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Speakers hum when PC is off/standby

Posted: Thu Nov 30, 2017 2:21 pm
by DeadOfKnight
I thought this was just normal since it has happened with every PC/sound card/speaker set I have ever owned, so I normally just turn them off if it gets annoying. However, a curious google search of this today tells me this should not be happening, but none of the forum topics I have read seem to offer any definite solution. It only happens when the speakers are plugged in AND the PC is off and it doesn't make a difference if I am plugged in via RCA or 3.5 mm audio output. Any ideas on what I could be doing wrong?

Re: Speakers hum when PC is off/standby

Posted: Thu Nov 30, 2017 2:25 pm
by Captain Ned
Ground loop, or dissimilar ground potentials between the computer and the speakers. Are they plugged into the same outlet/circuit/power strip?

Re: Speakers hum when PC is off/standby

Posted: Thu Nov 30, 2017 2:53 pm
by just brew it!
If everything's plugged into the same power strip (so no ground loops) and you still get the hum, you'll probably just have to live with it (turn speakers off when you turn off PC).

You may be able to mitigate by routing the wire that goes to the speakers from the PC as far as possible from any AC wiring.

Bottom line: Soundcard output probably goes into a "high impedance" (open circuit) state when the power is switched off. This means the wiring becomes a lot more susceptible to picking up interference (such as induced AC hum from nearby electrical wiring), since nothing else is driving it.

Re: Speakers hum when PC is off/standby

Posted: Fri Dec 01, 2017 6:03 am
by farmpuma
You might also try reversing the speaker's power cord plug. Ungrounded power cords generally have a ribbed wire on one side which should generally be plugged into the longer slot.

Re: Speakers hum when PC is off/standby

Posted: Fri Dec 01, 2017 4:46 pm
by ludi
farmpuma wrote:
You might also try reversing the speaker's power cord plug. Ungrounded power cords generally have a ribbed wire on one side which should generally be plugged into the longer slot.

I wouldn't expect a difference. This is double-insulated equipment with a transformer-isolated power supply of some sort (which includes both linear supplies and switchers). The only ground reference in the equipment would be the 0V point of the DC power supply.

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 07, 2017 1:30 pm
by DeadOfKnight
Everything is plugged into an UPS. Maybe I need to ensure PC and speakers are plugged into the same side that has the backup battery?

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 07, 2017 1:31 pm
by just brew it!
DeadOfKnight wrote:
Everything is plugged into an UPS. Maybe I need to ensure PC and speakers are plugged into the same side that has the backup battery?

Definitely worth a try.

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 07, 2017 1:34 pm
by DeadOfKnight
just brew it! wrote:
DeadOfKnight wrote:
Everything is plugged into an UPS. Maybe I need to ensure PC and speakers are plugged into the same side that has the backup battery?

Definitely worth a try.

Also I was wrong about it not humming if not plugged into the sound card, last night I unplugged it and plugged it back in and it didn't make a difference, still had a loud buzzing noise. Maybe I just need to try to route the cable away from all other cables.

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 07, 2017 1:35 pm
by ludi
DeadOfKnight wrote:
just brew it! wrote:
DeadOfKnight wrote:
Everything is plugged into an UPS. Maybe I need to ensure PC and speakers are plugged into the same side that has the backup battery?

Definitely worth a try.

Also I was wrong about it not humming if not plugged into the sound card, last night I unplugged it and plugged it back in and it didn't make a difference, still had a loud buzzing noise. Maybe I just need to try to route the cable away from all other cables.

Hmm...either it's picking up interference as you suspect, or the power supply is failing.

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 07, 2017 1:42 pm
by DeadOfKnight
ludi wrote:
DeadOfKnight wrote:
just brew it! wrote:
Definitely worth a try.

Also I was wrong about it not humming if not plugged into the sound card, last night I unplugged it and plugged it back in and it didn't make a difference, still had a loud buzzing noise. Maybe I just need to try to route the cable away from all other cables.

Hmm...either it's picking up interference as you suspect, or the power supply is failing.

Well lately it's been louder and more obnoxious than usual, prompting me to post in here. I have a 9 month old that just started crawling around, and she recently got under my desk and was pulling on cords until I stopped her. I think that is more than likely the cause. I'll rearrange them and see if that doesn't change anything.

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 07, 2017 1:43 pm
by just brew it!
DeadOfKnight wrote:
just brew it! wrote:
DeadOfKnight wrote:
Everything is plugged into an UPS. Maybe I need to ensure PC and speakers are plugged into the same side that has the backup battery?

Definitely worth a try.

Also I was wrong about it not humming if not plugged into the sound card, last night I unplugged it and plugged it back in and it didn't make a difference, still had a loud buzzing noise. Maybe I just need to try to route the cable away from all other cables.

OK, that's a sign that the speaker input is overly susceptible to induced noise when not actively being driven. Yes, re-routing the cable may help.

If you're willing to do a little soldering you could make a pass-through adapter to connect in-line between the soundcard and speaker cable, to reduce the effective input impedance of the speakers; this should "ground out" most of the hum. Simply bridging each of the L and R signals to common through resistors of 100 ohms or so (exact value non-critical as long as it is in that general range) would probably yield significant improvements, with perhaps a slight reduction in output volume (but since these are amplified speakers, you could compensate by simply turning the volume up a bit on the speakers).

Technical explanation: Reduced input impedance means more current is required to drive the input to a given level. Induced noise (especially at low frequencies like 60Hz hum) is typically very low current, and so will have a greatly reduced effect. OTOH, your soundcard output is probably designed to be capable of driving headphones, so it should have no problem dealing with the lower impedance.

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 07, 2017 2:07 pm
by DeadOfKnight
I used to have an ASUS Xonar DX and Logitech z2300 speaker set. Now I have a Creative X-Fi Titanium HD and Corsair SP-2500 speakers. I've also used onboard sound in both setups. Like I said, this is an issue I have always had, which leads me to believe it's some sort of habit that I have. More than likely how I don't use a computer desk, but rather work tables and just throw all the cords behind it.

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 14, 2017 11:50 am
by DeadOfKnight
So the cable is half the problem. I couldn't get it perfect, but moving it did improve the issue. The other half of it is just high gain from the sub. I just had to turn it down and it isn't too bad. It's not silent, but it isn't nearly as loud and obnoxious.

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 14, 2017 1:16 pm
by just brew it!
You could still try my passive adapter idea too; I bet that would get rid of most of the remaining hum. It's all low-voltage, so you're not going to damage anything even if you screw it up and miswire it.

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 14, 2017 2:39 pm
by sluggo
Induced voltages can be a bear. The good news is, as jbi suggests, they are easy to kill with brute force. Pull the inputs to ground with a moderate resistance and you should be good to go.

Other tips: Old-school fluorescent lights throw off a big 60hz e-field. If you have any nearby, try turning them off. Similarly, in-wall wiring can be a problem - try moving the sub to a different outlet or move it as far as possible from the wall to see if it makes a difference. And if you're willing to do a little soldering ... when the bulk capacitors in the sub's power supply get old, ripple current (I'm assuming the hum you're hearing is 60/120 Hz) goes way up. I don't know how old your sub is, but you could try swapping those caps out for something new and fresh and bigger.

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 14, 2017 3:24 pm
by DeadOfKnight
Maybe all I need is to get shielded cables for audio? It just dawned on me that maybe I should have mentioned this before. I've never spent the extra money on fancy cables and this could be the result. Also, is there any benefit of using either RCA or 3.5 mm over the other?

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 14, 2017 9:57 pm
by SecretSquirrel
DeadOfKnight wrote:
Maybe all I need is to get shielded cables for audio? It just dawned on me that maybe I should have mentioned this before. I've never spent the extra money on fancy cables and this could be the result. Also, is there any benefit of using either RCA or 3.5 mm over the other?


For what you are dealing with, there won't be a real difference. Many 3.5mm cables have a single ground surrounding the two signal wires. So if, for some reason, one of the two wires isn't driven, it could leak noise into the other channel. If both channels are working ok, then it will be functionally equivalent to RCA cables. If your 3.5mm cable has two separate cables then it will be absolutely equivalent. Before someone points it out, I'm ignoring situations where having an RCA input might have other implications, like the high impedance phono inputs on a audio amp.

When dealing with audio between stages (i.e from sound card to amplifier) you want to output as large a signal as practically possible from the output stage and have the sensitivity (volume or gain) as low as possible on the input. You obviously don't want to distort the output signal, but a sound card driving an audio amp should be able to run at full volume output. Ideally you control the actual volume with the last device in the chain, but if you want control of the volume from you computer, then start with the volume maxed on the sound card, and turn the amplifier volume up till it is a loud as you would ever need. Now turn down the computer volume to your normal levels.

By using the largest possible output from one device to the input of another, the signal to noise ratio is as high as possible. The noise is still there, its just quieter relative to the signal you want.

--SS

Re: Speakers hum when PC is off/standby

Posted: Thu Dec 14, 2017 11:36 pm
by DeadOfKnight
I just ordered this cable on Amazon: http://a.co/5gMzC96

Re: Speakers hum when PC is off/standby

Posted: Fri Dec 15, 2017 12:10 am
by just brew it!
If the existing cable is unshielded, then yeah better cables would probably help.