Buzzing noise from the speakers

[lewdicrous]

2 hours ago, mvainult said:

Greetings

 

I have the same set of speakers and didn't use them for a while because of the static. Now I realized it was coming ONLY when the screen was showing something and decided to pick it apart. After unscrewing i took out a white ribbon cable from a separate module which was connected to the display in the front. After keeping it unplugged and turning it on the static was mostly and it was all good. As I just discovered this I'm not sure what the extra module did, but I suspect there is some magnetic affection from electricity

I currently only use the subwoofer. The static is only noticeable when the speakers are connected, at least that's how it is for me.

[H713]

Here's some information that is useful to consider when dealing with this kind of thing. It isn't comprehensive (and feel free to correct and add to it- I'm not perfect), but it's clear to me that there is a disconnect between people who hang out on some of the more technical audio discussion boards and places like the LTT forum.

 

The most common cause of buzz / hum is grounding related. Specifically, ground loops / ground noise. Some PCs have VERY noisy grounds, and some interfaces do a better job of dealing with it than others. I've even seen a faulty monitor power brick cause problems with this. A lot of people think that GND = GND, but that's not really the case. Ground connections have a finite impedance, and there are very real (and often very large) currents flowing through ground connections. By ohms law, we know that this will result in some small (but not insignificant) voltage drop. There's your noise. The Wikipedia article does a better job of explaining ground loops than I can, and it's well worth reading. Grounding is an issue for all electrical systems and I've seen some very bizarre and obscure issues in computers that are caused by a flaky ground connection.

 

https://en.wikipedia.org/wiki/Ground_loop_(electricity)

 

A very common situation is to have two pieces of audio equipment, say an amplifier / powered monitors and a preamplifier or DAC connected together by an RCA cable. It's pretty common for both of these devices to reference audio ground (the outer shield of the RCA connector) to chassis ground, and it's also fairly common for chassis ground to be tied to mains Earth. We're already creating a perfect storm. Now let's say you plug your powered speakers into an outlet on the other side of the room. Now we've made things worse. Now let's say that outlet is on a totally different circuit (also quite common). Even worse.

Balanced audio (often seen using XLR or TRS connectors) can be a good solution to this, and it's ubiquitous in the pro-audio industry for this reason.

 

https://en.wikipedia.org/wiki/Balanced_audio

 

It's also very good for reducing interference with very long cable runs. Most of the induced noise will be common-mode (that is to say, equal in amplitude and phase on both the hot and the cold lines) and will be attenuated by the common-mode rejection of the input amplifier. The CMRR is never infinite, but in a well-designed input it's pretty good at low frequencies, gradually diminishing as frequency increases due to stray capacitances and the decreasing open-loop gain of the input amplifier.

 

 But... there are caveats. For one, there's usually a third connector (shield) in balanced audio. If that's connected on ONLY one end (usually on outputs, not on inputs), all is well. The shield is grounded (usually to mains Earth) and works the way it should. BUT... some people get the lofty idea of grounding BOTH ends of the shield... and we create a ground loop. This isn't usually as catastrophically noisy as with unbalanced connections, but it's still a problem.

 

Further complicating balanced audio are phase issues. This isn't nearly the problem it was 30 years ago- the industry has largely standardized on XLR wiring (Pin 2 hot, Pin 3 cold, Pin 1 shield), but you still occasionally see some (usually very old) equipment which is wired for pin 3 hot.

Driving equipment with a balanced input from an unbalanced output is relatively straight forward. Tie XLR Pin 3 and Pin 1 to the shield of the RCA connector, then use Pin 2 of the XLR as the center conductor. Driving an unbalanced input from a balanced output is a much bigger mess, and it depends on how the balanced output is designed- how you treat a transformer vs. a standard differential output is not the same. Consult the manufacturer's manual for reference.

 

Faulty caps are another very common cause of noise. If your speakers (or if they're passive, the amplifier) is connected to AC power and nothing else, with the volume turned all the way down (if possible), and you still hear objectionable buzzing, there's a good chance that this is where the problem lies. Troubleshooting power supplies isn't too hard, but you should know what you're doing. The EEVblog forum, Audiokarma and DiyAudio are all better discussion boards to discuss power supply troubleshooting (or repair of audio equipment) than the LTT forum.

 

 Much less common, but still occasionally a problem is insufficient input filtering. You rarely see this on modern equipment, even cheap consumer gear. Where it's common is in older equipment that was designed in an era when switchmode power supplies were much less common and noise on the AC line was much lower. My Quested monitors are a good example of this- the Omniphonics amplifiers were designed in the late 1980s by a tiny English manufacturer. There's absolutely NO input filtering on the AC mains input and it uses a toroidal power transformer with a relatively wide bandwidth. Even after a full recap of the amplifiers and some grounding modifications, there's still some audible noise. It's not bad enough to cause an issue, but in a quiet room you can certainly hear it. If I plug a lamp with a dimmer or a really crappy switching power supply into the same outlet, the noise is bad enough to be annoying.

 

TL;DR: H-713 sometimes forgets that not everyone finds analog electronics interesting.

Edited February 21, 2021 by H713
Added a link.

[BigBottle69]

I experienced the same problem w/this device. It was fine the 1st 2 months but then the buzzing began. And now this company won't take it back even though I am perfectly within the warranty time.

[Avinashvinni]

i also have the same speaker set F&D F550x and in the first few months it was fine and now buzzing and thunder like sounds come from the sub if i just connected to the mains.

one thing i observed is that i took my unit to a repair shop and connected it to their socket and boom everything is fine, the repair shop guy was like ~ looks fine naa what can i do ???

i think it is due to the wiring in my house or grounding.

but i have got my grounding status confirmed by an electrician and he said its all fine.