Phantom powered Teensy

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Somnitec

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I'm doing an audio project in which it would be convenient to work with as little cables as possible, and as such I started wondering if it would be possible to power the Teensy from 48V phantom power directly over the audio line?

In the diagram below a made a rough sketch of what it could look like in my, inexperienced, mind. To make a balanced signal, I use a simple trick where a mono signal send directly to the L channel of the DAC, and inverted to the R channel of the DAC to make a balanced signal. There should be some caps added to stabilize power, but I omitted those for simplicity sake. The Step-Down convertor should work in a frequency plenty above the audible range to prevent unwanted noise.

Would this work? And as a follow up question, could this reduces issues with ground loops?

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Thanks!
 
At the very least you'll need DC blocking capacitors between the DAC pin and the 48V phantom power. You might also wish to attenuate the 1.2Vp-p DAC output to whatever range your mic input expects.
 
Yes you can definitely run from the phantom power, but DONT use too much! it's only intended to run small pre amps and so on; so be sure to check your current usuage.

Those resitors you dont need at all, unless you want to deliberably limit the current using them.
You'll need to isolate the DACs, like paul says. Consider using op amps to buffer and invert the signal, two birds one stone, you can also use one to have a manual volume control if you're that way inclined.
 
Thanks Paul! Amazingly quick reply!

Edward, when I leave out the resistors, I'm shorting the hot and cold line of the XLR right? To avoid this, some resistors seem necessary, but how would I figure out what would be the ideal values to use? (potentially including a bit of attenuation)
 
In theory, you could use inductors instead of resistors, for minimal loss of DC power. But in practice, those would need to be really huge inductors, probably also in series with smaller ones to achieve high enough impedance over the entire audio band.

You could also trying using an audio impedance matching transformer to attenuate the signal, but also in practice those are hard to find in these modern times.
 
Ahh yes, oops. Come to think of it I'm sure I've seen a matching transformer with a centre tap used for the phantom power. The problem with those resistors is you'll get about 10mA from them and you'll be burning aboout 95% of your power in them!
 
Yeah, a center tapped or dual winding would be great. As long as the DC current in each side is closely matched, their fields can cancel, so you can avoid a gigantic core or air gap needed to avoid DC saturation.

Of course, the windings still need high enough inductance to not load the audio too much.
 
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