Inovonics MAP II 231 User manual

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•
INSTRUCTION MANUAL
"MAP I I"
dULTIBAND AUDIO PROCESSOR - MODEL 231 ·
) I
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. .
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INSTRUCT
.I
ON
MANUAL
"MAP
I
I"
MULTIBAND
AUDIO
PROCESSOR
-
MODEL
231
July,
1979
503-B
Vandell
Way,
Campbell,
CA
95008
(408)
374-8300

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TABLE OF CONTENTS
I. GENERAL INFORMATION ... • •......... . 2
II . FUNCTIONAL DESCRIPTION AND SPECIFICATIONS . . 2
III.
IV.
v.
VI.
VII.
Selectable High - Pass Filter - Gated A.G.C. -
Multiband Compression - Phase Follower -
"
Integrated" Peak Controller - Asymmetrical
Modulation - Remoting the Peak Controller -
Selectable Low- Pass Filter - Pink Noise
Source - "Proof" Mode - Stereo Interconnec-
tion - Specifications
INSTALLATION . . . .
10
Unpacking and Inspection - Mounting -
Connection to AC Power - RFI - In/Out
Connection and Considerations - Polarity
OPERATION AND ADJUSTMENT
• • • 12
Preliminary - P.C.B. Strapping Options -
Suggested Initial Setup Procedure - Program
Response Shaping - Cautions - Clipping
Depth -
CIRCUIT ·DESCRIPTIONS • • • 1 7
A.G.C . Amplifier - Bandpass Compressor -
Peak Controller - Power Supply
CALIBRATION PROCEDURES
Note - Equipment Required - A. G.C. Amplifier
Assembly - Bandpass Compressor Assemblies -
Peak Controller Assembly
APPENDIX . . . . . . . . . . . . . . . . . . .
Addendum , FM Peak Controller Option - Parts
Lists - Schematics - Warranty
-1-
. 22
• 26

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-
I.
GENERAL INFORMATION
The
Inovonics
MAP
II
is
a
second-generation
multiband
broadcast
audio
processor
designed
primarily
for
AM
and
AM
-
stereo
service.
The
MAP
II
functions
to
enhance
per
-
ceived
signal
loudness
and
thus
extend
the
effective
area
of
station
coverage.
When
properly
adjusted
,
the
MAP
II
will
so
process
the
audio
program
as
to
increase
trans
-
mitter
modulation
density
to
a
figure
approaching
theo
-
retical
maximum,
while
still
maintaining
an
unusually
high
value
of
program
listenability.
This
manual
is
divided
into
various
sections
that
best
describe
the
operation,
design
philosophies
and
set-up
of
the
MAP
II
.
It
is
highly
recommended
that
this
manual
be
thoroughly
read
prior
to
putting
the
MAP
II
into
service
.
II.
FUNCTIONAL DESCRIPTION
AND
SPECIFICATIONS
The
MAP
II
is
comprised
of
several
interrelated,
but
functionally
-
unique
subsections.
Rather
than
simply
to
list
performance
specifications,
a
detailed
functional
description
of
MAP
II
operation
is
given,
"
specs"
relative
to
the
described
subsection
appearing
in
the
text.
An
accompanying
block
diagram
of
the
MAP
II
appears
on
page
3.
Data
no
t
expressed
or
implied
in
the
descriptions
or
drawings
is
tabulated
at
the
end
of
this
section.
Selectable
High
-
Pass
Filter
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
subjective
consideration:
thus
the
MAP
II
offers
three:
50,
70
and
l00Hz
.
Actual
rolloff
characteristics
are
graphed
in
Figure
2.
The
L.F.
cutoff
frequency
is
-
2-

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)
Input
Gain
~][~
I
w
I
Pink
Noise
So
urce
~]
"Test"
"Proof
"
~I
Line
Amp
50
/
70
/
100Hz
H.
F>.f_,__
)
(Inhibit
Bus)
Bandp
ass
Compr
e
ssor-1
of
8
"\'
(Compression
Meter)
)
B.
P.F.
B.P.F.
I
~
[
"
Compre
ssi
on'
' "
Equalization
":
(Overcomp
.
Bus)
(A
.G.C
.!
Clip
/
Limlt
Meter)
'\'
"
Metering
"
Peak
Limiter
Drive
t
1
1u
1 , ~ - -
Ac
ti
ve
~
...----.
1
~~1~
riw--.. C
lipper
"'---.
Limit
er
""-
..
"
Rotator
"
I\;
,
~
Output
Level
Asymmetry
Clipping
Depth
Fi
g . 1
MAP
I I
Block
Diagram
+
Pha
se
Detector

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.........
•
f
selected
with
a
series
of
straps
on
the
A.
G.C.
AronJ4fier
~ard.
Strapping
instructions
are
given
on~ge
12.
Gated
A.G.C
.
In
the
typical
broadcast
situation,
program
levels
tend
to
wander
up
and
down
a
bit,
frequently
as
a
resu
l t
of
operator
inattention,
personnel
shift
changes
or
from
other,usually
human
influences.
Thus
the
first
major
funct
ion
al
block
of
the
MAP
II
is
a
slow,
gain-riding
A.G.C.
This
effectively
erases
long
-
term
input
level
variations
and
presents
subsequent
processing
stages
with
a
constant
r.m.s
.
input
value.
Capture
range
of
the
A.G
.
C.
is
±1odB,
and
A.
G.C.
gain
may
be
selectively
displayed
on
the
front
panel
meter.
Correction
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
erroneous
gain
"hunting"
caused
by
non
-
program
no
ises.
Gating
threshold
sensitivity
is
preset
at
a
value
which
will
open
the
gate
when
midband
program
energy
rises
above
-
25dB
relative
to
nominal
program
"
zero
"
level
.
Multiband
Compression
The
"he
art
"
of
the
MAP
II
and,indeed
,
the
key
to
its
operation
is
the
division
and
processing
of
the
program
signal
within
multiple
frequency
bands
.
The
majority
of
.audio
level
compressors
act
on
the
broad-
band
signal,
regulating
circuit
gain
as
a
function
of
program
level.
This
is
general
l y
accomplished
by
deriving
a
DC
control
voltage
from
the
audio
signal,
and
utilizing
this
voltage
to
regulate
circuit
gain.
In
order
to
remain
unobtrusive
in
its
action
, a
compressor
must
be
relatively
fast
-
acting;
that
is
it
must
follow
the
envelope
of
the
audio
program
quickly
enough
to
reduce
sudden
input
increases,
and
must
release
quickly
to
avoid
"holes"
and
audible
fade
-
up
when
the
input
level
returns
to
normal
.
Unfortunately,
th
is
fas
t
action
is
not
con
-
sistent
with
low
distortion,
particularly
at
low
frequen
-
cies,
as
a
necessarily
short
rectifier
filter
time
constant
-4-

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results
in
amplitude
modulation
of
the
program
by
its
own
harmonic
products.
The
obvious
alternative
is
to
independently
compress
high
and
l
ow
frequencies,
tailoring
the
rectifier
filter
time
constants
to
the
subject
portions
of
the
spectrum
.
In
this
manner
,
low
frequency
distortion
remains
at
an
acceptably
low
le
v
el
wh
i
le,
at
the
same
time
,
compression
is
rapid
at
voice
frequencies
and
above.
In
its
uti
l
ization
of
th
i s
multiband
approach,
the
MAP
II
div
i
des
th
e
audio
spectrum
into
eight
separate
bands.
While
this
might
seem
an
unnecessary
number
of
divisions,
the
advantage
is
several
-
fold
.
In
the
first
place,
many
of
the
undesirable
side
-
effects
of
dynamic
range
compres
-
sion
are
automatically
eliminated.
For
instance,
low
frequency
components
cannot
"punch
holes"
in
the
program
if
they
are
processed
separately
in
the
initial
compression
stage.
Secondly,
the
greater
t
he
number
of
bands
of
pro
-
gram
division
,
the
higher
the
energy/bandwidth
product
,
or
"program
dens
i
ty."
Thirdly,
with
multiple
frequency
bands
and
flexibility
of
compression
parameters,
program
response
may
be
"
shaped
"
in
a
manner
similar
to
that
afforded
by
a
graphic
equa
l
izer.
Both
the
input
and
out
-
put
level
of
each
of
the
eight
MAP
II
Bandpass
Compressor
assemblies
is
variable
over
a
24dB
range
for
optimum
static
and
dynamic
response
tailoring
.
Moreover,
the
ta
i l
or
ed
s
ou
nd
will
remain
consistent
almost
regardless
of
the
program
source
: "
automatic
equalization,"
as
it
were.
Figure
2
plots
the
Bandpass
Compressor
character-
istics
and
overall
MAP
II
response.
OdB
-5
-10
OdB
-s
-10
-15
-
20
/
i,
I
V
20
Hz
.._
_ -
s}
l(o.,
~
I,,,
Ir
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1
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Hz H
igh
Pass
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,,
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3
/
v-
i.-1,,o
fv'
~
/
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v,
k'
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V ' /
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/
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Ii
II'
,,
V V
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I
i,
50Hz
1
OOHz
200Hz
I I I
(Overall
~
~
~ , I~
)\_10 ~5
Low
Pass
7KHz
'
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4
5
6
7
8
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I,
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..........
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Fig.
2
K
L,
r-,.
~
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)<
V
..,
~
17
l\r-,.
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~
./~
I/
r'v
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SOOHz
1
KHz
2t<Hz
St<
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OK
Hz 20t<Hz
-5
-

www.SteamPoweredRadio.Com
Multiband
compression
is
not
without
its
own
family
of
potential
problems
.
If
it
is
not
handled
properly,
audible
side
-
effects
can
range
from
simply
"
curious"
to
"downright
awful."
A
significant
difference
in
actual
level
compressi
on
between
adjacent
bands
can
cause
an
audible
"swishing"
or
"pha
sing
"
effect.
To
guard
against
this,
each
of
the
MAP
II
Bandpass
Compressors
monitors
its
neighbors
,
changing
gain
as
necessary
to
keep
com-
pression
differences
within
limits.
Also,
the
Compressors
utilize
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
exceedingly
smooth
sound,
even
with
consid
-
erable
compression
in
effect.
Nevertheless,
a
control
loop
from
each
of
the
Bandpass
Compressors
back
to
the
A.G.C.
circuit
guards
against
overcompression
by
reducing
A.
G.C.
gain
and
flashing
a
warning
indicator
when
any
of
the
Compr,esso
rs
works
too
hard.
Phase
-
Follower
Asymmetrical
modulation
of
positive
and
negative
peaks
yields
a
modulation
advantage
only
when
the
program
mate
-
rial
is
asymmetrical
in
nature
.
Most
music,
because
it
is
a
blend
of
complex
waveforms
which
are
not
phase-
related,
ha
s 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
modulat
ion
of
an
AM
carrier,
program
peaks
should
be
predominantly
po
sitive-going.
Current
prac
tice
is
to
switc
h
program
phase
whenever
neces
-
sary
to
assure
the
highest
incidence
of
positive
modulation.
Common
phase
-
switching
techniques
usually
cause
an
annoying
"click"
or
"pop''
at
the
instant
of
reve
rs
al.
The
Phase
-
Follower
of
the
MAP
II,
on
the
other
hand,
features
a
novel
"phase
-r
otat
ion"
circuit
which
gently
and
inaudibly
"rolls"
the
phase
through
a
180
-
degree
shift
when
required
£or
max
-
imum
positive
modulation
.
Sensitivity
of
the
phase
-
detection
circuit
0£
the
Phase
-
Follower
is
fixed,
yet
a
£unction
of
the
-6-

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degree
of
p
eak
limiting/clipping
in
effect.
With
a
consistent
lOdB
of
peak
reduction
,
asymmetry
of
10%
will
cause
a
phase
reversal.
With
lSdB
peak
reducti
on
, 5%
asymmetry
will
initiate
a
"roll."
"Integrated"
Peak
Controller
The
MAP
II
Peak
Controller
represents
the
most
radical
departure
from
previous
processor
peak
reduction
systems.
To
satisfy
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
its
operation:
the
output
from
the
Pha
se-
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
quantitatively
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
limitin
g/
clipping
ratio
.
"Clipping
Depth"
may
be
set
to
a
desired
value,
and
once
set
will
remain
constant
regardless
of
program
content
. An
optimum
operating
peak-to-average
ratio
may
thus
be
selected,
from
a
very
clean
signal
without
audible
clipping
,
to
a
slight
degree
of
clipping
for
a
definite
gain
in
loudness
with
negligible
sacrifice
in
listen-
ability,
or
even
heavier
clipping
for
decided
modulation
advantage
with
an
attendant
audible
harshness
,
partic
-
ularly
on
voice.
Because
of
the
interrelated
limiter/clipper
circuit
,
Peak
Controller
attack
time
is
virtually
instantaneous
.
Even
the
f
irst
half-cycle
of
a
20kHz,
20dB
overload
is
reduced
to
the
final
limited
peak
value.
The
release
time
is
fixed
at
a
value
which
yields
less
than
1%
dis-
tortion
at
SOHz
with
lOdB
limiting.
Nevertheless,
a
stra
p
on
the
Peak
Controller
board
permits
a
speed-up
in
release
time
by
a
factor
of
4.
The
result
is
a .
tradeoff:
an
audible
modulation
advantage
against
an
increase
in
low
frequency
distortion
.
The
1%
disto
rt
ion
frequency
moves
up
to
200Hz,
and
distortion
at
SOHz
incr
ea
ses
to
about
3%.
Both
Peak
Limiting
and
Clipping
Depth
may
be
selectively
displayed
on
the
front
panel
meter.
-7-

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Asymmetrical Modulation
The MAP II permits the value of positive modulation peaks
to be continuously adjusted up to 150% of the negative
peak value . Although positive modulation is legally re -
stricted to 125%, many plate - modulated transmitters require
drive in excess of +125% to reach the legal maximum. It
must be warned, however, that transmitters which fall into
th i s catego r y are incapable of linear operation up to +125%.
The , very slight gain in perceived signal loudness must be
weighed aga i nst probable high signal distortion in these
cases.
Remoting the Peak Controller, etc.
The Peak Controller can be unplugged from the MAP II, and
with an accessory chassis may be operated at a remote
transmitter site . The MAP II then remains at the studio
with a " bypass" card in the Peak Controller slot.
The "bypass " card allows the MAP I I to be used in services
other than AM broadcast. W.i.th appropriate external pro -
vision for overmodulation protection , the MAP II can be
-. -·- used for FM; two fo r s tereo. Other uses include "maximum -
loudness " signal processing in the production room or
recording stud i o.
Selectable Low- Pass Filter
An active Low- Pass Filter follows the Peak Controller
and serves to restrict the bandwidth of the MAP II 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 fre -
quency of 7, 10 or lSkHz may be se l ec t ed, actual r o l loff
characteristics are graphed in Figure 2. Selection is
made with a series of straps on the Peak Control l er board,
and inst r uctions are given o~
'--. --
'
Pi - nk Noise Source
A digitally - generated, pseudo - random Pink Noise generator
is an integral part of the MAP II. Pink Noise is a very
- 8-

www.SteamPoweredRadio.Com
useful audio test signal; its constant-power - per - octave
(or equal fractions thereof) ene r gy distribution and
characteristic crest factor more closely approximate
program meterial than do discrete oscillator tones . A
switch substitutes this test signal for the input program
in any operating mode to aid in system setup and mainte -
nance.
"Proof" Mode
A
single button places the MAP II in " Proof ..
11
The A.G. C.
is defeated and Bandpass Compressors are inhibited, with
their input and output slide pots electronically zeroed.
The Peak Controller is similarly defeated, and both the
High - and Low-Pass Filters are electronically set to their
obvious ex t remes . All signal - path circuitry is otherwise
active .
Stereo Interconnection
Two MAP II's may be interconnected for stereo operation.
The • eight Bandpass Compressors are slaved for identical
opera t ion on a band - for - band basis, and one Phase Follower
may be slaved to the other or both defeated, depending on
which system of AM - stereo transmission is ultimately approved.
MAP II Specifications
This is a tabulation of those specifica t ions which are not
specifically expressed in the text of the discussion or
obviously impl i ed in the drawings.
Frequency Response (when set "flat " ): ±ldB , 50Hz-15kHz
Distortion (at any operating point): <0.3% above 200Hz;
. <l.0 % at SOHz
Noise: Better than 65dB below 100% modulation
Input: Balanced, -30 to +l0dBm
Output: Balanced, Oto +20dBm; +24dBm clipping level
Power: l00/120/220/240VAC, 30W; 50/60Hz
Physical: 7" x 19" x 9"; 16 lbs.
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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
f
or
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
MAP
II
is
packaged
to
mount
in
a
standard
19
-
inch
equipm
e
nt
rack,
requiring
7
inches
of
rack
spece
p
er
unit.
The
MAP
II
generates
negligible
heat,
and
itself
is
unaffected
by
wide
variations
in
the
ambient
operating
temperature.
Connection
to
AC
Power
-
----
The
MAP
II
may
be
operated
at
any
of
the
four
common
inter
-
national
AC
power
mains
voltages:
100, 120,
220
and
240VAC.
The
power
cord
supplied
is
fitted
with
a
U.S.
-
standard
m
ale
connector,
but
the
cord
conductors
are
color
-
coded
in
ac
cor-
dance
with
IEC
standards.
n
efore
connecting
the
MAP
II
to
a
source
of
AC
power,
verify
that
the
vo
l
tage-sele~tor
PC
card
in
the
fuseholder/power
connector
as
s
embly
is
oriented
appropriately
and
that
the
I
p~oper
fuse
is
installed
as
specified
on
the
rear
panel.
RFI
The
MAP
II
is
specifically
designed
to
operate
in
close
proximity
to
broadcast
transmitters;
neve
rtheless,
care
should
be
exercised
in
locating
the
unit
away
from
abnor
-
mally
high
RF
fields
.
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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
MAP
II
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.
Should
the
equipment
shich
feeds
the
MAP
II
require
output
loading,
an
external
600-ohrn
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
MAP
II
output
amplifier
(ahead
of
the
line
output
transformer)
is
virtually
zero.
However,
as
the
output
transformer
has
some
reactance,
it
is
impor
-
tant
that
the
output
be
terminated
in
600
ohms
to
minimize
overshoot.
The
output
clipping
level
of
the
MAP
II
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
MAP
II
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
.
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IV. OPERATION AND ADJUSTMENT
The Inovonics MAP II is a fundamentally more complex device
than most other broadcast audio processors, and hosts a
full complement of accessible controls which materially
affect both the technical composition and the subjective
audio quality of the transmitted program signal.
The various adjustments are identified on the inside of
the removable front adjustment cover. Despite the seem-
ingly obvious meanings of the control function descriptions,
it is highly recommended that the outlined procedure be
carefully followed for initial setup. Subsequent readjust -
ment to secure a desired effect should be made only after
it has been established that the unit functions properly
and predictably in accordance with the initial setup pro-
cedure.
jAll adjustments are made "on the air," utilizing
L:,, rogram feed and the station Modulation Monitor.
a typical
Preliminary - P.C.B. Strapping Options
Input Gain Range
The MAP II accommodates line input levels between -30
and +lOdBm. 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., position #10.
~
or line i nput levels between -30 and - lOdBm, a
should be placed across terminals A and B. For
levels between - 10 and +lOdBm, the strap should
removed.
strap
input
be
Strapping to select the MAP II low-end rolloff frequency
is afforded on the A.G.C. Amplifier P.C.B., pos it ion #10.
The three cutoff frequencies are 50, 70 and lOOHz, the
· actual rolloff characteristics graphed in Figure 2 .
---
For ~ utoff, no strap is required. 0 or 70Hz, strap
'-...::_,) '- -
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--

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C
to
D.
For
lOOHz
cu
t
off,
strap
C
to
D
to
E.
The
H.P.F.
is
automatical
l y
defeated
in
the
"Proof"
mode
.
Low-Pass
Filter
Strapping
to
select
the
high
-
end
rolloff
frequency
is
afforded
on
the
Peak
Controller
P.C.B.,
position
#9
.
The
three
cutoff
frequencies
are
7,
10
and
lSkHz,
the
actual
rolloff
characteristics
graphed
in
Figure
2 .
For
~
rolloff
,
strap
E
to
F
to
Hand,
separately
,
J
t ~
L.
For
lOkHz
rolloff,
strap
E
to
F
and,
sep
-
arately
,
J
to
K.
For
7kHz
rolloff,
no
strap
is
required
.
Th
e 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
perc
ei
ved
lou
dness
(fast
release)
and
low
signal
distortion
(slew
release).
With
lOdB
limiting,
the
compromise
release
value
yields
about
1%
distortion
of
a SOHz
sine
wave;
correspondingly
less
distortion
at
higher
frequencies
.
An
alternate,
faster
limiter
release
time
is
provided
in
the
MAP
II;
its
optional
use
can
result
in
a
per
-
ceptible
increase
in
program
loudness,
but
at
the
expense
of
greater
lQli.
frequency
signal
distortion
.
Because
the
selectable
hig°h=pass
filter
is
provided,
however,
a
user
can
opt
to
roll
the
low
frequencies
off
and
utilize
the
faster
release
with
no
apparent
program
degradation
.
U
he
faster
release
time
is
enabled
by
strapping
terminals
Mand
Non
the
Peak
Controller
P.C.B.,
po
sit
ion
#9.
As
-
Just
cautioned,
however,
this
should
be
done
in
conjuncti
on
with
70Hz
or
,
preferrably
, lOOHz
low
-
end
rolloff.
Suggested
Initial
Setup
Procedure
This
procedure
is
performed
with
the
MAP
II
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.
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1.
Set
the
individual
COMPRESSION
and
EQUALIZATION
slide
pots
to
center
(0dB)
.
Turn
all
trim
controls
fully
counterclockwise.
The
PROOF
and
PINK
NOISE
buttons
should
be
"
out
"
(normal
operation).
2.
Depress
the
A.G
.
C.
RANGE
metering
button.
With
a
normal
program
input,
advance
the
INPUT GAIN
control
for
a
center
-
scale
meter
indication
.
3.
Individual
COMPRESSION
meters
should
be
indicating
up
to
l0dB
compression
in
the
most
active
bands.
Adjust
the
individual
COMPRESSION
slide
pots
for
about
l0dB
compression
in
each
band.
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.
Program
Response
Shaping
Since
the
MAP
II
affords
independent
control
over
both
the
input
to,
and
output
from
each
of
the
eight
Bandpass
Com-
pressors,
frequency
characteristics
of
the
program
may
be
tailored
to
complement
a
specific
programming
format
in
m
uch
the
same
manner
as
with
a
Graphic
Equalizer.
Even
with
all
controls
set
to
the
0dB
mid
-
position,
the
MAP
II
will
impart
a
"bright"
sound
to
the
program
.
This
is
due
to
spectral
energy
distribution
in
typical
music
and
speech
signals,
and
the
tendency
of
multiband
processing
to
bring
up
the
higher
frequency
bands
wh
i
ch
a
re
by
nature
lower
in
energy
l2vel
.
Should
it
be
desired
to
counteract
this
phenomenon,
the
input
COMPRESSION
controls
should
be
adjusted
for
a
similar
amount
of
indicated
compression
in
each
band,
and
the
output
EQUALIZATION
controls
set
for
a
complementary
gain
or
loss.
Thus,
if
Band
6 COMPRESSION
control
is
set
to
+6dB
for
l0dB
indicated
common
compression,
the
EQUALIZATION
control
should
be
set
to
-
6dB.
This
will
result
in
minimum
response
change
or
"coloration"
of
the
program
material
.
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If, as anticipated, it is desired to modify the program
response to achieve a particular "sound, " then both the
COMPRESSION and EQUALIZATION controls can be used to effect
the change. It is advised that the COMPRESSION controls
still be used to obtain a similar degree of indicated
compression in each band, and the EQUALIZATION controls
then set for the desired program response. Although both
the COMPRESSION and EQUALIZATION controls have identical
action below compression threshold, once the threshold has
been exceeded the action of the COMPRESSION control is
reduced by the factor of the compression ratio. Thus the
EQUALIZATION adjustment gives the maximum range and most
predictable and flexible control over actual response shaping .
Some Cautions
1 . Starting with the MAP II set as per the Suggested
Initial Procedure, make alr changes for subjective
purposes in small steps, listening carefully to the
results each time.
2. Avoid large differences between he adjustments in
adjacent bands. The QUALIZATIO settings between
adjacent bands should c:rt- exceed 6d ._-;) and indicated
compression should lose t o the same value
in each band.
3. Monitor the OVERCOMP indicator and back-down com-
pression if the LED flashes more than just occa-
sionally.
4. REMEMBER: Increasing compression in a particular
band will not make that portion of the spectrum
particularly louder except at low program levels.
Use the EQUALIZATION control to shape response.
Clipping Depth
The degree of program clipping which the user wishes 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 pro-
gram material.
By depressing the CLIPPING DEPTH metering button, a more-
or-less quantative indication of clipping depth is displayed
on the front panel meter.
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With
the
pointer
remaining
in
the
"white"
zone,
clipping
is
very
light
and
inaudible
with
any
program
material.
When
the
pointer
indicates
in
the
"
gray
"
area,
clipping
is
heavier
and
yields
a
definite
modulation
advantage.
Some
"
harshness"
may
be
audible
on
voice,
however.
When
the
meter
indicates
in
the
"black
" ,
clipping
is
quite
heavy
and
will
certainly
be
audible
,
probably
objection-
able
on
voice
and
even
some
music
.
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V. CIRCUIT DESCRIPTIONS
A.G.C. Amplifier
Input signals to the MAP II are isolated by input trans-
former T2 on the "mother" board, then fed to input amplifier
IC2 on the A.G.C. Amplifier assembl y . 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 over 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 50, 70 or l00Hz rolloff frequency is
selected by strapping terminal D, or both D and E to
terminal C, essentially at ground via FET QB . QB is turned
off in the "Proof" mode to return the filter to SOHz, "full
bandwidth" response.
The first half of IC3 is the active gain control element
of the A.G.C. Amplifier. This circuit, the "Santana" con-
figuration, utilizes FET QlA as an active variable resist-
ance 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
positive-going portion of the output of variable-gain stage
IC3 is amplified by common-emitter stage Q4, the negative-
going by common-base stage Q5. 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 .
res, a unity-gain buffer amplifier, isolates the filter
from R33, the FET pinchoff calibration adjustment.
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-
Output from the A.G.C. variable~gain stage is sampled by
the Gating Circuit. The first half of IC4 i~ a bandwidth-
limite .d voltage amplifier stage with - 3d.B 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 presented to one input of a com -
parator 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 Gating 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 slowl y raising residual
noise to an annoying level during program pauses.
IC6 is a comparator which constantly monitors the Bandpass
Compressor " overcomp" bus. Should any of the eight Bandpass
Compressors afford more than about 15dB 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 the
output stage which feeds the eight Bandpass Compressors.
The R/C networks ahead of this amplifier compensate for
Bandpass Compressor gain inequality at the passband limits
of 50Hz and lSkHz.
Bandpass Compressor
Circuitry for each of the eight Bandpass Compressor assem -
blies is identical; only filter and rectifier time constant
values differ £or the various , passband frequencies.
Amplifier is bused to the
R3, the COMPRESSION slide
The input signal from the A.G.C.
inputs of all eight compressors.
control is a variable input gain
the first bandpass filter section
"Proof" mode Q2 is turned off and
fixed gain from the Rl/R2 divider
through Ql.
attenuator which feeds
through FET Q2. In the
an input signal with
is routed to the filter
The first half of ICl is a single bandpass filter stage
centered at mid-band. Because it is rather broadly tuned,
-18-