About the MILO HP-4/MILO power amplifier

With the introduction of the MILO high-power curvilinear array loudspeaker, Meyer Sound performed a marriage of sorts: We combined the high-power, direct-coupled FET power amplifier from our X-10 loudspeaker with the power supply from our M3D line array loudspeaker. The union of these two technologies represents another stage in an ongoing evolution – some might say revolution – spanning 15 years of Meyer Sound power amplifier topologies.

With nearly limitless current reserves, each channel of MILO’s HP-4 four-channel amplifier delivers 1125 watts into a 4-Ohm load. The power supply uses a generous 30 Ampere @ 115V toroidal transformer with separate primary windings – each with its own 15 Ampere, resetable circuit breaker. With six 22,000 microfarad 85° C Cornell Dubilier electrolytic filter capacitors, a "soft start" circuit and a bypass relay controls the inrush current required to charge 132,000 microfarads of capacitance.
An electrostatic shield between the primary and secondary windings eliminates AC transients and noise from entering the amplifier along with a high-current RF filter on the AC inlet. A separate housekeeping power supply manages power control of the multi-tap primary windings for automatic switching of the low and high line voltages by selecting transformer taps for AC Voltages from 85 V to 265 V. The housekeeping supply also manages shutdown on faults: The system will automatically restart if it shuts down because of an over-voltage condition.

MILO’s circuitry for the driver and output stages provides pure Class A operation. Four pairs of high-current, complementary V-FET transistors in each output channel provide 10 watts of pure Class A and 200 watts of Class A/B; the amplifier will only enter Class H operation during extremely loud musical passages. V-FETS are high-speed (72 ns Rise Time) and low on resistance compared to lateral FETS commonly used in audio amplifiers.

A fast-acting DC servo circuit keeps DC from ever reaching the output. The DC detection circuit instantly shuts down the power supply, providing protection for both amplifier and loudspeaker. No relays are used in the output of the amplifier. The heat sink is forced-air cooled with temperature sensing to control the variable-speed low-noise and backup fans.