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> 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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