Интегральные усилители — Sugden Audio A21

The A21 is the pure Class A integrated amplifier at the centre of the A21 series from Sugden Audio, a firm run by J E Sugden & Co Ltd in West Yorkshire that has handcrafted amplifiers in Britain since 1967. Its lineage goes back to the original A21 of that year, which British engineer James Sugden designed as the first production Class A transistor amplifier. The circuit has since been upgraded step by step rather than replaced, and Sugden notes that many first-generation units are still in daily use after fifty years. The current version carries a US price of USD 3,650.

Key specs that matter

Rated output is 25 W per channel into 8 ohms. Response is held within plus or minus 1 dB from 10 Hz to 20 kHz, while the wider bandwidth extends from 6 Hz to 200 kHz. Noise sits more than 83 dB below full output. Line inputs need 170 mV to drive the amplifier to full output. The optional phono stage accepts moving magnet cartridges at 3 mV with 47 kohm loading and moving coil types at 0.2 mV with 470 ohm loading. The case measures 92 mm high, 430 mm wide and 355 mm deep, and the packed weight is 11 kg.

Engineering and use context

Sugden builds the output section as a single-ended voltage rail circuit biased fully into Class A, so the output devices conduct across the entire waveform instead of handing over between halves. The company offers two versions. The standard A21 includes the MM/MC phono input next to four line inputs, while the A21L omits the phono board and uses line inputs only - it can be retrofitted with phono capability later if a turntable joins the system. Around the back sit one pair of stereo binding posts, a pre-out, a tape out and an earth terminal for the record deck ground lead. A handset controls volume remotely. The slim front panel keeps the unit shallow enough for a standard equipment rack, and Special Signature editions of the A21 are also offered with further refinements.

Pairing

With its modest output, speakers of reasonably high sensitivity and a benign impedance curve suit the amplifier best, particularly in a room of around 20 m2. Through the pre-out, owners may later add a stronger stereo power stage or a powered sub, and the tape out feeds a recorder. Vinyl owners can connect either cartridge type directly to the phono version without a separate stage.

Alternatives

The Sugden Masterclass IA-4 is the larger Class A integrated amplifier from the same maker, rated at 33 W per channel into 8 ohms.