For the AC power part of the issue have a look at.....
http://www.corcom.com/catalog/filters/default.htm

Their products are available from all the standard parts houses.... and they
are approved by the regulatory bodies. You certainly could make your own
but if it could cause a fire it's best to buy it.

As for the Microphone input issue..... my solution on a Millennia Media HV-3
was to connect the pin 1 ground to a lug on one of the XLR mounting bolts
with a very short piece of wire..... then run shielded cable from the XLR
to the PCB with the shield connected at the XLR pin 1 end and floating on
the PCB end. You should be able to try this with minimal change to
your existing unit. The shields on the input will not be part of your star
grounding scheme but I believe you will not find any negative effects.

If you are in a very strong RF environment it would also be good to put a
couple of ferrite beads or RF chokes in series with the signal leads at the
XLR.... then add RF bypass capacitors on the input of the PCB.

The HV-3 had the pin one ground at the PCB about 4 inches inside the
case.... I had trouble with it before modification in a venue with bad light
dimmer noise. I have previously had problems with an Ampex mixer picking
up an FM broadcast station about a mile from the transmitter prior to it
being modified in a similar fashion.

Regards:
Eric


"R. Foote" wrote in message
om...
"Eric K. Weber" wrote in message
...
Greetings:

I was just trying to point out a possible source of problems if the
preamp
is used in an area with strong RF fields.

Thanks, I just wanted you to know that none of the grounds are daisy
chained...Rf is something we don't have here in our area... We are 70
miles from any radio gear except the scarce municipalities and vehicle
radios.

The resistance to ground is not
the issue... with 100 foot of antenna (microphone cable).... and 6
inches
or so of it inside the case, the issue is the wavelength of the piece
inside the case.

So, if I understand, having the pin1 gnds that much closer would make
that much difference? Like I have them in the single pre? I may only
make single pres in half rack cases from now on so I can have symmetry
in the grounding, since this is something I struggled over with the
dual unit.

The non RF bypassed power supply wires entering the case could
also be a source of trouble.

The dual pre has AC entering the case as will the single unit by weeks
end. How would I rf bypass the transformer wires entering the case? Or
would this only be an issue with remote dc supplies? (since the
internal dc supply has .1uf bypasses on each rail after the filter
cap) Any suggestions?


If your venues are not near high power transmitter it may not be an
issue.

And again a very nice layout and construction job.....

Rgds:
Eric

Thank you!

Roger