A musical instrument bracket assembly is mounted on a top end of a post and has a base, a pivot bracket, a pivot pin, a compression knob and a standoff rod. The base has a tongue. The pivot bracket is mounted pivotally on the tongue and has a standoff hole, two pivot wings, a gap and a stationary compression fitting. The pivot wings extend down from the standoff hole and are mounted pivotally on opposite sides of the tongue. The stationary compression fitting is formed on one of the pivot wings. The pivot pin extends through the pivot wings and the base. The compression knob is attached to the pivot pin and has a rotatable compression fitting corresponding to the stationary compression fitting. When the compression knob is turned to an adjusting position, the compression fittings release the pivot bracket and the standoff rod with a single action.