Hum turntable mp3

[westnorm]

I had a deep loud hum when I was recording using Audacity from a Technics slBD3 turntable onto my Dell Inspiron laptop through a Griffin Imic usb adapter. THen, I disconnected my laptop from its ac charger and ran off battery power, and the hum is gone. Something to do with the ac-dc transformer?

 

[soundguruman]

The laptop charger does not provide ripple free power. This is why you need to run it off batteries.
Also if the charger has a three prong power cord, it can cause a ground loop.
A power adapter, available at the hardware store, changes a three prong power plug into a two prong power plug.
If your charger has three prong power plug, the adapter may stop the ground loop.