Integrated Amplifiers

Well-built and keenly-priced, this entry-model to Line Magnetic's comprehensive tube range does get rather warm – the AC mains transformer (centre) readily reaches 55oC – so adequate ventilation is vital. Its specification is rather sparse, although the claim for 2x40W output is broadly met in practice with 2x43W/8ohm and 2x38W/4ohm being achieved via the 8ohm and 4ohm taps, respectively, at <1% THD. This is well within the compass of two EL34s operating in push-pull and there's even a hint of headroom under dynamic conditions, albeit with distortion relaxed to 2%, allowing the LM-34IA to deliver 49W/8ohm via the 8ohm tap and, via the 4ohm tap, 50W, 66W and 33W into 4, 2 and 1ohm loads [see Graph 1, below]. Overall gain is set at a sensible +39.5dB, residual hum and noise is acceptable at –66dBV (0.5mV) and the A-wtd S/N ratio is just a few dB below 'average' at 82.8dB (re. 0dBW).

As expected, distortion climbs with output level and at low bass frequencies through core saturation in the EI-style output transformers – from 0.35%/1kHz to 0.75%/20Hz at 1W/8ohm [black trace, Graph 2] and from 0.55%/1kHz to 2.3%/20Hz at 10W/8ohm [red trace]. These figures are not excessive, suggesting some compensation at work, and neither are these primarily 2nd/3rd harmonics the root cause of any colour attributable to the LM-34IA's sound. Instead it is excessive output impedance – a full 6.05-4.90ohm from 20Hz-20kHz, dropping to 1.79ohm/100kHz via the 8ohm tap (and a damping factor just shy of unity) – that serves up a deal of uncertainty in the 'sound' of this amplifier when partnered with a random choice of loudspeaker. PM