dbx 161, 160 Service Manual
ISITIAL
FACTORY TEST 6
ALIGN?!ENT
PROCEDL7RE
TEST
EQUIWENT
QU_41\T l7-Y
1
1
1
1
1
1
DBX MODELS
WITHOUT
REQUIRED:
ITEM
Signal Oscillator
Digital Multimeter
Oscilloscope
Wide
.
Range db
Harmonic distortion meter
+ 3 db meter
(optional)
Ii47 & R39 (LATE
Deter
(cal_ref.
lb0
1 volt)
AND 161
160 & 161)
TYPE OR EQUIVALENT
Kron-Hite 4200, Heath 1272
Dana 3300, B
Any (covering audio band)
DBX
SK-C-1026, HP 427
DBX
SK-B-1070, Heath
GR1500, CR1900
DBX SKC-1071
&
K 282,
Digitec
lM58, HP330,
2110
1
NOTE:
Resistor Substitution Box
On model 160, tie It -
II
terminals to Gnd,
Any.
to 470K
k w 57.
values, typically
for normal testing.
10K
Revised 4-70-77
350325-03
DBX MODELS 160 - 161
INITIAL TEST OUTLINE
SEQUENCE OF STEPS:
1) Supply Trim
2) RMS Trim
3) VCA & RMS Symmetry
4) Level Calibration
5) Threshold Calibration
6) Gain Change & input zero calibration
7) Output Calibration
8) Input Tracking
g)
Compression Circuit Calibration
10)
(R78)
Correct Value Test
11) Clipping
12) Response
13) Signal Clamping (Model 160 only)
14) Noise
15) Seal Pots
16) Burn-in
.
350025-03
160/161
P-3 .
INITIAL PROCEDURE
Before
1)
2)
274)
3)
4)
applying
power to unit,
Supply Trim: Put resistance substitution box across R14 and measure
voltage at
+ 50 MV
place.
(+)
side of C7. Turn sub box until voltage is
(+14.950
to + 15.050).
Check (-) side of C8 to verify that it is -15 volts + 200
check mechanical zero of meter.
Solder appropriate resistor in
+15
-
DC
volts
MV
(-14.800 to -15.200)
RMS
Trim: (205) Connect sub box across the two RMS trim pins, and measure
the offset at the input pin of the RMS module.
voltage is zero + 15 MV,
-
(209) With input of 1.228 VRMS at 100 Hz,
the trim pin on the
RMS
and solder appropriate resistor in place.
place sub box between + v and
module.
Drop input level to - 60 db and adjust
sub box until a symmetrical waveform is observed on
Trim the sub box until
camp
pin, insert
value chosen in R36 spot (typ 8K to 75KR)
VCA & RMS Symmetry:
Set oscillator to 1.228 VRMS
a) 100 Hz (Tune for peak on distortion meter) Set front panel
compression knob to
control counter clockwise from
"0"
db.
Turn trim pots R27 and R34 until distortion reads minimum.
"3" and output gain to
"3~"
until external db meter reads
+20.
Turn threshold
Level Calibration:
Set oscillator to 1.228 VRMS
a)
100Hz
turn R63 until the voltage at the end of R79 (closest to
the center of unit) is
-.Oll
VDC
Threshold Calibration:
5)
Turn front panel
knob and position so that pointer indicates just past
"Threshold Control" until both led's are off.
"1V"
and retighten.
Loosen
(When both leds are off the input signal is at threshold level.) (See
fig. 1.)
Step the oscillator up and down in 10 db steps verifying that
the threshold level matches the input signal at successive calibration
marks on the threshold dial.
,03
350025-03
6.
GAIN CHANGE AND INPUT ZERO CALIBRATION
Set oscillator to 100 Hz at
6.1
Set "THRESHOLD" fully Cw.
6.2
"COMPRESSION" fully CCW.
Set
6.3
Place
6.4
on the DBX
Place
6.5
"0"
Repeat steps 6.4 and 6.5.
6.6
"METER" switch to
160/161
meter.
"METER" switch to "INPUT" and adjust rear panel pot R62 for precisely
on the DBX
160/161
meter.
1.228VRMS.
"GAIN CHANGE" and adjust
7. OUTPUT CALIBRATION
7.1 Place
precisely
"OUTPUT GAIN"
the
"MBTER"
switch to
"0"
on the DBX
control so that it points
"OUTPUT" and adjust
160/161
meter. If
overlay at the same time that the DBX
7.2 With the requirements of step 7.1 met,
"O+~lDB.
8. INPUT TRACKING
8.1 Place "METER" switch to
for a reading of precisely
"INPUT and step oscillator to
-30 on the DBX
P4
R51
for precisely
"0"
the "OUTPUT GAIN" control for
necessary adjust the knob on
"0"
precisely to
160/161
meter reads precisely
on the front
"0".
the external DB meter should read
Adjust R56
160/161
-3ODB.
meter.
/7
9. COMPRESSION CIRCUIT CALIBRATION
Set
9.1
9.2
9.3
9.4
"THRBSHOLD"
Set "COMPRESSION" fully CW.
Place "METER" switch to "OUTPUT"
Step oscillator to
fully CCW.
-4ODB,
and adjust the "OUTPUT GAIN" control for a
convenient reading on the external DB meter.
oscillator to
than
Adjust the
9.5
22DB.
160/161
on the DBX
meter.
+lODB.
"OUTPUT GAIN" control for a convenient reading on the DBX
160/161
to obtain this reading.
Set "COMPRESSION" to
9.6
(E.G.
The change on the External DB meter must be less
-3ODB).
meter should be less than
(150K
Nominal)
"4".
Step oscillator to
GAIN" control for a convenient reading on the External DB meter.
Step oscillator to
Adjust R43 to obtain this reading.
10K
(Recheck if R43 is adjusted1
VALUB
TEST
control fully CW.
1OOHz
at
1.228VRMS
"COMPRESSION" control from fully CCW to fully CW while
lo.
(~78)
read
10.1
10.2
10.3
10.4
(E.G.
-3ODB)
-2ODB.
(7.5K)
to
CORRECT
Set "THRESHOLD"
Apply
Set "OUTPUT GAIN" control for a reading of
+3DB
meter.
Vary
the
watching the External DB meter.
meter must be less than
+2DB.
(E.G.
-4ODB).
Step the oscillator to
Trim R58 with
Adjust "OUTPUT
+lODB.
+1DB.
-3ODB.
The External DB meter should
If necessary change
"0"DB
on the External
The change on the External DB
-4ODB.
Step the
j--Y
The change
RlO2
R41
11) Clipping:
Step oscillator to +
output gain up until clipping is observed on the scope.
clean and should occur well after + 20
1Odb
and rotate compression control fully CCW.
Clipping should be
dbm
output for 160 and at
for 161.
12) Response:
Vary the frequency of the oscillator with
output of the unit is constant + 1 db from 30 hz to 20
Odb
output, and verify that the
KHZ.
13) Signal Clamping (Model 160 only)
For 160's turn power on and off,
does not contain a transient larger than the signal.
observing scope to check that the output
After power is switched
on the output should climb to normal, smoothly, in about a second.
14) Noise:
Short input terminals
and
observe noise output of unit.
With covers on,
noise should read less than -80 dbm.
15) Seal pots with wax (all except R62).
+18
P5
Turn
dbm
16) Burn-in:
Place in burn-in rack with appropriate power applied.
(120 or 240 volts).
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