Hi Jim,
I don't have any noticeable hum on my C21. I however the swamping resistor
is a good idea. If I may ask - how and where did you install it?
Howie WA3MCK
On Tuesday, May 30, 2017, Josh Gibbs <gibbsjj@xxxxxxxxx> wrote:
> Hi Dan,
>
> The manual says I should be using 8 Ohm headphones, which is what I am
> using.
>
> I tried the swamping resistor that Gary suggested. 220 Ohms knocked the hum
> down to where I almost can't hear it at my normal listening level. The AF
> control is now on '5' rather than '2' to achieve my preferred listening
> level. Works for me!
>
> When listening to the internal speaker you can't really hear the hum - I
> think this is because the speaker has very little bass response. Its VERY
> noticeable / annoying on headphones.
>
> I imagine the hum is due to a ground loop somewhere. I have not been
> successful in finding it, but the swamping resistor is working for me.
>
> I'd still be interested to hear from other C21 owners to know if they have
> a high level of hum when listening via headphones. The hum totally
> disappears when running on external 12VDC, but the transmitter can not be
> operated due to lack of 23V unregulated power required for the T/R switch.
>
> Thanks,
>
> -Josh WA7FPV
>
> On Tue, May 30, 2017 at 12:08 PM, Dan W8KMX <w8kmx@xxxxxxxxxxxxx
> <javascript:;>> wrote:
>
> > I would suggest it is an impedance mismatch on the
> > headphones. I guess you are using low impedance earphones
> > and maybe you should put in a matching transformer or get a
> > pair of high impedance earphones to try.
> > Dan, W8KMX
> >
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