which could not be too long to be contained completely on one support. Initially, the plate was put in motion by a spring loaded with a crank, then thanks to the progress of the technology the electric motor was introduced.
Over time, there were different types of motion transmission from the engine to the plate: the first electric motor turntables used pulley traction, later replaced by rubber belts (belt drive), still used in many devices. Until the end of the 1970s pulley traction machines were also in production, which with particular mechanisms allowed the loading of multiple discs and their sequential reproduction. But they were not very high quality turntables because the automations caused great vibrations to the device itself.
A trend introduced recently in the use of belt drive is to move the motor outside the plate, considerably increasing the weight of the same to increase the moment of inertia and stabilize the speed of rotation.
Since the end of the 70s, the technology that connects the rotating plate directly to the driving shaft (direct drive) also appears; currently, to ensure maximum regularity in the rotation of the plate, the motor is controlled by an electronic circuit driven by a quartz oscillator. In some professional models the direct drive of the turntable is controlled by a potentiometer that adjusts the rotation speed so as to change the pitch of the disc reproduced. This pitch can go from - 1/8 to + an octave compared to playing the vinyl record at correct rpm. This function is defined as Pitch Adj. And is used mainly by Disc Jockeys who take care of mixing songs in continuous sequence, putting them "in time" with the same number of rhythmic beats.
Some more sophisticated models include the motor and the reading arm on two separate frames; these conceptual changes in the construction of the turntables have favored a reproduction quality more and more accurate and free from disturbances deriving from the vibrations, that even if imperceptible, the operation of the electric motor would provoke inserting rattles and buzzes in the sound reproduction. On the other hand, two-frame turntables require a technically accurate installation to avoid introducing arm angles and consequently reading the stylus.
Another technique introduced to combat the war on vibrations, this time outside, which could interfere with the correct sound reproduction of the discs is the use of conical feet that are mounted with the tip as a support of the turntable frame. these support points would limit the transmission surface of any environmental vibrations to the maximum.
To give the most demanding audiophiles the ability to quickly perform comparative tests on different models of reading arms and loudspeakers, some high-end turntables provide the possibility of mounting up to 4 reading arms.
The actual reproduction is done by placing the reading pin (pick-up) on the disk; this is supported by an arm provided with a suitable counterweight to obtain a pressure of the head on the predefined and calibrated disk. The arm can be connected to a joint placed on the base of the turntable so as to follow the path determined by the groove of the disc.
At the end of the seventies, some manufacturers offered turntables equipped with a tangential arm, ie arms that follow the shape of the head tangentially to the diameter of the disk, thus avoiding different reading modes deriving from the curvature of the path (tangential error), almost inevitable with articulated arms. Turntables equipped with tangential arm always have a high cost, due to the high degree of engineering and precision of their realization and for some models vertical operation is foreseen.
When the pick-up is placed on the disc, the irregular profile of the groove causes the needle to vibrate; this vibration is used to generate weak electrical signals from a coil included in the head body. This electrical signal is sent to the preamplification circuit; from here the signal is sent to the final amplifier, which transfers the signal to the speakers, finally turning it into sound.
