Power Amplifiers

Lexicon ZX-7 Multi-Channel (300 watts x 7) Power Amplifier

ARTICLE INDEX

Harman International owns a number of very fine audio companies, including Mark Levinson and Lexicon. Each of the companies benefits from trickle down technology that is developed at Mark Levinson, which is the top of the line.

Mark Levinson products, some of which we have reviewed, have unsurpassed performance, and the price of the products reflects that. Lexicon is no slouch either, and the price is not much lower than Levinson gear. Sort of like comparing a Mercedes to a Rolls Royce. The Rolls has more prestige perhaps, and is several times the price, but you ride in style regardless of which car you own.

Anyway, what I am saying is that if you can't afford to buy Mark Levinson, you really are not settling for second best if you get Lexicon. When the products are that good - and they are - trying to define differences is not easy.

Specifications

  • Power: 300 Watts RMS into 8 Ohms x 7; 450 Watts RMS x 7 into 4 Ohms
  • Fully Balanced Design
  • MFR: 20 Hz - 20 kHz, + 0.1 dB, - 0.2 dB
  • THD+N: 0.05% 20 Hz - 20 kHz
  • Input Sensitivity: 3 Volts for Full Output
  • Input Impedance: 10 kOhms
  • XLR and RCA Inputs for All Channels
  • Dimensions: 9.7" H x 17.3" W x 20.3" D
  • Weight: 145 Pounds
  • MSRP: $10,000 USA
  • Lexicon

The Design

The subject under examination here is the Lexicon ZX-7, which is their new 300 watt per channel power amplifier, obviously aimed at the home theater and surround sound music market.

It's a fully balanced (differential) design, with each amplifier channel being a module inside the chassis. The modular approach seems to be the one that manufacturers have settled on, as it makes assembly and maintenance much easier. If one channel goes bad, you slide the defective module out and slide a new one in. No messing around with circuit boards that have electronics for more than one channel on them. The only parts that are shared by all the modules are two toroidal transformers.

The front of the ZX-7 is very conservative (as is Mark Levinson). The quality of chassis machining is there, but without any frills. The front plate is thick and routed with the Lexicon logo.

The only control is the On/Off push-button that moves the amplifier from Standby to On.

The rear panel has XLR and RCA input jacks for each channel, one pair of binding posts for the outputs, and two AC power cord jacks with on/off toggles. These switch power on to the two toroidal transformers. Two are required because the ZX-7 can output 3,000 watts into 4 ohms, which means one 20 amp circuit won't handle it. You need two.

This amplifier is big and very heavy. Don't try to lift it by yourself. I had a friend help me shift it into position for the listening and bench tests. I have had enough torn shoulder rotator cuffs from trying to move big amps by myself. The last one took two years to heal.

In Use

I tested the ZX-7 with a home built media server, McIntosh MCD201 SACD player, Lexicon MC-12B SSP, Final Sound electrostatic speakers, and Carver Amazing Mark IV ribbon speakers. Cables were Legenburg and Nordost.

I will tell you that this amplifier really puts out the juice. With all the test media, including music and movies, the room just shook with music and sound effects.

lexicon-zx-7-amplifier-movie-the-kingdom.jpg

You know from past reviews that I am a big action movie fan, and The Kingdom is just such fare. Whether the bullets were whizzing at good guys or bad, I ducked for cover. Deep bass explosions were no problem for the high current capability of the ZX-7 either. I set the Lexicon SSP to not crossover anything to a subwoofer when using the Carver ribbon speakers (electrostatic speakers really need to be crossed over at about 50 Hz even when using full range panels), and the 12" woofers in each Carver were really moving some air.

Eastern Promises is not a bang, bang, boom, boom film, but it certainly has action. The soundstage was perfect, and voices were crisp and clear, without being overly sibilant.

lexicon-zx-7-amplifier-movie-eastern-promises.jpg

In general, the sound had just enough snap to it, so that everything was clear and detailed to a very enjoyable level.

It got pretty warm during use. It's a Class A/B design, and I suspect it is biased about 10 watts into Class A.

Surround sound music, such as Mozart Flute Concerto and Symphony No. 41 (Telarc SACD) sounded wonderful too. Some consumers wonder why anyone would need so much power, and the reason is overhead. Most of the time you probably would be listening at 10 watts or less, but along comes a big transient, and 300 watts will give you about 13 additional dB of dynamics.

All instruments remained distinct, even at high output, suggesting low IMD, and that turned out to be the case, as you will see in the bench test results section below.

If you want to test an amplifier (speakers and subwoofer too), try organ music like this Telarc SACD. No problem for the ZX-7. If you want to play it with the most efficiency, let your subwoofer do the 20 Hz - 50 Hz stuff, and use your SSP or receiver crossover to high pass everything else.

lexicon-zx-7-amplifier-music-mozart.jpg

lexicon-zx-7-amplifier-music-baroque.jpg


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.

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.