Усилители мощности моно — Fluo DM250

FLUO, the Winchester amplifier maker behind the Fast Linear Ultimate Operation name, places the DM250 in the middle of its three power amplifiers. It is a two-channel unit built as a pair of mono amplifiers inside one enclosure, and it goes a step further than the smaller DM125 by giving each side its own mains transformer fed through its own power cord. According to the company, this brings the DM250 closer to the behaviour of its separate M500 monoblocks, because a large current draw on the right channel no longer affects the left, and vice versa.

Key specs that matter

Output is 250 W per side into an 8 ohm resistive load and 500 W into 4 ohms. Into 2 ohms the short-term rating of 1,000 W is trimmed to about 900 W by the required mains fuse, a 6.3 A slow-blow type that limits long-term draw to 1,450 W for each channel. Idle consumption is 100 W, measured on 230 V mains. Input impedance is 40 kOhm on the balanced XLR socket, wired with pin 2 positive, and 20 kOhm on the unbalanced RCA socket. The enclosure has a footprint of 485 by 535 mm and stands 270 mm tall.

Engineering and use context

FLUO builds the output around one high-current MOSFET die per channel. The company rates this device at 388 A of peak current, while its circuit needs no more than 38 A even into a difficult 2 ohm speaker, so the transistor stays within the lowest tenth of its range, where it is most linear. Internal resistance of the device can fall to 0.022 ohm, roughly a hundredth of a hard speaker load. To keep resistance low elsewhere, the power supply current leaves the circuit board through 2.5 sq mm wires, returns to the board, and travels by wire again to and from the output relays. FLUO notes that a 105 micron copper track would need to be about 25 mm wide to match those wires, and admits that the approach adds hand-assembly time. Supply capacitors are specified for low internal resistance even at 100 kHz. Signals at 200 kHz and 201 kHz are filtered out, since together they can produce a 1 kHz tone inside the audio band.

Pairing

The company points to low-impedance speakers with heavy-coned woofers as the kind of load its low output resistance is meant to grip. For a source, the FLUO PRE1 keeps 20 kOhm on both the plus and minus legs of each XLR input and drives its outputs from 75 ohm on RCA and 150 ohm on XLR.

Alternatives

The FLUO DM125 keeps the same enclosure and dual mono circuit at half the rated output, with per-channel capacitors, rectifiers and transformer windings.