110v outlet question: what does this mean?

Not a good sign. What happens to the hum as you move the radio to point in different compass directions?

Or what happens if you move the radio to the same plug as the fan and the toaster oven? Or just move the radio in the room? Does the hum change?

What about another room/another circuit - same situation? Take both your radio and your fan.

Just thinking - what would a loose neutral in the breaker box do? Could there be some kind of ground loop happening that is influenced by slight capacitance/inductance changes on the loop?

WT

Rick--

Is the door bell stepdown transformer on the same circuit?

Tut

Rick-

Having been raised in an older house without a ground wire connected to the outlets, I learned early that radio hum can often be cured by reversing the plug.

More modern equipment has a polarized plug with one blade wider than the other. The wider blade goes to the neutral wire in the outlet. The narrow blade goes to the hot wire. If your radio's plug is not polarized, you may have unplugged it a couple of months ago, and had a 50-50 chance of plugging it back opposite to the way it was before.

The neutral wire is not exactly the same as a ground wire, although they might be tied together back at a power pole down the block. The radio may be picking up some kind of power line hash when its "neutral" wire is connected to the hot side of the outlet.

I used to use a dot of fingernail polish on the narrow-slot side of an outlet, with a corresponding dot on the plug of a radio that worked better plugged-in one way.

Fred

They darn well better be tied together in the service panel in the house, but that's not to say there won't be a slight voltage difference between them at a receptacle if there's other loads on the line.

No transformer in the apartment wiring. Separate apartment intercom system, presumably on it's own common area wiring for the building and completely independing of the apartment wiring.

Rick

Hi

Of course. That's one of the first things I tried - reversing the radio plug in the outlet - and the hum went from bad to slightly worse. It's a transistor boom box thing with an internal power supply - not using an AC/DC wall wart.

FWIW this is relatively new wiring in the building, circa 1981 the entire building was gutted and all new services put in.

But this hum problem has only surfaced in the last 8 weeks or so.

Could this be one of those situation where a "plug in the outlet" tester (about 6 bucks at a hardware store or Radio Schlock) would show anything relevant?

Rick

Hi

Tried that first, thinking the radio - and being AM recption on top of it - may be having a bad time due to some RF interference it was picking up. Repositioning the radio has no effect on the hum. Picked it up & rotated it. Left it on the counter where it's located & rotated it. No better, no worse.

FWIW this is a *strong* signal from the station I'm tuning with no reception problems. (50,000 watt station and I'm all of 5 miles away from the tower) If the station is cleanly tuned in, or you start moving the tuning off frequency, the hum level doesn't change.

Rick

Ok, here we go:

Oh - wait. *Now* I'm back to a phase where the hum problem has simply disappeared. When it does go away, some times it stays like that for a day or two. Some times only for a few hours. But I'll report in the answers to these questions as soon as the problem returns. It always does.

Another question along this line is: Could this be completely outside the wiring in the apartment or the building? I know the building is fed from pole mounted wiring with a pole mounted transformer very close to where the feed is split out for the building. (About 20 yards down from the transformer location.)

I'm just trying to figure out if this flaky AM hum problem indicates a serious wiring problem - like a floating ground - wherever the souce may be coming from.

Rick

Doubtful.

Hi..

Haven't followed the thread, so if I repeat someone else I apologize...

Wondering if your building might possibly be on one of those flat rate electric water heating plans? Where the hydro utility puts a signal on the line to turn off the heaters during peak demand periods?

If so, then that plus a perhaps marginal electrolytics in the radio might be an explanation.

Just thinking...

Ken

Ken & Rick-

Of course it would help if you had laboratory equipment to analyze the spectrum of the power line signal, as well as to determine how the noise was getting into the radio.

Something is generating a signal that is somehow coupling into the radio and coming out the speaker. Ken's idea suggests that it might be getting into the radio through the power line, but either at the intermediate frequency of the radio or through the audio section, either directly or by rectification.

I'm a little skeptical about the radio having faulty electrolytics, but they could have aged if it is an older radio. I would want to try a line filter of some kind, just inside the radio. Perhaps as simple as putting a 0.1 Microfarad 600 volt capacitor across the line, with leads as short as practical. However, I recall cases where such a filter made things worse!

Fred

I, too, am skeptical about the electrolytics causing the hum..... if they were bad I would expect the hum to be there all the time no matter what other things were switched on and no matter where the radio is plugged in. Is the hum present on all stations or just a few the local strong stations???-- Best Regards, Daniel Sofie Electronics Supply & Repair

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You might want to shut off the breaker and check for a loose connection on the AC power outlets in the kitchen. You may want to replace them if the they don't hold the plug tightly. They should be less than a $1 each. Figure they were last served in '81 - that's 24 years ago.

Also, if your boombox has batteries install, you may want to remove them if you're only using it on AC.

Don't get the cheap under $1 outlets, at least go for the decent grade stuff, they're only about $1.50 and will last much longer. I found the cheap ones get loose after a couple years.

Also use the screw terminals or clamp type backwire terminals, don't use the cheap push-in backwire, they get loose after time and can heat up, they ought to be agaist code but the unions wouldn't let that happen, saves too much time installing.

1. Make sure the station (or an adjacent one) hasn't changed to IBOC/(HD Radio), This is where they add a bunch of digital crap to the channel that's a high compression digital (RealAudio style) stereo signal. One test is that they don't run IBOC during the night because the skip signals will really screw up the radio all over the continent.
2. It might be another device on the circuit with a tranformerless power supply where the diodes in the power supply hooked right to the power line switching on and off modulate any radio signals picked up on power line.

Mark Zenier snipped-for-privacy@eskimo.com Washington State resident

Rick wrote in news: snipped-for-privacy@rcn.com:

One question that no one else seems to have asked: is the loudness of the hum changed by the volume control? Specifically, does the hum stay the same level and only the radio signal changes in volume as you adjust the volume control? Or does the hum also go down as the volume control is turned down?

Rick (different one)