The Neumann U77 is a rare bird, produced by Neumann for four years only in the late '60s. This is the pre-cursor to the U-87i, but with more U-67 characteristics. These were Neumann’s first transistor microphones, and were powered with a proprietary system the company called T-Power. The valve microphones that the U77 “replaced” (such as the U47 or U67) have a high voltage for the valve, so it is easy to use a high voltage (they typically use 60V or 70V) to charge the capsule. Phantom-powered microphones do not have this high voltage, there is a maximal 48V coming in, so after some filtering there’s only 40V available to charge the capsule, which is only just enough to do the job.
T-power is only 12V, and this is not enough to properly charge a condenser capsule, so most T-powered mics have an internal DC-to-DC converter that produces a higher voltage (60V in case of the U77) from the 12V. This means that the U77's capsule is charged with a higher voltage than the U87, which gives it a significantly higher output signal, quieter noise floor and greater “reach”, which adds a great deal of flexibility to recording possibilities.
Some would say that compared to a 60-volt polarized capsule, an underpowered 48-volt microphone displays a lack of detail and resolution; T-powered mics potentially perform closer to the specs of a valve mic like the U67 than to phantom-powered transistor mics like the U87. This similarity is reinforced by the U77 employing the K67 capsule, the same as in the U67. This particular microphone was fitted with a new Neumann K67 capsule in 2013.
Engineers who work with the U77 typically lavish praise on the sound of the microphone, with its liquid mid-range, warm and clear; solid and pleasing low-end, and clear and extended highs. J. Mike Perkins, an American studio owner, writes that “the U77 is an excellent choice for a good singer with a clear voice and will bring out more ‘head’ voice. Compared to a U87, the U77 sounds like someone removed a filter or a cloth over the mic and suddenly you heard everything more clearly. It's also faster sounding than a U87 and the U87 seems to ‘smear’ things a bit in comparison and I assume this is due to the transformer in the U87 (but sometimes you might want that sound). The output of the U77 is also much higher, more like the tube U67. Although "clearer" than a U87, the U77 is in no way harsh or ‘zingy’.
U77's were mostly sold new in Europe and were purchased more by broadcast facilities and less by recording studios. They were also used to record sound for film and TV as some of the popular Nagra tape recorders used for that had built in T Power supplies. The U77 can also be run quite nicely by an internal standard normal 9-volt battery unlike the U87 (but the battery life is less than 8 hours). U77's came with both the 3 blade large Tuchel connector and with an XLR connector. You need to be careful not to plug a phantom powered mic into a T volt power supply.
A U77 is something special. I believe it is the best solid state large diaphragm mic ever made. I think the added current from the T Power is a big part of its sound. When you hit a U87 hard it tends to crap out because the phantom power can't give it enough current to reproduce a loud transient sound as good as a U77. The lack of the transformer also reduces the ‘smear’ you sometimes get with a U87 by comparison”.
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