curing huming in speakers

[Thunderchild]

I bought a set of speakers form a car boot sale, the had not transformer so I run them off the computer power supplies 12 V rail, this is there is a lot of hissing even when the volume is turned off and when a hard disk powers up you here a whining sound, I'm assuming that this is all coming in on the power supply.

I thought to cure it maybe a diode in series with the +12 V followed by an inductor again in series and then followed by a large capacitor, basically a low pass filter with a blocking diode.

 

[Hero999]

You have two problems:

One the speakers are picking up noise from the 12V rail which you can hear.

Two, you have an earth loop as the ground at the input is connected to the ground at the sound card which is causing another probem with hum.

The only way to solve these problems is to use an isolated power supply for the speakers, whether this be using a separate transformer or an isolated DC-DC coverter running from the PC power supply.

 

[Menticol]

Do the following, it's my empiric knowedge but always work for me, and the ground loop goes away!

Wrap a wire around the base of the 3.5m.m. plug, and connect it to the point where the ground of the speaker meets the 0V rail

Make sure your computer, printer etc. are connected to the same outlet, and properly grounded. I swear it, I was picking noise through my printer USB connection

Check the attached drawing

ps: Also solved the ground loop when I have connected my DVD player and TV to my computer's LINE IN, if anyone has the same problem

 

[kchriste]

connect it to the point where the ground of the speaker meets the -12V rail

You mean the 0V rail.
May or may not work, but worth a try.

 

[Menticol]

You mean the 0V rail.

OHH I'm sorry!!! I was distracted, it's 0V as you said

 

[Mikebits]

curing huming in speakers

I was gonna suggest teaching the speakers the lyrics

 

[Externet]

Computer switching power supplies and high fidelity do not mix.

 

[Mikebits]

A well designed analog system should have no problem with switched supplies and PC noise. Most of the interference is higher frequency than audio. Hiss may be high frequency garbage. Hum is most likely ground loops.

 

[Hero999]

Most of the interference is higher frequency than audio.

The problem is that non-linear elements in the audio amplfier cause lead to detection, i.e. demodulation, for example there are plenty of stories of people hearing AM radio broadcasts from audio amplifiers.

 

[Menticol]

Now when your are talking about that...

Poorly grounded car stereos start to picking up interference, and the noise is proportional to engine's RPM

what's the reason? I don't think it's the engine electronics bay, because the effect is also seen on old cars and public transportation.

 

[picbits]

Now when your are talking about that...

Poorly grounded car stereos start to picking up interference, and the noise is proportional to engine's RPM

what's the reason? I don't think it's the engine electronics bay, because the effect is also seen on old cars and public transportation.

Its quite often because a car alternator acts as a 3 phase generator which gives "almost" DC. It also relies on the battery to act as a smoothing capacitor.

 

[Thunderchild]

The problem is that non-linear elements in the audio amplfier cause lead to detection, i.e. demodulation, for example there are plenty of stories of people hearing AM radio broadcasts from audio amplifiers.

yes that happened to me I built a so called RIAA preamp and all it would do was pick up a radio station

the noise is more of a hiss plus all the noise generated by the hard disk motors, I was thinking the diode followed by a filrtering circuit may isolate the speakers from the rest of the 12 V rail

 

[Hero999]

That won't work, try what Menticol suggested, failing that you need an isolated supply.

You could also add feedthrough capacitors and ferrite beads on the supply lines but you need to solve the ground loop problem first.

 

[Menticol]

Its quite often because a car alternator acts as a 3 phase generator which gives "almost" DC. It also relies on the battery to act as a smoothing capacitor.

Thank you Picbits, that question gave me insomnia for years! here is another, to finaly sleep well: My home's eletrical outlets are 115V, 60hz, well grounded (I hope!). Appliances work fine.

Somedays, a high pitched buzz is heard from a fan (those models with electronic panel) and my computer's ¿voltage stabilizer? (don't know the english name for that, the device absorbs spikes and interferences). The duration of the sound is random, but no more than 10 seconds.

The noise is higher pitched than a 60hz hum. No clue what causes it, my neighbors are only aged persons without Tesla Coils, Rail Guns, Lasers, EMP's

 

[Hero999]

Another option would be to use an audio isolation transformer but that would reduce the sound quality and itself be a potential point of noise pick-up if it isn't a torroidal type.

 

[tonigau]

Somedays, a high pitched buzz is heard from a fan (those models with electronic panel) and my computer's ¿voltage stabilizer? (don't know the english name for that, the device absorbs spikes and interferences). The duration of the sound is random, but no more than 10 seconds.

This is most likely the control signal used by the power company to disable/enable the off-peaK hot water system. It has caused me some annoyance in the past when recording.

Sleep well Menticol

 

[Menticol]

Thank you by your answer Tonigau!