ATI Audio DP100 User Manual

Page 5

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DISASSEMBLY

1. Remove AC power.
2. Remove nine (9 - Count’em) pan head screws using a Phillips head screwdriver.
3. Remove the screws, two (2) per XLR connector using a Phillips head screwdriver.

Save the screws.

4. With your thumbs on the end XLR connector inserts and your fingertips on the sides

of the cover, gently slide the cover forward about an inch until the connector shells
clear the inserts. Lift the cover clear and pull the line cord grommet free of the cover.
A dot of silicone grease or spray will help the grommet slide smoothly over line cord.

5. Re-assembly is the reverse of the above.

ADJUSTMENTS

Avoid the temptation to diddle the internal trimpots R21, R22, R35 and R36 just to see
what effect they cause. All are sharp null type settings, which are greatly degraded by
even slight maladjustment. Replacement of either A1 (National LF347N) or A2
(Signetics or Exar NE5533) will not require pot readjustment.

COMMON MODE REJECTION

Replacement of any resistors R23 through R34 will require readjustment of either R35 or
R36 to maintain maximum common mode rejection (CMR). Apply 10Vrms at 120Hz
between ground (Pin 1) and Pins 2 and 3 (tied together) of XLR input J5, measure at J7
and adjust R35 for the best null. Repeat for J6, J8 and R36 if necessary. An 80dB CMR
(less than 200uV output) is attainable but may be difficult to measure without a tuned
voltmeter.

DISTORTION

Replacement of any resistor R13 through R20, T2 or T3 will require readjustment of
either R21 or R22 for minimum distortion. Apply sufficient 20Hz input signal at J1 or J2
to drive a loaded output measured at J3 or J4 (pins 2 to 3) to +20dBm. Measure Total
Harmonic Distortion (THD) and adjust R21 or R22 for best null. If you cannot detect a
good null, your Audio generator may well have far more 20Hz distortion than even the
un-nulled contribution of the Interface, which is typically less than .1%. As an alternate
adjustment means, turn the pots full CCW and adjust the generator for +19dBm output
level, rotate the trim pot CW until the output increases just 1dB to +20dBm. Turning the
pot farther CW can cause instability. When nulled using superior test gear such as the
AMBER 3501, THD measurements of .004% at 20Hz and +22dBm output are to be
expected.

This manual is related to the following products:

MM100