Hum on speaker line

Charles - K5UA

There is a significant amount of hum on the speaker output line into my powered Yamaha speaker. I have to decrease the Yamaha speaker gain so low that I barely get enough audio with the Flex volume at max. Otherwise the hum is such a component of the audio it becomes distracting. Grounding the speaker to the Flex does not help, so I don't think it is a ground loop. There is no hum in the headphones. Any ideas?

Ken - NM9P

It sounds to me like you have a bad cable (an open ground?) between the rig and the amp/speakers. Or perhaps your powered speaker's power supply has taken a hike.

A remote possibility is that the ground connection at the rig has gone bad.

Dale KB5VE

Charles disconnect the cable from the flex, does the hum still persist? If it does then unplug the cable from the speaker, if there is still hum it is in the speaker. Also I assume this hum is there when no transmit signal is present. Even the Bose speaker system that is universally accepted as a excellent choice has some slight background white noise when the volume is turned wide open. If the hum does go away when you unplug it from the flex then you know it is associated with the flex.

Charles - K5UA

No hum when the cable is disconnected from the 6500, no hum when the cable is disconnected from the speaker, BUT no hum when my headphones are plugged into the 6500 speaker jack on the back, and no hum when the speaker jack is used to drive a portable LogiTech powered stereo speaker system.  Therefore, I must conclude that there is a ground loop present between the Yamaha powered speaker (which runs on 115 AC power) and the 6500. I plugged the Yamaha into the same power **** as the power supply for the 6500, and also on a different power ****. No difference.

I will experiment with another powered speaker, just to confirm that the problem is isolated to the Yamaha powered reference speaker (living proof that expensive is not always better). Nice speaker except for the hum. I guess to be fair I should also drive the speaker with a different source other than the 6500 to see if a hum exists.

Thanks for the ideas.

Dale KB5VE

From my old sdr 1000 days there is a hum eliminator they sell for audio equipment. I had to get one for the recieve cable on my sdr 1000. I believe it eliminates a ground loop. Radio shack sold them at one time. Plugs are the 1/8 and 1/4 standard.

Charles - K5UA

I think that's what I need to do Dale. I have a Jensen 1:1 isolation transformer that I can put between the 6500 audio output and the Yamaha powered speaker. It has a 60 db attenuation of hum isolation. I was also wondering if driving an unbalanced speaker with one side of a stereo output could be part of the problem? My tests with the headphones and the Logitech stereo speaker are both stereo devices. Any audio engineers out there can comment on this?

Dale KB5VE

You know it is funny before you made your post I was thinking the speaker you use is a single input and I wonder if that could make a differnce. It just might make a difference since the is a load on only one channel. Good question. I sent you several emails with isolation devices. It makes sense that unplugging the speaker from the radio that using a isolation device should also stop the hum.

Robert -- N5IKD

My radio is plugged into the computer Line-In. I get a hum if the radio is turned off or the cable is unplugged. I just disable the Line-In device in Windows when the radio is not in use.

Charles - K5UA

Hi Robert, I don't have the radio plugged into the computer at all. The speaker is simply plugged into the ext speaker output of the 6500. I'm still wondering if using only one channel of the 6500's external stereo output to feed the single speaker is causing some sort of unbalanced current flow that is causing the hum. Will do more testing on a different powered speaker system. Not a serious problem, but I would like to know why it is happening. Baffling.

Tim - W4TME

Charles - Yes.  Try stereo powered speakers.