icyberct Posted June 27, 2012 Share Posted June 27, 2012 I volunteer at a local church as the technical director, and recently I set out to eliminate some noisy static and ground loop noise from our sound system. I eventually discovered that the issue was the XLR cables that were used to hook the various devices together (I am convinced that the company that set it up had no idea what they were doing). Unfortunately, ever since then we have had an issue with our speakers popping fairly loudly every minute or so. If I turn the system on and let it sit there, it will pop for 15 minutes or more and then stop, but if I run sound through the system the popping seems to go away quickly. The harder I run it, the less it pops, and after a while it will quit popping all together. It is almost as though we have to warm up the system before we can use it. I thought that perhaps we were still having grounding issues, but even if I disconnect all inputs from the amp it continues to pop. I have noticed that the signal light on the right channel of the amp is lit even when there is no sound going through the system, and eventually the light will go away and the popping is no longer audible. I am hoping that someone will have run across this problem or will have some suggestions as to what it could be. I have already spent way too many hours trying to solve the problem and have just ended up frustrated. Thanks ahead of time for any help! Link to comment Share on other sites More sharing options...
DrV Posted June 27, 2012 Share Posted June 27, 2012 Specifically "popping" rather than just noise, I associate with an electrolytic which has leaked electrolyte onto the PCB. Have a look for some oily-looking deposit on the input PCB maybe in the area of U101/U201 which are the 33079 chips just behind the input XLRs. You might also try careful application of freezer spray in that area or gentle and precise prodding with a plastic knitting needle. Could also be something as simple as a dirty connector which you may be able to cure by simply removing and replacing it a few times with a squirt of switch cleaner. However, as it is affecting both the signal path and the sig present light it must be very near the input. If it goes up and down with the gain control then there is only U101/U201 and the passives around them. Dave Link to comment Share on other sites More sharing options...
laolu Posted June 28, 2012 Share Posted June 28, 2012 I just thought it could also be an issue of an oscillating input section, since it had somehow to do with the inappropriate wiring, which may have had just enough capacitance to prevent swinging… :wacko: Link to comment Share on other sites More sharing options...
icyberct Posted June 28, 2012 Author Share Posted June 28, 2012 I went to the building today and opened up the amp. Checked the inputs like you suggested, Dave, and I didn't find a single problem with the board. Everything looked in pristine condition. I reassembled the unit and when I put it back in the rack, it no longer was causing any popping and the signal light was off as well. I ran it through its paces and everything seemed to work just fine. How strange... I'm going to see what happens over the next few weeks. Hopefully the problem will not return. I did think of something today. We have a Community SC21.1 system controller right before the amp in the signal chain. There is a wire going from the channel 2 output on the amp to the input on the system controller. I am starting to wonder if that could be the cause of the problem, although it would seem strange being as it is coming from the output. Thanks again for everyone's help! Link to comment Share on other sites More sharing options...
TimmyP1955 Posted July 1, 2012 Share Posted July 1, 2012 Unless the processor input has a sense circuit for limiting purposes (which I've heard of only on Nexo units), I can't imagine why the amp output is feeding it. My guess is that this connection should be removed. Link to comment Share on other sites More sharing options...
icyberct Posted July 1, 2012 Author Share Posted July 1, 2012 Unless the processor input has a sense circuit for limiting purposes (which I've heard of only on Nexo units), I can't imagine why the amp output is feeding it. My guess is that this connection should be removed. As far as I know, that is the purpose for the extra connection. Granted, I don't really like how it works, but I am a little hesitant to completely remove the system controller from the signal chain. I guess I should do some tests to see how often it limits the system (if ever). Link to comment Share on other sites More sharing options...
timsabre Posted July 2, 2012 Share Posted July 2, 2012 Unless the processor input has a sense circuit for limiting purposes (which I've heard of only on Nexo units), I can't imagine why the amp output is feeding it. My guess is that this connection should be removed. Most good system controllers have a sense input from the amp output - it's so they can detect problems such as clipping or asymmetry on the amp output and prevent speaker damage. Do not remove it. Link to comment Share on other sites More sharing options...
TimmyP1955 Posted July 9, 2012 Share Posted July 9, 2012 Most good system controllers have a sense input from the amp output - it's so they can detect problems such as clipping or asymmetry on the amp output and prevent speaker damage. Do not remove it. Please give examples. Nexo are the only ones I've seen. Link to comment Share on other sites More sharing options...
dbuckley Posted July 9, 2012 Share Posted July 9, 2012 Celestion SRC1 Meyer MA-1 Edited to add - though in both those cases I think its just to detect power input to the loudspeaker, so as to prevent thermal damage. Link to comment Share on other sites More sharing options...
mackerr Posted July 9, 2012 Share Posted July 9, 2012 Celestion SRC1 Meyer MA-1 Edited to add - though in both those cases I think its just to detect power input to the loudspeaker, so as to prevent thermal damage. I'm not familiar with the Celestion, but the Meyer M series, and the similar Apogee P series have been out of production so long many here may not even know what they are. It is certainly not the case that most system controllers have sense lines. Mac Link to comment Share on other sites More sharing options...
dbuckley Posted July 9, 2012 Share Posted July 9, 2012 I'd have though that there were enough passive UPA-1s out there that there would still be rackloads of M-1A (got the name right this time!) processors doing service every day. Link to comment Share on other sites More sharing options...
timsabre Posted July 9, 2012 Share Posted July 9, 2012 I'm not familiar with the Celestion, but the Meyer M series, and the similar Apogee P series have been out of production so long many here may not even know what they are. It is certainly not the case that most system controllers have sense lines. I'm sorry, I may be out of date then. When I used to run a hire co a few years ago we had GAE and L-Acoustics systems which both had system controllers with feedback from the amp outputs. It's surprising if they have stopped designing them that way as it's a good way of protecting the speakers. Anyway the point stands that if you have an installed system controller which does have amp feedback, you shouldn't remove it. Link to comment Share on other sites More sharing options...
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