speakers buzzing!

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sean.laub

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Hello! Just signed up to ask this question...and perhaps more as time goes on :)

Here's my situation.

I have an m-audio delta audiophile soundcard and a pair of computer speakers (logitech z313) that when paired produce a buzzing sound. The audiophile connects by the red and white rca cables and the computer speakers connect by a 3.5 mm jack. So I bought an adapter (3.5 mm female connecting to rca males) to connect the 3.5 mm jack of the speakers to red/white rca cables, which can then be plugged into the soundcard. Apparently the speakers think this is a bad idea and hum quite loudly when i pair the two.

When I plug 3.5 mm headphones into the adapter and then into the soundcard, I do not hear the buzzing.

When I plug the 3.5 mm jack of the speakers to the onboard audio input on the motherboard, I do not hear the buzzing. (note that I have a separate soundcard while the motherboard has onboard audio).

Also, when I simply touch the 3.5 mm jack of the speakers I hear the buzzing. Not sure if this helps but it's something I noticed.

I spent some time reading about this and not sure how to proceed from here, hence the registration and first post. I feel like it's a grounding thing but I'm not sure if I understand how that would be fixed given my situation.

Any help greatly appreciated!
 
Hi Sean,
It is not good practice to connect the uncontrolled output of a good quality "semi-pro" soundcard directly to monitors especially, wtgr, cheap PC monitors which tend to have a high input sensitivity.

The usual path for a good PCI soundcard is to a monitor controller* or, as in my case, a small mixer. Thus the level from the soundcard which is vastly higher than the speakers were designed for, can be tamed for good results.

The reason you don't hear the buzz when connecting headphones to the Delta's (2496?) output is because the card is not designed to drive such a very low impedance load, it wants to "see" a few 1000 Ohms not a few tens!

I have found a manual for the speakers but it does not help a lot! I was trying to see if it had a 3 pin mains plug and therefore an earth? Looks not to be so. Were it so you might have had a hum/earth loop but this does not seem likely.

*This could be as simple as my fave DIY proj', a pot in a tin...Or in this case a STEREO pot in a tin!


Dave.
 
Touching the 3.5mm jack of powered speakers makes a buzz - that's normal, and a good test of if it's working. If, when you plug this into the Delta, you get a permanent hum then I'd suspect grounding issues - if both devices are grounded via either the ground(earth) cable or chassis, then this often causes hum. If neither are grounded then any hum will often change as you touch the metal work. So these hums may come from too many ground paths or not enough, or even poor design of one or other of them that means that the ground connections are at different potentials. If one is just a volt different to the other, through any reason, then joining this to something else means current flows. Since we're dealing with tiny voltages and amplifying them, hums can appear and vanish often seeming to be quite random. The cure, or even just a reduction come from experimenting lifting or adding audio grounds. NOT messing with the mains ground which is there for safety, not hum reduction. Lifting grounds here in the UK is a test failure for certain if it's done on the mains cable connectors.

A transformer will often solve the problem, but sometimes, just disconnecting the screen on the RCA cables at one end does the trick. If the M-Audio is grounded and so are the speakers, this I reckon is the most likely problem. Try a few experiments and see what happens.
 
I bet the Logitech speakers have a cheap wallwart transformer that is ungrounded and unpolarized. You could try turning it around the other way in the socket.
 
mjbphotos said:
I bet the Logitech speakers have a cheap wallwart transformer that is ungrounded and unpolarized. You could try turning it around the other way in the socket.
Click to expand...

The manual, such as it is, shows a mains cable exiting one of the speakers and terminating in a bi-pin plug. But they use the same low res' "diagrammatic" picture of the plug for both USA and French manuals and there is none for UK so I suspect the speakers are non- earthed and I BLOODY HOPE! double insulated.


This is unfortunately often the noobs problem when they start to interconnect gear of mixed parentage and class and do not have Clue One about electrics.

Dave.
 
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