phantom power pinout

[nukeitout]

For some reason I can't figure out what pins are powered for phantom power, can anyone help me out? I guess I could just wait until I get home and get out the multimeter, but I'm not home and I'm impatient... Which two pins are powered and which is the +?

 

[MCI2424]

For some reason I can't figure out what pins are powered for phantom power, can anyone help me out? I guess I could just wait until I get home and get out the multimeter, but I'm not home and I'm impatient... Which two pins are powered and which is the +?

Both signal pins carry +48Vdc in REFERENCE to ground. ONE standard (modern) is pin 1 is ground.

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


This standard CAN be different for some older machines, so watch out.

 

[Minion]

Yes, Both pins 2 and 3 carry the +48v phantom power were pin one is the ground pin.....

 

[PinkNoise]

"I could just wait until I get home and get out the multimeter"

Your question has been answered - - but a WARNING!

Never go prodding around a microphone which uses an output transformer with a multimeter. There is a risk that you'll magnetize the transformer core. The same advice applies to other low-level audio transformers used, for example, in mic preamps, and tape heads.

 

[boingoman]

Your question has been answered - - but a WARNING!

Never go prodding around a microphone which uses an output transformer with a multimeter. There is a risk that you'll magnetize the transformer core. The same advice applies to other low-level audio transformers used, for example, in mic preamps, and tape heads.

Could you explain the principle behind this???

 

[PinkNoise]

Magnetized transformer cores

Could you explain the principle behind this???

When measuring continuity or resistance with a multimeter, DC is passed through the component. This generates a magnetic field, and if the component is in the form of a coil around a laminated metal core (as you'd find e.g. in a transformer or tape head) the field is concentrated and can magnetize the metal. In the case of audio low-level transformers etc. the cores will be made of expensive metals such as Mu-metal or Radio-metal, whose properties are damaged by magnetism. My guess is that the result may be increased low-frequency distortion. I've always wondered if demagnetizing the item brings it back "like new", but I've never found a definitive answer to that. I could look in the bible, "Radiotron Designer's Handbook", which contains much about audio transformers, but I'll leave that to you!

 

[mshilarious]

When measuring continuity or resistance with a multimeter, DC is passed through the component. This generates a magnetic field, and if the component is in the form of a coil around a laminated metal core (as you'd find e.g. in a transformer or tape head) the field is concentrated and can magnetize the metal. In the case of audio low-level transformers etc. the cores will be made of expensive metals such as Mu-metal or Radio-metal, whose properties are damaged by magnetism. My guess is that the result may be increased low-frequency distortion. I've always wondered if demagnetizing the item brings it back "like new", but I've never found a definitive answer to that. I could look in the bible, "Radiotron Designer's Handbook", which contains much about audio transformers, but I'll leave that to you!

While true, the effect is dependent upon the design of the transformer. Any transformer suitable for use as a microphone output (or input) transformer has to be designed to accept small DC currents without magnetizing the core, otherwise the transformer would be damaged by phantom power, which has much larger current than a multimeter. Unless you switch the multimeter to diode check or something (still less current than phantom), even then I suspect the audio transformer shouldn't be damaged.

 

[dgatwood]

While true, the effect is dependent upon the design of the transformer. Any transformer suitable for use as a microphone output (or input) transformer has to be designed to accept small DC currents without magnetizing the core, otherwise the transformer would be damaged by phantom power, which has much larger current than a multimeter. Unless you switch the multimeter to diode check or something (still less current than phantom), even then I suspect the audio transformer shouldn't be damaged.

Agreed. Even though phantom power theoretically cancels itself out in the transformer, the reality is that phantom supplies are rarely perfect 48VDC out both wires. If there's a voltage difference, you'll have the same problem. I'd be really shocked if a mere 1.5V (probably with massive current limiting built into the meter) would even approach the power levels needed to cause a permanent charge.

Somebody call MythBusters.

 

[mshilarious]

Agreed. Even though phantom power theoretically cancels itself out in the transformer, the reality is that phantom supplies are rarely perfect 48VDC out both wires. If there's a voltage difference, you'll have the same problem. I'd be really shocked if a mere 1.5V (probably with massive current limiting built into the meter) would even approach the power levels needed to cause a permanent charge.

It certainly doesn't cancel if you hot swap the cable, which a manufacturer has to presume users will do. In fact I have measured it, and it's more current than the 1mA or so that diode check will get you, and certainly more than the 0.1mA or less you get on resistance.

 

[PinkNoise]

I'd be really shocked if a mere 1.5V (probably with massive current limiting built into the meter) would even approach the power levels needed to cause a permanent charge.

Sorry - but you're absolutely wrong here.

 

[boingoman]

Sorry - but you're absolutely wrong here.

A link or two that backs you up would be appreciated.

 

[crazydoc]

And as a manufacturer of preamps with transformers on the input,
I would also recommend turning the phantom off before removing the mic, and on after connecting.

The current pulses generated by connecting with power on are of short duration, but can be of surprisingly high amplitude depending on the various circuit configurations, and these pulses are what can magnetize transformer cores. Mic and mic-pre alike.

The input capacitors of transformerless preamps have the full 48 volts with respect to ground if the phantom is powered up first, plugging a mic in will discharge this power thru the mic and the cable capacitance, this can be a strong spike.

In transformer coupled preamps, the current is limited by the 6K8 resistors, but the 7ma of dc smacked repeatedly into a core can be an issue over time. That's why Studer recommends demagging the cores of the input transformers in the older boards.

I'd rather not magnetize anything, so removing the phantom is best before changing connections.

Read more here:
http://recforums.prosoundweb.com/index.php/mv/msg/1521/0/0/3472/