Lamplighter Posted February 17, 2019 Share Posted February 17, 2019 I'm currently in a venue where the hearing loop sounds really awful. Lots of hum, audio distorted and strange noises. Initial investigation , unplug inputs all is quiet. Check input feed with battery amplifier, clean. I'm not used to loop systems so my diagnosis may be way off track, either a faulty loop or a failed amplifier. I think that the two most likely failure modes for a loop are short circuited turns or an earth contact. I feel that the strength and evenness of the field rule out an open circuit and make the possibility of a shorted turn unlikely. A stray earth is a possibility and I will be looking at that tomorrow with a megger. If the loop meters out then I will try the amplifier "on the bench" What would be a suitable load to simulate a loop? Any practical advice would be welcome and should I be looking at anything else.Brian Link to comment Share on other sites More sharing options...
sandall Posted February 17, 2019 Share Posted February 17, 2019 What would be a suitable load to simulate a loop? Most decent loop amps can cope with down to < 0.2R, so a few yards of bell-wire, or a load of WW resistors in parallel should work. A 100W light-bulb would also probably work, but I haven't tried it. Link to comment Share on other sites More sharing options...
Simon Lewis Posted February 18, 2019 Share Posted February 18, 2019 I'd check that the gain and compression haven't been turned up to 11... or that the sending device isn't overloading the input. Also, if there's a monitor point, check that the signal is clean there. You've got a good handle on loop cable faults - check it's not open circuit or grounded... problems such as cable crushing or insulation melted against hot water pipes is not unusual... Link to comment Share on other sites More sharing options...
ninjadingle Posted February 18, 2019 Share Posted February 18, 2019 Is it a perimeter loop or phased array? For a perimeter loop - any other cables recently been run in running alongside the loop? Phased array - any floor works been carried out recently such as seating replacements? How are you testing it? As you're local if you'd like someone wearing a real set of hearing aids to have a listen then shout (loudly!), I don't mind coming down to have a listen. Link to comment Share on other sites More sharing options...
Lamplighter Posted February 18, 2019 Author Share Posted February 18, 2019 Thanks for your replies. I am using my own hearing aids so hopefully getting an accurate picture or the loop performance. It is a single loop though I am a little wary of the feed cable which at first sight seems not to be twisted pair. I am planning to try tracing the feeder and find the feed point so that I can see the number of turns. The Input level is well within the amp spec and adjusting the input gain doesn't improve the quality. I haven't touched the master preset/ compression adjustment as the signal indicators look about right. I would come back to this after metering the loop. The other possibility that I was gong to investigate is the possible pickup of the loop/feeder by the input lead. Investigation time is limited as I am Into show week with other more pressing duties. I hope to find a bit of time tonight.Brian Link to comment Share on other sites More sharing options...
Lamplighter Posted February 18, 2019 Author Share Posted February 18, 2019 To wrap this up the loop metered out ok, but on close examination the dip switches on the line input channel had been flipped to mic and phantom power. I had previously checked for dc on the input and not found anything so possibly there is a fault with that supply. Restoring the dip switches produced a nice working system. Again thanks for your comments.Brian Link to comment Share on other sites More sharing options...
Simon Lewis Posted February 18, 2019 Share Posted February 18, 2019 Thanks for reporting back.... useful to file away as another thing to check when the customer says, "we've not touched anything - but now it doesn't work..." ;-) Link to comment Share on other sites More sharing options...
Lamplighter Posted February 18, 2019 Author Share Posted February 18, 2019 Or I've been feeding the mixer into that channel and it just worked, New non tech management! Link to comment Share on other sites More sharing options...
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