Fairchild 870 User manual

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INSTRUCTION MAN U AL
MODEL 870 70W AMPL IFIER
Serial N o.
FAL<CHILD . '{ .t.'CO~ING EQUIP MENT CO RPORATION
10-40 45th Avenue, Long I s land City , N.Y. 11101
212 784-6163 IB870/769- l

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MODEL
870 70
WATT
AMPLIFIER
DESCRIPrION
The
FAIRCHILD
MODEL
870 power
amplifier
is
designed
to
meet
the
need
for
a
high
quality
profess
ion
al
monitor
amplifier,
ca
pable
of
delivering
70
watts
rms
int
v
an
8
ohm
load
with
peak
power
capability
to
100
wa
t
ts
.
Output
pow
er
of
70
wa
t
ts
is
obtain
ed
thr
oug
hout
the
entire
audio
ran
ge
of
20
hz
to
20
Khz
.
Fully
transistorized
solid
s
tate
cir-
cuit
incorporates
full
protecti
on ag
ainst
overload
,
short
cir-
cuit
or
o
pen
circuit
. The
entire
amplifier,
with
the
exception
of
out
p
ut
transistors
and
the
power
suppl
y
section
,
is
lo
cated
on
plug
-
in
card
.
This
all
o
ws
instant
ac
cess
to
any
critical
compon-
ents
in
the
unit
f
or
p
urposes
of
r e
pair,
maintenanc
e
or
inspection
.
The
FAIRCliILD
MOD
EL
870
amplifier
features
extremely
low
distortion,
excellent
transient
response,
flat
freque
n
cy
response,
hi
gh
inp
ut
imped
ance,and
output
circuit
protection
.
Suggested
us
es
for
the
870
include
applic
a
tions
in
studio
monitor-
ing,
sound
re
-
enforcement
and
in
the
reco
r
ding
field
.
OPr:RA
T
IO
N
T
he
FAIRCHILD
MODll 870
amplifier
has a
self
-
cont
ained
power
sup
p
ly
.
Audio
signal
of
.8
volts
across
input
produces
70 w
atts
across
the
1:oad. The
lOOK
bridgin
g
input
allows
operation
of
the
amp
lifi
er
at
any
source
with
imp
edan
ce
up
to
100
,000
ohms . The out
put
imp
e~an
ce
is
only
a
small
fr
a
ction
of
the
recommended
lo
ad
impedance
so
that
damping
factor
of
the
o
utput
i s
extremely
high
and
~dth
avera
ge
load
exce
e
ds
20.
\.lhen
more
than
one
speaker
is
conn
ected
ac
ro
ss
the
output,
the
lo
ad
impedance
sh
ould
not
be
lo
wer
than
4 ohms
in
order
t o
pr
event
pre-
matu
re
action
of
the
overload
protection
cir
cuit
.
Because
volta
ge
at
the
output
of
the
amplifier
is
ab
out
28
volts,
it
can
be
used
as
a 25
volt
line
for
soun
d
re-enforcement
ins
tal
lation
s .
Many
speakers
can
be
b
ri
dged
off
t he
output
of
the
870
amp
lifi
er
with
step-down
speaker
tr
ansformers
between
each
of
t
he
speakers
and
the
output
of
the
power
amplifier.
The
design
of
the
870
is
such
th
at
there
are
neither
transformers
nor
capacit
o
rs
in
the
ou
tput
circuit
. Load
to
the
amplifier
is
con
-
nected
dire
c
tly
to
the
ou
tput
transistors
.
Balanced
power
supply
elimina
t
es
the
need
for
b
ulky
and
perf
ormance-
deteri
o
rating
cou
pling

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870 IB
elements (transformers and electrolytics). Under normal ope rati ng
condit i ons, gain control of the amplifier input is set to less than
half wrzy in order to obtai n high monitoring levels.
INSTALLATION
The MODEL 870 amplifier can be rack mounted usin g the FAIE CHILD
662RJ 1 rack mounting frame or similar mounting arrangement. The
662RM takes 514" of rack space. The power amplifier should be
mounted
so that enough air can circulate around the unit keeping
the temperature of the output transistors at the ambient l e vel .
The
amplifier should not be mounted close to low level circuits
containing microphone transformers or wires,in order to prevent
induction of AC fields g enerated by the power transformer into
adjacent equipment . In mobile installations, it is advisable
t o add reinforcing struts to provide regidity t o the mounting.
CONNECTIONS
Input wires to the 870 amplifier should be shielded . Preferably
two conductor wire should be used.
TERMINAL 1
2
3
4
high side input
low side input . Shield of the input
cable should be tied to the low side
of Terminal 2. The other side of the
shield should be left disco..i.nected or
floating .
output high side
output low side
CAUTION should be exercised in gro unding. If the g round
of the output circuit also hap pens to be common
gr ound to the input circuit, high frequency os-
cillation may occur disabling the amplifier.
OPERATI NG INSTRUCTIONS
Operation of the FAIRCHILD 870 amplifier is essentially the same
as any other power amplifier. However, because of the efficient
power supply circuit and large filtering capacitors, the amplifier
will not cease to amplify after the power switch is turned off for
at least several seconds . There is nothing wrong with such a long
turn-off time as this indicates that there is ample amount of re-
serve p ow er in the power supply to provide smooth and clean DC to
the amplifier circuit .
- 2-

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POWER
OUTPUT
INPUT
LEVEL
INPUT
IMPEDANCE
OUTPU
T
IMPEDANCE
SUGGEST
LOAD/IMPEDANCE
FREQUENCY
RESPONSE
THD
NOISE
DAMPING
FACTOR
POWER
REQUIREMENT
DIMENSIONS
WEIGHT
CONTROLS
WARRANTY
870
IB
SPECIFICATIONS
70
watt
rms
into
8
ohms
.8
volts
for
70
watts
across
8
ohms
lOOK
bridging
Less
than
5%
of
load
impedance
8
ohms
or
higher;
4
ohms
minimum
±
.5
db,
20
hz
to
20 Khz
Less
than
.4
%
at
full
power
typical
•
2';
~
or
better
-85
db
below
rated
output
20
or
more
117
volt
AC;
50
or
60
cycles
at
1
amp
13"
X
6"
X
4"
1W2
lbs
On-Off
switch
Input
gain
con
t
rol
S
ee
standard
warrant
y
policy
.
To
validate
warranty,
complete
and
return
the
warranty
~eg
istr
at
ion
ca
rd
include
d
with
this
manual.
If
there
is
any
question
on
this
or
any
other
FAIRCHILD
profession-
al
product,
please
do
not
hesitate
t o
contact
our
Customer
Service
Department,
FAI
RCH
ILD
RECORDING
EQUIP
MENT
CORPORATION,
10-40
45
th
Avenue, Long
Island
City,
New
York
11101.
A
TT
ACHH.1:liTS
Schematic
diagram
870 096668
-3-

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NOTE
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4.3K
C6
1
50
/
50V
R9
10
0
i!ERO
ADJ
DI
I
N3754
RIB
(SEE 1
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D3
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N3754
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NOTE
3)
C9
25
0
/ 6V
NOTES:
I.
UNLESS OTHERWISE SPECIFI
ED
AL
L
RES
ISTORS
ARE
IN
OHMS 8
l/2W
.
ALL
CAPAC
ITORS ARE IN MFD.
2. SET BIAS
FOR
20
MA
QUIESCENT CURRENT.
07
404
11
D4
3. THERMALLY CONNECTED
TO
HEAT
SINK
FOR
OUTPUT
TRANSISTOR.
4. D6,D7,D8
8
D9 REPLACED BY
VARO
RECTIFIER
NO
.
247
.
5.
FULL
LOAD AT
1.
5ADC.
I .
HEAT
SINK.
IN16l2R
RIO
.
33
,ow
3
Rl7
20
AF
5.i
OUTPUT
s.n
CIO
.I
r·
06
404
11
.....
..
c.
.
C-9ss6a
ISSUE
I.
4/24/69
70W
AMPLIFIER
(870
)
SCHEMATIC
DIAGRAM
FA
I
RCHILD
RECORD
I
NG
EQU
I
PMENT
CORPORATION
10
~0
•~
AY
C:
L I C I N Y.