Hi Monty:
I just added a jumper around (well, actually over) my L4. No need to risk
possible PCB damage by completely removing the RFCs.
73,
Tom N0SS
At 17:50 11/02/2008, Monty Shultes wrote:
I bit the bullet and removed L4 and L7 this morning. It is not
difficult; they are both on the back of the front panel board. I
jumpered the pads with wire. I am now getting superb audio reports
from critical local stations that were guiding me in reducing RF on
my audio. My MC-60 mic is back in good graces.
It works.
Monty K2DLJ
Even in balanced audio systems, the same rules apply. Had the K3
been designed with a truly balanced, 3-stage instrumentation input
for its mic pre-amp, the inclusion of L4 and L7 on the shielded
return paths would have the same effect. The saving grace in an
instrumentation-input circuit (or in the alternative, an audio
transformer input) is the inherently large common-mode rejection
ratio (CMRR) across a very broad frequency span that limits the
presence of RF on a twisted-pair audio line, even in the total
absence of the cable shielding. For nearly 100 years, the Bell
System and its progeny have used unshielded twisted-pair balanced
audio systems in the presence of outrageously-high RF fields with
no measurable detriment to performance in many instances.
Paul, W9AC
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