Adding Phantom Power To a Nagra III

[FilmAndTape]

Hi all,

 

I need to use my beautiful Nagra III with condenser microphones and I am looking for a way to add phantom power. I bought a Neumann BS945 phantom power supply. Instead of plugging it into my Nagra I measured to see if any of the phantom power made it to the output socket. To my surprise pins 2 & 3 of the output socket both have 50 volts on them. Would I destroy the preamp of the Nagra by plugging this in?

 

Thanks!

 

Matthew

[Jim Rillie]

Hi Matthew,

 

Pins 2 and 3 of the Female 3 pin XLR input on the power supply should be like you measured (unloaded about 50v is OK.) The mic plugs in to this connector.

The normal input for a mic signal is Female, so the 48v should not be present. If I remember correctly some Nagra IIIs had a male  input and needed an adapter to work with a normal XLR cable, or a female to female cable.

 

[DHB]

I have only a IV-S - which can itself provide assorted phantom power to its mic sockets - so I can't comment specifically on a III. (..And, as Jim says, the European IV-S (those with no sync head and 2.75mm record and play heads) DID - unusually - have male mic inputs, and do need a female to female adaptor or cable.)

 

But the Neumann - or any other brand of external 48v phantom power, like the very small 'Xvive' in-line supplies, or AKG's own 9v injectors - will send power UP the mic cable to the mic, and not DOWN the cable to the recorder, so they won't send - if connected correctly - 48v  into the recorder, but send it only UPSTREAM to power a condenser mic.

 

Be sure to plug the mic's male connector into the phantom power box's female socket, and the male plug from the phantom box into the recorder's female mic input, and all should be OK.

[FilmAndTape]

That confirms my suspicion that phantom power voltage should not be present downstream... Glad I didn't try it out, especially since very few people still work on Nagra IIIs.

 

Thanks for your responses!

 

Matthew

[Throwback]

I strongly suspect that this is a floating voltage (due to isolation transformer) and that there is (effectively) no current on the output: connect a circuit (not your Nagra) and measure the (hopefully, lack of) current.

 

Cheers,

 

Roland

[dela]

Regarding the male and/or female XLR connectors: It is a bit random if a given Nagra has male or female XLR connector... According to some (old) national standards, any voltage output connector should have a female output connector to avoid touching live pins. Even if it was only a very low voltage. On some markets there was no such demands, so there they were supplied with the "correct" female input connectors. It was quite easy to change connector, so many users simply retrofitted female connectors, since the chassis cutout allowed for both male and female connectors.

 

In the microphone input example, the male/female issue was actually the other way round: The input connector (with the 48V phantom supply) ought to be seen as a (supply voltage) output, and thus in any case should have a female connector. But I guess that the legislators didn´t bother about technicalities...

 

In any case the Nagra III is completely indifferent to DC across the input; It is transformer coupled. So there is no risk having a DC potential between hot/cold and ground.

 

[Matthew Steel]

At its most basic, a phantom supply is just a power supply with its negative connected to pin 1 and resistors to pins 2 and 3.  We have an older ancient Neumann N80 supply that I believe did just that until I modified to add DC blocking capacitors.

 

If the Nagra is indeed transformer coupled then it won't be bothered by the DC.

Edited May 16 by Matthew Steel
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