[Oublie]

Hi,

Not sure if this is the right place but i'm guessing this is more of a tweak than a amp specific issue. I seem to have a 'hum' coming from my headphone jack. My equipment is as follows.

Computer
Trust USB soundcard
NAD 3020B amplifier set to run in lab mode (no ultrasonic or subsonic filters) with clipping off set to 8 ohms.

Ultrasone HFI 2200 ULE
Stax SRD4 with SR40 electrets
Stax SRD7 SB MKII with Lambda Normal Bias

The hum seems to only be coming from the headphone jack on the amp as i can't detect it through the energisers.

So far i've tried switch the amp back to normal running mode with the filters in place, moving the power cable and changing the power socket the amp is connected to.

This only started happening a few days ago as up until then the headphone socket was totally silent. I'm no expert but it sound like it could be from the mains (240v 50/60hz)

Any ideas or suggested items to check or changes to make would be much appreciated.

 

[Jolida302]

You can try to put a power plug adapter without ground (if it exists in USA) on each of your device, one after the other, and see if it suppress the hum.

 

[Oublie]

Quote:

Originally Posted by Jolida302 /img/forum/go_quote.gif You can try to put a power plug adapter without ground (if it exists in USA) on each of your device, one after the other, and see if it suppress the hum.

I'm in the UK so don't know if thats applicable here.

I'm going to try running the power amp seperately from the pre to see if it's still there. It's very strange that it has only just started happening when nothing in my setup has changed. Could it be a transformer issue?

 

[Jolida302]

That's strange indeed.
By without ground, i mean a simple bi polar plug, without the ground. If you can find such adapter, you can try to plug each device this way and see if it changes something.

 

[Oublie]

Quote:

Originally Posted by Jolida302 /img/forum/go_quote.gif That's strange indeed. By without ground, i mean a simple bi polar plug, without the ground. If you can find such adapter, you can try to plug each device this way and see if it changes something.

Thanks Jolida, I'll give that a try but would not grounding the amp not cause a problem?

 

[Jolida302]

Quote:

Originally Posted by Oublie /img/forum/go_quote.gif Thanks Jolida, I'll give that a try but would not grounding the amp not cause a problem?

In theory, it's more secure to have the ground, but at least you can try and maybe you'll find from which element the problem comes from. Ground issues may be quite complex.

 

[Oublie]

Thanks,

Ill try tonight

 

[Know Talent]

go to Equi=Tech's website and look at their technical paper library! They have a comprehensive discussion of ground loops and how to combat them based upon real circuit analysis vs. the plugging "magic" boxes in open outlets approach

 

[Uncle Erik]

It's probably not a ground loop. If it didn't happen before, then there's probably something giving you RFI.

Typical sources are fans, refrigerators, AC motors of any kind, dimmer switches, air conditioners, fluorescent lights, computers, and much more.

Are you running any of these near your rig? Have you moved anything around?

 

[Andrew_WOT]

Solutions:
- Lifting the ground with 3-prong to 2-prong adapter.
- Ebtech Hum-X
- Cutting the ground wire on USB cable
- This one interesting Sound On Sound Forum
some insulating tape around usb plug.

Personally I have only tried and use option one.

 

[selfdivider]

I agree with Uncle Erik... sounds like RF issue to me. You can get interference from your neighbors, too, if you live in an apartment...

 

[Oublie]

Quote:

Originally Posted by Uncle Erik /img/forum/go_quote.gif It's probably not a ground loop. If it didn't happen before, then there's probably something giving you RFI. Typical sources are fans, refrigerators, AC motors of any kind, dimmer switches, air conditioners, fluorescent lights, computers, and much more. Are you running any of these near your rig? Have you moved anything around?

Hi, nothing has changed and i do mean nothing everything is exactly as it was computer phones etc are all configured the same way, no new devices have been plugged in but saying that there is one thing.

I just installed a new electric cooker downstair in the kitchen. however, the cooker runs of its own 30amp fuse in the consumer unit (fuse box) so i don't know whether this is having an effect i'm going to try switching the cooker off at the mains and pulling the fuse on the consumer unit to see if it makes a difference. I doubt if it would but it really is the only new device in the whole house.

 

[Oublie]

Quote:

Originally Posted by Andrew_WOT /img/forum/go_quote.gif Solutions: - Lifting the ground with 3-prong to 2-prong adapter. - Ebtech Hum-X - Cutting the ground wire on USB cable - This one interesting Sound On Sound Forum some insulating tape around usb plug. Personally I have only tried and use option one.

Andrew,

I don't think its usb related as the noise is there is no direct usb connection to my rig just the usb sound card. When I plug the ultrasones into the sound card directly it's as quiet as the grave.

 

[Oublie]

One more thing to note guys is that the 3020b uses the power amp as the headphone source not the preamp (afaik) via a resistor to drop the wattage down to a level usable for phones. I don't know if its possible but could this be caused by a faulty headphone socket or resistor as i'm not getting any hum through my electrostatics which are connected to the speaker outputs on the back.

thanks.

 

[Andrew_WOT]

Quote:

Originally Posted by Oublie /img/forum/go_quote.gif Andrew, I don't think its usb related as the noise is there is no direct usb connection to my rig just the usb sound card. When I plug the ultrasones into the sound card directly it's as quiet as the grave.

Headphones do not have separate ground to the wall to close the loop, the amp does. But if you still have it w/o direct connection from USB card to amp, then it's not USB.