Testing Phantom Power

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whyseye

whyseye

Well-known member
I recently happened into a DMP2 (or so), and I'm really thrilled with what it's doing for my motley assortment of cheap dynamic mics - some stuff I thought was unusable actually has some interesting character, given enough clean gain.
However, I don't have any condenser (or ribbon....sigh) mics yet, and I'm not sure how to test the phantom power output. I don't really have any sort of test equipment handy (am recouping from ankle surgery, and still basically stuck in the house) ....
Is there some old-timer's trick that will allow me to check these babies out more completely with everyday household items?
If not, what's the best way once I'm more mobile?
 
Why,

You'll need a digital voltmeter, black lead stuck in pin one socket and the red lead stuck into two or three (both are the same phantom wise). Set it to DC volts and it should display around +48v.

If the display jumps around, you'll need to look at it with a scope to see if its noisey.

Maybe someone else has a trick I don't know.

Bob
 
Take a mic cable and rip the female end off. Plug the other end into the preamp and turn the phantom on. Touch the wires to you tounge. If your hair starts on fire, the phantom is fine.

Seriously, if you don't have a mic that needs it, why are you worried about it?
 
Farview said:
Take a mic cable and rip the female end off. Plug the other end into the preamp and turn the phantom on. Touch the wires to you tounge. If your hair starts on fire, the phantom is fine.
Click to expand...

Replace your tongue with a flashlight bulb and this will work... (the bulb will go supernova and burnout, but you'll see it happen, and it is fairly household)
 
The tounge thing was a joke, please don't try this at home.
 
Farview said:
Take a mic cable and rip the female end off. Plug the other end into the preamp and turn the phantom on. Touch the wires to you tounge. If your hair starts on fire, the phantom is fine.

Seriously, if you don't have a mic that needs it, why are you worried about it?
Click to expand...

I don't have a mic that needs it YET...........

.......also got a couple extra DMP2s more than I need, and I'd like to be able to ascertain their working condition before any attenpts to sell them....

....thanks.
 
Farview said:
The tounge thing was a joke, please don't try this at home.
Click to expand...

It is one of those things you'll only do once...
 
Farview said:
Take a mic cable and rip the female end off. Plug the other end into the preamp and turn the phantom on. Touch the wires to you tounge. If your hair starts on fire, the phantom is fine.
Click to expand...

OK.....I tried your method, and it works great!

Now.......only five more channels to test........ :eek:

:D
 
whyseye said:
OK.....I tried your method, and it works great!

Now.......only five more channels to test........ :eek:

:D
Click to expand...

I'd wait till a bit of your hair grows back...
 
The current is really low, like 7ma, it won't hurt! A christmas tree light might work!
 
Here's the cheapest way I know, for a go/no-go test.

You probably don't have a shitload of LED's lying around like I do, so buy one of these or similar:
http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=276-026

Stick it in your XLR socket between pins 1 and 2 or 1 and 3. Make sure phantom is on. If it doesn't light up at all, or very faintly, switch the leads (turn it around). It should glow fairly brightly if you have phantom power. You may have to jiggle the leads in the sockets a little to make contact. Check between both pins 1 to 3 and 1 to 2.

This won't hurt the preamp or the LED, as it is in series with a 6.8K current limiting resistor (in the preamp) that will drop the voltage appropriately. The LED may glow faintly when reverse biased as its reverse breakdown voltage is exceeded.
 
Farview said:
The tounge thing was a joke, please don't try this at home.
Click to expand...

When I was working at an Air Force base in Colorado Springs, the MPs told some idiot to do this with jumper cables to check his battery.

:D
 
bgavin said:
When I was working at an Air Force base in Colorado Springs, the MPs told some idiot to do this with jumper cables to check his battery.

:D
Click to expand...
Natural selection at it's finest. It's time to thin the heard.
 
whyseye said:
I don't have a mic that needs it YET...........

.......also got a couple extra DMP2s more than I need, and I'd like to be able to ascertain their working condition before any attenpts to sell them....

....thanks.
Click to expand...
Are you the guy who bought the set of three off ebay? Man that was a steal. I did'nt bid because I thought that the guys feedback was a little sketchy. If it's you Congrats.
 
Be Loveless said:
I did'nt bid because I thought that the guys feedback was a little sketchy. If it's you Congrats.
Click to expand...

.....yeah, it's me, I was scared of the feedback, too. :eek:

Seems like everything is in like new condition as advertised, but I got really reamed on the shipping - curses! :mad:

Oh well - the price was right, my mics have never sounded better....and once I can check out phantom power, one or two of these puppies will be up for sale....

....then, Delta 410, here I come! ;)
 
Farview said:
Take a mic cable and rip the female end off. Plug the other end into the preamp and turn the phantom on. Touch the wires to you tounge. If your hair starts on fire, the phantom is fine.

Seriously, if you don't have a mic that needs it, why are you worried about it?
Click to expand...

Damn that was going to be my reply :D
 
crazydoc said:
Here's the cheapest way I know, for a go/no-go test.

You probably don't have a shitload of LED's lying around like I do, so buy one of these or similar:
http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=276-026

Stick it in your XLR socket between pins 1 and 2 or 1 and 3. Make sure phantom is on. If it doesn't light up at all, or very faintly, switch the leads (turn it around). It should glow fairly brightly if you have phantom power. You may have to jiggle the leads in the sockets a little to make contact. Check between both pins 1 to 3 and 1 to 2.

This won't hurt the preamp or the LED, as it is in series with a 6.8K current limiting resistor (in the preamp) that will drop the voltage appropriately. The LED may glow faintly when reverse biased as its reverse breakdown voltage is exceeded.
Click to expand...

.....If the resistor is dropping the voltage, how do I know whether it's giving me 48v, or less? Or is this really more of a power-or-not test, with the assumption that if it's hot, it's probably putting out 48v? Even the voltmeters I looked at online have presets for 50v, but nothing specifically 48v.

I have read that certain preamps give less that 48v phantom power, which is OK for some mics, but not for others (this seemed to be an issue people had with the Audio Buddy, and one I was hoping to avoid by stepping up slightly in the line, albeit with older gear).

Otherwise, I love the idea of being able to test at that price.....
.....OK for my personal purposes, but if I'm gonna sell any, I really would be more comfortable being able to vouch for them with the certainty that they test as they should.

Looks like I may have to wait til I can pick up or borrow a voltmeter.
Boogers!
 
whyseye said:
.....If the resistor is dropping the voltage, how do I know whether it's giving me 48v, or less? Or is this really more of a power-or-not test, with the assumption that if it's hot, it's probably putting out 48v...

Looks like I may have to wait til I can pick up or borrow a voltmeter.
Boogers!
Click to expand...
That's pretty much it.

If there's a Harbor Freight Tools near you, they sell these regularly on sale for $3 - $4. It will check your voltage.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=35761

The other thing is to check the voltage when it is under load by one and two mics. (But I guess you can't do this - no mics. :)) You hook up the mic and then check the voltage (you'll have to take the case off the pre or the mic to do this) to make sure the load doesn't drop the voltage too much.
 
whyseye said:
Even the voltmeters I looked at online have presets for 50v, but nothing specifically 48v.
Click to expand...

This is just the range setting... it will measure anything up to 50 volts... and yes, the true test is the volyage under load...
 
crazydoc said:
Here's the cheapest way I know, for a go/no-go test.

You probably don't have a shitload of LED's lying around like I do, so buy one of these or similar:
http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=276-026

Stick it in your XLR socket .....
Click to expand...

Will any LED work? I could probably cannibalize a flash-ready light from an old camera or flash, which I do have a bum-full of lying around....

If the resistor on the preamp is bringing down the voltage, does it matter which LED, or is there an inherent problem with some LEDs that I'm still too ignorant to understand?

Once I'm back out in the world (soon, very soon) I'll still go get a real tester, but I love the quick-and-dirty aspect of the LED. I've picked a bunch of similar tricks for testing/repairing camera gear for those real-world occasions when you absolutely have to do it yourself, or miss the moment.
Then, I give it over to the pros for proper care!
 
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