Усилители мощности моно — ModWright Instruments KWA 99

The KWA 99 is a solid-state monoblock power amplifier from ModWright Instruments of Amboy, Washington, designed by company owner Dan Wright and hand-built in the USA. ModWright announced it on 19 June 2023 and showed it for the first time at Pacific Audio Fest 2023 in SeaTac later that month. The company presents it as a follow-on to its KWA 150SE amplifier, packed into a compact enclosure at a lower price point, in the same way as its PH 9.0 tube phono stage.

Key specs that matter

Each chassis delivers 100 W into 8 ohm and 200 W into 4 ohm, with 450 W peak. Gain is 26 dB, and the owner's manual lists an input impedance of 47 kilohm. Frequency response runs from 10 Hz to 150 kHz at +0 and -1 dB. The noise floor is -90 dB unweighted, and THD stays under 0.05%. Each monoblock is 26.7 cm wide, 16.5 cm high including the footers and 40.6 cm deep including the 2.5 cm binding posts, and weighs 13.6 kg, or 15.9 kg as shipped. Units are built for 120 V, 220 V or 240 V mains, and the warranty period runs for five years from purchase.

Engineering and use context

Current-production Exicon lateral MOSFETs form the output devices. The circuit runs in Class A/B with a high Class A bias, though not in pure Class A, and the fully exposed heatsinks exist to carry the heat that such high bias produces while keeping distortion low. There is no global feedback. The RCA and XLR inputs are both transformer-coupled to the input stage with a floated ground, and that coupling also blocks DC from the source. Internal thermal protectors cut power on overheating, while short-circuit and over-current faults are handled by ModWright's TSP (Total Silent Protection) circuit, placed outside the signal path, which mutes the affected output. The output is a single pair of 5-way binding posts, red for positive and black for negative, and the amplifier cannot be bridged. Amber-lit VU meters on the front have a dimmer knob. After switch-on, blue internal LEDs flash for about 45 seconds while the amplifier warms up and stabilises, and a rear switch turns them off. A 12 V mini-jack trigger input switches the amplifier on and off with the rest of the system.

Pairing

ModWright tested the KWA 99 into 2 ohm loads, and if a speaker drops too low in impedance the over-current circuit mutes the output. The company designed it to work with its LS 99 tube preamplifier, which switches both monoblocks through the trigger link.

Alternatives

The ModWright Ambrose A30 is a single-ended Class A tube monoblock with three EL34 output tubes and a 12AT7 driver, rated at about 30 W with zero feedback.