RB991 Audible Hum/Buzz

[JohnSC]

Hi,

I am getting an audible buzz coming through my fronts. I am sure it is the amp as it is present with all other equipment switched off and it does not change when I turn on the processor or DVD etc.

Is this a common fault with this amp? Does any one have any tips on how to correct it?

Thanks

[eelco74]

It is not supposed to hum. When I auditioned my RB-981, I also tried the 991. It was dead silent.

Have you tried differente interconnects. When 1 interconnect is broken, the system will hum. Also check the phase of you mainsocket.

Unplug the amp.
Only connect the mains
Use a voltage meter on AC to see the potential voltage between the case of your amp and a grounding point.
Unplug the mains and put it back upside down
Again check the voltage.

The lowest seems so be the best.

Also check all the other equipment this way. I found this eliminated most hum problems.

[JohnSC]

Thanks. I'll try the interconnects. I am pretty sure the phase is ok. Here in Australia, it is very difficult to mix the phase as each point in the socket is a different shape.

[JohnSC]

Ok. I've tried the interconnects actually disconnecting each one in turn to try and narrow it down. I've even tried different power circuits and power cords. No luck.

I then tried using 2 channels of my 1075 for the fronts and I didn't notice any buzz through the speakers! This leads me to believe it is the 991 amp. Any ideas? What could cause this? Perhaps it needs a mod or repair? Could it be an earthing problem?

Any ideas would be much appreciated. :cry:

[GosonFletchy]

Maybe your input resistors are open. There should be a 10 ohm input resistor on each input, so if you take a ohm reading from the ground of one input to the other, you should get 20 ohms or resistance (or very close to it anyways). If those resistors have opened up then you could definitely hear a hum because of it.

G.