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