Humming from radio speaker -- how to eliminate?

[Tymekeeper]

First post. This is more of a radio-specific question than a clock question, but maybe someone has some ideas.

I have a GE C4331B clock radio that I picked up from eBay. The speaker gives a low-pitched hum whenever the radio is on, regardless of volume. In other words, it still hums when the volume is turned all the way down, and does not change with the radio volume. It comes on when the radio is switched on, and stops when the radio is shut off.

After doing some initial research on what causes speaker hum, I've determined that this is 60 Hz hum, which this site https://www.psaudio.com/ps-how/how-to-find-and-fix-hum/ says is "typically a result of poor shielding, cable problems, or close proximity to strong magnetic fields."

I've opened up the radio and I am guessing it is coming from the transformer right underneath the speaker.

I thought maybe there is a ground wire disconnected somewhere, so I bought a second one of the same radio on eBay to compare, and to my surprise, that one has the exact same hum!

Does anyone know if there is a way to eliminate this hum? I'd like to use this clock radio in my home office -- the clock itself is in great shape, and the radio tunes easily and plays clearly (other than the hum).

[Guest]

Hello and welcome!

If it is coming FROM the speaker, it is not the transformer. However, the transformer itself can hum or buzz mechanically, if the plates contained inside, are de-laminating. That's a different issue, though.

So, it could be what you've already described or possibly the main filter capacitor (Usually the largest capacitor in size and capacitance on these little radios) leaking some current into the signal path. Most likely a 470uf or 1000uf unit. I do not have the schematic handy for this model.

Another issue that can cause this, although rarer, is a failing coil in the speaker itself.

[Tymekeeper]

Thanks. The hum is definitely coming from the speaker. Interestingly I also get the same hum when plugging a set of headphones into the headphone jack, i.e. hum is heard through the headphones. I thought maybe the transformer is what is generating the magnetic field that is making the speaker hum. Something is generating some kind of current that gets transmitted through the speaker.

[Guest]

Yes, as I said, most likely a filter capacitor leaking DC current. The headphone jacks on these units are tapped directly into the output that also goes to the speaker so it'll have the same issue.

Also, double check for ground connections that may be loose and also any cracked solder joints on the board. A quick way to test for that is to gently push in various areas of the board surface with a non-conductive tool. Anything with a loose/cracked connection may change the tone of the hum.

[howiflippedyourclock]

I have the same radio and hear the same humming noise even when the radio is turned off. Were you able to find a solution to this problem? I also hear a ticking sounds from the internal components that is also very loud and distracting. I haven't opened the unit up yet but am afraid of what I'll find.