Below
audibility.
INTERMODULATION
OR
HARMONIC
DISTORTION
Less
than
1%
at
any
level
up
to
+18
dbm
output
(no
limiting).
Less
than
1%
at
10
db
limiting
and
+12
dbm
output.
\
ATTACK
TIME
(adjustable)
»2
milliseconds
in
positions
1,
2,
and
6.
«4
milliseconds
in
positions
3,
h,
and
5.
RELEASE
TIME
(from
10
db
of
limiting)
Position
1:
.3
seconds.
Position
2:
.8
seconds.
Position
3:
2
seconds.
Position
:
5
seconds.
Position
5:
Automatic
function
of
program
material:
2
seconds
for
individual
peaks,
10
seconds
for
multiple
peaks.
Position
6:
Automatic
function
of
program
material:
.3
seconds
for
individual
peaks,
10
seconds
for
multiple
peaks,
25
seconis
for
consistently
high
program
level.
COMPRESSION
RATIO
Variable
from
1:1
to
1:20
above
a
predeter-
mined
level.
Predetermined
level
factory-
adjusted
to
+2
dbm.
SEPARATION
Left-Right
position:
60
db
Vertical-Lateral
position:
0
db
POWER
REQUIREMENTS
117
volts,
50-60
cycles,
3
amps
STABILITY
Unit
maintains
stability
of
gain,
gain
reduction
and
balance
over
a
range
of
line
voltage
fluctuations
fran
100
to
127
volts.
CONTROLS
MECHANICAL
DIMENSIONS
WEIGHT
TUBE
COMPLEMENT
SPECIFICATIONS
contd.
a)
b)
c)
a)
e)
f)
2
Input
Gain
Controls
Step
attenuator:
1
db
per
step.
2
Threshold
Controls
Continuously
variable.
2
Time
Constant
Switches
6
positions
each,
so
as
to
provide
fixed
and
variable
time
constants
for
any
type
of
program
material.
2
Metering
Switches
3
positions
each,
which
permits
the
measurement
of
plate
current
of
each
set
of
control
tubes.
Mode
Switch
Left-Right
position:
2
independent
limiters.
Vertical-Lateral
position:
matrixing
input
and
output,
left
and
right
in
and
out,
limiting
action
vertical-lateral.
ON-OFF
Switch
Standard
19"
rack,
1h"
panel
space,
depth
behind
panel
11".
Approximately
65
lbs.
8-6386;
1-608;
1-5651;
2-12AX7;
2-12BH7;
1-EL3h3;
4-6973;
1-GZ3
(5v4).
Kee
fOX1OTOTHE
INCH
359.5
KEUFFEL
6
ESSER
CO.
wine
in
es
&
DB
LIMITING
——>—
_—
INPUT
AND
OUTPUT
CONNECTIONS
LEFT
CHANNEL
-
INPUT
Terminal
1
Tie
point
(no
internal
(Z
=
600
2)
connection
)
Terminal
2
High
Terminal
3
Low
Terminal
)
Ground
(chassis)
RIGHT
CHANNEL
-
INPUT
Terminal
5
Tie
point
(no
internal
(Z
=
600
&)
comnection)
Terminal
6
High
Terminal
7
Low
NOTE:
If
a
floating
circuit
is
used,
it
is
necessary
that
Terminals
3
and
7
be
strapped
to
Terminal
)
(chassis).
LEFT
CHANNEL
-
REMOTE
METER
Terminals
8
and
9
RIGHT
CHANNEL
-
REMOTE
METER
Terminals
10
and
11
CAUTION:
Terminals
8,
9,
10,
and
11
are
240
V
above
ground.
LEFT
CHANNEL
-
OUTPUT
Terminal
12
High
(Z
=
600
&)
Terminal
13
Low
Terminal
Uy,
Ground
(chassis)
RIGHT
CHANNEL
-
OUTPUT
Terminal
15
High
(Z
=
600
2)
Terminal
16
Low
Terminal
17
Ground
(chassis)
Any
standard
VU-Meter
can
be
used
as
a
Remote
Meter
if
the
internal
rectifier
is
removed.
A
variable resistor
of
approximately
10K
should
be
used
in
connection
with
the
Remote
Meter.
This
variable
resistor
(Ohmite
CLU-1031)
enables
the
zero
of
the
Remote
Meter
to
coincide
with
zero
on
the
meter
in
the
unit
(see
"REMOTE
METER
CONTROL"
illustration).
If
desired,
Fairchild
Recording
Equipment
Corporation
can
supply
such
Remote
Meter
(order
Fairchild
Part
No.
A-2329)).
REMOTE
METER
CONTROL
R-
OHMITE,AB
OR
SIMILAR
QUALITY
POTENTIOMETER
M-ANY
STYLE
VU
METER
WITH
|
IOK
RECTIFIER
REMOVED
OR
FAIRCHILD
PART
A-
23294
CAUTION
-
REMOTE
METER
LEADS
ARE
APPROX
250V
ABOVE
GROUND
REMOTE
THRESHOLD
CONTROL
CIRCUIT
~
REVERSED
/
i
THE
FADERS
MARKED
"F"ARE
GANGED
20STEP-
2008
BRIDGED
T
FADERS
BALANCE
AND
ZERO
ADJUSTMENTS
The
unit
normally
maintains
the
balance
and
zero
adjustments
over
awide
range
of
power
line
voltage
changes
as
well
as
tube
aging.
Small
unbalances
in
the
order
of
1/)
db
do
not
normally
produce
any
ill
effects
in
operation.
If
it
is
necessary
to
re-adjust,
the
procedure
is
as
follows:
1.
Allow
the
unit
to
warm
up
for
at
least
a
half
hour.
2.
Adjust
the
BALANCE
control
until
same
meter
reading
is
obtained
in
both
BALANCE
positions.
3.
With
the
METERING
switch
in
zero
position,
adjust
the
ZERO
control
for
a
meter
reading
of
zero.
lu.
Repeat
step
2
if
necessary.
5.
If
above
procedure
does
not
produce
reasonable
balance,
exchange
one
or
more
of
the
6386
tubes.
6.
Repeat
the
above
procedure
for
the
other
channel
if
necessary,
NOTE:
Do
not
adjust
R313
(B+
ADJ)
inside
the
amplifier
unless
the
voltage
on
Pin
8
of
V302
(EL3h)
deviates
from
20
V.
THRESHOLD
ADJUSTMENTS
Through
the
use
of
the
AC
and
the
DC
THRESHOLD
controls,
it
is
possible
to
adjust
this
unit
to
any
operating
point
between
a
limiting
amplifier
and
a
compressing
amplifier
(see
"INPUT
VS.
OUTPUT
CURVES"
where
(3)
indicates
the
curve
the
unit
is
adjusted
to
from
the
factory).
The
slope
and
position
of
the
curve
are
functions
of
the
desired
output
level
and
the
position
of
the
AC
and
the
DC
THRESHOLD
controls.
Before
adjustirg
these
controls,
the
desired
output
level
at
3
db
and
10
db
of
limiting
respectively,
must
be
chosen.
The
3
db
limiting
point
is
controlled
by
the
DC
THRESHOLD,
the
10
db
limiting
point
by
the
AC
THRESHOLD.
The
AC
THRESHOLD
control
is
located
on
the
front
panel
as
a
kno
adjust-
mnt,
whereas
the
DC
THRESHOID
control
is
located
inside
the
chassis
as
a
screwdriver
adjustment.
The
adjustment
procedure
is
as
follows:
1.
Set
the
AC
THRESHOLD
control
to
zero
and
adjust
the
INPUT
GAIN
control
for
unity
gain.
2.
Turn
both
the
AC
am
the
DC
THRESHOLD
controls
to
their
full
clockwise
rotation.
3.
Apply
a
signal
to
the
input
3
db
higher
than
the
desired
output
level
and
adjust
the
DC
THRESHOLD
control
to
desired
output
level.
h.
Increase
the
input
signal
to
10
db
higher
than
the
desired
output
level
and
adjust
the
AC
THRESHOLD
control
to
desired
output.
5.
Repeat
Sters
3
and
wmtil
the
desired
slope
and
position
are
obtained.
6.
Repeat
the
above
procedure
far
the
other
channel
if
necessary.
REMOTE
THRESHOLD
control
is
possible
in
different
ways.
One
way
which
does
not
involve
changes
in
the
670
circuit
is
the
external
method,
where
ganged
T-faders
are
used
at
in-
and
output
(see
"REMOTE
THRESHOLD
CONTROL
CIRCUIT"
illustration).
This
will
involve
a
loss
in
level
of
approximately
10
to
16
do
which,
for
example,
can
be
compensated
for
by
using
a
line
amplifier,
such
as
FAIRCHILD
MODEL
722.
359-5
10
X
10
TO
THE
INCH
WADEIN
U.S.A,
KEUFFEL
&
ESSER
CO.
Kee
Hitt
tg
a8
nt.
NORMAL
OPERATION
To
simplify
the
initial
setting
up,
here
is
the
standard
procedure:
1.
Observe
if
any
shipping
damage
has
occurred
and
make
certain
that
all
tubes
are
firmly
seated
in
their
sockets.
2.
Mount
the
unit
into
a
relay
=sck.
3.
Connect
input
and
output
leads
as
specified
under
"INPUT
AND
QUTPUT
CONNECTIONS."
4.
Check
the
LEFT-LAT
and
RIGHT-VERT
metering
as
outlined
in
"BALANCE
AND
ZERO
ADJUSTMENTS."
5.
Set
the
INPUT
GAIN
controls
to
unity
gain
(approx.
10
db
attenua-
tion).
6.
Set
the
LEFT-LAT
and
RIGHT-VERT
TIME
CONSTANT
switches
to
position
3.
7.
Tum
the
LEFT-LAT
and
RIGHT-VERT
AC
THRESHOLD
controls
on
the
front
panel
to
zero.
8.
Turn
the
MODE
SELECTOR
switch
to
Left-Right
position.
9.
The
unit
is
nov
set
up
as
TWO
independent
limiters.
It
can
be
used
for
TWO
separate
program
sources
or
for
the
"ping-pong"
type
of
stereo.
10.
To
secure
the
desired
degree
of
limiting,
advance
the
AC
THRESHOLD
control
until
the
desired
amount
of
limiting
or
desired
output
level
is
achieved.
11.
Turning
the
AC
THRESHOLD
controls
completely
counterclockwise
removes
the
limiting
action
completely.
The
unit
is
now
a
simple
Unity
Gain
Line
Amplifier.
12.
The
wit
is
adjusted
in
the
factory
to
conform
to
curve
3
(see
"INPUT
VS.
OUTPUT
CURVES").
This
curve
is
achieved
by
advancing
the
AC
THRESHOLD
controls
fully
clockwise.
13.
Should
a
different
Input
vs.
Output
Curve
be
desired,
see
"THRESHOLD
ADJUSTMENTS."
Generally
speaking,
a
pure
peak-limiting
action
is
required
for
operations
having
a
definite
overload
point
(such
as
100%
modulation
in
transmitters),
whereas
a
lesser
sloped
curve,
somewhere
in
between
compressor
and
peak-limiting,
is
useful
in
recording
applications.
The
pure
peak-limiting
opera-
tion
generally
produces
maximum
volume
within
given
overload
limits;
but
if
a
great
deal
of
limiting
is
used,
it
tends
to
become
somewhat
cbvious
since
all
peaks,
irrespective
of
their
initial
value,
will
get
reduced
to
the
same
level.
Milder
sloped
curves,
on
the
other
hand,
will
tend
to
give
a
greater
apparent
dynamic
range.
Us.
15.
16.
17.
NORMAL
OPERATION
contd.
It
should
be
remembered
that
the
standard
VU-Meter
is
only
an
average
reading
instrument.
A
W
indication
of
"0"
in
complex
program
material
may
result
from
actual
peak
values
as
much
as
10
db
higher.
In
setting
up
limiting
curves,
this
should
be
kept
in
mind.
Individual
beliefs
and
previous
habits
often
influence
the
form
of
limiting
desired.
It
is
with
this
in
mind
that
we
have
provided
a
tool
flexible
enough
to
be
set
up
to
fulfill
almost
any
requirement.
The
TIME
CONSTANT
switches
give
a
wide
choice
of
constants.
Position
3
is
merely
a
first
suggestion
for
a
general
purpose
timing
circuit.
With
certain
popular
music
or
speech
a
much
faster
time
constant,
such
as
positions
1
or
2,
might
be
more
desirable.
For
classical
music
a
much
slower
position,
such
as
h,
is
useable.
Positions
5
and
6
combine
fast
release
with
slow
release
and
can
be
useful
if
a
great
amount
of
automatic
level
correction
is
required.
These
positions
should
also
make
the
limiter
action
least
audible
since
they
will
reduce
overall
program
level
if
continual
limiting
persists.
So
far
the
unit
has
been
described
as
TWO
separate
limiters.
If
it
is
desirous
to
use
the
unit
for
correcting
the
respective
lateral
and
vertical
components
in
transferring
tapes
to
stereo
disks
or
dubbing
original
tapes
to
the
master
tape,
the
Vertical-
Lateral
position
is
advantageous.
In
this
position,
each
stereo
channel
is
divided
into
its
respective
lateral
and
vertical
components.
The
upper
channel
now
acts
as
a
limiter
for
the
lateral
component,
the
lower
channel
as
a
limiter
for
the
vertical
component.
As
“long
as
the
amount
of
lateral
and
vertical
component
reduction
in
each
channel
is
identical,
no
deterioration
of
separation
will
occur.
However,
often
it
is
advantageous
to
reduce
the
vertical
component
more
than
the
lateral,
resulting
in
some
loss
of
separation.
Limiting
the
lateral
and
vertical
components
can
be
of
great
help
in
producing
good
stereo
masters
with
only
negligible
loss
of
separation.
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NOTES
1,
RESISTORS
DESIGNATED
IN
OHMS,
10%
&
1/2W
UNLESS
OTHERWISE
SPECIFIED
2.
CAPACITORS
ARE
DESIGNATED
IN
MFD
UNLESS
OTHERWISE
SPECIFIED
3.
€301
SUPPLIED
AS
PART
OF
1303
&
HAS
A
VALUE
OF
5/630
VAG
SCREWDRIVER
ADJUSTMENT
FRONT
PANEL
5.@)
SCREWDRIVER
ADJUSTMENT
BENEATH
FRONT
PANEL
6
8
KNOB
ADJUSTMENT
FRONT
PANEL
7.
ALL
SWITCHES
SHOWN
IN
CCW
POSITION
EXCEPT
$301
-13V.
TO
-14.5V.
$101
&
$201
METER
SELECTOR
POS.
1
BALANCE
2
ZERO
3
BALANCE
$102
&
S202
TIME
CONSTANT
POS.
1-6
AT401
&
AT201
INPUT
GAIN
R105
&
R205
BALANCE
R115
&
R215
AC
THRESHOLD
R117
&
R217
DC
THRESHOLD
R142
&
R242
ZERO
$301
MATRIXING
POS,
1
LEFT
&
RIGHT
2
LATERAL
&
VERTICAL
R313
REG
B+
ADJ
RE
ms
$70,
beers
LITE
%
wane
Other manuals for 670
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