KevinE Posted March 25, 2010 Share Posted March 25, 2010 Sometimes disconnecting the screen at one end will work, sometimes it can leave the connecting lead more susceptible to picking up interference from lighting dimmers or switching transients. It would be better in the long run to find out if you have a genuine hum loop then try to isolate that and leave the audio cable screen intact, since this is what should form the signal return rather than some mains earth loop. PS by 'isolating a hum loop' I do not mean snipping off mains earth connections anywhere! The audio transformer way is perhaps the best bet if you dont mind the cost. Link to comment Share on other sites More sharing options...
Jordan Posted March 25, 2010 Author Share Posted March 25, 2010 These audio transformers from Rapid Electronics work well. I put a pair of them into my amplifer to give it a balanced input. I would recommend putting them into the optional mu-metal can to avoid hum pick-up. David Thanks David, I think I'll give those a try at that price. I may need some advice on how to connect them up. A concurrent post has been automatically merged from this point on. Sometimes disconnecting the screen at one end will work, sometimes it can leave the connecting lead more susceptible to picking up interference from lighting dimmers or switching transients. It would be better in the long run to find out if you have a genuine hum loop then try to isolate that and leave the audio cable screen intact, since this is what should form the signal return rather than some mains earth loop. PS by 'isolating a hum loop' I do not mean snipping off mains earth connections anywhere! The audio transformer way is perhaps the best bet if you dont mind the cost. Cheers Kevin, I have been experimenting today with various configurations including disconecting the screen at one end but nothing was succesful. The quietest connection is still the TS jack - TS jack in the TRS socket on the apex so I will run with that untill I fit some transformers. Thanks again and thanks to everyone who has contributed sugestions. Link to comment Share on other sites More sharing options...
Sound Man Posted March 25, 2010 Share Posted March 25, 2010 The internal wiring of the amplifier can be altered to solve this hum issue but you would need to know what you were doing. David If you've got access to a test meter, without any leads connected to the BK amplifier, check if mains earth is connected to signal earth. If it is then this will be the cause of the hum issue. David Link to comment Share on other sites More sharing options...
Jordan Posted March 31, 2010 Author Share Posted March 31, 2010 The internal wiring of the amplifier can be altered to solve this hum issue but you would need to know what you were doing. David If you've got access to a test meter, without any leads connected to the BK amplifier, check if mains earth is connected to signal earth. If it is then this will be the cause of the hum issue. David I have taken the amp out of the rack and opened it up. There is continuity between mains earth and signal earth but I dont know what to do about this. The signal input cable runs from beneath the amp module circuit board to the TS jack socket on the back panel where it is connected core - tip, shield - sleeve. It is then parraleled to the XLR socket where it is connected core - pin2, shield - pin1. There is no connection to chassis/earth at these points so it must be elsewhere in the circuit. There are a couple of green/yellow cables running from the amp modules to the chassis where they are connected via a component that I dont recognise (choke maybe?). Link to comment Share on other sites More sharing options...
jamesperrett Posted March 31, 2010 Share Posted March 31, 2010 I've just noticed in a recent Highlights flyer that CPC are selling a passive unbalanced to balanced convertor for around 12 quid. The frequency response spec seemed impressive so they must be using a reasonable transformer. Using one of those would solve your problems. Unfortunately the CPC website search doesn't bring it up (as usual) so you will need to find the flyer or be very persistent with the website. Cheers James. Link to comment Share on other sites More sharing options...
Jordan Posted April 5, 2010 Author Share Posted April 5, 2010 These audio transformers from Rapid Electronics work well. I put a pair of them into my amplifer to give it a balanced input. I would recommend putting them into the optional mu-metal can to avoid hum pick-up. David Just been looking at the data sheet for these http://www.vigortronix.com/gallery/product...fication-49.pdf I am not exactly sure what I am looking at and could do with some advice about connecting them. Is this a dual channel device? I assume I would connect the balanced signal to the primary side and the amp input to the secondary side but what goes where? Link to comment Share on other sites More sharing options...
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