Integrated Amplifiers

Although TAD's M2500 power amplifier [HFN Feb '10] – the launch platform for its Class D architecture – is a more powerful design, into 8ohm at least, its technical 'fingerprint' is clear to see in the performance of this new A1000 integrated model. Distortion, for example, remains very low indeed at 0.0003% from 20Hz-800Hz and is <0.002% through the midrange up to about 40W/8ohm, increasing to just 0.01% at 150W/8ohm. In both the M2500 and A1000, distortion rises at higher frequencies [see Graph 2, below] as does the output impedance, both a function of the reactive output filter and the latter being the cause of response variations when loaded by a 'real' loudspeaker [see boxout]. So, distortion increases from just 0.0015%/1kHz to 0.021%/20kHz (re. 10W/8ohm) before rising to 0.28%/20kHz at 100W/8ohm. Gain is a generous +41.6dB but noise, as we saw in the M2500, is 10-20dB higher than we'd expect from a contemporary Class AB or Hypex/Purifi Class D amplifier, realising a 75dB A-wtd S/N ratio here (re. 0dBW).

So what about power? TAD rates the A1000 at 250W/4ohm and, in practice, it achieves 2x185W/8ohm and 2x310/4ohm with – unusually for a Class D amp – an increase under dynamic conditions to 240W, 422W and 787W into 8, 4 and 2ohm loads, respectively [see Graph 1, below]. Note that while distortion also increases more markedly into lower impedances, into the lowest 1ohm loads the A1000 is protected at 763W (27.6A), making this integrated more tolerant of very difficult loudspeaker loads than the M2500, which cuts off at 435W/1ohm (20.8A). This being a Class D design, the A1000 also achieves a full 85% efficiency when servicing a 2x150W/8ohm output. PM