Phantom Power newbie

[abc123]

I am amateur hobbyist recorder of acoustic guitar and vocal into my Fostex 4-track using Nady SP-1 dynamic mic. I recently posted a request for advice on an omni mic so I could record another player/singer along with me in impromptu sessions. Among the mics mentioned in replies to my post was a Nady CM100 condenser which I bought for $39.99. (OK -- I am a very low-budget amateur.) Now I realize that I need phantom power for this mic and have ordered a phantom power supply.

My question is -- Is my assumption correct that I can plug my CM100 into this power supply and then use the extension cord (which I also bot) to plug into my 4-track and I will have a live mic?

 

[crazydoc]

That is the assumption. I don't know what "extension" cord you are talking about. As far as I know, you plug the mic into the power supply with an xlr mic cable, and another of the same from the supply to the recorder (I assume it has xlr inputs).

What phantom supply did you order?

 

[abc123]

Thanks crazydoc --- Yes -- should have said cable -- with ends xlr male & female. What I have on back order is NADY SMPS-1 PHANTOM POWER supply at $29.99. The cable is LO-Z MIC CABLE 20 FT KC on sale at $4.99. I today ckd on eBay and saw some mighty interesting Phantom Power units at better prices than the above --- including one that was battery powered --- but will stick with what I have ordered. The battery power was a question to me since I wondered what batteries it took to produce the necessary power (49V?). As I said I am a real newbie on all of this.

 

[dgatwood]

The battery power was a question to me since I wondered what batteries it took to produce the necessary power (49V?). As I said I am a real newbie on all of this.

It's not that hard at all. I have a little 12v power supply for a few low current 12v devices that I built with about $2 worth of parts at Fry's that runs on a 9v battery.

In electricity, P = VI, i.e. watts = volts * amps. With a little bit of conversion loss, you can adjust the ratio of V (volts) to I (amps) as long as P (power, in watts) remains constant (loss notwithstanding) without violatiing any of the laws of thermodynamics....

For AC, this is typically done with a transformer, which results in either a lower voltage at a higher current or a higher voltage at a lower current.

For DC, this is typically done with a voltage regulator.... Like I said.... $2 part at Fry's... plus the breadboard, of course.

Of course, generating 48v requires different voltage regulators, and I haven't seen any that operate in that voltage range, but AFAIK there's no reason you shouldn't be able to find one... just probably not at Fry's.

 

[abc123]

Thx for brief tutorial. I think I came across that equation before but did not memorize it. Seems as tho it is a good one to know. Using your 9v to 12v conversion, theoretically then a battery operated 48v Phantom Power supply could work with 4/9v batteries which would be simple enuf. Or maybe I am jumping to conclusions. Maybe I will inquire of the eBay seller to find out what batteries are being used.

 

[dgatwood]

Thx for brief tutorial. I think I came across that equation before but did not memorize it. Seems as tho it is a good one to know. Using your 9v to 12v conversion, theoretically then a battery operated 48v Phantom Power supply could work with 4/9v batteries which would be simple enuf. Or maybe I am jumping to conclusions. Maybe I will inquire of the eBay seller to find out what batteries are being used.

Feel free to correct me if I butcher the math here.... I would expect them to start with... say a 12V power source, as that's a common configuration for such things---8 standard 1.5V Alkaline cells (AA, AAA, C, D) or 10 standard NiCd cells (1.2V apiece, same sizes). Assuming a conversion at 100% efficiency (impossible, of course), you'd have a fourth the amperage of the power source, since you're quadrupling the voltage. (Makes the math easier to use nice whole numbers....)

Most mics draw somewhere on the order of 1 mA, and most phantom power supplies only produce... maybe 10 mA. So to match that, you'd need 40 mA at 12V. Actually more than that, since 100% efficiency isn't possible, but for now, we'll pretend it is.

A 1.5V Alkaline AA cell can have a total capacity as high as 2850 mAh, so assuming it can put out 40 mA continuous (I'm fairly certain that's WELL within its capacity), a stack of 8 of them in series should be able to provide the power for such a circuit for... more than 71 hours of continuous use. Basically, the voltage may be high for phantom power, but the current draw is peanuts.

Again, that's assuuming 100% efficiency of voltage conversion, where realistic efficiency is a fair bit lower, but... 71 hours off eight AA batteries... ample safety margin for pretty much any sane usage.

 

[crazydoc]

Thanks crazydoc --- Yes -- should have said cable -- with ends xlr male & female. What I have on back order is NADY SMPS-1 PHANTOM POWER supply at $29.99. The cable is LO-Z MIC CABLE 20 FT KC on sale at $4.99. I today ckd on eBay and saw some mighty interesting Phantom Power units at better prices than the above --- including one that was battery powered --- but will stick with what I have ordered. The battery power was a question to me since I wondered what batteries it took to produce the necessary power (49V?). As I said I am a real newbie on all of this.

That unit and cable should get you started OK.

Here's directions from Harvey on building a battery powered supply. I can't find the original thread where it was posted. As he says, the current drain is so minimal that the batteries should last a good long time.

https://homerecording.com/bbs/showthread.php?t=105128