The early vibraphones used motors that were intended to power record-player turntables and had limited or no speed-adjustment capabilities. Whatever speed adjustments were possible were made by moving the drive belt among a small number of pulleys (usually three) of varying diameters. Later, variable-speed AC motors became available at reasonable prices. These motors allow the adjustment of the rotating speed by a potentiometer mounted on a control panel near the motor. They typically support rotation rates in the range 1–12 Hz. These motors remained the preferred solution until the 1990s and are still in use by some manufacturers.