Topic: T Power mics (a.k.a. 12 V parallel power) (a.k.a. A-B power)

[Shawn]

I'm curious if anyone here has run T Powered mics. Is there anything I should be aware of? how did you power them? Has anyone ever used any 48v to T Power adatpers? I was looking at using these to convert the phantom from my pre to t power:

http://www.thebroadcastshop.com/sales/detail.asp?partno=PSC-FPSC0010A&aid=froogle

can anyone think of any reason that wouldn't work? thanks for the help.

[DSatz]

T powering was a big deal in the mid-1960s and 1970s mainly because it was available in Nagra recorders, Sennheiser shotgun mikes and Schoeps hypercardioids. (Neumann also made T-powered condenser microphones briefly.) But the system has been obsolete for 20 years and I would be surprised if in the whole world, even ten new T-powered microphones are sold per year by all manufacturers combined. Even Schoeps has made them a footnote in their catalogs, though they can still make CMC 4-- amplifiers on request.

Number one thing to know is that it's definitely not a compatible powering system the way (proper) phantom powering is--it can be deadly to a ribbon or other dynamic microphone if you leave T powering switched on and connect a microphone that wasn't designed to handle it.

On a technical level the DC runs right along with the audio signal in the two modulation leads of your balanced cable. So it is important to use a very clean DC supply (preferably batteries), because otherwise any hum or hash in the supply will become irretrievably mixed into the audio. This isn't the case with phantom powering, which can have some hum or other noise in it and still be OK--the common mode rejection of the preamp will bridge it out to a very great extent.

You always have to make sure that a "T" power supply is free of any DC on its audio output(s). Normally that will be the case, but with gear you haven't used before, it's worth checking.

Be aware that if you happen to be using Neumann "fet 70"-series T-powered microphones (KM 73/74/75/76 or U 77), their output circuits were designed for the line inputs of Nagra recorders, not for the mike inputs; they have absurdly high output levels when connected to conventional microphone inputs.

Also there used to be some bizarre disagreement between Kudelski and everyone else as to the proper polarity of T-powered microphones, so there are some T-powered microphones which will seem to be wired "out of phase" when compared with all other standard microphones.

All in all I feel that I have lived a good, long life as an engineer without ever using one of these. The only advantage which they have over 12-Volt phantom-powered microphones is that it can be a little simpler to connect them to unbalanced microphone inputs.

--best regards

[Shawn]

thanks for the info.

[rokpunk]

i've got a couple of old t-powered sennheiser shotgun mics. no biggie....just plug the mic into the little battery pack box and you are good to go...at least, that's how it is with my sennheisers.