Clock radio works great on batteries, but hums when plugged in to the converter...
 

I have a clock radio/sound machine that works perfectly with the batteries, but has a loud hum when hooked up to the power converter. Is this a function of the power converter? If I were to remove the plug from the power converter and attach the wires to the battery leads would I get the same results? The specs for the recommended power converter are 9v 500mA. I only have a 9v 400mA. Could this make a difference?

This is something I bought from Goodwill and have a week to return. Thanks!

It's on the way out. I think it would e easier and cheaper to just replace it. :)

You can try the 400ma power supply. If it works, it may produce the same sounds, if not, the clock won't power up - no harm.

I bet AC is getting through your converter and you are hearing a 60hz AC hum.

If your power adapter is really CHEAP or OLD or CHEAP AND OLD, it's possible the transformer inside there is leaking and making dirty power. the mA rating shouldn't make a difference.

If you have another adapter handy or want to try to grab a new one, it -might- get better.

Buy rechargeable batteries.

Could be... the power converter was from a cordless vac.

EMI - don't sleep to close to it...

Put an RF Choke on the power cord near the radio. You can buy them at Radio Shack for a buck or two.

The fourth 9v power supply I found worked great. No hum at all.

The ones that produced the hum were probably the wrong milliamp rating... too much or too little?

The one that works is 1100mA. All that didn't work were below the recommended 500mA.