9B-ST power frequency hum

thomaspf · « **on:** 9 Feb 2004, 12:56 am »

Hi,

I am rearranging my system and would like to get rid of an annoyance in my setup. I do have a SP1.7 hooked up with balanced cables to my 9B-ST. They are both plugged into the same wall dual power outlet. The active subwoofer is plugged in the SP1.7 via balanced cable but unplugging it does not make a difference.

When I power up the system and the SP1.7 comes I get a rather loud ground loop hum emitting from the 9B-ST chassis. I can play a stream of zeros at 0db and the signal is almost free of ground noise but the ampifier is physically vibrating. When I turn the SP1.7 off it makes no noise whatsoever.

What should I try to get this under control. The hum is very audible from my listening poition and somehow defeats the black background coming from this amp otherwise.

I read that the 9B-SST has upgraded grounding. Is this a known problem that was addressed in the upgrade from ST to SST?

Any help is appreciated.

Cheers

Thomas

James Tanner · « **Reply #1 on:** 9 Feb 2004, 02:39 am »

Hi Thomas,

Do you mean you hear hum from the amp as if the transformers are buzzing or hum through the speakers?

james

thomaspf · « **Reply #2 on:** 9 Feb 2004, 03:16 am »

Transformers are buzzing loud and audible.

Very low hum in the signal if I record it and run a fourier analysis over it.

Any thoughts?

Cheers

Levi · « **Reply #3 on:** 9 Feb 2004, 03:52 am »

Sounds like you have a line noise problem. Sometimes dimmers does that. I once heard that sound coming from the amp and it is annoying. It just misterously disappeared one day. huh.

James Tanner · « **Reply #4 on:** 9 Feb 2004, 12:26 pm »

HI Thomas,

I agree it sounds like noise on the power line rather than the amplifier. The amplifier has 5 independent transformers so the chances of them all be bad is not likely.

james

lowrider · « **Reply #5 on:** 9 Feb 2004, 01:54 pm »

The same happened to me when I added a second power to my system, had to disconect the ground in the wall socket or the PCs, no more hum...

I dont know if it is safe or not, I had it this way for over 2 years without any problem...

thomaspf · « **Reply #6 on:** 9 Feb 2004, 07:41 pm »

O well,

I will try the cable without ground connected first. Probably won't pass any inspection.

Cheers

Thomas

jethro · « **Reply #7 on:** 9 Feb 2004, 10:25 pm »

Those tall halogen "Torchiere" floorstanding lights can cause problems as well. The toroidal transformer of my H/K AVR-7000 would buzz loudly (mechanical buzz) when the lamp was on. Moving the lamp to the other end of the house and on a separate circuit only slightly improved the buzz. The lamps are kind of dangerous so I didn't feel too badly turfing the lamp.

thomaspf · « **Reply #8 on:** 10 Feb 2004, 12:14 am »

The only other equipment I turn on for the hum to appear is the SP1.7 which is connected via Bryston balanced cables.

It would be kind of sad if they don't get along. When I turn off the SP1.7 and connect a different source to the amp directly there is no hum.

I found a spare cable and will try the hooking it up without grounding tonight.

Cheers

Thomas

thomaspf · « **Reply #9 on:** 10 Feb 2004, 03:54 am »

I clipped the grounding pin off the spare power cable and replaced the factory power cable on the 9B-ST with it.

There is no difference in the hum with or without ground connected, so let's look at other possibilities.

My start switch stopped working a while ago and I plug and unplug the amp to turn it on or off. Could that have an impact?

Any other recommendations?

Cheers

Thomas