Интегральные усилители — ModWright Instruments KWH 225i

The KWH 225i is a hybrid integrated amplifier from ModWright Instruments, hand-built in Amboy, Washington, combining a valve preamplifier stage with a solid-state output stage. It takes the output stage of ModWright's Reference KWA 150SE power amplifier and the controls of the discontinued KWI 200 integrated amplifier, adds a valve preamplifier and raises the power. It is a current product in ModWright's range.

Key specs that matter

Output is 225 W into 8 ohm and 400 W into 4 ohm at 0.04% THD, with the first 25 W in Class A. The preamplifier stage uses two 6922 valves, which can be replaced by 6DJ8, ECC88 or 7308 types, and they bias themselves. The rear panel offers three RCA inputs, a balanced XLR input and an RCA home theatre bypass input that can also be used as a power amplifier input, and outputs are an RCA preamplifier output and two pairs of five-way binding posts. Gain is 30 dB, frequency response 20 Hz to 100 kHz, input impedance 20 kOhm, input sensitivity 2 V RMS and maximum input 6 V RMS. The amplifier measures about 451 x 165 x 445 mm and weighs about 29 kg.

Engineering and use context

The amplifier works in Class A/B with zero global negative feedback. Voltage amplification happens in the triodes at the input, while the solid-state output stage supplies the current for low-impedance loads. The input is transformer-coupled to protect against DC, thermal sensors monitor the heat sinks, and ModWright's Total Silent Protection disconnects DC at the output outside the signal path. A remote controls power, volume, mute, input selection and display, with volume shown from 01 to 99. After switch-on, the outputs stay muted for about 45 seconds during the valve warm-up period. A user-installable solid-state phono board adds one RCA input with 50 dB of gain for moving-magnet and high-output moving-coil cartridges, with loading of 50, 100, 500, 1,000 ohm or 47 kOhm and 100 pF. The amplifier needs about 5 cm of ventilation space around it, and ModWright gives a five-year warranty in North America to the original owner.

Pairing

Its rated output gives the KWH 225i ample reserves for both easy and difficult speaker loads. The home theatre bypass input integrates it with a surround processor, and the preamplifier output can feed a subwoofer.

Alternatives

ModWright currently builds no other integrated amplifier alongside the KWH 225i.