the loud hum is caused by one of two things: a short across the ground and 
audio wires...or one of the wires not connected.
Easy enough for either to happen when soldering onto microphone plugs.
The high/low impedance switch would have nothing to do with this...the only 
thing it would do is reduce the audio level when switched to low impedance.
Sounds like your guy may have missed the most obvious problem of a short or 
bad connection and rewired what didn't need rewiring.
There is absolutely no reason to open the mic and fiddle with the wiring 
inside.
As I said, mics are super simple, there are two wires connected to the audio 
element, that go from the element down to the plug on the end of the 
mic...the shield and ground pins are shorted together on the back of the 
plug...some mics will have a switch to turn it on and off...and this one 
obviously has an impedance switch which puts a resister in line to 
compensate.  The result of this resister is simply lower audio due to 
impedance mismatch ...nothing else.  There may have been an issue with the 
cable, but again, cutting one end off to access the wires is easy enough and 
you just use the wires you need...no need to rewire plugs and the mic or 
anything else like that lol.
If I remember, your radio has a 4 pin mic plug...common ground, PTT, audio 
and audio ground or is the fourth pin plus voltage...anyway, it's pretty 
basic stuff.

73
Colin, V A6BKX


-----Original Message----- 
From: Michael Ryan
Sent: Monday, November 2, 2015 11:47 AM
To: [log in to unmask]
Subject: Apex Electronics 850

Colin:
The mic is what's referred in the subject, which is a dynamic.
I don't understand the complete rewiring of the mic either considering its
a 3 pin XLR mail which has the connections you mentioned. The cable OK but
both?
This mic has a high low impeedence swich, maybe 1 of the connections went
there. When I plugged in the mic, all I got was a loud humm.
I'm gonna see the guy who did this on Sat and get the full explanation
because the now both the mic and cable can't be returned due to tampering.
I'm told it works but how well who knows. It's probably another 70 bucks in
the junk box. Not a big fan of Heil because of the cost but this time an
extra 50 bucks to have it work out of the box with no issues might have
been worth it.

73:
Mike DE VO1AX

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