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I hear the radio on my SSL Xlogic channel

Discussion in 'Logic' started by tomtom, Mar 24, 2005.

  1. tomtom

    tomtom Guest

    Hi,

    I recently purchased a XLogic Channel.
    The other day, I crancked the pre up to record some soft voice over and started to hear the radio.

    I just rewired the lines between the studio and recording room with new cables, so it's been checked more than twice with a multimeter and a microphones, they are all fine. This is all connected and normalled to a Signex Isopatch. I have checked all the connections, they are OK.

    In my rack, there's an API lunchbox underneath the SSL channel and there's a Summit Audio Dual Tube Preamp above it.

    If I connect a microphone DIRECTLY on the back or the front input, I get a clean signal. No more radio.

    Using the same signal path, I switched the preamps. None of them picked the radio up. Strange...

    What is happening? Can somebody help? Thank you.

    Thomas
     
  2. therecordingart

    therecordingart Well-Known Member

    I have a cheap Fender amp that has radio chatter that came through, I took it to be fixed and was told it was a bad ground. Was he blowing smoke up my ass? I don't know, but it was only $20 to fix.
     
  3. JonLewis

    JonLewis Guest

    Yes, picking up radio stations is bad grounding. Without a proper ground the audio path acts as an antenna; it can be particularly worse if you are near a radio transmitter tower. Sounds like you narrowed it down to one particular unit causing the problem. Chances are there is a bad connection on a circuit board or power supply of the unit causing the problem. Take it to a reputable tech; he can find the problem and fix it. It should not cost you much to have it fixed (unless it is under warranty, then it won't cost you a thing). There are also other possibilities of a ground loop or contaminated ground in your system, but that would cause the same thing problem in other (or all) pieces of gear.
    Good luck,
    -Jon
     
  4. tomtom

    tomtom Guest

    thank you all for your help!

    Thomas
     
  5. dpd

    dpd Active Member

    Not always. Good grounding is absolutely essential around high RF fields, but unbalanced I/Os can cause problems, too. Use balanced I/Os as much as possible in these situations.
     
  6. JoeH

    JoeH Well-Known Member

    Your tech may not be able to reproduce it in the shop. It sounds like you have a unique situation in that it probably only happens in that specific location, with the gear wired up in that configuration.

    Balanced cabling is always the smartest way to go, but as others have mentioned, it could be a bad ground, or something odd in that circuit that acts up under those specific conditions. Sometimes it can be fixed with something as simple as ferrite beads on the legs of each of the XLR inputs, other times you'll need to get into the unit and do some detective work. Swapping parts and modules is the first way to begin tracking it down.

    If it continues to be bad enough, the $$ spent on a "house call" from your tech will be well worth it.

    Good luck with it. Hope it's at least an entertaining station for now. :shock:
     
  7. tomtom

    tomtom Guest

    Thank you all for your replies. I spent some time today at the studio, and I just found out that the problem arises when I switch in the Dynamics section of the channel. Otherwise, it is as clean as you would expect from SSL. The unit is still under guarantee, so I'll check with them.

    T.
     
  8. tomtom

    tomtom Guest

    Here is more I found out, just in case you could help furthermore.

    If I connect a microphone through the studio lines (60 feet long cable)
    through the patch to the SSL channel, I get the radio when the DYN IN switch is engaged.

    I any other case (microphone plugged in directly, or plugged into the patch to the SSL channel, nothing happens at all...

    Of course, my lines are all symetric and my patch is an isopatch, so there are no ground interconnection between signals...

    Do you think that my 60 feet multipairs cable could act as an antenna?
     
  9. dpd

    dpd Active Member

    It may be that the RF energy is getting into the console and only rectified back into audio when the dynamics section is switched in.

    Been a long time but you may be able to find some RFI filters you could plug into the front end of the console on the offending lines
     

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