User manual

Operating Basics
AM700 Audio Measurement Set User Manual
2-33
Configurations using unbalanced loads are more susceptible to ground loops. The
best method for driving an unbalanced load is to use the floating ground feature of
the generator. With floating ground selected, the analog output of the generator can
be grounded at the load end of a signal cable, thereby reducing the effects of any
ground-loop currents. The best practice in all cases is to use the same power source
for the AM700 and the device under test, whether using balanced or unbalanced
signal connections.
NOTE. The floating common is shared by both analog generator outputs. If the loads
on the two generator outputs are at different potentials, ground currents can still
flow, regardless of the AM700 connections.
Channel A and Channel B are the input connectors for balanced analog audio
signals. For polarity test purposes, the AM700 follows the AES standard
(AES14-1992) that pin 2 is +, pin 3 is –, and pin 1 is common. The analog inputs are
balanced, differential inputs. The common is connected to ground and cannot be
floated. It is common practice to float the generator common if it is determined that
the measurement needs to float to reduce ground loops.
Using Single-Ended Inputs. To help reduce pickup of extraneous noise, it is best to
connect pin 3 (– input) to pin 1 (common) when using single-ended inputs. The
input impedance is reduced from 200 kΩ to 100 kΩ (the 600 Ω and 150 Ω
terminations remain accurate within an added 0.3%, and the accuracy of the
measured signal amplitude remains within the specified measurement accuracy of
the AM700.
These XLR connectors provide connection for AES/EBU balanced digital audio
signals. Digital Out is the output connector for the digital signal from the internal
generator. Digital In is the input connector for digital audio signals.
Analog In
Digital Inputs
and Outputs