Integrated Amplifiers

The superb symmetry of the ATM-1e’s left and right channels is an example of what can be achieved with genuinely precise tube matching coupled with the highest quality output transformers. Many ‘Far East’ amps show poor matching, but the ATM-1e offers a full 65dB volume range to within ±0.5dB (2nd dot from the ‘Min’ end of the ‘Attenuator’ scale), stereo separation that’s >80dB (re. 20Hz-20kHz), and distortion that reduces from 1.3%/20Hz to 0.25%/1kHz (re. 10W/8ohm) on both channels [see Graph 2]. Noise, too, is very low, promoting a wide 88dB A-wtd S/N ratio (re. 0dBW). Naturally, distortion increases progressively with output from 0.02%/1W to 0.25%/10W and then 0.5% at the rated 35W (all re. 1kHz/8ohm from the ‘High’ tap). So the ATM-1e meets its spec. at a ‘proper hi-fi’ 1% THD limit, rather than its rated 5%, squeezing out that little bit more under dynamic conditions. Relaxing the THD limit to 3%, the ATM-1e delivers an impressively consistent 44W (‘High’ tap), 43W (‘Low’ tap), 43W and 36W into 8, 4, 2 and 1ohm loads, respectively [Graph 1].

While the amplifier ‘warms up’ swiftly – distortion is almost solely 2nd/3rd harmonic and decreases from 0.025% at switch on to 0.018% after 5 minutes and 0.017% after 30 minutes (all re. 1W/8ohm) – there is a gentle increase in gain from 29.4dB to 29.7dB over the first hour of use. If you are super-sensitive, and all else being equal, the ATM-1e/speaker pairing will become ~0.3dB louder over this period... Otherwise, the response is good to –0.3dB/20Hz, –0.25dB/20kHz and –3.5dB/100kHz via both ‘High’ and ‘Low’ taps into 8ohm and 4ohm while the 1.2-1.6ohm output impedance is lower than with most tube amps, ensuring a reduced variation in response with different speaker loads. PM