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Does the UH400 have DIN standard phantom power? Is the 48 Volt setting actually 48 Volts?

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It is a gentle statement to say that our phantom wiring is merely unconventional. The UH series has always had an unbalanced input. Mics used with the plug-on units usually go right into the unit and a balanced input was unnecessary. Given that, a balanced phantom feed would be a waste of effort. So pin 3 has phantom power on it but audio is tied to ground with a series 500 Ohm resistor in series with a 20 uF capacitor. Pin 2 is audio in (hot) and is tied to the phantom voltage with a 1k resistor and goes to an amplifier with a 1k input impedance. (See FAQ Is the XLR input to the plug on UH transmitters a true balanced input?)

If that isn't enough, the 48 Volts is really a regulated 42 Volts to compensate for our lower impedance feed resistors. Forty two Volts is an approximation of what the usual 2 mA, 48 Volt mic "sees" from a 48 Volt supply due to voltage drop in the DIN specified 6.8k feed resistors. One of our goals was to be able to operate higher current pro mics. With the 1k feed resistors and 42 Volts , we can provide 7 mA with reasonable voltage drop. Just don't think we cheated you on Volts if you measure the phantom voltage with a meter without a mic load. 

There is yet another facet to our madness. The lower voltage and reduced resistor loss means less power has to be supplied by that overworked 9 Volt battery that you have to buy. By using constant current diodes instead of larger lossy resistors the supply noise is still well filtered but we don't have big power losses. This arrangement also meant we didn't have to use huge 63 Volt capacitors to filter out supply noise on a 48 Volt supply. We can use 50 Volt parts on the 42 Volt lines. The inside of the UH400 is really packed and figuring out how to get around those large caps is one of the things that kept us from doing phantom power years earlier.

Finally, by using lower value feed resistors, we can accommodate some older pro mics that want 12 to 15 Volts at about 10 mA . Doing this much current with 6.8k resistors would waste a lot of valuable battery power. In fact we make a T-power adapter that takes advantage of our capability of delivering relatively large currents at low voltage

Posted 1 year agoby LectroAdmin
#83