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Ribbon Mics and Phantom Power

What is Phantom Power?

Royer R-122 and SF-24 microphones have miniature preamps built into their cases which require DC power to operate (48 volts). Phantom power is a method of applying that power through the microphone cable from a remote supply. This supply can be a stand alone unit or may be incorporated in the audio mixer. It's called phantom power because it comes from outside the microphone and is not supplied from an internal battery.

The ribbon elements in some vintage ribbon microphones can be harmed or even destroyed by the presence of phantom power. For this reason, it is commonly recommended that phantom power be turned off when using ribbon microphones. Leaving phantom power on can result in a stretched or completely blown ribbon. In some cases, the microphone may still operate, but at a greatly diminished capacity.

Royer ribbon microphones are not usually affected by the presence of phantom power. However, we still recommend that you deactivate phantom power when Royer microphones are being connected or disconnected simply because other abnormal conditions may exist that could cause problems. Turning the phantom power on or off after the mic is connected should pose no problem whatsoever.

Note: Our phantom powered models are not included in this discussion. They require phantom power to operate and obviously will not be damaged by phantom power.

Here are a few conditions that should be avoided, as they can damage any ribbon microphone regardless of brand or type:

Shorted, Miswired or Damaged Microphone Cables

Electrically shorted, damaged or improperly wired microphone cables can allow phantom power to damage a ribbon element. If ground (Pin-1) is accidentally miswired, or shorted, to leads two (Pin-2) or three (Pin-3), damaging phantom power can reach the ribbon element. Make certain that your microphone cables are in good working order, in proper phase reference, and that Pin-1 is always at ground potential.

Cross-Patching Microphone Tie Lines

This is the leading cause of blown ribbons in professional studios!

Many studios use patch bays for the convenient routing of signals. The microphone/mic-preamplifier section of a patch bay normally has two rows. The upper row corresponds to lines that run to various microphone panels (studio, isolation booth, etc.) and this is where the microphone is connected. The lower row represents the microphone preamplifier inputs. This upper row is "normaled" to the lower row. Each insert is a full-break patch point, which enables an engineer to crosspatch or redirect microphone lines to various mic-preamp inputs.

The microphone/mic-preamplifier section is the only portion of a patch bay that has DC power present in the form of phantom power. If phantom power is on, ribbon microphones can be damaged when cross-patched through a patch bay.

Here's what happens. Patch cables utilize "tip-ring-sleeve" connectors. When a patch cable is inserted into either the upper or lower row, the phantom power is momentarily shorted to connections that phantom power should not be applied to. In other words, as the connector is inserted, it is, in effect, acting (temporarily) like a miss-wired cable and applying phantom power to the wrong leads. Ribbon mics are particularly intolerant to this because, in the brief moment that a patch cable is being inserted into a phantom-power-charged patch bay, phantom power is applied directly to the ribbon element through the transformer! Each brief patching-related jolt of phantom power across the ribbon element is equivalent to a year or more of recordings made on the mic. A ribbon element that is designed to last ten or fifteen years before replacement can literally be blown overnight by patch bay mishaps.

The only safe way to reroute mic tie-lines that are present at the patch bay is to be certain that phantom power is deactivated before patching. Cross-patching these lines while "hot" often results in damage to ribbons and even some condenser microphones. Since DC voltages are present on these lines, cross patching with the volume control up can also result in damaged monitor speakers and shaken eardrums!

Damaged or Worn Out Connectors

Damaged or worn out XLR connectors can create problems, particularly when phantom power is present, due to a higher potential for short circuits. Always replace connectors that have any appearance of damage or that are obviously worn out.

Electrical Outages

Electrical blackouts, brownouts, and power surges can raise havoc with microphones of all types - ribbon, dynamic and condenser types included. Modern consoles have well designed, regulated supplies that turn power on gently even if power is removed momentarily, but many older boards and preamplifiers were designed with unregulated supplies that can surge wildly when power is first applied. In the case of a brownout, voltage "spikes" can damage any gear that is connected, including microphones. With ribbons, a serious voltage spike can blow the ribbon element to pieces, just like a fuse. If this happens, a re-ribbon servicing will be required to restore the mic to new working order

A Note Regarding All Phantom Powered Microphones

Modern equipment contains sophisticated power-regulating mechanisms that minimize the chance of voltage spikes ever reaching a microphone. They provide a soft-start and smooth ramp-down when AC power is turned on or off at the console or mic-preamp. With older or faulty equipment, problems like leaky electrolytic blocking capacitors, faulty components, shorted diodes or regulators, etc. can lead to uneven power being supplied to the microphone. Because microphones are designed to work within balanced conditions, uneven power can create a number of hard-to-pinpoint problems like low output, distortion, degraded frequency response, and other performance issues.