Thanks Byron. Grounding to PS ground had no effect.
I don't see a 4.7 Ohm resistor anywhere... are we talking a resistor on the
audio board? Here is the schematic for the audio board:
https://drive.google.com/file/d/0B_pjAwEfeYcdUk9JWDROazFLVkE/
view?usp=sharing
All the schematics for the boards are here:
https://drive.google.com/open?id=0B_pjAwEfeYcdWVoxTWlMbU9xODg
-Josh
On Mon, Jun 5, 2017 at 2:02 PM, Byron Cordes <byroncordes@icloud.com> wrote:
> Try grounding ground side of speaker to ground from power supply.
> If hum is still there there is a 4.7 ohm resistor that might be shorted
> Or a 270 uf cap open both feed the audio amp
>
> Byron Cordes
>
> > On Jun 5, 2017, at 3:42 PM, Josh Gibbs <gibbsjj@gmail.com> wrote:
> >
> > Hi Chris,
> >
> > The hum is present in the speaker, just not so noticeable because it is
> > much less sensitive and much further from my ear. I suspect the speaker
> is
> > less responsive to frequencies below 120Hz than my headphones, which
> helps.
> >
> > I have tried other headphones. I have also listened to the audio directly
> > at the output of the audio amp board. Even when I short the input to the
> > audio board to ground, I can still hear the hum. Even when I powered the
> > pre-amp and audio amp boards via external 12VDC the hum remained. I'm
> > pretty confident the hum is magnetically coupled. The only time I don't
> > hear the hum is when I power the radio entirely from external 12 VDC.
> >
> > Is this normal for this rig, or is there a problem? That is what I'm now
> > attempting to determine!
> >
> > The radio works great otherwise, and I likely would never have noticed
> > anything if I hadn't plugged in my headphones =)
> >
> > I've learned a lot while working on this radio, which was one of my goals
> > in buying it. Big thanks to the the awesome amount of knowledge of the
> > Ten-Tec list, and willingness to share it!
> >
> > 73,
> >
> > -Josh WA7FPV
> >
> >> On Mon, Jun 5, 2017 at 12:29 PM, Chris Howard w0ep <w0ep@w0ep.us>
> wrote:
> >>
> >>
> >>
> >>
> >> I'm not an electronics whiz. But to me, if you're getting
> >> the noise in headphones but not in the speaker, it sounds
> >> like the headphone cord is picking it up.
> >>
> >> If you have cracked capacitors in the power supply,
> >> I wonder if you've got a 120 Hz spark gap going there.
> >> The headphone cord is acting as an antenna and picking it up.
> >>
> >> How to test that theory, turn down the audio on the Century 21.
> >> Use the same headphones on some other piece of electronic
> >> equipment in close proximity to the C-21 and see if you get the noise.
> >>
> >>
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|