- Written by John E. Johnson, Jr.
- Published on 21 January 2008
On the Bench
THD + Noise measurements were made within an 80 kHz bandwidth.
At 1 kHz and 5 volts output into 8 ohms, THD+N was 0.006%.
At 20 volts, THD+N was 0.004%. This is 50 watts of power, which probably covers 99% of the signals we listen to.
At 10 kHz and 5 volts, THD+N rose to about 0.01%.
And at 20 volts, distortion was 0.144%. Having more distortion at higher frequencies is the way most amplifiers perform.
IMD at 5 volts into 8 ohms was less than 0.04%.
And at 20 volts, IMD was actually less, at 0.014%. If you look at the peaks around the 2 kHz fundamental, they are higher than the ones in the 5 volts graph. The reason the distortion number is less is because the fundamental is higher in relation to the distortion peaks than in the 5 volts test. Note also that there are more IM peaks around the 4 kHz, 6 kHz, 8 kHz regions (multiples of 2 kHz) than in the 5 volt test, but IM measurements only take into account the peaks at ± 250 Hz around the fundamental (2 kHz), so this is why showing the actual graph is important, rather than just giving a number.
For THD+N vs. Frequency into 8 ohms (1 kHz set to 5 volts or 20 volts output), distortion for both voltages stayed below 0.05% from 10 Hz to 4 kHz, then rose.
At 4 ohms, the distortion at 20 volts and 20 kHz was at 0.5%.
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%.
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.
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.