Home Patrol headphone jack ground noise issue?

[kc2rgw]

O.k. so I have a pretty nutty configuration with a mixer and amplified speakers that I run all my shack audio outputs into. There's scanners, ham radio equipment, computer sound etc.

Swapping out the 396XT for the HP-1, I get a horrendous ground buzz. Both are plugged into their chargers, into the same circuit. Both are using the exact same audio cord into the mixer.

The HP-1 buzzes very loud (loud as received audio ouput) while on it's DC wall wart, but still has a ground loop buzz even if not on the DC supply at all, which is odd.

As soon as squelch opens on the HP-1, no more buzz, perfectly silent whether plugged into it's DC supply or not.

It sounds like it's a design flaw in the headphone output.

Has anyone had this same issue and have you tried the line-out jack yet as an alternate?

Does anyone know if that 2.5mm line-out jack is stereo or mono?

I really like this unit otherwise, but this is very irritating.

 

[jackj]

Are you using an outside or external antenna on the scanners? If an outside antenna then try using the antenna the HP-1 came with to see if the ground loop is through the antenna. The HP-1 may not have the sleeve of the headphone jack at ground potential which is causing a current flow through the ground side of your mixer board. You could try using an audio transformer out of an old transistor radio as an isolation transformer to break the ground current if all else fails. Ground loops can be a bear to trouble shoot, good luck.

 

[kc2rgw]

External antenna, same one used with the 396XT as well.

I removed the antenna just to check and the ground buzz actually got worse heh.

Yeah I've tried many different combinations now of routing the audio. Skipping my compressor, using 3.5mm to RCA into the mixer, 3.5 to 3.5 into an input with a pre-amp in it etc. Nothing breaks the loop.

I can try running it off my shack DC supply, I don't have a cig plug pigtail here to try though. My luck, the factory DC to DC converter will be horrendously RF noisy on the HF bands. Trouble is, it still buzzes when running on its batteries so I think running it on my DC supply won't fix it.

What's curious is that as soon as the squelch opens, the loop is gone, not even a bit of noise. Something tells my they will need a circuit revision to fix this one.

Frustrating as the audio sounds so nice when not using the internal speaker.

Somewhere around here I have some 1:1 isolation transformers too, of course finding them will be the trick.

 

[kc2rgw]

Fixed it, Radio Shack 270-054

Ground Loop Isolator - RadioShack.com

270-054 line isolator fixed the issue...so it's definitely how the audio circuit in the Home Patrol is designed.

At least the issue is fixed, but it's very irritating that out of this whole bench of equipment, my latest $500 toy left off a $1 component to better handle its audio circuit.

 

[ka3jjz]

There's another tip to go to the Home Patrol wiki...best regards...Mike