In part three, we defined the basic system configuration, discussed the selection criteria for the head unit and loudspeaker transducers, and included calculations to estimate the required amplifier power. Table 1 summarizes the results of the calculations from part three. In this month's article the component selection process will continue, with particular emphasis on amplifiers, interconnects, loudspeaker cables, and power cables.
Amplifiers
Last month, I established that each loudspeaker transducer would be powered by its own amplifier, preferably a monoblock. Robert Harley, editor of The Absolute Sound, says, "Monoblocks generally perform better than a single stereo unit for several reasons. First, because the two amplifier channels are in a separate chassis, there is no chance of interaction between channels. Consequently, monoblocks typically have better soundstage performance than stereo units. Second, monoblocks have completely separate power supplies, including power transformers; left- and right-channel amplifier circuits don't have to share their current source. This gives monoblocks the ability to provide more instantaneous current to the loudspeaker, all other factors being equal." Harley concludes, "If you want all-out performance and can afford them, monoblocks are the way to go."1
In addition to my preference for monoblocks, I prefer amplifiers that don't use cooling fans. I find fan noise in most amplifiers to be both audible and annoying. Fan-less operation was particularly important in my system because the amplifiers would be located directly overhead, essentially within 0.5 to 1.0 meters (20 inches to 39 inches) from the listening position. Therefore, it was important to find amplifiers with the necessary power output (as shown in Table 1) that didn't use fans.
Finally, and most importantly, I required the amplifiers to possess audiophile-grade sound and build quality. Although there are a number of high-quality amplifiers available, those manufactured by Genesis I.C.E. met my design requirements.2 Table 2 shows the Genesis Dual Mono and Dual Mono Xtreme amplifiers exceeded my power requirements as specified in Table 1. It's important to note that the subwoofer would demand considerable current from the Dual Mono Extreme, since its impedance was estimated to be 2.67 ohms (each isobaric pair would be wired in series and the three pairs would be wired in parallel). Table 2 also shows the maximum power consumption of the amplifiers.
In addition to superb sound quality and fan-less operation, the Genesis amplifiers possessed numerous attributes that were appealing to me as an engineer. First, I liked their ingenious, but elegantly simple design. The polished extruded aluminum chassis isn't only aesthetically gorgeous, but also an excellent heat sink and a secure mounting platform. Second, I liked the build quality. While many manufacturers mount the amplifier connections directly to the circuit board and "poke" them through the chassis, the Genesis Series III line of amplifiers, instead, solidly mount each of the connections to the chassis to isolate the stresses induced by the attached cables from the circuit board. These solid connection points accept wires terminated with crimp sleeves or ferrules, which I prefer instead of spade terminals. Third, the chassis fuses are located conveniently next to the power input connections. This is an important consideration for competitors, since IASCA requires access to fuses in 45 seconds or less and fuse replacement in 5 minutes or less.3