McCormack Power Drive DNA-1 power amplifier 1995 Measurements

Sidebar: 1995 Measurements

The McCormack DNA-1 Deluxe had very similar measured performance to that of the DNA-1, but bettered the original in some respects. I'll report only the differences in measured performance (see my original review for the full measurements).

Distortion levels into lower impedances were lower in the Deluxe than in the DNA-1. Fig.1 shows the THD+N percentage vs frequency curves at 2.83V into 8, 4, and 2 ohms. It can be seen that reducing the load impedance doesn't result in appreciably higher levels of distortion. For comparison, the DNA-1 had much higher distortion into 2 ohms (more than 0.1% in the midband and treble)—a trait not seen in the Deluxe.

Fig.1 McCormack DNA-1 Deluxe, THD+noise (%) vs frequency at (from bottom to top): 1W into 8 ohms, 2W into 4 ohms, 4W into 2 ohms.

I measured a slightly higher output impedance in the Deluxe: 0.06 ohms at 1kHz compared to 0.01 ohms for the standard DNA-1. These are both very low values, however, and mean that the amplifier won't interact to any significant extent with the loudspeaker's impedance. DC offset was a low 0.7mV from both the left and right channels.

The Deluxe's maximum power output is specified as 150W into 8 ohms, 300W into 4 ohms (both equivalent to 21.8dBW). With clipping defined as 1% THD, the DNA-1 comfortably exceeded its specifications, putting out 178W into 8 ohms (22.5dBW), 315W into 4 ohms (22dBW), and 530W into 2 ohms (21.2dBW). These figures are with both channels driven at 1kHz—except the 2 ohm measurement, which was made with one channel driven so as not to blow the 8A rail fuse. The THD percentage vs output power plots are shown in fig.2. The amplifier's clipping behavior is unusual in that it soft-clips before the distortion shoots up. The sharp "knee" in the distortion traces typical of solid-state amplifiers is absent.

Fig.2 McCormack DNA-1 Deluxe, distortion (%) vs output power into (from bottom to top at 10W): 8 ohms, 4 ohms, and 2 ohms.

These measurements indicate that the DNA-1 has an excellent ability to deliver current to low-impedance loads. While not in Krell territory in this regard, the Deluxe's ability to increase its output power as the impedance drops is unusually good for an amplifier in this price range. (A Krell will run all day long driving both channels at full power into half an ohm.)

Fig.3 shows the DNA-1 Deluxe's intermodulation spectrum when driven at 75W into 4 ohms. The harmonic distortion levels are moderate in level, though upper-order components are apparent. Their presence didn't correlate with my impression of a smooth treble and liquid textures. The sonically benign third harmonic is, however, the highest of the distortion products at around 0.05%—significantly lower than in the original.

Fig.3 McCormack DNA-1 Deluxe, spectrum of 50Hz sinewave, DC-1kHz, at 75W into 4 ohms (linear frequency scale). Note that the third harmonic at 150Hz is the highest in level at -66dB (0.05%).

I also performed an FFT on the Deluxe's output when it reproduced a combination of 19kHz+20kHz at 150W into 4 ohms (fig.4). The intermodulation components at 1kHz, 2kHz, 18kHz, and 21kHz are moderately high in level, although the rest of the spectrum is fairly clean.—Robert Harley

Fig.4 McCormack DNA-1 Deluxe, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 150W into 4 ohms (linear frequency scale).

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