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Old 30th March 2010, 07:20 PM   #1
kzsolt is offline kzsolt  Hungary
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Post RF filtering

On a line level input some RF noise can forward to PREamp. Nearly all of the manufacturer protect just the hot pin from this kind of signal. But the shield of line (connector) can work like antenna. For example if I plug the tuner at power off state to amp the the CD sound quality is go down. The problem is the same if I plug the LP player (with MC transformer) to amp.
Click the image to open in full size. The only reason is the RF interference go trough the shield of line input and make garbling in the internal signal of the amp.

So anybody know some magic box to filter RF signal from hot and shield point of RCA line connector?
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Old 30th March 2010, 08:38 PM   #2
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The shield should be connected to the enclosure, which should be metal. Open your amp and measure the resistance between signal ground and enclosure. It may have been 'lifted' to reduce earth loops, especially if the unit is designed to be plugged into an earthed mains power socket.
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Last edited by richie00boy; 30th March 2010 at 08:40 PM.
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Old 30th March 2010, 08:39 PM   #3
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Quote:
Originally Posted by richie00boy View Post
The shield should be connected to the enclosure, which should be metal.
And earthed.
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Old 31st March 2010, 06:02 PM   #4
kzsolt is offline kzsolt  Hungary
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"The shield should be connected to the enclosure"
This is littlebit complicated.
The shield of line input normally separated from enclosure. This "wire" go trough the internal panels and somewhere (maybe at power supply) connected to enclosure. This prevent doing a ground loop.
The situation is mouch complex if the apm has separated L and R and power ground. The solution is mainly depend from the manaufacturer. But nearly in any case the RF modulated grond wire go trough the all amp and spread garbling signal everywhere...

"And earthed"
And what if the AMP got just L and N?
Beleve me, the AC earh help not too mouch to give us from RF signals.
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Old 6th April 2010, 07:24 PM   #5
kzsolt is offline kzsolt  Hungary
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Wink Unexpected success

First time I start to study this problem I never expect this kind of big success.
  • The solution (compromise) is using ferrite rings. For normale cable with one loop for unflexible with X flow trough (always on high inpedance input side).
  • Additionally filter all of the AC power with O +LC-LC filter. There the all of the high current device (eg. TV or PWRAMP) has separated filter.
  • During the disc (CD,DVD,BR,Vinyl) play all antenna must be disconnected including sat and cable.
  • And for all connected equipment the AC L and N must be matched.
  • The audio system must be optically separated from video system (eg. the TV and the BB player audio must connected trough optical cable).
The result is clear picture at video and linearity low distortion and precise stage in any time at audio. This is very important because at day (especially because from 6PM to 9PM the RF and AC interfence is high and disturb any audio and video reproduction).

My only worry is the video distribution. I not found equipment to seprate player and TV trough optical isolation. But this is major important because the HF video signal from TV can disturb reading of any kind of discs...
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