At 12:47 AM 12/1/2011, Carey Fisher wrote: > > Question: did you try swapping the polarity of the mic connections? > > > Yes, I tried swapping the plug around but it should work either way sin= ce >the plug is symmetrical and non-polarized. I think I have an issue with >the electret bias supply. The Plantronics data sheet seems to call for >5VDC thru a 265 ohm resistor whereas I'm using a 2.2k resistor that's >typical for many handheld comm mics. I'll change the resistor and see wha= t >happens. Gosh - that's a really high current for an electret mic. That sounds=20 more like what a carbon mic wants to see. I wonder if they have an=20 electret-to-carbon interface in that headset. Just a thought - have you contacted Plantronics yet? I needed to=20 modify one particular model of their phones and they were extremely=20 helpful in sending schematic diagrams for that unit. I lucked out -=20 this was a phone that they had designed themselves as opposed to many=20 of the units that they sell that were designed and manufactured by a=20 third party - and that Plantronics has zero documentation for. It can take a while to work your way through to the right person -=20 Plantronics is a large organization spread over several=20 facilities. But the lady whom I first spoke with promised that she=20 would have the right person return my call - which happened a few days late= r. For what its worth, I used to be a radio station broadcast technician=20 (they used to call us broadcast engineers but I know better these=20 days) back in the late '70s. Plantronics was one of the few=20 telco-type equipment suppliers that we trusted and their technical=20 support was second to none. I'm truly happy to say that they have=20 maintained that level of support. So: try giving them a call. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .