The THD+N vs. Power Output measurement shows that the ZX-7 delivered 400 watts into 8 ohms before clipping (defined as 1% THD+N), and 600 watts into 4 ohms. At the spec of 300 watts into 8 ohms, distortion is 0.01%.
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The measured Frequency Response was 10 Hz – 50 kHz, - 1 dB. Depending on the output voltage, the response rolled off. Notice that at 20 volts, it drops suddenly at about 72 kHz. Apparently, as voltage rises, the ZX-7 is designed to limit the frequencies out of the audible band.
Conclusions
The Lexicon ZX-7 is some kind of amplifier. Clear, detailed, and with enough power for even the most demanding aficionado, it is a highly recommended addition to your home theater portfolio.