Tonader Power (T power)

Tonader Power, T Power, T12 or AB Power all refer to a method of powering microphones via their cable. This system uses 180 ohm feed resistors and a 12V supply but does not send the DC power as a common mode signal like Phantom Power. The powering is unbalanced and shares the same path as the audio signal. Therefore T12 needs greater design attention to keep hum, noise and crosstalk out of the powering system.

On a normal 3 pin XLR connector the positive voltage is applied to pin 2, negative to pin 3. However, the reverse is occasionally found, positive to pin 3 and negative to pin 2. The screen does not form part of the circuit so a T Powered microphone will work without screen continuity, unlike a Phantom Powered microphone.

As there is 12V DC across the signal wires care must be taken to ensure that dynamic or ribbon mics are not inadvertently connected to cables with active T12 power, otherwise they may be permanently damaged.

Historically, before the advent of DC-DC converters, the 12 volts of T-power was much easier to generate from portable battery-powered equipment, than the 48 volts required by early phantom systems. This explains its previous ubiquity in film work, where the system still lingers on! Sennheiser have been a major supplier of T-power mics over the years.
It still has some popularity in the film area, not least because it is still easier, and cheaper, to generate T-power from a radio-mic transmitter, where a cordless link to a mic is required.

A simple but effective tester for Tonader Power, nicknamed a Bright Eyes, is easy to construct.

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