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Theory of Operation
3–34
AM700 Audio Measurement Set Service Manual
In the flat panel display version of the AM700, two small relay boards are used
to completely isolate the internal generator signal from the cable to the Acquisi-
tion board when it is not being sent to the acquisition. This reduces the genera-
tor-to-acquisition crosstalk to –140 dB or below. Earlier versions of the AM700
used a relay T-switch on the Acquisition board to shut off the signal when it was
not needed.
The other output impedance choices of either 150 W or 600 W are switched into
the output path as selected by the user. Half of the output impedance minus the
fixed 5 W per side is added to produce the total. For example, for a total of
150 W output impedance,70Wadditional impedance is added to each side.