PB-96

  Balanced Audio Patchbay - User Guide

The MTR PB-96 is a 48-way stereo jack patchbay, 19" 1u high, for interconnection of audio signals from many different pieces of equipment. The jack sockets at the front and rear are stereo, allowing balanced interfacing and even midi connections. It will operate unbalanced if mono jack plugs are used.

The unit is supplied from the factory 'half normalised', i.e. when nothing is plugged into the front, the top rear jack is connected to the bottom one of a pair, until a jack plug is inserted into the bottom front socket. When this happens, the link is broken, and the signal is sent to wherever this lead is connected. Normalised pairs are typically used to connect to and from the insert points on a mixing console, or Group Outs to Tape In's, etc.

At the same time, a parallel signal can be tapped off from the top front socket without disturbing this 'normal' link: useful when the socket is wired to a channel insert point of a mixer, allowing an extra aux or monitor mix to be created. This arrangement is also called 'Sniff and Break'. The link can always be broken, of course, by inserting an unconnected lead into the bottom socket.

To convert to 'un-normalised' use, scratch hard with a sharp point through the silver-coloured track marked "T" (tip) on the printed circuit board, to make a clean break through the track. Also cut the track marked "R" (ring) if using balanced connections. These breaks can be re-soldered at a later date if your requirements change. Un-normalised pairs are usually used for frequently changing patches such as auxiliary sends and returns, etc.

When un-normalised, the circuit is broken if a plug is inserted into either the top or bottom socket, so that anything can be patched to and from anything else. Should hum occur due to earth loops, the "E" (earth) track can also be cut in the same way.

An alternative (and easier) method of un-normalising is to undo the black fixing nut from the top rear socket, and remove the circuit board. Rotate the board horizontally through 180° (don't turn it upside down) and insert what were the two rear sockets into the holes on the front panel, snapping the rear upper socket into the semicircle in the metalwork. Replace the fixing nut.

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MTR Ltd, Ford House, 58 Cross Rd, Bushey, Herts, WD19 4DQ   UK
Tel: +44-(0)1923-234050   Fax: -255746    e-mail: mtrltd@aol.com    www.mtraudio.com