https://www.prosoundtraining.com/wp-content/uploads/2023/02/SACLogo_50.png 0 0 https://www.prosoundtraining.com/wp-content/uploads/2023/02/SACLogo_50.png 2010-07-30 09:21:192010-07-30 09:21:19Phantom Power thread opens doors for other thoughts.
By Jim Sorensen
More thoughts on Phantom Power.
Perhaps the power supply that Ray’s thinking about was not designed to cover all things possible but it was designed to provide power to a capacitor microphone made by the same manufacturer and I’ll bet it does that very well.
As to using it with some snake that might have a shorted pair or be used by an inexperienced tech who shorts the phantom power out of ignorance or by accident, I’m not sure what one can reasonably expect from the maker of the power supply. It’s not being used correctly.
No one would consider it a fault of the manufacturer if someone used miswired or defective network cable on a network system but, using Ray’s logic, the manufacturer should have somehow anticipated that and designed for that possibility. Now, I realize there are myriad details in the network analogy that perhaps don’t pertain in the power supply situation but the single fact remains…you can’t be expected to design a system for every alternative…you have to have upper and lower limits and, at some point, you have to freeze the design to some specific set of specs. That’s why things have specifications and why warranty’s limit the responsibility of manufacturers to what those specs permit.
It would be like buying a Civic and then using it to haul concrete blocks at a construction site. Would it work? Maybe. For a while. Would that “abuse” permanently damage the Civic? Probably. Is that what you’d expect? I imagine it is.
This very problem may be why the BBC “practice” recommends using capacitor microphone power supplies near the microphone with the implication that a single cord from the microphone to the supply be employed as opposed to running the phantom power through all the wiring and patch points which might be between the “stage” and the console.
One of the other comments was that by trying for miniaturization we loose some of the “fudge factor” in device ratings. That’s absolutely true but it’s also, sadly, irrelevant. If the example microphone power supply uses a 1/8 watt resistor and if that’s consistent with a good design…note, two “ifs” (pass me an “if” gate!)…then when something happens that causes that resistor to be too small, there’s a problem. As long as the system is used as specified by the manufacturer, things should be OK. Now, Ray makes a good point right here. There are “bumps and grinds” associated with using microphone power supplies normally, so perhaps a little more “armor plating” is appropriate. (Pass me an “it depends gate” s’il vous favor.) (That’s “Frenish” or is it “Spanench.” If I had written “…appropriate – hey.” I would have been writing in “Canadian.” Using “fer sher” or “rilly” I’d be speaking in “Californish.” “S’il vous favor, you-uns” would be Eastern Tennesseean Frenish or Spanench. I’m just trying to be a citizen of the world!)
Next comment: Russ is right! Neil did do it right! And that comes from another “old broadcast engineer.” Broadcast engineers have had to deal with very high levels of RF and other forms of EMI for generations and have found that the techniques used by Neil at SSI and by most of us OBE’s* when wiring in those (or regular) environments produce (relatively) noise free results.
There are admittedly more complex ways to accomplish the same things, for example some of the fine work by Jim Brown, but the simple act of putting the sensitive stuff “inside a grounded metal box” to keep the errant signals out of the “real” circuits is a pretty good solution. (Brown made the “ground” somewhat frequency sensitive…it’s a little more complicated than that but this concept helps understand his work.)
I have to mention Brother Whitlock’s transformers but also point out that sometimes…note the word “sometimes”…these are used to correct for badly designed or installed wiring, or wiring not intended for the purpose, and should be considered more of a repair than a foundation design component. Obviously, there are also designs which require transformers and they should be used…not some alternative that tries to act like a transformer but is really a “transistor.” Also: If you wish to use a transformer, get the best available and that means paying attention to everything including the glop in the can if they use it. Core iron, wire quality and gauge, insulation, shielding materials, connectors all matter, sometimes in a bigger way than you’d think. Choose wisely. (Whitlock and I disagree almost violently on politics but certainly not on transformers!)
Keep it out of the red!
* OBE = Old Broadcast Engineer…not an award you get from the Queen. Just so we’re clear about that.