Bad Screeching Noise

Sonny Jenkins · Post by **Sonny Jenkins** » 28 Jan 2015 6:44 am

My BIAB is played from my lap top to my amp. When I'm on lap top with battery,,,,everything is fine,,,,when lap top is plugged into charger,,,I get a loud screeching noise,,,,impossible to play when plugged in. Opinions????

Jack Stoner · Post by **Jack Stoner** » 28 Jan 2015 7:39 am

Probably a "ground loop hum" problem. When two devices are plugged into AC power and then connected you can get the ground loop hum. The fact that it does not do it when the Laptop is on battery confirms the AC power ground loop hum.

When you use the AC power, use a "ground lift" AC plug adapter on the Laptop and see if that fixes the problem. CAUTION, only use the ground lift adapter when it is connected to the Amp.

Sonny Jenkins · Post by **Sonny Jenkins** » 28 Jan 2015 7:46 am

hmmmm,,,,I have a "ground loop isolator" cable from radio shack that I used to use for something?,,,,I could use that from the lap top to the amp,,,,maybe that would help? Not sure what a "ground lift adaptor" is?

Jack Stoner · Post by **Jack Stoner** » 28 Jan 2015 9:59 am

The AC Power "ground lift" adapter goes between the AC power socket and your power cord plug.

Here's an example:

Sonny Jenkins · Post by **Sonny Jenkins** » 28 Jan 2015 10:13 am

whoaaa,,,like the name implies,,,,"lifts" or eliminates the ground! Would I really want to do that? Would the cable I mentioned be effective to block out the hum?

Dave Potter · Post by **Dave Potter** » 28 Jan 2015 10:52 am

Sonny Jenkins wrote:whoaaa,,,like the name implies,,,,"lifts" or eliminates the ground! Would I really want to do that?

The "ground" connection is there to protect against malfunctions. A correctly wired circuit powering a properly functioning appliance doesn't need it. Years ago, 2-wire power plugs/cords were the standard for household circuits, and lots of things, lamps and small appliances, etc, are sold with only 2-wire power cords even today.

Jack Stoner · Post by **Jack Stoner** » 28 Jan 2015 11:23 am

As long as you are connected to the amplifier, its still grounded. I assume you are using a shield/grounded audio cable to connect between the PC and the amp.

I can't say about the cable you have, as I have no idea what you have.

The "ground loop" problem is a difference in voltage of the two grounds caused by the design of the equipment and how the grounds are treated, and thus it causes the hum. You can get a ground loop hum from two AC powered devices even if they are plugged into the same power strip.

Jeff Newman used to advocate cutting the ground pin off of power plugs, but that was bad advice.

John Booth · Post by **John Booth** » 28 Jan 2015 11:34 am

Sonny Jenkins wrote:whoaaa,,,like the name implies,,,,"lifts" or eliminates the ground! Would I really want to do that? Would the cable I mentioned be effective to block out the hum?

Yes. No worries. It's done all the time to kill hums from crappy bar wiring

Sonny Jenkins · Post by **Sonny Jenkins** » 28 Jan 2015 11:42 am

As a matter of fact these are plugged into the same power strip. I have a ground lifter around here somewhere,,,I'll see if I can find it and try it. This is more of a screeching noise than a hum,,,almost like a feed back noise. I think I bought this radio shack gizmo several years ago to address the ground hum of some other equipment,,,it was a low hum,,,it eliminated it.