> This is not correct. There is nothing wrong with connecting an
> unbalanced mic to a balanced input -- you simply unbalance the
> input by grounding one side of the input. You lose the benefit of
> the balanced circuitry's ability to reject noise, but the input
> will work fine. The correct wiring is simply hot to one side,
> shield to the other side AND the chassis.
That is *NOT* what is happening ... the mic connection does not
simply "unbalance" the mic input because one side of the preamp
is still not grounded. What is happening is that the mic is
connected to the preamp in a balanced configuration but the
shield is left floating on the mic end and tied to the mic
return at the transmitter input. The mic return is then tied
back to the chassis through an RF choke (DC return).
What happens is that you now have a shield (unbalanced for RF
pickup) over top of the twisted pair (nicely balanced) mic
leads. Worse, the RF choke from mic return to ground makes
it almost certain that any RF on the mic shield will be forced
through the preamp instead of being bypassed harmlessly to the
chassis/ground.
It would be better if the mic return (and shield) was connected
directly to the chassis at the mic connector than the present
situation ... but not as good as if the shield were connected
to the chassis (usually PTT ground) and the mic treated as a
floating/balanced input.
73,
... Joe, W4TV
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Jim Brown
> Sent: Saturday, June 07, 2008 12:46 AM
> To: Elecraft List
> Subject: RE: [Elecraft] K3: 6M SSB audio hash
>
>
> On Fri, 6 Jun 2008 21:22:41 -0400, Joe Subich, W4TV wrote:
>
> >There is a significant problem in using balanced input with any
> >"amateur mic" - including Icom, Kenwood, Yaesu and Heil. Yaesu,
> >Kenwood and Heil connect the shield of the mic cable to the mic
> >return and not chassis (ground). Icom uses the shield as the
> >mic return.
>
> >When the shield of the mic cable is tied to the low side of a
> >balanced input, RF that SHOULD go to ground/chassis is forced
> >through the mic preamp instead. With the shield tied to the
> >mic return there is effectively a 10' piece of wire (antenna)
> >connected to the mic input unless the mic return is tied to
> >the chassis and the chassis is connected to a solid RF ground.
>
> This is not correct. There is nothing wrong with connecting an
> unbalanced mic to a balanced input -- you simply unbalance the
> input by grounding one side of the input. You lose the benefit of
> the balanced circuitry's ability to reject noise, but the input
> will work fine. The correct wiring is simply hot to one side,
> shield to the other side AND the chassis.
>
> I do have a serious quarrel with the W2IHY equalizer though -- it
> is FAR more complex and expensive than needed to get great audio
> from a pro mic with a ham rig. All you really need for an
> equalizer is a good quality capacitor of suitable value in series
> between the mic and the mic input of the radio. The capacitor is
> chosen to provide a low frequency rolloff fairly high in the
> audio passband. See
>
> http://audiosystemsgroup.com/HamInterfacing.pdf
>
> I have used a circuit like this with an EV RE16 and several rigs.
> Total cost about $0.50. It would work equally well with any good
> low-Z dynamic mic. I've also changed values in coupling
> capacitors in the K2 to achieve the same result, and that works
> quite well too. You don't need the capacitor with a K3, of course
> -- the equalizer in DSP does the job.
>
> Pro dynamic mics are easily connected to ham rigs -- since
> they're balanced, one side of the balanced output goes to the mic
> input, the other side goes to audio return, and the shield goes
> to the chassis. I've done this quite successfully with an Omni V,
> a TS850, and FT1000MP. By successfully, I mean that I get VERY
> competitve, clean, contest-quality audio that cuts through QRM
> and noise.
>
>
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