Cross-Patching Microphone Tie Lines

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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!

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