Inovonics 215 Manual
www.SteamPoweredRadio.Com
TAB
LE
OF
CONTENTS
I .
GENERAL
INFORMATION
•.••
..
• •
•••
.
..•
2
I
I.
FUNCTIONAL DESCRIPTION
AND
SPECIFICATIONS.
.
2
III.
IV.
v.
VI.
VII.
Ga
t
ed
A.G
. C. -
Average
Level
Compressor
-
AM
"Integ
r
ated"
Peak
Controller
-
FM
Peak
Controller
-
"Proof
0
Mode -
Stereo
Inter
-
conne
c
tion
-
Spec
i f i
cations
INS
TALLATION
Unpacking
and
Inspection
-
Mounting
-
RF
I -
I
n/Out
Conn
e
ction
and
Consid
e
rations
-
Polarity
OPERATION
AND
ADJUSTMENT
Preliminary
- P .
C.B.
Strapping
Option
s -
Sugge
s
ted
Initial
Setup
Procedure
-
Clipping
Depth
7
9
CIRCUIT
DESCRIPTIONS • . • . • • .
12
A.G
.
C.
Amplifier
-
Average
Level
Compres
s
or
-
AM
Peak
Controller
-
FM
Peak
Controller
-
Bypass
Assembl
i
es
-
Power
Supply
CALIBRATI
ON
PROCEDURES
Not e -
Equipment
Required
- A. G. C.
Amplifie
r
As
s
emb
l y - C
ompre
s
sor
Assembly
-
AM
Peak
Controller
-
FM
Pe
ak
Controller
.
18
APPENDIX
• • • • . 24
Parts
Lists
-
Schematics
Warranty
-
1-
www.SteamPoweredRadio.Com
I.
GENERAL
INFORMATION
The
Inovonics
215
is
a
broadband
audio
processor
primarily
intended
for
AM,
FM
and
TV
broadcast
use,
although
certain
features
make
it
attractive
also
for
sound
re
-
enforcement
and
some
studio
r
ecording
situations.
The
215
presents
an
as
-
needed
approach
to
audio
processing,
as
the
basic
unit
consists
of
a
chassis
supplied
with
signal
bypass
assemblies.
Plug
-
in
options
then
provide
the
three
processing
functions
of
(1)
gated,
·
gain-riding
A.
G.C.,
(2)
average
level
compression
and
(3)
peak
control
with
phase
-
optimization
and
asymmetrical
operation
for
AM
broadcast,
or
variable
frequency-selective
characteristics
for
FM
broadcast
and
recording.
Options
may
be
provided
singly
to
perform
specific
processing
functions
or
to
complement
existing
equipment,
or
the
215
may
be
''fully-loaded"
and
stand
alone
as
a
complete
processing
system.
II.
FUNCTIONAL DESCRIPTION AND
SPECIFICATIONS
A
description
of
each
of
the
three
processing
functions
of
the
215
follows.
Specifications
relative
to
the
described
subsection
are
given
in
the
text
.
Performance
data
not
expressed
or
implied
in
the
descriptions
is
tabulated
at
the
end
of
this
section.
Gated
A.
G.C.
(-
01
option)
In
the
typical
broadcast
situation,
program
levels
tend
to
wander
up
and
down
a
bit,
frequently
as
a
result
of
operator
i~attention,
personnel
shift
changes
or
from
other,
usually
human
influences
.
Thus
the
first
major
functional
block
of
the
215
is
a
slow,
gain-riding
A.
G.C
.
This
effectively
erases
long
-
term
input
level
variations
and
presents
subse-
quent
processing
stages
with
a
constant
r .
m.s.
input
value.
-2-
www.SteamPoweredRadio.Com
Capture
range
of
the
A.G.C.
is
±lOdB,
and
A. G. C.
gain
may
be
selectively
displayed
on
the
fron
t
panel
meter.
Correc-
tion
rate
(response
time)
is
about
O.SdB/second,
slow
enough
not
to
alter
program
dynamics.
A
frequency
-
weighted
"gating"
feature
inhibits
A.G.C
.
action
during
program
pauses,
and
slowly
returns
gain
to
OdB
in
event
of
extended
signal
loss.
The
gating
circuit
has
-3dB
sensitivity
points
at
300Hz
and
3kHz
to
guard
against
erro
-
neous
gain
"
hunting"
caused
by
non
-
program
nois
es.
Gating
threshold
sensitivity
is
prese
t
at
a
value
which
will
open
the
gate
when
midband
program
en
ergy
rises
above
-
25dB
rel-
ative
to
nominal
program
"zero
"
level.
It
is
generally
acknowledged
that
program
components
below
a
particular
frequency
contribute
nothing
to
perceived
program
quality
and,
in
fact,
may
sabotage
intelligibility
and
both
perceived
and
measured
program
loudness.
The
choice
of
a
low-end
cutoff
frequency
is,
nevertheless,
a
matter
for
sub
-
jective
consideration;
thus
the
215
offers
three:
50,
70
and
lOOHz.
The
L.F.
cutoff
frequency
is
selected
with
a
series
of
straps
on
the
A.G.C.
Amplifier
board
.
Strapping
instructions
are
given
on
page
9.
A
digitally
-
generated,
pseudo
-ran
dom
Pink
Noise
generator
is
an
integr
al
part
of
the
215
A.G.C.
Amplifier
assembly
.
Pink
Noise
is
a
very
useful
audio
test
signal;
its
constant
-
power
-
per
-
octave
(or
equal
fractions
thereof)
energy
distribution
and
characteristic
crest
factor
more
closely
approximate
pro
-
gram
material
than
do
discrete
oscillator
tones.
A
switch
substitut
es
this
test
signal
for
the
input
program
in
any
operating
mode
to
aid
in
system
setup
and
maintenance
.
Average
Level
Compressor
(-
02
option)
Program
dynamics
are
firm
l
y-y
et-unobtrusively
compressed
by
t
he
21S's
averaging
Comp
res
sor
assembly.
This
circuit
util
izes
gain
-
control
circuitry
yielding
a
"soft
knee,"
or
gentle
transition
from
linear
to
compressed
operation.
In
fact,
the
actual
compression
ratio
increases
as
more
compression
is
employed,
With
lOdB
or
so
of
indicated
compression
the
ratio
is
about
2:1
,
increasing
to
4
:1
at
lSdB
.
The
result
of
this
program
-
controlled
compression
ratio
is
an
exce
edin
g
ly
smooth
sound,
even
with
considerable
compression
in
effect.
Never
-
theless,
a
control
loop
from
the
Compressor
back
to
the
A
.G.C.
circuit
guard
s
againstovercompression
by
reducing
A.
G.c.
gain
and
flashing
a
warning
indicator
when
the
Compressor
works
too
hard.
Compressor
attack
and
release
ti.mes
are
fixed
at
-3-
www.SteamPoweredRadio.Com
values
insuring
an
optimum,
rapid
operation
consistent
with
an
acceptable
distortion
figure
at
low
frequencies
.
The
AM
"
In
t
egrated
"
Peak
Controller
(-
03
option)
Asymmetrical
modulation
of
positive
and
negative
peaks
yields
a
modulation
advantage
only
when
the
program
material
is
asymmetrica
l
in
nature.
Most
music,
because
it
is
a
blend
of
complex
waveforms
which
are
not
phase
-
related
,
has
a
very
even
balance
of
peak
energies.
Solo
instruments
and
the
human
voice
,
on
the
other
hand,
possess
a
more
or
less
fixed
relationship
·
between
the
phase
of
the
fundamental
tone
and
the
harmonics
.
This
leads
to
an
appreciable
and
consistent
imbalance
between
positive
and
negative
peaks,
and
can
be
used
to
modulation
advantage.
To
maintain
optimum
asymmetrical
modulation
of
an
AM
carrier,
program
peaks
should
be
predominantly
positive
-
going.
Current
practice
is
to
switch
program
phase
whenever
necessary
to
a
ss
ure
the
highest
incidence
of
positive
modulation
. Common
phase
-
swit
c
hing
techniques
usually
cause
an
annoying
"
click
"
or
"
pop"
at
the
instant
of
reversal
.
The
Phase-Follower
of
the
215,
on
the
other
hand,
features
a
novel
"phase
-
rotation"
circui
t
which
gen
t
ly
and
inaudibly
"
rolls
"
the
phase
through
a
180
-
degree
shift
when
required
for
maximum
positive
modulation.
Sensitivity
of
the
phase
-
detection
circuit
of
the
Phase-Follower
is
fixed
,
yet
a
function
of
the
degree
of
peak
limiting/clipping
in
effect.
With
a
consi
s
tent
lOdB
of
peak
reduction
,
asymmetry
of
10%
will
cause
a
phase
reversal
.
With
lSdB
peak
reduction,
5%
asymmetry
will
initiate
a
"roll."
The
215
AM
Peak
Controller
represents
the
mos
t
radical
depa
r-
tur
e
from
previous
processor
peak
reduction
systems
.
To
satis£y
the
particular
requirements
for
optimum
AM
carrier
modulation,
an
interrelated
peak
limiter/clipper
circuit
functions
without
compromising
the
features
of
either.
Here
is
the
basic
principle
of
i
ts
operation
:
the
output
from
the
Phase
-
Follower
is
fed
to
a
true,
low
-
distortion
peak
limiter
of
the
Santana
configuration.
This
is
followed
by
an
active
hard
clipper
with
the
unique
ability
to
quantita-
tive
l y
monitor
the
degree
of
clipping
it
performs
.
This
information
is
routed
back
to
the
peak
limiter
through
a
control
loop
which
allows
adjustment
of
the
limiting
/
clipping
ratio
.
"Clipping
Depth"
may
be
set
to
a
desired
value,
and
once
set
w
il
l
rema
i n
constant
regardless
of
pr
ogram
content
.
An
optimum
operat
i
ng
peak
-
to
-
average
ratio
may
thus
be
sel
-
ected,
from
a
very
clean
signal
without
audible
clipping,
to
a
slight
degree
of
clipping
for
a
definite
gain
in
loudness
-4
-
www.SteamPoweredRadio.Com
with
negligible
sacrifice
in
listenability,
or
even
heavier
clipping
for
decided
modulation
advantage
with
an
attendant
audible
harshness,
particularly
on
voice.
Because
of
the
interrelated
l
imiter/clipper
c
ir
cuit,
Peak
Controller
attack
time
is
virtually
instantaneous.
Even
the
first
half
-
cycle
of
a
20kHz
,
20dB
overload
is
reduced
to
the
final
limited
peak
value.
The
release
time
i s
fixed
at
a
value
which
yields
less
than
1%
distortion
at
SOHz
with
lOdB
limiting.
Nevertheless,
a
strap
on
the
Peak
Controller
board
permits
a
speed-up
in
release
time
by
a
factor
of
4.
The
result
i s a
tradeoff
:
an
audible
modulation
advantage
against
an
increase
in
low
frequency
distortion.
The
1%
distortion
frequency
moves
up
to
200Hz
,
and
distortion
at
SOHz
increases
to
about
3%.
Both
Peak
Limiting
and
Clipping
Dep
t h
may
be
selectively
displayed
on
the
front
panel
meter.
The
215
permits
the
value
of
positive
modulation
peaks
to
be
continuously
adjusted
up
to
150%
of
the
negative
peak
value.
Although
positive
modulation
is
legally
restricted
to
125%,
many
plate
-
modulated
transmitters
require
drive
i n
excess
of
+125%
to
reach
the
legal
maximum
.
It
must
be
warned,
however,
that
transmitters
which
fall
into
this
category
are
incapable
of
linear
operation
up
to
+125%.
The
very
slight
gain
in
perceived
signal
loudness
must
be
weighed
against
probable
high
s i
gnal
distortion
in
these
cases.
An
active
Low-
Pass
Filter
follows
the
AM
Peak
Controller
and
serves
to
restrict
the
bandwidth
of
the
processor
output.
Higher
-
order
harmonics
generated
in
the
limiting/clipping
process
are
significantly
attenuated,
thus
substantially
reducing
the
tendency
for
the
modulated
carrier
to
"splatter"
into
adjacent
frequencies
.
Moreover,
transmitter
power
is
not
wasted
in
modulating
those
audio
frequencies
normally
lost
in
the
AM
broadcast
receiver
. An
H.F.
cutoff
frequency
of
7,
10
or
15kHz
may
be
selected.
Selection
is
made
with
a
series
of
straps
on
the
circuit
board;
instructions
are
given
on
page
9.
The
FM
Peak
Controller
(-
04
option)
The
FM
Peak
Controller
is
very
similar
to
the
AM
assembly
in
the
concept
of
an
"integrated"
limiter
/
clipper,
but
the
phase
-
following,
asymmetrical
modulation
features
are
,
of
co
ur
se,
no
t
included
.
Instead
,
complementary
pre-limiting
pre
-
emphasis
and
post-limiting
de
-
emphasis
are
employed
to
satisfy
the
requirements
of
FM
broadcast
pre
-
emphasis
. A
series
of
circuit
board
straps
permit
selection
of
the
standard
7
5ps,
"
Dolby"
25ps
or
"flat
"
characteristics.
-5
-
www.SteamPoweredRadio.Com
The
optional,
faster
release
time
selection
and
variable
Clipping
Depth
features
are
retained
in
the
FM
Peak
Controller,
but
it
is
anticipated
that
these
will
be
used
conservatively
(if
at
all)
in
FM
broadcasting.
The
low-pass
filter
which
follows
the
limiting
circuitry
is
fixed
for
a
high
-
end
roll-
off
beginning
just
above
lSkHz.
"Proof"
Mode
A
single
button
places
the
215
in
"Proof
. "
The
A.
G.C.
is
defeated
and
Compressor
inhibited.
The
Peak
Controller
is
similarly
defeated,
and
both
the
High-
and
Low-Pass
Filters
are
electronically
set
to
their
obvious
extremes.
All
signal-
path
circuitry
is
otherwise
active.
Stereo
Interconnection
Two
215's
may
be
interconnected
for
stereo
operation.
Com-
p
ressors
are
slaved
for
identical
operation,
and
one
Phase
Follower
may
be
slaved
to
the
other
or
both
defeated,
depending
on
which
system
of
AM-stereo
transmission
is
ultimately
approved.
215
Specifications
This
is
a
tabulation
of
those
performance
specifications
which
are
not
expressed
in
the
texts
of
the
foregoing
discus-
sions.
Frequency
Response:
±ldB
,
50Hz-15kHz
Distortion
(with
lOdB
Compression
and
lOdB
Limiting-only):
<O.
3%
THD
above
200Hz,
<l.
0%
THD
at
SOHz.
Noise:
Better
than
60dB
below
100%
modulation
.
Input:
Balanced,
-30
to
+lOdBrn
Output:
Balanced,
Oto
+20dBrn;
+24dBm
output
clipping
level.
Power:
l05-130VAC
(230V
available),
50/60Hz,
20W
Physical:
3-1/2"
x
19"
x
9";
8
lbs.
-6-
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III.
INSTALLATION
Unpacking
and
Inspection
Upon
receipt
of
the
equipment,
inspect
at
once
for
shipping
damage.
Should
any
such
damage
be
observed,
notify
the
carrier
at
once;
if
not,
proceed
as
outlined
below.
It
is
suggested
that
the
original
shipping
carton
and
materials
be
retained
should
future
reshipment
become
necessary.
In
the
event
of
return
for
Warranty
repair,
shipping
damage
sustained
as
a
result
of
improper
packing
for
return
may
invalidate
the
Warranty.
It
is
important
that
the
Warranty
Registration
card
found
at
the
front
of
this
manual
be
returned;
for
not
only
does
this
assure
coverage
of
the
equipment
under
terms
of
the
Warranty,
but
the
user
will
automatically
receive
specific
servicing
or
modification
information
should
it
be
issued.
Mounting
The
215
is
packaged
to
mount
in
a
standard
19-inch
equipment
rack,
requiring
3-1/2
inches
of
rack
space
per
unit.
The
processor
generates
negligible
heat,
and
itself
is
unaffected
by
wide
variations
in
the
ambient
operating
temperature.
RFI
The
215
is
specifically
designed
to
operate
in
close
prox-
imity
to
broadcast
transmitters;
nevertheless,
care
should
be
exercised
in
locating
the
unit
away
from
abnormally
high
RF
fields.
In
some
installation
situations
an
RF
ground
loop
may
be
formed
between
the
input
or
output
cable
shield
grounds
and
the
AC
power
cord
ground.
Use
of
a
"ground-
lifting"
AC
adapter
should
remedy
the
problem,
but
the
chassis
of
the
unit
should
somehow
be
returned
to
earth
ground
for
safety.
In/Out
Connection
and
Considerations
The
215
input
and
output
connections
are
brought
out
to
a
rear
panel
screw-terminal
barrier
strip.
Both
the
input
and
output
are
balanced
(transformer-isolated),
with
ground
terminals
provided
for
cable
shields.
-7-
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Should
the
equipment
which
feeds
the
215
require
output
loading
,
an
external
600-ohm
resistor
should
be
placed
across
the
processor's
input
terminals;
otherwise
the
input
is
"balanced-bridging"
with
a
characteristic
input
impedance
of
l0K
or
more.
The
source
impedance
of
the
215
output
amplifier
(ahead
of
the
line
output
transformer)
is
virtually
zero.
However,
as
the
output
transformer
has
some
reactance,
it
is
important
that
the
output
be
terminated.
in
600
ohms
to
minimiz
e
over-
shoot.
The
output
clipping
level
of
the
215
is
+24dBm.
To
permit
positive
peak
excursions
to
reach
+125%,
the
nominal
100%-
modulation
sine
wave
output
level
should
be
kept
at
+18dBm
or
below.
Polarity
The
input
and
output
of
the
215
are
each
marked
with+
and
-
designations
to
aid
in
maintaining
proper
phase
in
stereo
applications,
or
proper
asymmetrical
modulation
of
program
peaks.
In
the
latter
case,
the+
output
terminal
will
be
positive-going
with
positive
modulation
peaks.
-8-
www.SteamPoweredRadio.Com
IV.
OPERATION
AND
ADJUSTMENT
Th
e
variou
s
adjustments
are
identified
on
the
inside
of
the
removab
l e
fron
t
adjustment
cover
.
Despite
the
seemingly
obvious
meanings
of
the
control
function
descriptions,
it
is
highly
re
c
ommended
that
the
outl
i
ned
procedure
be
care
-
fully
followed
for
initial
setup.
Subsequent
readjustment
to
secure
a
desired
effect
should
be
made
only
after
it
has
been
established
that
the
unit
functions
properly
and
pre-
di
ctably
in
accordance
with
the
initial
setup
procedure.
All
adjustments
are
made
"on
t
he
air,
"
utilizing
a
typical
program
feed
and
the
stat
i
on
Modulation
Monitor.
Pre
l
iminary
- P .
C.B.
Strapping
Opt
ions
Input
Gain
Range
The
215
accommodates
line
input
levels
between
-
30
and
+l0dBm
.
To
extend
resolution
of
the
INPUT GAIN
control,
the
overall
40dB
range
is
broken
into
two,
20dB
ranges
selected
by
a
strap
on
the
A.G.C.
Amplifier
P.C.B.,
or
Peak
Controller
P.C.B.
if
the
A.
G.C
.
and
Compressor
options
are
not
used.
For
line
input
levels
between
-30
and
-l0dBm,
a
strap
should
be
placed
across
terminals
A
and
B.
For
input
levels
between
-
10
and
+l0dBm,
the
strap
should
be
removed.
High
-
Pass
Fi
lter
Strapping
to
sel
e
ct
the
215
low
-
end
rolloff
frequency
is
afforded
on
the
A.G.C.
Amplifier
P .
C.B
.
The
three
cut
-
off
frequencies
are
50,
70
and
l00Hz.
For
50Hz
cutoff,
no
strap
is
required.
For
70Hz,
strap
C
to
D.
For
l
00Hz
cutoff,
strap
C
to
D
to
E.
The
H.P.F.
i s
automatically
defeated
in
the
"Proof"
mode
.•
Low-
Pass
Fi
l
ter
Strapping
to
select
the
high
-
end
rolloff
frequency
is
-9
-
www.SteamPoweredRadio.Com
afforded
on
the
AM
Peak
Controller
P.C
.
B.
only.
The
three
cutoff
frequencies
are
7,
10
and
15kHz.
For
lSkHz
rolloff,
strap
E
to
F
to
Hand,
separately,
J
to
K
to
L.
For
l0kHz
rolloff,
strap
E
to
F
and,
sep-
arately,
J
to
K.
For
7kHz
rolloff,
no
strap
is
required.
The
L.P.F.
is
automatically
defeated
in
the
"Proof"
mode.
Peak
Limiter
Release
The
limiter
portion
of
the
Peak
Controller
has
a
release
time
selected
and
fixed
at
a
value
which
is
an
optimum
compromise
between
high
perceived
loudness
(fast
release)
and
low
signal
distortion
(slow
release).
With
l0dB
limiting,
the
compromise
release
value
y
ields
about
1%
distortion
of
a
S0Hz
sine
wave;
correspondingly
less
distortion
at
higher
frequencies.
An
alternate,
faster
limiter
release
time
is
provided;
its
optional
use
can
result
in
a
perceptible
increase
in
program
loudness,
but
at
the
expense
of
greater
low
fre-
quency
signal
distortion.
Because
the
selectable
high-
pass
filter
is
provided
on
the
A.G.C.
amplifier,
however,
a
user
can
opt
to
roll
the
low
frequencies
off
and
utilize
the
faster
release
with
no
apparent
program
degradation.
The
faster
release
time
is
enabled
by
strapping
terminals
Mand
Non
the
AM
Peak
Controller
P.C.B.,
and
P
and
Hon
the
FM
version.
As
previously
cautioned,
this
should
be
done
in
conjunction
with
70
or
l00Hz
low-end
rolloff.
Suggested
Initial
Setup
Procedure
This
procedure
is
performed
with
the
215
in
the
program
chain,
"on
the
air"
and
fed
with
typical
program
material.
For
convenience,
this
procedure
also
appears
inside
the
front
cover
of
the
unit.
1.
Turn
all
trim
controls
fully
counterclockwise.
The
PROOF
and
PINK NOISE
buttons
should
be
"out
11
(normal
position).
2.
Depress
the
A.G.C.
RAJ.~GE
metering
button.
With
a
normal
program
input,
advance
the
INPUT
GAIN
control
for
a
center-scale
met
er
indication.
3.
Adjust
the
COMPRESSION
slide
pot
for
an
indicated
-10-
www.SteamPoweredRadio.Com
compression
of
about
l0dB.
4.
Depress
the
PEAK
LIMITING
metering
button.
Advance
the
PEAK
DRIVE
control
for
an
indicated
5-
l0dB
of
peak
reduction
.
5.
Advance
the
OUTPUT
LEVEL
control
for
negative
modu-
lation
peaks
of
95-100%
as
indicated
by
the
Modulation
Monitor
.
6 .
Advance
the
POSITIVE
PEAK
AMPLITUDE
control
for
desired
positive
peak
modulation
to
125%
as
indicated
by
the
Modulation
Monitor.
Clipping
Depth
The
degree
of
program
clipping
which
the
user
wished
to
employ
in
is
made
variable
with
the
CLIP
DEPTH
control
.
This
adjustment
is
made
subjectively,
and
the
final
setting
should
be
arrived
at
only
after
sampling
all
types
of
program
material.
By
depressing
the
CLIPPING
DEPTH
metering
button,
a
rnore-or-
less
quantative
indication
of
clipping
depth
is
displayed
on
the
front
panel
meter
.
With
the
pointer
remaining
in
the
"white"
zone,
clipping
is
very
light
and
inaudible
with
any
program
material.
Wnen
the
pointer
indicates
in
the
"gray"
area,
clipping
is
heavier
and
yields
a
definite
modulation
advantage.
Some
"harshness
11
may
be
audible
on
voice,
however
.
When
the
meter
indicates
in
the
"black",
clipping
is
quite
heavy
and
will
certainly
be
audible,
probably
objectionable
on
voice
and
even
some
music.
-11-
www.SteamPoweredRadio.Com
V.
CIRCUIT
DESCRIPTIONS
A.G.C.
Amplifier
Input
signals
to
the
215
are
isolated
by
input
transformer
T2
on
the
"mother"
board,
then
fed
to
input
amplifier
IC2
on
the
A.G.C.
Amplifier
assembly
.
The
40dB
input
gain
range
is
divided
into
two
20dB
segments
by
strapping
Rl
in
or
out,
and
the
INPUT GAIN
control
R4
gives
20dB
variable
control
ov~r
the
input
signal
. ·
TEST
switch
Sl
selects
between
the
normal
program
input
and
the
internal
Pink
Noise
test
signal
generator.
ICl
is
·a
monolithic,
pseudo-random,
digital
"white"
noise
source
.
The
filter
comprised
of
R6- 9
and
C2-5
imparts
a
3dB/octave
falling
characteristic
to
the
noise,
yielding
"Pink
Noise"
with
constant-power-per-octave
bandwidth.
The
second
section
of
IC2
is
the
active,
selectable
high-
pass
filter.
The
SO,
70
or
lOOHz
rolloff
frequency
is
sel-
ected
by
strapping
terminal
D,
or
both
D
and
E
to
terminal
C,
essentially
at
ground
via
FET
Q8.
Q8
is
turned
off
in
the
"Proof"
mode
to
return
the
filter
to
S0Hz,
"full
band-
width"
response
.
The
first
half
of
IC3
is
the
active
gain
control
element
of
the
A.G.C.
Amplifier.
This
circuit,
the
"Santana"
config-
uration,
utilizes
FET
QlA
as
an
active
variable
resistance
across
the
inverting
input
of
the
operational
amplifier.
QlB,
a
parameter-matched
"dummy"
FET,
is
placed
across
the
non-inverting
amplifier
input
and
cancels
the
channel
non-
linearities
of
QlA.
This
permits
control
of
the
audio
signal
at
levels
which
would
otherwise
be
above
the
low
distortion
operating
range
of
the
FETs.
Q4
and
5
comprise
a
"Baxandall"
full-wave
rectifier.
The
posit
i
ve-going
portion
of
the
output
of
variable-gain
stage
IC3
is
amplified
by
common
-
emitter
stage
Q4,
the
negative-
going
by
common-base
stage
QS
.
Thus
equal
positive
and
negative
information
cause
similar
currents
at
the
collector
junction.
Q6
imparts
additional
DC
gain
to
the
rectified
signal
which
is
then
filtered
by
the
network
R31/Cl6
and
R32/Cl7.
The
long
time
constant
of
this
dual
filter
pre-
vents
the
A.G.C.
circuit
from
following
the
program
enve
-
lope,
insuring
control
over
only
long-term
signal
variations
.
ICS,
a
unity-gain
buffer
amplifier,
isolates
the
filter
from
R33,
the
FET
pinchoff
calibration
adjustment.
-
12-
www.SteamPoweredRadio.Com
Output
from
the
A.G.C.
variable-gain
stage
is
sampled
by
the
Gating
Circuit.
The
first
half
of
IC4
is
a
bandwidth-limited
voltage
amplifier
stage
with
-3dB
points
at
300Hz
and
3kHz
.
This
insures
that
the
amplified
signal
will
primarily
consist
of
legitimate
program
material,
rather
than
non-program
noise.
This
signal
is
rectified
by
CRS
and
6,
the
resultant
DC
pres-
ented
to
one
input
of
a
comparator
utilizing
the
second
half
of
IC4.
The
other
comparator
input
is
held
at
a
fixed
DC
potential
by
divider
R41/42
with
a
small
amount
of
positive
feedback
through
R43
to
impart
hysteresis
to
the
Gatipg
function.
Gating
logic
is
fed
back
to
the
Baxandall
rectifier
circuit
to
return
the
A.G.C.
amplifier
to
a
nominal
0dB
gain
figure
when
the
program
.
signal
falls
below
the
Gating
threshold.
The
circuit
is
thus
prevented
from
slowly
raising
residual
noise
to
an
annoying
level
during
program
pauses.
IC6
is
a
comparator
which
constantly
monitors
the
Compressor
"overcomp"
bus.
Should
the
Compressor
average
more
than
about
lSdB
compression,
IC6
will
toggle
to
illuminate
the
OVERCOMP
indicator
and
to
override
A.G.C.
action
and
reduce
circuit
gain.
The
A.G.C.
amplifier
and
Gating
circuits
are
inhibited
in
the
"Proof"
mode
via
CRl0
and
11.
The
second
half
of
IC3
and
transistors
Q2
and
3
form
an
output
stage
to
feed
the
Compressor
assembly.
Terminals
Hand
F,
must
be
strapped
when
this
assembly
is
used
in
the
215~
the
RC
network
thus
shorted
is
required
£or
use
with
the
Model
231
Multiband
Audio
Processor.
Average
Level
Compressor
An
input
signal
of
constant
long-term
level
from
the
A.
G.C.
Amplifier
assembly
is
routed
to
the
Compressor
assembly
via
R3,
the
COMPRESSION
control.
R3
affords
±12dB
control
over
the
input
to
the
Compressor,
and
a
corresponding
control
over
the
amount
of
compression
in
effect.
The
first
half
of
ICl
buffers
the
input
signal
and
drives
the
variable-gain
stage
.
QS,
with
its
current-source
collector
load
Q6,
is,
in
effect,
a
single-stage
operational
amplifier.
Gain
of
this
stage
is
roughly
set
by
the
value
ratio
between
input
resistor
Rl3
and
feedback
resistor
RlS.
Amplifier
gain
is
varied
by
Q4,
the
saturation
resistance
shunting
the
amplifier
summing
mode
to
ground.
Transistor
saturation
resistance
is
not
symmetrical,
if
a
transistor
were
placed
in
the
ground
leg
of
a
typical
resistance
-13-
www.SteamPoweredRadio.Com
voltage
divider,
an
AC
signal
would
be
severely
distorted
.
The
single
stage
operational
amplifier,
on
the
other
hand,
is
simultaneously
depleted
of
loop
gain
as
the
input
signal
is
shunted,
assuming
a
non
-
linear
characteristic
cancelling
that
of
the
saturation
transistor.
Gain
reduction
is
thus
effected
without
distortion
.
The
output
from
the
compressor
is
buffered
by
half
of
IC2
and
fed
to
a
"precision"
full-wave
rectifier
composed
of
IC3
and
associated
components.
Q3,
normally
on,
is
turned
off
in
the
"Proof"
mode
to
inhibit
compression.
·
The
rectified
signal
is
buffered
by
Q9
and
filtered
by
Cl0
and
R44.
The
time
constant
is
selected
for
optimum
response
vs.
distortion.
Half
of
IC2
further
buffers
the
filtered
DC
to
drive
both
the
gain
-
controlling
transistor
Q4
and
the
front
-
panel
meter
through
its
linearizing
network
of
CR13
and
14
1
R48
and
49.
The
second
half
of
ICl
buffers
the
compressed
program
signal
and
feeds
the
Peak
Controller
.
AM
Peak
Controller
The
Compressor
output
feeds
the
summing
mode
·
of
the
Peak
Controller
input
amplifier
ICl.
The
one
half
of
ICl
is
a
voltage
amplifier
stage
for
signals
from
the
Compressor
assembly.
Variable
feedback
resistor
R4
is
the
LIMITER
D.
RIVE
control
and
affords
a
20dB
drive
adjustment.
The
other
half
of
ICl
provides
additional
voltage
gain
for
the
Phase
Follower
detector
and
control
circuit.
Positive
and
negative
peaks
are
rectified
by
CRl
and
2,
respectively,
and
held
by
associated
capacitors
CS
and
6.
Rl7
and
18
sum
the
peak
levels
such
that
the
polarity
of
DC
across
C7
will
represent
program
peak
predominance.
One
half
of
res
monitors
this
DC
and
toggles
(with
a
certain
fixed
hysteresis)
to
provide
polarity
switching
logic.
FET-input
IC2
performs
the
phase
"rotation
"
function.
With
tne
non-inverting
input
held
at
ground
through
FET
Ql,
IC2
inverts
the
program
signal.
When
Ql
is
off,
the
program
polarity
is
not
inverted
.
Ql
is
turned
on
and
off
slowly
through
the
RC
network
of
R28
and
CB
to
provide
an
inaudible
180
-
degree
program
phase
reversal.
IC3
buffers
the
signal
appearing
across
Ql
to
"linearize"
the
FET
DC
control
voltage
for
minimum
signal
distortion
during
the
actual
period
of
phase
"rotation."
The
remaining
half
of
ICS
drives
the
front-panel
POLARITY
indicators.
-
14-
www.SteamPoweredRadio.Com
-
Q2
and
one
half
of
IC4
comprise
a
"Santana"
configuration,
the
linear
gain-control
portion
of
the
Peak
Controller.
The
Santana
circuit
is
described
on
page
12.
The
output
of
this
circuit
is
fed
to
the
bases
of
transistors
Q6
and
7.
The
emitters
of
these
devices
are
biased
a
few
volts
positive
and
negative,
respectively,
and
the
base-emitter
junctions
provide
hard
clipping
of
the
program
signal.
The
emitter
bias
of
Q7
can
be
varied
to
provide
asymmetrical
peak
clipping
for
increased
positive
modulation.
In
addition
to
their
clipping
duties,
Q6
and
7
further
per-
form
a
rectification
function
to
control
gain
of
the
Santana
Circuit.
Q8,
a
unity-gain
inverter,
follows
Q7
to
provide
the
same
polarity
of
collector
current
for
negative-going
peaks
as
Q6
does
for
positive.
Q9
gives
additional
control
loop
gain
which
is
made
variable
with
CLIPPING
DEPTH
control
R57.
Thus
a
signal
composed
of
(and
proportional
to)
the
clipped
portion
of
the
program
signal
is
rectified,
filtered
by
R63,
64
and
Cl4,
buffered
by
one
half
of
IC4
and
used
to
vary
program
gain
prior
to
clipping.
In
this
way
the
degree
of
program
clipping
can
be
kept
constant
regardless
of
pro-
gram
content.
When R57
is
fully
CCW
(minimum
resistance)
control
loop
gain
is
at
maximum
so
that
virtually
no
meas-
urable
clipping
at
all
results
in
linear
gain
reduction.
Increasing
the
value
of
R57
reduces
control
loop
gain
so
that
Q6
and
7
must
conduct
harder
to
effect
gain
reduction;
this
increases
clipping
action.
Output
from
the
limiter/clipper
is
routed
to
the
variable
low
-
pass
filter.
This
consists
of
one
half
of
IC6,
C9
and
10
and
the
various
resistors
which
can
be
strapped
for
high-
end
cutoff
frequencies
of
7kHz
(no
straps),
l0kHz
(E
to
F
and
J
to
K),
or
lSkHz
(E
to
F
to
Hand
J
to
K
to
L. )
The
remaining
half
of
IC6,
along
with
Q4
and
5
and
associated
circuitry,
makes
up
the
line
output
amplifier.
Gain
is
variable
over
a 20dB
range
with
OUTPUT
LEVEL
control
R38 .
Chassis-mounted
output
transformer
T3
permits
"
balanced"
operation.
FM
Peak
Controller
The
compressor
output
feeds
the
summing
mode
of
the
Peak
controller
input
amplifier
ICl.
The
one
half
of
ICl
is
a
voltage
amplifier
stage
for
signals
from
the
Compressor
assembly.
variable
feedback
resistor
R4
is
the
LIMITER
DRIVE
control
and
affords
a 20dB
drive
adjustment.
-15-
www.SteamPoweredRadio.Com
The
second
half
of
ICl
provides
pre-limiting
pre-emphasis.
Proper
strapping
of
terminals
C,
D
and
E
selects
either
a
25
or
75µs
characteristic.
Ql
and
one
half
of
IC2
comprise
a
"Santana"
configuration,
the
linear
gain-control
portion
of
the
Peak
Controller.
The
Santana
circuit
is
described
on
page
12.
The
output
of
this
circuit
is
fed
to
the
bases
of
transistors
QS
and
6 .
The
emitters
of
these
devices
are
biased
a
few
volts
positive
and
negative
,
respectively,
and
the
base-emitter
junctions
provide
hard
clipping
of
the
program
signal
.
In
addition
to
their
clipping
duties
,
however,
QS
and
6
further
perform
a
rectification
fuhction
to
control
gain
of
the
Santana
circuit.
Q7,
a
unity-gain
inverter,
follows
Q6
to
p
rovide
the
same
polarity
of
collector
current
for
negative-going
peaks
as
QS
does
for
positive.
Q8
gives
additional
control
loop
gain
which
is
made
variable
with
CLIPPING
DEPTH
control
R34.
Thus
a
signal
composed
of
(and
proportional
to)
the
clipped
portion
of
the
program
signal
is
rectified,
filtered
by
R40,
41
and
Cl3,
buffered
by
one
half
of
IC2
and
used
to
vary
program
gain
prior
to
clipping
.
In
this
way
the
degree
of
program
clipping
can
be
kept
constant
regardless
of
pro-
gram
content.
When R34
is
fully
ccw
(minimum
resistance),
control
loop
gain
is
at
maximum
so
that
virtually
no
meas-
urable
clipping
at
all
results
in
linear
gain
reduction.
·
Increasing
the
value
of
R34
reduces
control
loop
gain
so
that
QS
and
6
must
conduct
harder
to
affect
gain
reduction;
this
increases
clipping
action.
Output
from
the
limiter/clipper
is
routed
to
the
low-pass
filter
comprised
of
Rl5
and
16,
C6
and
7
and
one
half
of
IC3.
This
filter
begins
its
high-end
rolloff
just
above
lSkHz.
The
remaining
half
of
IC3,
along
with
Q3
and
4
and
associated
circuitry
makes
up
the
line
output
amplifier.
Gain
is
variable
over
a
20dB
range
with
OUTPUT
LEVEL
control
Rl7.
Capacitors
C8
and
9
can
be
selectively
strapped
across
feedback
resistor
R40
to
provide
25
or
75µs
de-emphasis,
complementary
to
the
pre-limiting
pre-emphasis.
Bypass
Assemblies
Two
plug-in
"bypass"
cards
may
be
used
in
place
of
the
various
functional
assemblies
in
the
215,
so
that
any
one
assembly
or
pair
of
assemblies
may
be
used
alone.
One
card
has
no
active
circuitry,
and
merely
routes
the
input-to-output
.
This
card
is
used
to
bypass
the
A.G.C.
Amplifier
assembly,
the
Compressor
assembly
or
both
assemblies.
-16-
www.SteamPoweredRadio.Com
The
other
bypass
card
includes
an
input
amplifier
and
an
output
line
-
drive
amplifier,
and
is
used
to
replace
the
Peak
Controller
assembly
only.
The
first
half
of
ICl
accepts
input
signals
directly
at
its
summing
mode
from
a
preceeding
Compressor
assembly
or
via
an
input
resistor
network
if
the
Compressor
has
been
bypassed.
In
the
latter
case,
terminals
A
and
B
can
be
strapped
if
necessary
to
increase
input
gain
by
20dB.
OUTPUT
control
R4
provides
20dB
of
variable
gain.
Terminals
C
and
D,
associated
with
the
output
amplifier,
afford
a
l0dB
gain
change.
Between
the
A
to
B,
C
to
D
strappings
and
the
variable
control,
the
Peak
Controller
bypass
assembly
can
be
assigned
any
value
of
circuit
gain
which
may
be
required
in
an
installation
situation.
Power
Supply
The
215
Power
Supply
con~ists
of
chassis
-
mounted
power
transformer
Tl
and
rectifier
and
regulator
components
mounted
on
the
Power
Supply
PC
board.
Diodes
CRl-4
and
filter
capacitors
Cl
and
2
provide
the
raw
positive
and
negative
DC
supplies.
Total
supply
regulation
is
the
function
of
two
"three
-
terminal"
monolithic
regulators,
ICl
and
2.
The
Power
Supply
assembly
also
includes
the
pushbutton
swi
t
ches
for
power,
"Proof"
mode
and
metering
selection.
-
17
-
www.SteamPoweredRadio.Com
VI.
CALIBRATION
PROCEDURES
NOTE:
Prior
to
shipment
from
the
factory,
the
215
was
"burned-in"
for
an
appropriate
period
and
carefully
aligned
utilizing
calibrated
test
gear
and
special
fixtures
to
facilitate
adjustment.
As
the
processor
contains
no
components
suseptable
to
ageing,
routine
alignment
is
discouraged.
Field
calibration
should
be
restricted
to
those
instances
in
which
a
circuit
failure
has
necessitated
replacement
of
critical
components.
EQUIPMENT REQUIRED
1.
Stable
Audio
Oscillator,
H.P
.
200
CD
or
equivalent.
2.
AC
Voltmeter
with
dB
scale,
H.
P.
400
Dor
equiv
.
3.
Oscilloscope
wi
t h lmHz
bandwidth.
4 .
Processor
Extender
Card
A.G.C.
Amplifier
Assembly
A.
Preliminary
1.
Connect
the
oscillator
to
the
215
input.
2.
Extend
the
A.G.C.
Amplifier
assembly.
3.
Make
a
temporary
connection
to
the
"top"
of
R24 .
This
is
the
A.G.C.
assembly
output
and
should
be
connected
to
the
AC
voltmeter
.
Be
sure
the
other
side
of
the
voltmeter
input
is
returned
to
ground.
4 .
connect
clip
leads
or
other
temporary
shorts
across
R27,
R32
and
R47.
B.
FET
Null
and
Pinchoff
1.
Turn
R33
fully
CW.
2.
Apply
lkHz
at
a
level
which
yields
OdBm
output.
3.
Turn
R33
fully
CCW
and
adjust
Rl8
for
a
null
.
The
-18-
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