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1) 0.5V Reference Adjustment (RV4)
METHOD:
Adjust RV4 for 0.5V
±
0.005V at pin 7 of the
GT4124 device.
[DO NOT touch this adjustment again.]
RV4
GND
CONTROL
INPUT
A - IN
B - IN
STROBE
OUT
O/C
GND
GND
2) Span, 50% Gain & Control Offset (RV1, RV2 & RV3)
RV1
1V P-P TRIANGLE
WAVE AT15 kHz
(V = 0 to 1V)
DC OFFSET = 0.5V
CONTROL
INPUT
A - IN
B - IN
STROBE
OUT
O/C
GND
1.0V
RV2
RV3
TO
SCOPE
CHOLD
METHOD:
Temporarily put a short circuit across the C
HOLD
capacitor on pin 2 of the device. This will disable
the clamping action.
Apply 1.0V DC to A-INPUT and 0V to INPUT-B (this
may be done by leaving INPUT-B open with the 75
resistor connected to ground).
Adjust RV1, RV2 and RV3 to produce the best 0 to 1V
(1V peak to peak) triangle waveform at the output.
These adjustments interact and so should be repeated
until the best waveform is obtained.
Remove the short across C
HOLD
.
TEST SET-UP FOR GT4124 MIXER BOARD
NOTE: Initially set all trim pots to mid-position.
3) Crossfade Balance (No adjustments)
METHOD:
The crossfade balance (control breakthrough) is
measured over frequency by using a Network
Analyser or Waveform Generator. Both INPUT-A and
INPUT-B are terminated with their 75
resistors.
The control voltage of 0-1V p-p with a 0.5V DC
offset is swept over the frequency range desired.
4) Frequency compensation (C
COMP
)
SET TO 1V
FOR A - IN
AND 0V FOR
B - IN TESTS
CONTROL
A - IN
B - IN
STROBE
OUT
O/C
FROM NETWORK ANALYSER
V
SIG
= 0 dBm
C
COMP
TO NETWORK
ANALYSER
METHOD:
Connect either the A-IN or B-IN pins to the Network
Analyser Output Port. Terminate these inputs with
50
resistors. Connect the OUTPUT to the Input Port
of the Network Analyser.
Set the voltage on the CONTROL to 1V in order to mea-
sure the frequency response of the A-INPUT.
Conversely, set the CONTROL voltage to 0V for the
B-INPUT measurement. Adjust the compen-
sating capacitor C
COMP
for the flattest frequency
response on both channels.