3 The principle of MFB by current positive feedback

　Current positive feedback is so-called expanded electromagnetic damping .




　　Voltage and current are detected and observed in this circuit ..


　After the 4th wave ends, electric current is flowing, but this is flowing due to the
electromotive force of the speaker.

　　　The wave form is similar as for the electric current and the verocity and opposite in
derection. It suggests that it becomes verocity feedback if reversed current signal is
feedbacked.

　Actually the current signal which the suitable voltage signal is subtracted with the bridge is returned or only electric current positive feedback .But it is all right with both.

　　In addition when voltage is zero, verocity becomes visible. And I utilizes this afterwards.

K1529 current positive feedback amplifier

　100Hz four burst waves




　　In the voltage output amplifier as for the voltage waveform to the last it was faithful
to the input signal, but in this case voltage of the first wave is high and voltage that stops
the excessive movement of voice coil seems to occur.



　 It is understood well when it is compared with the verociy

For reference

　　Here I mention little, but let me look at the case of detection coil type verocity MFB.







　　It is controlled so strongly .

　Detection coil system MFB and electric current positive feedback are both verocity MFB,
but their characters are somewhat different.


　　Detection coil system MFB

　　1 Verocity MFB

　　2 Output impedance of amplifiers remains

　　3 The electromagnetic damping quantity decreases also due to the fact that MFB works

　　4 Influence of the voice coil inductance in high frequency remains .

　　5 There is no deterioration of electric current distortion


　　Electric current positive feedback

　　1 Verocity MFB

　　2 Output impedance of the amplifier goes down in regard to appearances

　　3 When electric current positive feedback works, it seems as if electromagnetic
　　　damping increases.

　　4　The influence of voice coil inductance in high frequency furthermore deteriorates.

　　5 Electric current distortion increase .

　　If you look at the diagram, it becomes clear.