Help! I need a scientist!

[PointyFox]

No AC. Even with the cable straight it still picks up a hum. Coiling it just magnifies it.

 

[Raketen]

Sounds like you are maybe describing mains hum, perhaps because the nature of electrostatic headphones they are sensitive to this? (Retaining charge after being unplugged? Similar to when you touch the jack of an active speaker and it hums).

Although the touching the amp thing is a bit confusing. I read somewhere that our bodies can act almost like antennae- possibly in touching the amp you are grounding/coupling yourself somehow and reducing the hum- maybe there is a dirty/resistive connection on one of the headphone plug's pins?

Just a wild guess though- could be just some more typical ground loop/amp electronics issue like others suggested.

 

[PointyFox]

Maybe my body AND my desk are acting as antennae? Not sure why the hum would go away if I touch the amp while it's plugged in. It works in reverse if the headphones are unplugged. I touch the amp and it increases the hum in the unplugged headphones.

 

[Raketen]

Maybe my body AND my desk are acting as antennae? Not sure why the hum would go away if I touch the amp while it's plugged in. It works in reverse if the headphones are unplugged. I touch the amp and it increases the hum in the unplugged headphones.

In this scenario you might be increasing the size of the antenna. Like when you loop the cable around you're just creating an inductive coil.

I wonder if there's a safe way to ensure the headphones are fully discharged- like if you could short the headphone cable's pins together when it's unplugged & see if it then still produces the hum when you hold it near the amp- but I don't know how these headphones work, not sure if it is ok to spontaneously discharge whatever residual charge they hold like that.

 

[PointyFox]

In this scenario you might be increasing the size of the antenna. Like when you loop the cable around you're just creating an inductive coil.

I wonder if there's a safe way to ensure the headphones are fully discharged- like if you could short the headphone cable's pins together when it's unplugged & see if it then still produces the hum when you hold it near the amp- but I don't know how these headphones work, not sure if it is ok to spontaneously discharge whatever residual charge they hold like that.

No hum when discharged, but I wouldn't expect there to be since they won't be able to make noise without having a high charge.

 

[ADUHF]

Is the amp on the same desk that you are putting the headphones on when this occurs?

 

[bigshot]

I don't have time to read all this. It is either a ground loop and it goes away when you run off batteries (which means you need to ground better) or it's RF interference and it happens in one location, but not others (which is more difficult to deal with if you are in the shadow of a high power AM radio tower).

 

[PointyFox]

I don't have time to read all this. It is either a ground loop and it goes away when you run off batteries (which means you need to ground better) or it's RF interference and it happens in one location, but not others (which is more difficult to deal with if you are in the shadow of a high power AM radio tower).

Would a ground loop cause a wooden desk to cause hum in a headphone that isn't plugged into anything?

 

[bigshot]

Nope. That would be RF interference. A wooden desk doesn't conduct, and you shouldn't get any ground loop when running on battery power. There's something nearby that is causing problems. I tracked one of mine down after a year. My TV set wouldn't receive channels 7 through 9 sometimes. Other times it was crystal clear. Then I turned off my smart lights when it was struggling to bring in a station and poof! Perfect sound and picture. I tracked it down to a single bulb. Try turning off and unplugging anything within 6 feet and see if you can find something in your room that is causing it.

 

[PointyFox]

Nope. That would be RF interference. A wooden desk doesn't conduct, and you shouldn't get any ground loop when running on battery power. There's something nearby that is causing problems. I tracked one of mine down after a year. My TV set wouldn't receive channels 7 through 9 sometimes. Other times it was crystal clear. Then I turned off my smart lights when it was struggling to bring in a station and poof! Perfect sound and picture. I tracked it down to a single bulb. Try turning off and unplugging anything within 6 feet and see if you can find something in your room that is causing it.

I just tried 5 different locations and the hum is the same in all of them. It must be coming from the amp itself. The amp is designed to not have a ground wire. It's interesting that RF would be conducted along the surfaces of my desk.

 

[bigshot]

Try in a different place. Another part of town. You may have a power transformer somewhere near your house. RF is not conducted by wood.

 

[PointyFox]

Try in a different place. Another part of town. You may have a power transformer somewhere near your house. RF is not conducted by wood.

Well, laminated wood. If I touch my headphone cable to any part of the desk including things that are sitting on the desk, the headphones hum.

 

[bigshot]

Is it a wooden desk or a metal desk? Take it to a friend's house and try it. That will tell you if the problem is your equipment or if it is your environment.

 

[PointyFox]

Is it a wooden desk or a metal desk?

It's MDF with some sort of plastic coating. It's not very conductive.

 

[bigshot]

Let me know the result of your test at another location. I can't offer anything more until that.