VU Meter – Mechanical Rest
Before electrically calibrating a VU meter you must be sure the mechanics of the meter are set correctly. All quality meters have a mechanical rest position where the needle should be lined up at when the unit is off.
The needle should be aligned over the first hash mark on the VU Meter Face. This is the Mechanical Rest Position. (see below)
Let’s have a look behind the meter face to see how this is accomplished. The small metal arm with the slot in it (shown below) connects directly with the needle movement. By moving the arm in either the left or right direction will cause the needle to go up or down on the scale.
On older style meters that are mounted to top of the equipment panels (shown below) there is a small plastic screw visible on the front of the meter. This plastic screw has a cam/pin on the back of it which fits into the slot on the arm. By turning this plastic screw you can adjust the needle position.
On newer style meters that are mounted behind the equipment panels (below left) there is no plastic screw on the front of the meter. The adjustment for this style meter is on the back. (below right)
The same thing applies – you turn the plastic screw and the needle will go up or down on the face of the meter.
IT IS VERY IMPORTANT TO REMEMBER THAT THIS ADJUSTMENT SHOULD ALWAYS BE MADE WITH THE POWER TO THE UNIT OFF.