Earth Hums

[kennaughton]

In setting up my home studio I find lots of noise and hum thru the system. All equipment is plugged into a double powerpoint. Shorts don't seem to be it. Could it be that I don't use balanced cables? Would power cables be interfering with audio cables? Any ideas?
Thanks
Ken

[jpryor]

First, balanced cables will help shield out noise, but if you have a ground loop, it isn't shielding that you need. Shielding helps prevent radio frequency and electro-magnetic interference (RFI & EMI). The hum you hear is AC hum generated (among other things) because there is a difference in impedance in grounds somewhere in your power circuit.

Check the power source. First and foremost make sure your phases are reversed (i.e. hot on neutral and neutral on hot); this will damage your gear.

Does your outlet have 3 conductors (hot, neutral, ground)? If so, where does the ground go (check this at your breaker box)? All the ground wires/neutral conductor for the entire house should be well grounded to ONE PLACE ONLY.

If you have older power (like mine) you'll only have 2 conductors and you now have 2 options. First, buy a 3 prong outlet and jumper the ground to the neutral side. Otherwise, you can create a new ground just for this circuit by jumpering the ground to a water pipe or other good conductor. The second option may not work if the neutral line is already being used as a ground and you don't want more than one ground.

Make sure all your equipment (except for a computer-based recorder) is plugged into one circuit (preferrably a circuit dedicated just for your musical gear). If you can't dedicate a circuit just for your gear, find out what else is plugged into that circuit. Even devices that aren't turned on are going to introduce AC noise. Also, devices not on that circuit could cause noise (especially TV's, computer monitors, and doorbells). There should be 2 main power lines coming into your breaker box. Leg A is 110 VAC and leg B is 110 VAC. Find the breaker for your music circuit and switch the hot leg being used.

I didn't mention this before, but if you aren't already, you might want to get a Furman power conditioner ($100). They are great for eliminating noise, interference, hum, and surge/spike protection.

As always, be sure you've de-energized any circuits you intend to work with. Electricity can bite! Let me know if this is useful.

[bdemenil]

I am looking at the Furman IT-1220 and IT-1210 - both expensive units that claim to eliminate hum. They are called Balanced Isolation Transformers. Worth the money or just a waste?


p.s. - I have a hum problem connecting my mixing board to my sound card. Also connecting bass amp to mixing board. Balanced lines help but do not eliminate it.

[texasbluesman]

perhaps another fix would be to use a gate. setting the threshold just slightly above the hum would eliminate it .