Chapter 4: Maintenance
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Grounding and Minimizing Noise
The line-frequency noise, or hum, should be eliminated when the HumSilencer Adaptive Noise
Cancellation System is enabled and activated. The following are some additional noise
minimization recommendations.
To avoid ground-loops, Molecular Devices recommends that you plug in the Digidata 1550B
digitizer to the same power strip as the amplifier. Also, be aware that each Analog Input BNC
on the Digidata 1550B digitizer is a single-ended input (all BNC shells are connected to signal
ground).
When noise in the system occurs, the first step is diagnosis. Take all instruments out of their
racks, and connect to one of them with only one BNC connection. Observe if the hum (50–60
Hz noise) is eliminated. Also observe if the hum is produced from headstage pickup by
shielding the headstage and watching the magnitude of the hum.
If the hum is eliminated at this step, connect the second BNC cable. If the hum is now
observed, there is probably a ground loop that is picking up an alternating magnetic field. Try
to eliminate the source of the alternating magnetic field from a cheap transformer or an electric
motor, such as found in a nearby fan or refrigerator. Try to rearrange the two BNC cables to
determine if their positioning tells you anything about the source of the alternating field. High
frequency components (20–50 kHz) might also appear if there is a ground loop. These can
originate from the switching power supply of the computer, or from a monitor, and can be
picked up in the analog signal inputs of the Digidata 1550B digitizer.
If removing the source of the alternating field is not possible, eliminate the ground loop by
constructing one of the connections between the two instruments without a shield. Make this
either with a naked unshielded wire, or with a BNC cable that has its shielding cut at one end.
Make a break in the shielding away from the interface, near the connection on the instrument
suspected of creating the ground loop.
Additionally, the quality of the AC power should also be checked. In particular, check for
proper grounding of the outlets.
For users of Molecular Devices microelectrode amplifiers, more information regarding noise
reduction procedures can be found in the user guides for the MultiClamp amplifier, Axopatch
amplifier, and Axoclamp amplifier.
