NS-10 noise and hum
 

I have been trying to isolate a hum in my NS-10s. I have my balanced monitor outputs running from my Apogee quartet going to a cheap QSC power amplifier, the outputs of the power amp are going out unbalanced to my NS-10s.
When I turn on my amp i get a low hum and what appears to be some noise from USB. I went to the local electronics shop and bought a consumer grade Ground Loop Isolator. I placed this unit between the Apogee outputs and my power amp as suggested and it did remove the USB noise however the low hum still exists.
When the Apogee is outputs are disconnected from the Power Amp the hum is still there so that makes me believe that the hum is coming from within the power amp itself.
What i did was take the unit and put it between the Power Amp outputs and the NS-10 speakers. That completely removed the hum noise however it appears my output volume is being attenuated as well, as I can't get nearly the output volume coming out the power amp as if I was running straight to the NS-10s without the Ground Loop Isolator in between.
From what I can guess the noise from the Amp is coming from an issue within the Amp itself or because of a poor grounding issue coming from my house power.
Can anyone tell me why the Ground Loop Isolator would be attenuating my volume from my power amp and if they have any suggestions for a different fix?
Thanks guys

Re: NS-10 noise and hum
 

Some things to consider:
1-A "cheap" QSC amp...what model is it and does it have balanced inputs?
2-"a consumer grade Ground Loop Isolator". Probably designed around -10 in/out level while the interface and amp are probably built to use +4(and who knows exactly what this "isolator" is actually doing)
3-is the power amp plugged into the same power circuit as the computer and interface? And, is the amp mounted in a rack with metal rack rail and maybe other gear that is fed from another power outlet?
4-assuming a ground loop, with balanced inputs on the amp, disconnecting the shield wire at the amp end might be a solution.
5-I doubt the "isolator" was designed to go between the power amp and speakers(any ground loop is happening between the amp and the interface)

Re: NS-10 noise and hum
 

1. ) Actually a QTX brand QA400 model, yes it does have balanced 1/4 and XLR inputs.
2.) Yes, probably the reason for the overall volume loss?
3.) Yes, I have all my gear coming from the same power circuit. I don't have any other outboard gear where my amp is racked. I also tried with the amp mounted in my rack and then removing the screws and leaving it "decoupled" and had no noticeable change in hum volume
4.) so disconnect the shield on the amp end on the balanced 1/4 cables from the Apogee to the amp?
5.) Yes, I think you are right. From what you described in point 2 the "isolator" is probably attenuating the hum at the expense of overall volume.

Thanks for your thoughts Dave, they are mucch appreciated!
I will give disconnecting the shield wire at the amp end a go and see how I get on.

Re: NS-10 noise and hum
 

If you get a hum from your speakers when there is no audio source connected to the amp, then your amp is faulty.


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Re: NS-10 noise and hum
 

1. ) Actually a QTX brand QA400 model, yes it does have balanced 1/4 and XLR inputs.
2.) Yes, probably the reason for the overall volume loss?
3.) Yes, I have all my gear coming from the same power circuit. I don't have any other outboard gear where my amp is racked. I also tried with the amp mounted in my rack and then removing the screws and leaving it "decoupled" and had no noticeable change in hum volume
4.) so disconnect the shield on the amp end on the balanced 1/4 cables from the Apogee to the amp?Yes(fingers crossed)
5.) Yes, I think you are right. From what you described in point 2 the "isolator" is probably attenuating the hum at the expense of overall volume.

I also agree with Jimmy. A humming amp with no signal is probably faulty:o