Spring Line Hum

[Tim Ressel]

This here unrelated story might help: I have been trying to hook up an
ultrasonic receiver to an opamp amplifier. What I got was volts of 60Hz. I
applied different shielding techniques, and even went balanced on the amp, to no
avail. After much scratching I figured out that I had a horrible impedance
mismatch between the usonic pickup and the amp. A 1K resistor across the amp
input terminals made the 60Hz go away completely. The signal is now as clean as
can be. 

The moral of this story: The problem may not be (solved by) shielding.



Tim Ressel--Compliance Engineer
Hewlett-Packard
Verifone Division
916-630-2541  
tim_r1 at verifone.com