Line Magnetic LM-34IA Integrated Amplifier Lab Report

Lab Report

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


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 5.7A


Distortion versus frequency at 1W/8ohm (black, 5Hz-40kHz) and 10W/8ohm (red, 20Hz-20kHz)

Power output (<1% THD, 8/4ohm) 43W / 38W
Dynamic power (<2% THD, 8/4/2/1ohm) 49W / 50W / 66W / 33W
Output imp. (20Hz–20kHz/100kHz) 6.05–4.90ohm / 1.79ohm
Freq. response (20Hz–20kHz/100kHz) –0.1dB to –0.85dB/–9.6dB
Input sensitivity (for 0dBW/40W) 30mV / 200mV
A-wtd S/N ratio (re. 0dBW/40W) 82.8dB / 98.8dB
Distortion (20Hz-20kHz, 1W/10W) 0.14–0.7% / 0.51–2.3% (8ohm)
Power consumption (Idle/Rated o/p) 150W / 232W
Dimensions (WHD) / Weight 377x190x345mm / 20kg
Price £1699

Line Magnetic Audio Co. Ltd
Zhuhai, China
Supplied by: VAL HiFi, Ashford, Kent
07717 477994