Large motional feedback system

• Introduction, requirements and system overview
• Power supply
• Input circuit
• Active cross-over filter unit
• LF amplifier with motional feedback
• MF amplifier with special distortion cancellation
• HF MOSFET amplifier with soft clipping
• Protections

Active cross-over filter unit:

The active cross-over filter unit is a fourthS-order three-way Linkwitz-Riley filter at 250 and 2500 Hz. It includes the linear characteristics of the loudspeaker units, measured after mounting.

The schematic is modelled using LTspice of which both the schematic and response are shown. LTspice is a freeware version of the well known SPICE simulator and is modified and made available by the semiconductor company "Linear Technology Corporation". The software van be downloaded here.

Note the ≈10% increased gain of the MF section to keep the summed response within +/- 1 dB gain variation.

Note also the important phase alignment of the units at the cross over frequencies guaranteeing a response that is not impaired by the direction of the listener in the vertical plane. This is a key benefit of the Linkwitz-Riley approach.

The LTspice code is found at the following zip-file of the filter model.

The power supply of the operational amplifiers is not drawn. It consists of standard +/-15 V series regulators that are supplied from the +/-20 V voltages from the Sub power supply-1 and is shared with the supply of the input section.