A system for controlling the pitch modification of the blades of a fan of a turbomachine, in particular for an aircraft, - the turbomachine comprising - a drive shaft extending along a longitudinal axis and adapted to be rotatably driven about said longitudinal axis with respect to a fixed structure of said turbomachine, - the blades radially mounted with respect to said drive shaft and adapted to be oriented at a blade pitch (θ) and - an orientation device configured to modify the pitch of the blades (θ) as a function of an axial load applied to said orientation device, - the control system comprising - a hydraulic actuator, configured to be rotatably integral with the drive shaft, in order to apply the axial load to said orientation device - a hydraulic pump, configured to be rotatably integral with the drive shaft, supplying the hydraulic actuator in order to apply the axial load to said orientation device as a function of the flow rate of the hydraulic pump, - which control system is characterized by the fact that it comprises - a connecting ring gear rotatably movably mounted about said longitudinal axis with respect to the fixed structure of said turbomachine, said connecting ring gear being mechanically connected to the hydraulic pump so that the flow rate of the hydraulic pump is proportional to the relative speed between the drive shaft and the connecting ring gear, - a magnetic coupling device configured to pilot the drive speed of the connecting ring gear in order to control the pitch of the blades independently of the speed of the drive shaft. - the turbomachine comprising - a drive shaft extending along a longitudinal axis and adapted to be rotatably driven about said longitudinal axis with respect to a fixed structure of said turbomachine, - the blades radially mounted with respect to said drive shaft and adapted to be oriented at a blade pitch (θ) and - an orientation device configured to modify the pitch of the blades (θ) as a function of an axial load applied to said orientation device, - a drive shaft extending along a longitudinal axis and adapted to be rotatably driven about said longitudinal axis with respect to a fixed structure of said turbomachine, - the blades radially mounted with respect to said drive shaft and adapted to be oriented at a blade pitch (θ) and - an orientation device configured to modify the pitch of the blades (θ) as a function of an axial load applied to said orientation device, - the control system comprising - a hydraulic actuator, configured to be rotatably integral with the drive shaft, in order to apply the axial load to said orientation device - a hydraulic pump, configured to be rotatably integral with the drive shaft, supplying the hydraulic actuator in order to apply the axial load to said orientation device as a function of the flow rate of the hydraulic pump, - which control system is characterized by the fact that it comprises - a connecting ring gear rotatably movably mounted about said longitudinal axis with respect to the fixed structure of said turbomachine, said connecting ring gear being mechanically connected to the hydraulic pump so that the flow rate of the hydraulic pump is proportional to the relative speed between the drive shaft and the connecting ring gear, - a magnetic coupling device configured to pilot the drive speed of the connecting ring gear in order to control the pitch of the blades independently of the speed of the drive shaft. - a hydraulic actuator, configured to be rotatably integral with the drive shaft, in order to apply the axial load to said orientation device - a hydraulic pump, configured to be rotatably integral with the drive shaft, supplying the hydraulic actuator in order to apply the axial load to said orientation device as a function of the flow rate of the hydraulic pump, - which control system is characterized by the fact that it comprises - a connecting ring gear rotatably movably mounted about said longitudinal axis with respect to the fixed structure of said turbomachine, said connecting ring gear being mechanically connected to the hydraulic pump so that the flow rate of the hydraulic pump is proportional to the relative speed between the drive shaft and the connecting ring gear, - a magnetic coupling device configured to pilot the drive speed of the connecting ring gear in order to control the pitch of the blades independently of the speed of the drive shaft.