Dwayne, I agree that that is too much current for the typical electret. But, the headset has a SHS1890-15 (amplifier?) between the plug and the actual headset. Maybe that's where the current is needed? I think I'll take your advice and contact Plantronics before I blow up the customer's headset. Thanks, Carey On Thu, Dec 1, 2011 at 11:07 AM, Dwayne Reid wrote= : > 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 > since > >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 > what > >happens. > > Gosh - that's a really high current for an electret mic. That sounds > more like what a carbon mic wants to see. I wonder if they have an > electret-to-carbon interface in that headset. > > Just a thought - have you contacted Plantronics yet? I needed to > modify one particular model of their phones and they were extremely > helpful in sending schematic diagrams for that unit. I lucked out - > this was a phone that they had designed themselves as opposed to many > of the units that they sell that were designed and manufactured by a > third party - and that Plantronics has zero documentation for. > > It can take a while to work your way through to the right person - > Plantronics is a large organization spread over several > facilities. But the lady whom I first spoke with promised that she > would have the right person return my call - which happened a few days > later. > > For what its worth, I used to be a radio station broadcast technician > (they used to call us broadcast engineers but I know better these > days) back in the late '70s. Plantronics was one of the few > telco-type equipment suppliers that we trusted and their technical > support was second to none. I'm truly happy to say that they have > maintained that level of support. > > So: try giving them a call. > > dwayne > > -- > 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 > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 Carey Fisher Chief Technical Officer New Communications Solutions, LLC 678-999-3956 careyfisher@ncsradio.com --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .