MyrddinE Posted December 22, 2004 Share Posted December 22, 2004 I have a set of Klipsch Promedia 5.1's, connected to a Creative DDTS-100, taking signal from the optical output on my NForce 2 onboard sound. Formerly, I had a double-ended jumper cable (both ends with a standard stereo mic plug) going from the mic out for the Promedia's to the line-in on my Soundblaster Live!... this is needed for me to get my headphones+mic setup to work. This worked until recently. Now, when I have the audio jumper cable plugged into ANY of the Live jacks, there is some nasty humming in the speakers. The volume of this humming is constant... it doesn't matter what volume I set the speakers to. If I plug headphones into the line-in on the sound card I hear nothing. If I plug headphones into the mic out on the speakers it works fine. If I use the jumper cable, I get nasty feedback as soon as it is plugged into any audio jack on my PC... from the onboard sound, or the SB Live card. The switchover event was me taking the speakers + digital decoder downstairs to use on the DVD player, which I had never tried yet. Worked great, watched a couple DVDs, then took it all back upstairs. Now, horrible feedback. As far as I can tell, nothing changed on the computer... and I really can't see what I could have done to the speakers to cause this either. It seems kinda like some 'buffer' in the system that should be protecting it from feedback through the mic-out is not working as it should. When I plug the jumper cable into any powered device, I get humming... including a tape recorder, though that's quieter. Suggestions? Quote Link to comment Share on other sites More sharing options...
DrWho Posted December 23, 2004 Share Posted December 23, 2004 it's called ground loop and it happens because your ground voltage isn't "0". Since it worked before in your exact configuration I would check cables for any flaws and make sure there's no hairs or anything jammed into the plugs or on the inside of your pc. However, there has got to be a way for you to hook up you sound so that you don't have to use this jumper cable technique. How exactly do you have everything set up, or want it to work? Btw, you should have posted this over in the promedia section on the forum (gotta scroll down a bit). You'll probably get more responses that way. Quote Link to comment Share on other sites More sharing options...
dodger Posted December 23, 2004 Share Posted December 23, 2004 See Above, if nothing wrong, make sure all power cables are properly grounded. dodger Quote Link to comment Share on other sites More sharing options...
MyrddinE Posted December 23, 2004 Author Share Posted December 23, 2004 ---------------- On 12/23/2004 4:03:28 AM DrWho wrote: it's called ground loop and it happens because your ground voltage isn't "0". Since it worked before in your exact configuration I would check cables for any flaws and make sure there's no hairs or anything jammed into the plugs or on the inside of your pc. ---------------- The electrician installed some new power outlets... I wonder if perhaps it was incorrectly done? I'll check that too, though I am not actually USING these new outlets yet, he may have messed up the one I am using. ---------------- On 12/23/2004 4:03:28 AM DrWho also wrote: However, there has got to be a way for you to hook up you sound so that you don't have to use this jumper cable technique. How exactly do you have everything set up, or want it to work? ---------------- I play online games that use voice chat frequently. I have a headphone with mic, so the other end of the headphones separate into a mic plug and a headphone plug. The back of the computer (where the mic would plug in) is several feet from the front of the promedia control (where the headphones plug in). To get around this, I jump the headphone out on the promedia's to the line-in on my second (mostly unused) sound card. Then my mic + headphone plugs can go near each other. ---------------- On 12/23/2004 4:03:28 AM DrWho also also wrote: Btw, you should have posted this over in the promedia section on the forum (gotta scroll down a bit). You'll probably get more responses that way. ---------------- I was not sure where problems should be reported... I didn't think this issue sounded like a promedia-specific problem, which is why I posted it here. And, from your description, it may well not be my promedias. Quote Link to comment Share on other sites More sharing options...
MyrddinE Posted December 23, 2004 Author Share Posted December 23, 2004 ---------------- On 12/23/2004 4:05:05 PM MyrddinE wrote: The electrician installed some new power outlets... I wonder if perhaps it was incorrectly done? I'll check that too, though I am not actually USING these new outlets yet, he may have messed up the one I am using. ---------------- Tadaaa! Problem found. I was wrong, I did plug my speakers (and just my speakers) into the new outlets. Likely there is a disparity in how the new and old outlets are grounded. This voltage difference resulted in the hum. Thank you, problem solved DrWho. Quote Link to comment Share on other sites More sharing options...
dodger Posted December 23, 2004 Share Posted December 23, 2004 Well it's good that you found that some outlets are not properly installed. Now it's just a matter of getting the electrician back. You can buy a small circuit tester that will "read"them for you. That way one can check to make sure all things are properly grounded. This one teetered between Technical and Pro-Media. Enjoy your Holidays! Quote Link to comment Share on other sites More sharing options...
MyrddinE Posted December 23, 2004 Author Share Posted December 23, 2004 ---------------- On 12/23/2004 4:17:13 PM dodger wrote: Well it's good that you found that some outlets are not properly installed. ---------------- For all I know, it's the old outlet that's bad, and the new ones that are good. In fact, chances are likely... so I'll probably move all my equipment over to the new outlets. But... my uptime... *sob* Quote Link to comment Share on other sites More sharing options...
DrWho Posted December 24, 2004 Share Posted December 24, 2004 ---------------- On 12/23/2004 4:05:05 PM MyrddinE wrote: I play online games that use voice chat frequently. I have a headphone with mic, so the other end of the headphones separate into a mic plug and a headphone plug. The back of the computer (where the mic would plug in) is several feet from the front of the promedia control (where the headphones plug in). To get around this, I jump the headphone out on the promedia's to the line-in on my second (mostly unused) sound card. Then my mic + headphone plugs can go near each other. ---------------- Ok, I finally understand your setup now (it took me a while to get it). If you ever wanted to simplify things, you could purchase a female to female 1/8" stereo miniplug adapter. What this will do is let you connect your headphones into your headphone jack and then plug your mic into the adapter and then plug your other cable into the adapter and then into the mic input on your first sound card (basically increasing the length of your mic cable). Doing this will reduce the amount of noise in your setup, allow you to use one sound card and increase the overall quality of both your headphones and mic. Technically, you're not supposed to run a headphone out into a line in because the impedance is different and the circuitry is slightly different between a headphone out and a standard line out. I dare say that the extra sound card is also soaking up a little bit of extra RAM as well which of course hurts your gaming performance You can get the part at radio shack for about a dollar. Btw, it makes perfect sense that the new outlets installed could be causing your problem. It's not too difficult for different circuits to have a slightly different "0" voltage on the ground which means that the grounds between two different devices see a voltage and thus current flows (thus creating the beautiful 60Hz hum). You might benefit by getting a powerstrip or a surge protector or even a line conditioner so that you can plug all your computer related devices into the same electric source (while also getting some fancy protection and cleaner power). Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted December 24, 2004 Share Posted December 24, 2004 the DOCTOR is in the house. Good troubleshooting, thought you might get this one. Looks like you're our resident PA guy and electrician now! Michael Quote Link to comment Share on other sites More sharing options...
Marvel Posted December 24, 2004 Share Posted December 24, 2004 As Dr. Who says, the hum could be from the new outlets being on a different 120V leg than the old ones. When you have 240 come into a building, it gets split into two 120 volt sides. Depending on the load on each side, there can be a difference in ground potential. Have a look at this article on the Peavey website, covering AC power distribution: http://www.peavey.com/support/technotes/soundsystems/acpowerdist.cfm Marvel Quote Link to comment Share on other sites More sharing options...
dodger Posted December 24, 2004 Share Posted December 24, 2004 Agreed. But the proximity of the outlets would lead one to believe that an electrician does not always go out of their way to either tie into a different gang box or change polarities. The possibility of the old outlets being two pronged could lead to a change. However, a good electrician, adding additional outlets, will check the outlets so that a factor of '0' or "proper' and the same wiring will be present, eliminating the potentials. Thus it is important that any grounding should follow code of a 4' rod. Attaching to water lines is questionable, at least. Or the electrician should check and either use baluns or capaitors as needed to eliminate the problem before it can begin. A good Master Electrician will do this. A surge protection unit with EMI/RFI filterings can still allow a ground loop if the outlets and grounding are not proper. dodger Quote Link to comment Share on other sites More sharing options...
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