Luxman Stereo Power Amplifier M-700u

A powerful drive circuit is necessary to amplify sound signals from a control amplifier with high fidelity and to exploit the performance of various speakers. M-700u has achieved the output of up to 840 watt + 840 watt @ 1 Ω instantaneously from the rated output of 120 watt + 120 watt @ 8 Ω and 210 watt + 210 watt @ 4 Ω. Speakers can be driven with its sufficient power under any load conditions. Moreover, the BLT mode allows the user to use the unit as a monaural amplifier with the rated output of 420 watt @ 8 Ω. A 4-parallel push-pull structure with 3-stage Darlington is used in this circuit to acquire such high power. The latest version, ODNF 4.0 circuit, that has achieved primary slew rate speed indicating the startup performance by feeding back only distortion components, ultra-wide bandwidth, and low level of distortion is adopted for the amplifier circuit, which is inherited from M-900u, our top-end model. Precise reproduction of a small sound signal has enhanced the elaborate sound expression and the expressive capability of tranquillity. Setting up to 6 W with which sound range can be practically and sufficiently acquired to the Class A operation range, it has made its high power consistent with sound expression of high density.
* ODNF is an abbreviation for "Only Distortion Negative Feedback".

In order to transmit the powerful drive force generated by the large-scale output circuit without any loss, super-thick wires for major current systems and large-capacity speaker relays with low resistance in which 4 contacts are connected in parallel are equipped. Transmission of thoroughly low impedance has been achieved, and 350 of the damping factor has been accomplished.

The beeline construction is adopted, which makes the internal configuration of the power amplifier reasonable and also makes the wiring route shortest. The traditional wiring pattern of the substrate with use of copper foil of approx. 100μm in thickness allows highly pure signal transmission to be achieved.

A loopless chassis structure is used for the cabinet to eliminate increased ground impedance and the effect of generated magnetic field. Gradation cast-iron insulator legs are attached to prevent resonance thanks to its characteristics of that the metallic structure becomes smaller from the center to the periphery of the leg.