dravenzouk Posted February 17, 2007 Share Posted February 17, 2007 -------------------------------------------------------------------------------- Up for discussion: the practice of jumping pin #1 to chassis ground - or not - in microphone/XLR cables. Different cable makers have different setups. Some put a little jumper lead from pin 1 to chassis ground and some do not. There is rarely any indication of how a particular cable is set up from the factory - you have to pull the connector apart to find out. Can't do that when buying sight unseen (internet) and lots of music stores freak if you start dismantling items on the shelf. Some users set up their cables with differently on each end - one end with the #1/chassis jump and the other without. As far as equipment/processors/gear goes, there are lots of wildly different schemes as far as where/when/how/if signal ground is connected to chassis ground. Many require major surgery to figure out which method a particular manufacturer used. So....on your cables, which do you prefer? Do you use different setups in different situations? What makes your decision? Do you have a particular make/model of cable that you prefer due to this? What factors are MOST important to you: RF interference/hum/shock hazard/connecting gear/cable length/etc.? aaaaaand......go. Link to comment Share on other sites More sharing options...
MarkPAman Posted February 17, 2007 Share Posted February 17, 2007 I can do no better than this: At the risk of opening a real can of worms... Connecting the cable screen to the shell of the connector is optional and the most common practice in professional audio community is not to earth the shells of XLR connectors. The reason is XLR shell can come easily in contact with metal railings or something else which is connected to earth elsewhere than your audio system. If your shells are not earthed, the connection is effectively isolated and nothing harmful will happen. However, if you have earthed the XLR connector shell to audio ground you can end up with a nasty earth loop and the resultant hum. Bob and add that use if snips will help if you come across any cables that have had the shell connected. Link to comment Share on other sites More sharing options...
mackerr Posted February 17, 2007 Share Posted February 17, 2007 As far as equipment/processors/gear goes, there are lots of wildly different schemes as far as where/when/how/if signal ground is connected to chassis ground. Many require major surgery to figure out which method a particular manufacturer used. So....on your cables, which do you prefer? Do you use different setups in different situations? What makes your decision? Do you have a particular make/model of cable that you prefer due to this? What factors are MOST important to you: RF interference/hum/shock hazard/connecting gear/cable length/etc.?To get a pretty definitive answer to this, drop a line to Tony Waldron at Cadac. Not only is he extremely well versed in the subject, he is also happy to explain the issues in order to educate potential client. Mac Link to comment Share on other sites More sharing options...
Bobbsy Posted February 17, 2007 Share Posted February 17, 2007 Just to be clear: in the quote from me up above, I was posting in a thread asking if Pin 1 should be connected to the shell of an XLR connector. My reply was referring to that only. Connecting Pin 1 to a chassis ground on a piece of equipment is both necessary and important to be done in the proper manner. The correct way to terminate pin-1 of XLR connectors is to bond it to the chassis immediately at the entry and exit points. It should not be connected to circuit signal ground. Equipment with pin-1 left open, or connected to circuit signal ground is said to suffer from a "pin-1 problem." As has been mentioned, Tony Waldron at Cadac is both an expert in this question and also a bit of an evangelist trying to get all professional gear wired properly. Alternatively, the first mention of the "Pin 1 problem" was in a paper by Neil Muncey (a Canadian electro acoustic system consultant) and a Google on "Pin 1 Problem" and "Muncey" will yield a multitude of results. Two particularly good ones are the papers by Jim Brown which should turn up near the top of your Google results. Bob Link to comment Share on other sites More sharing options...
J Pearce Posted February 18, 2007 Share Posted February 18, 2007 Much in agreement with everyone else, I prefer the shells to remain floating. There are some small arguments for grounding the shells, such as the shells mating before the pins will cancel any static between the lines, and grounding the shell creates a screen around the connector, thus continuing the screen provided by the braided screen in the cable. It would be interesting to hear Tony's opinion, I would ask him, but I don't see him much now, as I've moved away. Link to comment Share on other sites More sharing options...
jamesperrett Posted February 19, 2007 Share Posted February 19, 2007 Alternatively, the first mention of the "Pin 1 problem" was in a paper by Neil Muncey (a Canadian electro acoustic system consultant) and a Google on "Pin 1 Problem" and "Muncey" will yield a multitude of results. Two particularly good ones are the papers by Jim Brown which should turn up near the top of your Google results. I believe that Neil Muncy's recommendations have now been enshrined in an AES standard (but don't ask me the number). Cheers James. Link to comment Share on other sites More sharing options...
TeeJay Posted February 19, 2007 Share Posted February 19, 2007 Alternatively, the first mention of the "Pin 1 problem" was in a paper by Neil Muncey (a Canadian electro acoustic system consultant) and a Google on "Pin 1 Problem" and "Muncey" will yield a multitude of results. Two particularly good ones are the papers by Jim Brown which should turn up near the top of your Google results. I believe that Neil Muncy's recommendations have now been enshrined in an AES standard (but don't ask me the number). Cheers James. That would be AES48 This is something that's just been mentioned on the Theatre-Sound Mailing List also.A Wiki on the Pin 1 problem (including links to the papers by Jim Brown) is hereIt also includes a database on equipment and whether it mets the AES standard. Or at elast the beginnings of a database. I suspect more submissions would be welcomed. Link to comment Share on other sites More sharing options...
TallMike Posted February 19, 2007 Share Posted February 19, 2007 My $0.02 would be that floating shells seem to cause no problems. Link to comment Share on other sites More sharing options...
Bobbsy Posted February 19, 2007 Share Posted February 19, 2007 Just for reference, the "Pin 1 Problem", (i.e. connecting the from Pin 1 on an XLR to the chassis ground of equipment such as a mixer) is a rather different issue to whether or not you should bond the screen in a cable to the shell of the connector. As per the way I was quoted above, I believe in leaving the connector shell floating, but certainly advocate a proper chassis ground connection as per the various papers linked to...not that I ever expect to be involved in that level of equipment design! Bob Link to comment Share on other sites More sharing options...
TallMike Posted February 19, 2007 Share Posted February 19, 2007 Just for reference, the "Pin 1 Problem", (i.e. connecting the from Pin 1 on an XLR to the chassis ground of equipment such as a mixer) is a rather different issue to whether or not you should bond the screen in a cable to the shell of the connector. As per the way I was quoted above, I believe in leaving the connector shell floating, but certainly advocate a proper chassis ground connection as per the various papers linked to...not that I ever expect to be involved in that level of equipment design! Bob I understand what you mean, Bob Do you think that the solution to connecting the ground safely/properly should be as simple as a male/female XLR with a 'tail' that connects to the chassis ground of your favourite bit of kit? Doesn't sound like a tricky solution if it's required... Link to comment Share on other sites More sharing options...
Bobbsy Posted February 20, 2007 Share Posted February 20, 2007 Do you think that the solution to connecting the ground safely/properly should be as simple as a male/female XLR with a 'tail' that connects to the chassis ground of your favourite bit of kit? Doesn't sound like a tricky solution if it's required... If only was as simple as that! The trouble is, the "tail" you propose is often long enough to have significant inductive reactance at VHF, creating potentially big RF interference problems. From an RF point of view, the ideal solution would be to bond the cable screen to the XLR shell but, for the reasons mentioned above, the gains in the RF realm are more than balanced by the detrimental effects this can have on audio performance. For this reason, the solutions to the pin 1 problem proposed in AES48 (by the way, thanks TeeJay for digging out that reference) have to delve a bit more deeply into the design of the equipment. The AES48 link TeeJay posted is a worthwhile read, but I'd also repeat my recommendation of the paper by Jim Brown on the same topic. Part 1 is available HERE. Part 2 of the paper is HERE. Bob Link to comment Share on other sites More sharing options...
TeeJay Posted February 20, 2007 Share Posted February 20, 2007 Just for further reference - The link to the actual standard is here This is the direct link to a courtesy downloadable pdf. Or you can go to the AES standards page here, search for aes48 and pay for a hard copy to be sent BTW, I'm serious about adding more submissions to the database on the AES48 wiki. Admission time, I did help to set this up, though others did more of the nuts and bolts than I. Just contact the manufacturers on any pieces of your sound kit and ask them to explain how they are compliant with the standard. Then either submit the answer to the wiki, or you can PM me with the reply and I'll get it added. I've tended to have better results using actual product numbers rather than just asking about product ranges. As can be seen from the manufacturers statements in the database, some of the answers are wooly at best while some are very detailed (Rane currently have the best statement on there). The more that end users ask the makers about these sort of questions, the better quality products we should be receiving for our cash (leastwise, thats the theory!) Link to comment Share on other sites More sharing options...
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