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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Follow up Q posted by RioTubes on May 8, 2007 at 19:06:27:
Your power amps contain enough reserve charge in the filter caps to keep them on for a few seconds after the AC is switched off.If your source's output stage goes off more quickly than the amps, and loses control of the cables, then you hear the noise present in your cables and source acting as a passive antenna. This includes the AC wiring connected to the source.
If this only became apparent when you had dedicated lines installed to a plastic box, then something about the dedicated lines is improving their ability to pick up a radio station.
Does your old AC circuit use steel boxes? These are bad for sound, but do provide some shielding against radio waves.
To identify where the radio station is getting in to your system, listen to your amps with your source switched off but not unplugged. If you hear the radio station, then mute the amps and unplug the AC from the source component. Listen again to just the amps. If you still hear the station (but perhaps weaker) mute the amps and unplug the interconnect cables from the source. Listen to the amps again. If this causes lots of hum, obtain some cheap RCA jacks and solder 100-ohm or so resistors to them. Plug the input ends of the interconnect cables into these jacks and listen to the amps. Next, remove the interconnect cables from the amps and listen (always mute the amps or turn them off when changing anything about the input connections).
One of these changes will cause the radio station to disappear, or not. If not, then the amps are getting the radio signal directly through their power cords.
What you have here is a case of true Radio Frequency Interference (RFI). It is more serious than the typical RF noise, where there is no sound from the audio system in the absence of an audio signal, but it will have similar bad effects on your audio system's performance. If the radio station signal is getting into your dedicated AC lines, then the choices are to install shielding around the wires and outlet box (expensive) or filters on the AC for your equipment. Most of the filter techniques discussed on this forum will be helpful, and can be built for not much money.
If you can identify the radio station, try calling their engineering staff and asking for help. They may be able to specify a trap for their carrier frequency.
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Follow Ups
- Let me hazard a guess: - Al Sekela 10:50:30 05/09/07 (1)
- Thanks Al - RioTubes 16:31:46 05/09/07 (0)
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