Pre/Power Amplifiers

From an amplifier’s perspective, driving low impedance (4 or 2ohm) loads means supplying sufficient current to maintain the voltage across the load, while delivering very high power into higher (8ohm) loads is more about supplying the volts in the first place. This is why most 500W+ amplifiers are bridged designs, doubling the amplifier’s voltage envelope without complicating the PSU infrastructure. Emotiva’s amplifier modules [inset picture] feature two matched cards per channel, each mounted on its own heatsink with four pairs of power transistors running off ±60V rails. Each pair of cards forms a single balanced/bridged amplifier module (per channel) with a maximum 120V swing.

There’s a further twist to the tale here, for without resorting to a Class D technology Emotiva has still achieved cool-running efficiency by blending a Class AB output stage with a Class H stepped-rail PSU architecture on each amplifier card. This switches up to a higher voltage PSU rail only when signal conditions demand it, minimising waste heat. It’s not dissimilar to the ‘Achromatic Audio Amplifier’ used in Benchmark’s AHB2 power amp [HFN Mar ’15]. Like the AHB2, the XPA-DR2 also features a similarly compact and efficient switch-mode PSU, albeit rated at a rather more substantial 3kW in this far beefier amplifier. PM