Audio Systems: humming noise, bose 901 series, bose 901

Question
recently purchase a high powered amp 670/chan 8 ohms or 1000/chan @ 4 ohms. I hooked it up to bose 901 seriesVI speakersrated at 8 ohms. I noticed a humming noise from speakers with no music on when I reduced the volume conytol to zero the hum went away. is this normal or connection problem mis mathed components need you help

Answer
Hi Frank,

There are several possible causes of the humming noise.  You didn't mention if there was a turntable hooked up, but if there is, that needs to be properly grounded to your amp.

Your amp also needs to be properly grounded.  If not, that can cause hum, as well as the power supply to the amp itself.  You may have "dirty power" and may need to get a surge suppressor or "line power cleaner" to make sure the power to the amp is "clean".

Of course, you also need to make sure the speakers are wired properly - there are positive/negative sides to the cable wire and the pair needs to be plugged into the correct connections on the speakers, but I assume you've done that.

Last but not least, it could be that your amp is simply noisy - perhaps you didn't notice the hum before.  I'm not sure what the "670/chan" means, other than "670 amps per channel" and you could just be overdriving what the speakers can handle, or more likely, there are one or more components in your amp that are noisy, but when you turn the gain all the way down, it goes away.  It could be the Bose 901 series speakers are just not able to handle the amperage put out by the amplified and they're just being over-driven.

I'd try to test the amp with other speakers, if you recently purchased it, take it back to where you bought it and ask them to hook it up to some speakers but without any music playing, and see if you hear any hum.  If so, perhaps you've got a defective amp.  If the "670/chan" means 670 amps per channel, that's massive overkill for any home listening system.  Good luck!  Cheers, Wink