At 07:37 AM 5/16/2011, Mark E. Skeels wrote: >All, > >I want to configure a microphone to eliminate the possibility of >electric shock when it is used in (very) wet areas. > >The most important thing is that it not endanger the user via any >possibility of electric shock. You have two issues to deal with here. 1) Any passive microphone (dynamic, ribbon, etc) doesn't need any=20 form of power to operate. The acoustic signal is converted directly=20 to an electric signal. More sensitive or better-sounding mics usually have electronics=20 associated with them. These are typically Condenser Microphones,=20 which come a variety of styles. Classic (old-school) Condenser Mics require either an external power=20 supply (tube-type mics) or 48V phantom power. I'm talking about=20 Neumann condenser mics here. There is a related class of what I call classic condenser mics: those=20 that are RF-based. These have two RF oscillator inside them: one is=20 stable, the other is frequency-modulated by the movement of the mic=20 diaphragm. The resulting difference is demodulated down to base-band=20 audio. The oldest of these that I've seen were transistor-based and=20 required 48V phantom power. Modern electronic microphones (condenser mics) cover a vast=20 range. These sort of divide into two different family types:=20 electret or not. Electret mics need only a tiny amount of power=20 which can be obtained from an internal battery. Condenser mics=20 generally need phantom power but this can often be much less than=20 48V. For example, AKG 451 microphone bodies will operate from about=20 10V through 54V phantom power. Bottom line - choose a mic that doesn't need either an external power=20 supply or 48V phantom power. 2) Most microphones are made of metal and use shielded cable. This=20 is to reduce / eliminate hum caused by external fields. The shield=20 and microphone are normally grounded via the audio console. So - the mircophone is not normally the source of the=20 problem. Rather - it is a really good ground that someone is holding=20 onto. If that person contacts something that is live, it provides a=20 ready path for current. So: it would be nice if you could isolate that gro= und. It is sometimes possible to use a dynamic mic without a shield. You=20 need to use high-quality twisted-pair cable feeding a good quality=20 balancing transformer. Whether this is possible or not depends entirely on the microphone=20 used. You are going to have to try it yourself and see. However, I can tell you that I did this once in a trial many years=20 ago (local Champ Car / Indy race car track). The cable run was about=20 2000 feet of cat5 cable (4 pairs). One pair was connected to pins=20 2&3 of the Sennheiser dynamic mic (don't recall the model=20 number). The other end of the cable went through one of my balancing=20 transformers and into a Yamaha DM2000 console. Pin 1 of the=20 microphone was left floating. About 500 feet of that cable run had the cat-5 cable sitting right on=20 top of the 500 mcm and 1000 mcm cables running from the gen sets to=20 the power distribution for the site's power. This was the only=20 available cable route. The site was fully powered at the time of the test. The audio operator at the console (many, many years of broadcast and=20 recording-studio experience) said that the audio quality was=20 superb. He thought that it wasn't quite broadcast quality but was=20 eminently suitable for PA system use. He based this on listening to=20 the air tone (ambient noise) as well as listening to race cars off in=20 the distance. He then listened to the on-air talent doing his usual=20 talking (obviously much louder than ambient noise). Residual hum was=20 buried in the noise floor. We then took the cat-5 cable and connected each of the pairs to the=20 outputs of the Sennheiser receiver racks (+4dBu level) - the=20 resulting audio WAS broadcast quality and was used for the entire=20 (and all subsequent) events. The reason for the initial test was to convince the Broadcast=20 Technical Director that cat5 cable WAS a reasonable alternative to=20 running thousands of feet of heavy, thick DT12 (12-pair) cable=20 through rough terrain. We did end up using multiple runs of cat5=20 cable - much, much quicker and easier - and it worked well. Where I'm going with this is that it IS possible to=20 galvanically-isolate a dynamic microphone and still get good=20 results. It really depends on the type and quality of the microphone=20 chosen as well as the balancing transformer. The transformers I used were un-shielded 600R-600R with 1500V rated=20 insulation. I have lots if you need any (~8 each in quantity, ~10=20 each singly). You do have to be careful to keep them away from=20 magnetic fields (power transformers, etc). 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 .