Setup is as follows
Computer is an AM3 Gigabyte 785GMT-UD2H ( low emi ) with onboard audio ALC889A chipset. No front panel audio hooked up at all. Plugged into powerbar. Seetings in Ubuntu 9.10 audio options are set at ANALOG STEREO DUPLEX. ( should it be just ANALOG STEREO?? )
Computer powersupply is a passive FSP ZEN 400.
No wireless phones or routers except maybe somehwere else in the apartment building. None above me she is about 90 years old lol.
Audio out on motherboard has a 3.5mm splitter running to Audioengine A2 speakers ( self powered plugged into same powerbar ).The A2's have a small run of 14 gauge speaker wire connecting them to each other.
Other half of splitter has a 3.5mm adapter with unshielded elcheapo run-of-the-mill rca's on other end to a 1959-61 Heathkit AA-151 tube amp' AUX input terminals. No leaky or bulged caps- all appear in above average shape. Mint insides with brand new matched quad of el84 jj tubes. Has a pre and amp for each channel in it.
This amp is plugged into a different wall outlet but on same fused zone of room wiring, uses a 2 prong powercord end.
The tube amp is a dedicated headphone amp with nothing else hooked to it. Speaker terminals set to 8 ohm out of the 4,8, and 16 ohm options ( no headphone jack on the tube amp ) run about 20 feet of 14 gauge speaker wires to a custom headphone jack with LEFT and RIGHT positive wires having a 100 ohm metal oxide resistor on each. Also from same speaker outs runs about 20 feet of 14 gauge speaker wires to a Stax transformer box ( plugged into same wall outlet the powerbar is ) for SR5's and/or AT-705 electret box.
What happens is that from time to time there is a very faint radio station coming through my A2's when they are on with no music playing. Rarely.
When the tube amp is on there is a small hum equally in both channels of ( with the headphones easier to notice )
When I stop playing music the hum is still small, but then all of a sudden kicks up a fair bit I think after the audio player stops for a few seconds.
I had thought it was a ground loop so picked up a relatively cheap
inline rca groundloop isolator adapter.
When that is hooked up, I get the same local radio station except at
audible levels! and the hum is a fair bit louder as well. So that's going back to the store.
There is no hum when I just use the A2's by themselves with the tube amp off.
One thing in particular is that my cpu heatsink is massive and external to the case. Passive. Pictures here.
http://www.head-fi.org/forum/thread/397869/pictures-of-your-computer-rigs-post-them-here/4125#post_7503438
I did make a temporary stainless cage for it temporarily in case that was acting like an antenna but no difference.
I will switch the audio setting to simple Analogue Stereo, try a different extension cord to a separate wall outlet area, and try these new expensive shielded rca cables to the amp.
Other than that , I may need a recap in the transformer/power areas of the amp, swap all the speaker wire to shielded ( **** that sounds expensive )
Also going to try and rearrange wiring to avoid crossing power cables with speaker wires etc. That should be fun
Open to cable ideas, using digital out to a DAC etc.
Is that enough information? I feel like I am droning on.
