Ahten Posted January 4, 2008 Share Posted January 4, 2008 I have a Canford Beltpack BP111 that has a whistle noise in the earpiece when plugged into the talkback system. The other beltpacks are fine and changing the headset makes no difference. Perchance does anyone have a schematic / pcb overlay and suggestions as to how to fix this particular pack? I do have access to a full electronics lab' and test gear. Many thanks Ahten Link to comment Share on other sites More sharing options...
Mr Steve Posted January 4, 2008 Share Posted January 4, 2008 We've had similar problems occasionally. Things we've checked are: 1) that the small screw which holds the XLR-4 headset connector in to the belt pack has not come out and is rattling round inside2) that the mic gain pot isn't super high on the belt pack Link to comment Share on other sites More sharing options...
Andrew C Posted January 4, 2008 Share Posted January 4, 2008 When you are testing, it is no good testing it in isolation. Without other BPs connected, they tend to be unstable and whistle. Faults are indeed likely to be in the headsets or associated circuitry. Link to comment Share on other sites More sharing options...
paulears Posted January 4, 2008 Share Posted January 4, 2008 2) that the mic gain pot isn't super high on the belt packEr.... there isn't a mic gain? Gain is preset and has a limiter built in - the little adjusterment 'hole' is for sidetone - it just sets the amount of your own mic you hear in your own cans - everyone else gets it full! If the audio line is floating - maybe a dry joint on the XLR (or Mr steve's idea above) then they do take off with a piercing shreek - that would be my first fault finding area. Link to comment Share on other sites More sharing options...
enbee Posted January 4, 2008 Share Posted January 4, 2008 Don't know if this is any help, but we have the same packs and they have done the same thing. We have found that they only do it if we have one of our 2 channel different brand packs in the system, and its usually the one after the 2 channel that whistles. If you only have the BP111 units then it may be our solution has just been a fluke in which case, let us know how you fix it!!!! Link to comment Share on other sites More sharing options...
dbuckley Posted January 4, 2008 Share Posted January 4, 2008 One common error is miswired XLR4s, if the earpiece return and the mic ground are swapped you get feedback. Link to comment Share on other sites More sharing options...
Mr Steve Posted January 4, 2008 Share Posted January 4, 2008 Er.... there isn't a mic gain? Gain is preset and has a limiter built in - the little adjusterment 'hole' is for sidetone - it just sets the amount of your own mic you hear in your own cans - everyone else gets it full!Ah, I didn't realise this. Good to know. Thanks! Link to comment Share on other sites More sharing options...
ryandell Posted January 4, 2008 Share Posted January 4, 2008 Hi, Just adding my 2p's worth, When we were setting up for a show a few months back we had the same trouble. In the end we tracked it down to be the interconnecting XLR cable. But thats just my previous Experience, strangely enough the Thomann sssnake XLR cables kept giving off the screeching and high gain type effect You've Porbably already tried changing the cable, Havent you ? Hope this Helps Ryan Link to comment Share on other sites More sharing options...
CARWYN Posted January 9, 2008 Share Posted January 9, 2008 hiCheck that the wires are not touching each other inside Link to comment Share on other sites More sharing options...
harrydir Posted January 9, 2008 Share Posted January 9, 2008 2) that the mic gain pot isn't super high on the belt packEr.... there isn't a mic gain? Gain is preset and has a limiter built in - the little adjusterment 'hole' is for sidetone - it just sets the amount of your own mic you hear in your own cans - everyone else gets it full! Had a similar whistling problem which was fixed by resoldering the output 3-pin XLR (even though the pack was at the end of a chain, so this shouldn't matter). Slightly OT but I have had a debate about the sidetone screw before with a soundie much older than me - and proved on the system we were using that those screws DID alter mic gain, even though all manuals and logic would say it didn't. I have no insight or opinions to suggest how or why, but we definitely have a set of about 10 beltpacks on which its gain not sidetone on every one, believe me we tested it all, and this might be the case for the OP too! Link to comment Share on other sites More sharing options...
dbuckley Posted January 9, 2008 Share Posted January 9, 2008 Perchance does anyone have a schematic / pcb overlay and suggestions as to how to fix this particular pack? Getting back to the OP's original question... Production Intercom have their beltpack schematics on their site, and I would be stunned if there were any significant differences between them. I also note that when I suggested checking the XLR4 wiring I have failed to notice that swapping headsets made no difference, so that was a dull suggestion... Link to comment Share on other sites More sharing options...
boatman Posted January 9, 2008 Share Posted January 9, 2008 Production Intercom have their beltpack schematics on their site, and I would be stunned if there were any significant differences between them. Unfortunately both the beltpack and power supply schematics were pulled from that website some months ago. However there are probably some BR members who have a clandestine copy. :) Link to comment Share on other sites More sharing options...
dbuckley Posted January 9, 2008 Share Posted January 9, 2008 How frustrating. I'm sure I've got a copy of them at home somewhere :) Link to comment Share on other sites More sharing options...
Ahten Posted January 10, 2008 Author Share Posted January 10, 2008 Folks I am pleased to report that the screeching problem has been fixed - turned out to be a broken ground wire on the headset connector which just might have been touching one of the other pins. Obvious once I had opened the box up.Many thanks for all the suggestions, I really appreciate all the help and trouble people have gone to to help me out. Ahten Link to comment Share on other sites More sharing options...
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