Dorrough Loudness Monitor 40-A User manual

Donough
loudness
Monitor
Instnrction
Manual
Model
40-A
D()nnoucflElnffnfitNlcs
522lCollier
Place
Woodland
tlills,
CA91564
lblephone:
(2f5)
999-1132
|--

Dorcugh Loudness ltonitor
Model tlA-A
InstructionManual
TheoryofOperation
Theinputisfedintotheleftand
right
differential
amplifiers.
Thedifferential
inputsareconfiguredso
that
theinput
impedanceis20Kforbalanced
inputsand10K
for
unbalanced
inputs
(negative
terminalis
grounded
for
unbalancedoperation).
The
leftinputlevelis
controlled
by
R-13
and
theright
input
by
R-14.Theoutputofthesetwocontrols
arefedtoasumming
amplifier.
ThefeedbackresistorRl8 controls
theinput
sensitivity
ofthe
instrument.ltis
shipped
with
R-18as20K.
The
input
sensitivity
withthisvalue
feedbackresistor
is
-18dBm.
Changing
thevalueofR-18to100Kincreases
the
sensitivity
to-30dBm.
The
outputof
the
summing
amplifier
feedsa precision
rectjfier.Theoutputofthe
precision
rectifierfeedsasplit
tothe
PEAK
and
PERSISTENCEcircuits.
Sincethedesired
displayistobe
logarithmic,thesignals
are
fedtoconesponding
"linear/logarithmic"
converters.
The
outputs
oftheseconverters
feedthedisplaydrivers.
The
driver
forthePEAKdisplay
is
configured
asadot,
while
thedriverforthe
PERSISTENCEdisplay
is
configured
as
a harnranh
s vs, v, qY, ,.
Each
of
the40LEDsderivesan
inoutfrombothofthe
drivers,
withtheexceptionof
theredLEDsdesignated
as
-1, 0,+1.These
particular
LEDshave
noinputfromthedot
driver,andtherefore
donotdisplay
PEAKinformation.
This
provision
wasmadetoeliminate
possible
confusion
relative
toPEAKandPERSISTENTamplitudes
atthis
reference.With
the
exception
ofthese
LEDs,a steadystatesinewave
will
illuminatea bargraphata given
amplitude,
withthelast
displayed
LEDbrighterthanthe
remainder.This
gives
indicationthattheamplitudeof
thePERSISTENCEand
the
amplitudeof
thePEAKareequal,showing
proper
alignment
of
theinstrument.
Operation
Stereophonic
material,
in
the
form
of
leftand
rightinputs,
isfedtothemeteratthe
terminalstrip
locatedinthe
rear
ofthe
meter.
Individual
gain
controls
fortheleftand
rightinputsare
also
locatedonthe
rear
panel.
These
sources
feeda20Kbalancedbridging
amplifier.
Unbalanced
10K
bridging
inputisaccomplished
byconvert-
ingtheminus
(-) inputterminaltochassis
ground
onthe
rear
terminalstrip.
Themeterisshippedwith
theinputcontrolsset
for
+8dBmasreference
"0"
on
themeter
face.Levelsas
low
as
-30dBm canbereferencedto
"0"
bychanging
the
value
of
R-18
from20Kto 100K.
lf
yourprogram
referenceisdifferentthan
thatof+8dBm,
simpleadjustmentsor
someotherstandard
canbe
madeby
the
following
procedure.
Initial Set-up
Feeda10O0Hzsinewave,observing
polarity,
into
the
left
inputatastandardoperating
level
(i.e.,
+4, +8, etc.).
Adjusttheinputlevelcontrolontherear
panel
foran
indicationof
"0"
onthe
PERSISTENCE
scale.
The
oeak
excursion
andthe
persistence
amplitudeareequalunder
steadystatesinewaveconditions.
Next,removethesignal
from
the
left
channeland
feed
thesignalinthesame
polarity
tothe
rightinput,making
the
sameadjustment.
Followingthe
adjustments
forboththeleftandright
inputs,feedthe
signal
tobothinputs
simultaneously.
The
summingamplifierwillalgebraicallyaddthetwoinputs
for
an
indication
of+6 as
read
on
thePEAK
scale.
Different
amplitudesand
phase
anglesbetweentheleftandrightinput
signalswill
produce
ditferentalgebraicsums.Thisdisplay
isessentialinindicatingcenterchannelbuildupinsome
program
material.Thus,thisindicationwillaidtheoperator
inmakingthe
proper
adjustmentto
program
operating
level.
FieldAJignment
Allad
justments
forthealignmentoftheLEDdisplayare
locatedinternaltotheenclosure.
To
gain
access
tothese
controls,
theinstrumentis
placed
bottom-side-upandthesixscrewsareremoved.
Once
thescrewsareremoved,
place
theunitright-side-up
andthecabinetcanbeliftedfrom the
remainder
ofthe
chassis,exposing
the
adjustments
(see
illustration
'CHASSIS
LAYOUT").
Procedure
l. Connectthe
leftinput
toatestoscillator.
2. Feedasinewavetoneof10O0Hzata referencelevel
of
"0"dBm
into
the
instrument.
3 Adjusttheleftinput
gain
control
R-13forDS-1tobeoff
andDS-2.3.4tobeon.
4. Adjustthe input
signalto
-25dBm.
5. Adjust the
lowPERSISTENCElevel
control
R-44
sothat
onlythefirstLED
(-25d8) atthebottom
of
thePERSIS-
TENCE
scale
isilluminated.
6. AdjustthelowPEAKlevelcontrolR-46
so
that
only
the
firstLED
(-25d8) atthebottomofthe
PERSISTENCE
scalebrightens.
ThisindicatesthatboththePEAK
and
thePERSISTENCEdriversare
providing
current
tothisLED.
7. Changethe inputlevel
to+5dBm.
8 AdjustthehighPERSISTENCElevel
control
R-48
sothat
thebargraphisilluminatedupto+5dB.
9. Adjustthe high
PEAKlevel
control
R-49
sothatthe+5dB
LEDbrightens.ThisindicatesthatboththePEAK
and
thePERSISTENCEdrivers
areboth
providing
current
tothisLED.
10. Increaseinputlevel
to+14dBm.The+14d8LEDshould
indicate
drive
from
both
PEAK
and
PERSISTENCE
drivers.
11.Reduceinputlevel
to
Referencelevel
(i.e.,
+4,+8,etc.)
andsetthemeterinoutsfor"0"indication
on
PERSIS-
TENCE
scaleasdescribed
in
the
"lNlTlAL
SET-UP':
12.Alignmentisnowcomplete.
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522l
CollierPlace
Woodlandllills,CA91564