Усилители мощности стерео — Naim NAP 500 DR

The NAP 500 DR is a two-box stereo power amplifier from Naim Audio of Salisbury, England, where each unit is assembled by hand over several days. The first NAP 500 appeared in 2000. The current DR version carries the NA009 output transistors and the Discrete Regulator technology that Naim first used in its Statement amplifier, and the company says the design work took six years together with specialist parts suppliers.

Key specs that matter

Output is 140 W per channel into 8 ohm, and the amplifier is rated for prolonged output into 2 ohm, which is also its minimum load impedance. Gain is +30 dB. Two balanced XLR inputs present an impedance of 18 kohm, and the speaker outputs use 4 mm banana sockets. Frequency response is -3 dB at 1.5 Hz and at 100 kHz. The amplifier chassis is 432 mm wide, 160 mm high and 520 mm deep and weighs 25 kg in a brushed, black-anodised finish, with the supply housed in a second enclosure. Mains voltage can be 100 V, 115 V or 230 V at 50 or 60 Hz.

Engineering and use context

The transformer and the first power supply stages live in the separate 500 PS, which keeps electromagnetic interference away from the amplifier circuits. Inside that box a 1,100 VA toroidal transformer feeds 12 raw DC supplies. Each channel is built as a bridged amplifier, a topology that Naim says permits faster and less intrusive protection circuitry, and every channel has ten stages of local regulation based on DR modules, which reduces the dependence of the circuit on the power supply and on thermally induced noise. The NA009 transistor was developed over more than a year with a semiconductor specialist to widen bandwidth and cut distortion. An intelligent variable speed fan system provides discreet extra cooling only when required.

Pairing

Signal can arrive only over the two XLR sockets, so the matching preamplifier must offer a balanced output. The stated ability to sustain output into very low loads means low-impedance or reactive loudspeakers can be driven without derating the amplifier. Two cases have to be placed, one for the amplifier and one for the 500 PS, so shelf space for both units should be planned before purchase. In a Naim system the amplifier can be combined with the NAC 552 preamplifier, which also uses a separate power supply and DR regulation.

Alternatives

The Naim NAP 300 DR follows the same two-box layout with a separate 300 PS supply, NA009 transistors and DR regulation, delivering 90 W per channel into 8 ohm.