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Product Review - NAD 218THX Power Amplifier - December, 1996

By Daniel Long

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NAD 218THX

USA: NAD Electronics USA
89 Doug Brown Way, Holliston, Massachusetts 01746
Phone: 508-429-3600, Fax: 508-429-2426
Singapore: NAD Singapore Pte Ltd
55 Genting Lane, Singapore 349563
Phone 65-748-8918, Fax 65-748-9066


NAD 218THX Power Amplifier; Two channel power amplifier, power output 200w rms/ch into 8 Ohms (225 w rms/ch for 120 V USA version; all subsequent specs are for 230 V version only, check
http://www.nad.com.au/product/amps/218.html for more details about 120 V version); Frequency response 20 Hz - 20 kHz + 0.3dB; THD at rated output < 0.03%; Input impedance 47kOhm, 700pF; Slew rate > 100 V/msec; Damping factor > 200; Size 6 +" H x 19" W x 14 +" D; Weight 51 pounds; US$999; UK: Phone 011-44-181-349-4034, Fax 011-44-181-343-3871.

Introduction

What's almost 10 pounds heavier, about the same size as the NAD 208THX power amplifier, and differs by one character in the model number? If you guessed the 218THX, you're right. The 208THX still sits on top of NAD's power amplifier range, and the 218THX is more conservatively rated at 200W (225W USA version) into 8 ohms compared to the 208THX's 250W into 8 ohms. Also, when bridged, the 208THX puts out a shocking 1.8kW of power instantaneously into a 4 ohm load, while the 218THX is "only" rated at 1.2kW. Lastly, the 208THX costs US$1,699 compared to the 218THX's US$999.

So why the two "similar" models? I communicated with NAD's Cas Oostvogel, and it seems although physically the 218THX is bigger and heavier (due mainly to the size of the larger "Holmgren" toroidal transformer), it puts out current from a stiffer transformer, while the 208THX utilizes a dual rail system. Hence, the 208THX is able to supply more current instantaneously than the 218THX due to its more efficient design and operation. Also, as you probably know by now (if you don't, please go read the review of the 208THX which was published in May, 1996,
here in Secrets), the 208THX uses MOSFET output devices which are felt to sound more "musical", although less powerful per device, than bipolar-type devices.

Despite this, the 218THX's transformer weighs a very hefty 10.5kg (that's more than 23lbs, about half the weight of the whole amp!!) The 218THX uses a total of 8 capacitors (type not indicated) with a total of close to 40,000uF (each 4,700uF). Using 8 small caps instead of 2 large ones gives the advantage of lower ESR (Equivalent Series Resistance) and ESI (Equivalent Series Inductance), meaning a low power supply output impedance and a faster recovery time; this, explained Cas, should result in a better sounding amp.

Also, the 218THX's input stages are fed from a separate low-noise regulated supply; together with a carefully laid out PCB and "star" grounding, this results in a very noise-free output. And as my auditions show, the 218THX is absolutely quiet; no trace of irritating hum, even when used with the sometimes-hummy Audio Alchemy DLC.

So you're out looking for an amp for that home theater and you listen to music as well. Should you buy the 218THX or shell out an extra US$700 for the 208THX? Hopefully, this more in-depth look at the 218THX and how it compares with the 208THX will help you with this decision.

Front and Back

I must say the 218THX is about 30% more handsome than it's more powerful brother (actually 29.74825% according to calculations on my pocket sized Cray Computer). It now comes with a pair of very muscular-looking handles. On the front are the customary NAD LED indicators for Soft-Clipping Switch status and Power. Below the vertical array of LED's is the power button; when you power up the 218THX, the Power LED goes red initially but flips to green when "all's well" is detected (i.e., no shorts, no faults). Accompanying this red-green transition is something I like very much about the 218THX: the very loud and re- assuring "CLICK" of the protective relays dis-engaging. When I say loud, I mean it can be heard easily, from at least 12 feet across a room with two noisy toddlers screaming as loud as their lungs can pump out air (who needs an amp?).

Moving to the back, you see where money hasn't been spent (I hesitate to say "wasted" because that's a matter of opinion) on multiple sets of expensive speaker binding posts and the like. There are sets of balanced and unbalanced (RCA) line-level inputs as well as one pair (per channel) of speaker binding posts which take banana's or spades. Gone are the pair of hinged flaps that many people disliked on the 208THX. When we wired up the 208THX for comparison (my thanks to John Tan, an old friend who's now the Asia Pacific Sales Director for NAD, for the loaner), getting the speaker termination (in my case, banana's) in was not a problem; however this left the flaps almost at a 90 degree angle to the rear panel, which is a pain if you haven't got the space at the rear.

On the rear panel, you also get some slide switches for balanced/unbalanced operation and Soft-Clipping on/off. I did all the auditioning unbalanced (the input connections, not me!) direct from my Audio Alchemy DLC, and I left the Soft-Clipping switch off. My Mirage's M1090is were driven full range.

Music...

I used music that was quite dynamic first (this was also to facilitate break-in, as Cas suggested the 218THX needs about 40hrs of it). Well, he's right. More about this in a while. Out of the box, it was certainly very, very impressive, in that loud transients were cogently reproduced, having all the impact you could ever want. I used the Wilson Audio recording of "Winds of War and Peace" on WCD-8823 (Lowell Graham conducting the National Symphonic Winds) to determine if the 218THX could make the Mirages' flex the solid hollow-block concrete wall behind my listening area like my HSU sub can. With the HSU silent, the 218THX rattled my brains; I normally stretch my neck and lean the back of my head against the wall during this particular passage about a minute into track 1 (Liberty Fanfare). It didn't shudder the room quite as convincingly as the HSU does when it's playing, but the Mirages', driven full-range by my Audiolab, have never done this (happens only when played loud, which the Audiolab doesn't take too well to driving the Mirages' full-range).

On recordings with a strong and sustained bass line, the 218THX never let the Mirages' do their own thing. It dictated start-and-stop, especially of the four 6.5" woofers in the pair of Mirages. And again, this didn't change when I turned up the volume. It maintained this iron-grip as loud as I could stand. This was apparent on recordings such as Mickey Hart's new "Mystery Box" (Rykodisc RCD 10338), which is a fun CD. This is a good "crank it up" recording.

When I tried something less visceral (like the last track O Vazio, Tropic Affair on Reference Recordings RR-31CD) during the break-in, I found the presentation ever so slightly forward compared to the Audiolab. Images also tended to cluster in the vicinity of the two loudspeakers, even on recordings that present a very stable centrally placed image when reproduced by the Audiolab. I also tried some pink noise, and this proved to be slightly uplifted in the upper midrange and lower treble. Also, though extended, the very top end (which I believe you may not be able to hear, but instead perceive as airiness) tended to be a little grainy, again compared to the modestly-powered but very neutral Audiolab. This grain was apparent in that air didn't sound quite like air reproduced by a more neutral amplifier but instead sounded more like (slight) tape hiss.

This was present on most recordings. I decided to give the 218THX more time with LOUD music...

and Cinema

In the meantime, I watched movies with the 218THX again driving my Mirages full-range. The usual bass-workout movies like "True Lies", "Clear and Present Danger", "Twister", "Seven", all took turns in the Pioneer. Dolby Digital duty (DD or AC-3) was performed by the Marantz DP-870.

Truly impressive is how I would describe the experience. Bass had impact, effects were extremely startling if that was how it was on the LD. And that scene from "Heat" (if you've watched the movie, you know the ONE I mean!) If you've never played this movie loud, you don't know what you are missing. After the (long) shoot-out, you can almost smell the gunpowder and see where the bullets went!

Even during the initial hours of my time spent with the 218THX on movies, I noticed it's crisp upper-mids/treble, especially on soundtracks that were so. However, as I logged more hours, I thought it began to bother me less and less, until I hardly noticed it. Overall, however, the 218THX's 200 wpc were extremely valuable on demanding soundtracks, especially those with aggressive Dolby Digital mixes. After getting through the initial brightness, I was mostly caught up with what the 218THX did so well, that of doing full justice to the intense bass- punch and excitement of Dolby Digital soundtracks (mostly).

After the Fire

When I went back to music on the 218THX after almost 2 weeks of movies with intense sound tracks, I found the presentation still more forward than I prefer. However, that brightness in the mids/treble was now hardly noticeable. Whether I simply got used to it or otherwise, I can't say, but if I did, then it must have been a minor problem and hardly one to detract from the things the 218THX does right.

Compared to the 208THX

I found the 218THX to be even more of a muscle amp than the 208THX, which itself has earned accolades throughout the home theater world for it's superb performance as a bass amplifier (Tom Norton of Stereophile uses the 208THX to drive the enormous Snell SUB-1800's). In my opinion, the 218THX is the 208THX and more when it comes to meeting the demands of "here's my invitation"- type sudden explosions! When I watched this "True Lies" scene, the 218THX launched a wave into the room that pushed me back into my chair and held me there for an instant, something I didn't get to the same measure with the 208THX.

However, where the 218THX is firmly trounced is in the area of subtlety, resolution and liquidity, especially with music like the Golden String's original All- Star Percussion Ensemble. Using the 218THX, you would concentrate on the clarity and accurate reproduction of these percussive transients, and with the 208THX, you would also marvel at the beauty of these different types of instruments and simply enjoy the recording more. At the same time, these instruments take on more of a "body" when portrayed by the 208THX, and less that of a recorded entity.

Conclusion

For the money (US$999, S$1,350), I don't think you can realistically expect much better than the NAD 218THX's combination of high power control throughout the deep, mid and upper bass as well as most of the midrange and accuracy from there on upwards. It lacked the smoothness of the very best (in my case, the Audiolab and NAD's own 208THX were the comparison amps, so "very best" means them), but if you can live with this, the 218 is tough to beat. So, I give the 218 a hearty recommendation.

P.S. With regard to the 218THX's THX certification, this is only true if the amp is used with bridging set "off" and the unbalanced inputs are off. This contrasts with the 208THX's certification even when bridged (don't know about the input used).

Daniel Long
Singapore


Copyright 1995, 1996, 1997 Secrets of Home Theater & High Fidelity
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