Notes on Microphone Wiring, Powering and Patching Josephson Engineering microphones are equipped with industry standard "XLR" type connectors, wired in accordance with IEC 61938. Our mics operate with P48 phantom power, and are critical about the quality of phantom power they receive. Like all phantom-powered mics, any variation or noise in the phantom current will appear as a noise signal added to the audio. Many problems in studios and field installations can be avoided by using only XLR or multipin connectors for microphone wiring. Excellent guidance on running audio lines through wall and stage boxes, multipair and other studio wiring can be found in the AES standards AES48 and AES54, but even these standards assume that you're using XLR-type connectors for microphone signals. If you need to be able to reconfigure your mic wiring, an XLR panel is a good way to do this. Tip-ring-sleeve plugs and jack panels are convenient, but have several drawbacks when used with microphone signals. One is that isolation between channels is not good, particularly when some jacks carry line level signals and others are used for microphones. Another is that when you insert a plug into a circuit, first one side and then the other of the circuit is connected for an instant to ground. When the circuit carries phantom power, that means you have 48 volt transients across the audio pair. Some microphones and preamps can be permanently damaged by doing this. Josephson mics are protected from such transients, but it's still not a good idea. Third, t-r-s connections have a relatively high and constantly varying series resistance. From Ohm's law we learn that current (in this case the phantom power current being supplied to the microphone) through a resistance generates a voltage. It only takes a tiny change in resistance to cause a huge noise voltage to be generated, and this noise is added directly to the microphone audio. Finally, and this is the worst problem, most patch bays are wired with "normaling" jacks, which means that when there's no plug inserted, the upper jack is connected to the lower jack, usually so that a given audio circuit is normally connected to a given input. The normaling contacts are even more troublesome than the wiping contacts of the plugs and jacks -- yet more contact points to create noise. The best choice is to get rid of patch bays entirely. If this isn't practical, try to use XLR patch panels instead of the "phone" plugs and jacks intended for telephone line signals. XLR patch panels are available from many sources, some of them quite inexpensive. Even the cheapest of these is better than the best "phone" type patch bay, for microphone signals. If you have to use "phone" plugs and jacks, don't use normaling contacts for microphone signals. If you can't avoid using normaling contacts, be prepared for regular problems with noise, distortion and potential equipment damage. It makes little sense to spend time and money carefully placing a good microphone if the signal path is compromised by contacts that are not intended for microphone signals.