Soundsticks: Humming/buzzing mains powered USB speakers

[German_John]

Hey all,

I've had some used harman kardon soundsticks (II, I believe) for a while now. Today, they've started humming/buzzing.

The soundsticks are mains powered (16V) and connect to the sound source (i.e. a computer) via USB. I've determined the issue to be the USB cable, I think.

Unplugging both USB and power, then only plugging in power makes the hum go away. Re-plugging USB makes it start again. Unplugging USB but leaving them powered when humming does NOT stop the humming.

It's a low, 60ish Herz sound.

My best guess is that the cable broke near the USB connector on the back of the PC and power is leaking into data or something? Idk.

The problem is present on both my main desktop as well as my laptop.

The noise only comes from the bass speaker, not the sattelite tweeters/woofers.



Unfortunately, the USB cable is not replaceable by design. Of course, I could just cut it off and solder a new cable to it (and pray that I can insulate them...) but I'm not very good at soldering. Better than not having speakers though. Though before I go about cutting non-replaceable cables I wanna be sure that that's the right thing - and also where to cut the cord.

[Bombastinator]

Is it 60 cycle hum? 

[German_John]

6 minutes ago, Bombastinator said:

Is it 60 cycle hum? 

Sounds like it, yes. Sounds a lot more like the 60Hz example in this than the 120Hz. 

[Bombastinator]

2 minutes ago, German_John said:

Sounds like it, yes. Sounds a lot more like the 60Hz example in this than the 120Hz. 

60 cycle is what ac power runs at.  Implies there may be an analog type problem.  Some sort of bleed or field being generated from from the mains power.

[German_John]

2 minutes ago, Bombastinator said:

60 cycle is what ac power runs at.  Implies there may be an analog type problem.  Some sort of bleed or field being generated from from the mains power.

The problem doesn't occur when only plugged into the wall, only when also plugged into USB. Also persists with different outlets. 

Wouldn't that mean that it's not due to AC power?

[Bombastinator]

1 minute ago, German_John said:

The problem doesn't occur when only plugged into the wall, only when also plugged into USB. Also persists with different outlets. 

Wouldn't that mean that it's not due to AC power?

Not necessarily.  Analog stuff is funny.  If a field is being generated by the mains power wires and some wire or other isn’t sufficiently insulated and got inside that field it could affect it even though they are not even touching.  If a wire for example was hot glued out of the way and the hot glue came loose and the wire moved it might happen.  It’s low probability but it’s all I got.  Doesn’t mean there isn’t a better solution or that you’re not right.  I’m old low knowledge rather than a modern electronics engineer. 

It’s before 8am on a Sunday morning.  might need to wait a while for a good answer.

[German_John]

Just now, Bombastinator said:

Not necessarily.  Analog stuff is funny.  If a field is being generated by the mains power wires and some wire or other isn’t sufficiently insulated and got inside that field it could affect it even though they are not even touching.  If a wire for example was hot glued out of the way and the hot glue came loose and the wire moved it might happen.  It’s low probability but it’s all I got.  Doesn’t mean there isn’t a better solution or that you’re not right.  I’m old low knowledge rather than a modern electronics engineer. 

It’s before 8am on a Sunday morning.  might need to wait a while for a good answer.

Yeah, I'm in Europe so time zones are always an issue... 

 

Annoyingly, it has a proprietary 16V PSU (I think it might be a 3 pin DIN connector on the end or something) so I can't just chuck another PSU on there and call it a day.

Weird thing... the plug on the unit has 3 pins and a shield, but it's a two pin plug into the wall. I guess I can just multimeter it to see what comes out of where.