Very slight 60 Hz hum

[sassynapoleon]

As the title notes, I've got a very slight 60 Hz hum in both channels of my mainline. The hum seems to have a slight pulsing characteristic, with the pulses having a period of about 2 seconds. This hum is entirely independent of input selection and attenuator setting. I think the hum is slightly more pronounced in the high impedance position (which I normally don't use).

I'm using Focal Utopias under the low impedance setting. I've also tested using a pair of Sennheiser HD 650s on the high impedance setting and can hear the same hum. I think it's quieter on the 650s than on the Utopias.

As I said up front, this hum is very slight, to the extent I first thought it was background environmental noise (like a refrigerator). It's not particularly bothersome and is completely imperceptible with any signal input. I just figured I'd note it here to see if there's a known cause for this kind of hum.

 

[Doc B]

The pulsing aspect tends to point to outside interference as you suggest. You might try turning off other electronics and appliances one at a time to see if you can associate the noise with a specific piece of equipment that shares the power line.

 

[Paul Birkeland]

You can also try this mod:

https://forum.bottlehead.com/index.php?topic=11676.0

 

[amirhosein]

You can also try this mod:

https://forum.bottlehead.com/index.php?topic=11676.0

This might be placebo but the volume on my unit got much louder with this mod, also I think if feel way more alive with better separation. The base just has more energy specially!

 

[Paul Birkeland]

There should be absolutely no effect on volume level by doing that modification, but the process of doing the modification could disturb a solder joint that isn't all the way solid.