View Full Version : Audio Hum

14-04-2002, 11:55 AM
I'm trying to get some decent recordings of my old vinyls. I've got my turntable feeding into the amp and the amp output into the sound card - works fine but I can't get rid of the background buzz. Is it an earthing problem? All the leads are screened RCA type connectors with an adaptor to 1/8' at the sound card. The amp is an old but top quality Sony TA-4FA. I don't get the buzz through the amp speakers so I guess the turntable to Amp bit is okay. The sound is on-board the motherboard in the pc so upgrading the sound card isn't really an option. How can I cure it? Can I cure it? Please help if you can.
Ray A.

14-04-2002, 12:26 PM
Ray, you probably have an 'earth loop' meaning there are two paths that earth the signal shield. This allows a minute current to flow through the shield causing the hum. Try backing off / insulating the outer connections on the RCA plugs where they go into your soundcard adaptor - it will either work or get worse! If it gets worse, you may have to resort to inline signal isolating transformers.

14-04-2002, 02:46 PM
Ta, I'll give it go. I thought the shield was the signal return path - how can this work if the sheild is not continuous between the devices, or do I just isolate one channel shield?

14-04-2002, 03:38 PM
This a problem that is common with connecting multiple peices of equipment together. I have done alot of work on stages, where one is getting a audio feed from say the bass guitarists amplifier to feed through the P.A system, or there are several racks of amplifiers that may be working of different power sources. Earth loop problems on this scale can cause a problem that people have to shout over. One easy solution to see if this is the case, is to get a disused tapon plug, or extention cord, and swipe the earth pin off it. This breaks the loop. DO NOT USE THIS ON ALL THE GEAR as you create a hazard, using it on say the power for the turntable/amplifier does identify that this is the problem before you go cutting up your beatiful cables.

18-04-2002, 01:55 AM
With the system you discribe I would have thought that the signal into your sound card should be unamplified. If the sound card does its own amplification and you feed in an already amplified signal this will overdrive the amp causing a buzzing noise.

Regarding your query about shielding - it is normal practice to only connect the shield to one end of your lead unless it is being used as the signal return line.

14-05-2002, 10:15 PM
Did you manage to fix your audio hum problem.

Cheers Craig