Members PrActical_AV Posted June 16, 2007 Members Share Posted June 16, 2007 I was running sound the other day and had a bad buzz coming through the system. A guy came up to me and told me that the reason why I was getting the buzzing was that it was coming through a video camera that I was feeding a balanced signal to. I told him that it wasn't the case because I was giving the camera an isolated feed from the board. His response was, "is it passing ground? Because if it is, it's not isolated." Well, I already knew what was causing the buzz (bad eq unit in signal chain), but I told him I was using an isolated transformer and I didn't need to lift a ground (plus, the camera was running of of a battery). But was he right in the sence that if I didn't lift the ground, the signal isn't truly isolated? Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 16, 2007 Members Share Posted June 16, 2007 You must still use a ground lift IF the camera is connected to anything else in the outside worls. The video cable also carries a ground so if it was connected to a switcher or a projector, you have a second ground path. What kind of transformer did you use? Link to comment Share on other sites More sharing options...
Members PrActical_AV Posted June 16, 2007 Author Members Share Posted June 16, 2007 I was using a Whirlwind IMP 1x2 splitter. The camera was not connected to anything else and just ran off a high quality battery (Anton Bauer) to record. Link to comment Share on other sites More sharing options...
Members Gregidon Posted June 16, 2007 Members Share Posted June 16, 2007 Of course the easiest way to prove it wasn't the camera causing the buzzing would be to disconnect the camera. Just a thought. Link to comment Share on other sites More sharing options...
Members PrActical_AV Posted June 16, 2007 Author Members Share Posted June 16, 2007 Of course the easiest way to prove it wasn't the camera causing the buzzing would be to disconnect the camera. Just a thought. That would have probably worked too, but disconnecting the EQ out of the signal chain solved the problem and I wasn't too interested in proving him wrong - just solving the problem and learning for future reference. Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 17, 2007 Members Share Posted June 17, 2007 By any chance were you sending the direct out on the splitter to the camera? I am not absolutely positive about this model, but often one output of the splitter is NOT transformer isolate to allow phantom power to pass. It is also not ground lifted. The second output is. This would explain the problem. There are special 2 secondary winding splitter transformers but they are not as common. Link to comment Share on other sites More sharing options...
Members PrActical_AV Posted June 17, 2007 Author Members Share Posted June 17, 2007 Just to clarify, the camera was not the problem causing the buzz...it was a bad dbx 231 EQ that I picked up off of ebay - didn't realize how bad it was until that day. I was hoping to use the eq to reduce any feeback because the limited space on stage; I knew the person with the mic was probably going to be really close to the FOH speakers. The Whirlwind IMP Splitter 1x2 has two outputs, one is able to pass phantom power like mentioned and the other output is transformer isolated. The transformer isolated output went to the camera. Reading up on the Whirlwind IMP Splitter, it mentions that the transformer allows for AC signal to pass, but prevents DC from passing. It also has a switch for lifting the ground (which did not need to be engaged). Link to comment Share on other sites More sharing options...
Members JohnnyGraphic Posted June 17, 2007 Members Share Posted June 17, 2007 O.K. So, I was letting this idea tumble around in my little brain for a while. If I used an Aux output (impedance balanced) to a 1/4" out to a 1/8" to my camcorder, would this be acceptable? As it's already balanced, I should be o.k. right? If I understand the posts below, as long as it's running off of it's own battery power, I should be hum free right, since it's only connection is to the board. Oh, I was going to use one of the Audio Technica ATM hanging mic things near the board to capture the sound. Another alternative is to use my AT 3035 condenser. Any thoughts? Thanks! Johnny Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted June 17, 2007 CMS Author Share Posted June 17, 2007 O.K. So, I was letting this idea tumble around in my little brain for a while. If I used an Aux output (impedance balanced) to a 1/4" out to a 1/8" to my camcorder, would this be acceptable? As it's already balanced, I should be o.k. right?If I understand the posts below, as long as it's running off of it's own battery power, I should be hum free right, since it's only connection is to the board.Oh, I was going to use one of the Audio Technica ATM hanging mic things near the board to capture the sound. Another alternative is to use my AT 3035 condenser. Any thoughts?Thanks!Johnny As long as there's only one path to the power mains ground, there should be no hum caused by ground loops. If the camera needed to be connected to AC power for some reason, and/or if it needed to send a feed to a video board, then there would be two or more different AC power connections and trouble could start. In that case, by isolating the signals with transformers and by lifting one end of the ground for each interconnection, you can minimize or eliminate ground loop hums. Link to comment Share on other sites More sharing options...
Members JohnnyGraphic Posted June 17, 2007 Members Share Posted June 17, 2007 As long as there's only one path to the power mains ground, there should be no hum caused by ground loops. If the camera needed to be connected to AC power for some reason, and/or if it needed to send a feed to a video board, then there would be two or more different AC power connections and trouble could start. In that case, by isolating the signals with transformers and by lifting one end of the ground for each interconnection, you can minimize or eliminate ground loop hums. Thanks! Appreciate the info! Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 18, 2007 Members Share Posted June 18, 2007 The 1/8" input is balanced? Beware of DC bias for some condenser mics being present on some camcorder inputs. I always use an isolation transformer as sometimes these "special" features are not described. No need to cause problems with your own stuff. Link to comment Share on other sites More sharing options...
Members JohnnyGraphic Posted June 18, 2007 Members Share Posted June 18, 2007 The 1/8" input is balanced?Beware of DC bias for some condenser mics being present on some camcorder inputs. I always use an isolation transformer as sometimes these "special" features are not described. No need to cause problems with your own stuff. I wasn't really thinking about the actual 1/8" input, but was thinking more of the output from the mixer. So, I guess it isn't. O.K. Back to square one! And your 2nd paragraph I don't understand. So, how does this affect me if I'm running my aux output to my camcorder. I'm not running my condenser mic straight into it. Thanks for your patience! Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 18, 2007 Members Share Posted June 18, 2007 Because SOME camcorders are equipped to deal with unbalanced condenser mics onboard and there's a small DC bias voltage present that could cause problems with other equipment you hook up to that input... like the output of a mixer or even a dynamic mic that is connected using an adapter. Link to comment Share on other sites More sharing options...
Members JohnnyGraphic Posted June 19, 2007 Members Share Posted June 19, 2007 So this problem would manifest itself as hum or buzz in the PA system? Or a really nasty sounding recording on the camcorder? Both? Warts? Thanks again! Johnny Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 19, 2007 Members Share Posted June 19, 2007 Possibly hum and buzz, possibly distortion, could be only on the camcorder but depending on how the signal is sourced it's also possible to cause problems with the live sound via the mixer interconnection. Link to comment Share on other sites More sharing options...
Members JohnnyGraphic Posted June 19, 2007 Members Share Posted June 19, 2007 Just when I thought I had an easy way to get a good sounding recording on my camcorder, it turns out a lot more complicated than I was hoping! Thanks again for the insight! Johnny Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 19, 2007 Members Share Posted June 19, 2007 Then there's the issue of what level the camcorder wants to see. Is there a mic line switch available (either a hard switch or a software switch on the camcorder? Link to comment Share on other sites More sharing options...
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