At 09:38 AM 9/18/2012, V G wrote: >Currently, lecturers use a radio microphone link that transmits audio from >a small microphone and transmitter attached to their body to the podium, >where the audio is received (I assume via a standard 3.5mm jack) and sent >to the speaker system for amplification. This is something that I know a fair amount about. Most professional Wireless Mics have receivers with 3-pin XLR=20 connectors for the audio out. This normally at a 'hot' mic level -=20 somewhere between -40dBu to -30dBu. Semi-pro or hobby-grade Wireless=20 Mics will often have a 1/4" mono T-S jack (unbalanced) instead of the=20 3-pin XLR connector. Audio levels on the lower-cost receivers can be=20 all over the place, depending upon who makes the unit. Again,=20 though, assume a level somewhere between -40 to -20 as a starting=20 point, unless the unit specifically mentions having a line-level=20 output. This would then be -10dBv for hobby-grade units or +4dBm for=20 professional units. I believe that you should absolutely transformer-isolate the receiver=20 audio from your device. This ensures that you don't introduce=20 ground-loops into the existing system. So long as the input=20 impedance of the device that you are feeding is a standard 10K or so,=20 you would have no problems with loading down or otherwise affecting=20 the existing Mic receiver audio path. The output of the isolating transformer then feeds whatever device=20 you are using to capture or transmit the audio. FWIW, my company makes an inexpensive audio isolation module that=20 would work well for your application. They sell for somewhere near=20 Can $25 in small=20 quantities.=20 =20 .. I can also supply the bare transformers if your quantities get=20 large enough to justify this - you could then just include the=20 transformers on your custom audio capture card. These transformers are a standard part number but are custom=20 manufactured for us only when we place our annual orders (12 week=20 lead time). We purchase them by the thousands. 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 .