Radio Ghosts?

[cpl_crud]

Okay, I was a bit tired last night, and forgot to power down my monitors (M1 MkIIs) before I shut down my computer.

Just as the power supply of the computer shut off, there was about a second of voice through the monitors. That really creeped me out (we're talking aobut 0700 here after an all nighter), but I was dead tired so I just went ot bed.

I got up today and did a bit of experimenting. If I leave my montors on whilst hte copmuter shuts down, in that second after the power goes off, there's a blast of what appears to be a radio station. This happens with both of my soundcards (RMD Digi96 Pad8 and SB Audigy 2). This was a bit of relief because a) My monitors aren't haunted and b) I'm not going mad.

Has anyone else encountered something like this, or should I maybe consider revising conclusions a and b from teh previous paragraph?

 

[thegatekeeper]

try better cabling

 

[cpl_crud]

I don't think it's the cabling per se- it's klotz w/ neutrics...
Plus, when the computer's on (or off) there's practically zero self-noise.
It's only during that second where there's a surge of power (from the PSU turning off) that you get the noise.

My current thought is this- since the outputs of both the RME and the Audigy are unbalanced, the cable shield gets connected to the output. When the power goes off, there is a surge through the soundcard(s), which sends power down the cable (which would usually result in a pop).

However, since the unbalanced soundcard output then goes into a balanced cable to the monitor, this means that you're going to have 2 conductors on the cold side as opposed to the 1 condutor on the hot side. Whilst, normally, any RF would be either blocked by the shiled, or cancelled by the two conductors, this situation allows the sheild to act as an antenna, and the power surge from the sound card is then modualated, hence the radio noise instead of a pop.

Anyone else got any theories?

 

[karyoker]

If its the old type power supply with the absence of 60~ going into the rectifiers, the power lines are feeding rf into the power supply. The rectifiers are acting as detectors aand until the filters are discharged you have a crystal detector set. The remedy is put small pf caps to ground on the primary and across the filters.