Phantom Power Supplies

[W3SLK]

I'm considering getting/obtaining a nice condenser mic that requires phantom power, (I guess most do). Anyway, my mixer doesn't have a mic input with phantom power so I need to outboard it. Most that I have read about use a switcher as a supply. My question is how well do these swithcers hold out with RF loose in the house? I don't want to drop any $$ on one and it unable to withstand an RF environment. I do know that I'm asking this question in the right place. All points of view welcomed.

[kb3ouk]

if a switching supply can't take the RF, i imagine a suplly using a transformer could be built

[flintstone mop]

Mike(Y)
Try this link for some ideas.

I bet you bought a BLUE SPARK microphone or a used Marshall.

http://sound.westhost.com/project96.htm

or

http://www.tangible-technology.com/power/Phantom_Power_connect.html

Fred

[W7TFO]

Here is a link with the dope you need:

http://www.tangible-technology.com/power/Phantom_Power_connect.html

Mic on!

73DG

[W2PFY]

My phantom supply is built into the equipment. I never had a problem with any of it but I guess I don't know the answer to your question excepting to say that at the camp I have two switching power supplies to charge my batteries. They run at over two kilowatts DC output when charging. I wondered if RF would get into them and the answer is, No. Not a problem.

I think you would do well to buy a device rather than build something and here's a link just for examples of what's out there.

http://shop.ebay.com/?_from=R40&_trksid=m570&_nkw=phantom+power+SUPPLY

[W3SLK]

Terry, ur correct. I don't care to build one because everything I have would be way overkill. Fred, I'm leaning towards a Shure KSM32 or something in that vicinity. I might try a Behringer (B2?) if the opportunity presents itself. They are extremely cheap, (read as made in Chinka). However, I would like to get something USA or at least in this hemisphere. I won't turn my nose up to a good Neumann though.

Everything commercial seems to be a switcher. Maybe that is what you have in your board Terry. I may be worried over nothing. More research.

[WD8BIL]

Mike,
If you have a mixer just use the supplies in it. Most of those mics, mine included, will work well with a voltage 9V and above.

On my old Tascam board I used the +/- 15 volt supplies with the 6K resistors and 68uf cap shown in one of the links above.

[k4kyv]

I wouldn't worry so much about the switching supply malfunctioning in the presence of strong rf from my transmitter.  I would worry more about how it performs in the absence of rf. Namely, while I am trying to receive.

[KA2QFX]

I modified an old EQ into a multi-band compressor. It had a conventional single ended mic pre-amp and no phantom supply. I modified the preamp for differential input but still needed the phantom voltage.

I simply took the 12 volt AC off the transformer before before the rectifier and built up a simple multiplier (4-100uF caps as a half wave quadrupler). That then feeds the differential mic lines (XLR 2 & 3) through two matched resistors (5K each).   Worked fine, I had absolutely no hum or noise detectable. I thought I'd need to bridge them with a pot to null some error but no. 

I would avoid switching regulators if possible, but no doubt they can be made to work. I'm OK with simpler is better.

Mark

[W3SLK]

Thanks Mark. I was thinking about following Buddly's lead and tapping off the 12VDC supply on the mixer. I guess what I ought to do is buy a modern mixer. I have two mixer boards. One is a classic Bozak CMA-10-1 with a handful of CM-481 transformers and the other is a Russco 505 that dispite all my troubleshooting, every thing that comes out of it is a perfect square wave, and I think it is soley responsible for wiping out my mod transformer on my RCA rig. One thought I did have was picking up a cheap doorbell transformer and concocting a small doubler circuit ala your suggestion. That might work better and not be as noisy in the receiver as Don, K4KYV, has suggested.

[KA2QFX]

FB Mike,

I don't know if you need another transformer unless your making an external box to supply the phantom power to the mike. Just about any mixer/preamp should have a source of low voltage AC you should be able to multiply. The phantom supply is not isolated from ground as it requires pin 1 for DC return on the mic jack.  As long as both pins 2 & 3 see the exact same voltage you're good.  If you have transformer inputs with a center tap for your mic in  only one connection to the 48 Volts is needed. Otherwise I would still use two resistors, one to each side of the transformer, to supply the 48V.

Add a switch to eliminate the 48V for conventional mics.

[W4RFM]

A company broadcast people use called ROLLS, makes a very inexpensive phantom power supply used inline.  It will sell for $40.00 or less.  P.M. me and I will tell you more, so as not to be commericial on the forum.