Product Review - Meridian 558 Five-Channel Power Amplifier -
January, 2001

Colin Miller

Meridian 558 Five Channel Power Amplifier

Rated Power:  200 Watts RMS per Channel, all Channels Driven, into 8 Ohms

THD: < 0.05%

S/N: 100 dB

Size:  7 3/4" H x 19" W x 18 1/4" D

Weight: 115 Pounds

MSRP: $5,995 USA


Meridian America Inc., Suite 122, Building 2400, 3800 Camp Creek Parkway, Atlanta, Georgia 30331; Phone 404-344-7111; Fax 404-346-7111.

Meridian Audio Ltd., Stonehill, Stukeley Meadows, Huntingdon, Cambridgeshire, PE18 6ED, England; Phone [44] 1480 52144; Fax [44] 1480 459934; Web


One day my wife pipes in with, “A stereo is no more important than a cozy blanket on a cold day.”  THE NERVE! 

I spend a lot of time with audio and video equipment on a daily basis, work or play, night and day.  A couple nights ago, I had my first video dream - trying to calibrate a Sony VPH-G70 CRT projector for my parents who had a house plant bending the screen.  Maybe that was a nightmare.  But back to my wife . . .

My first reaction to her comment was to take offense.  After all, this is the same woman who has, on more than one occasion, questioned my ability to complete a competent solder job with my various A/V connections.  My soldering is adequate, thank you very much!  I don't go around talking smack about digital image processing in pre-press applications (her work), and this is the grief I get!

But after a cool-down period, I realized that a cozy blanket can be a tremendous luxury on a cold day.  In a way, one could extend, or perhaps narrow, the analogy to a premium quality outboard amplifier.

Just as you don't need a cozy blanket on a cold day, short of preventing yourself from getting sick and catching your death, you certainly don't need an ultra-high quality separate amplifier to allow you to either listen to music or a movie.  A basic receiver will drive almost any loudspeaker with enough fidelity to allow you to hear most of the dialogue, at volume levels that most people would consider entirely adequate.  Some people actually use the speakers in their television to watch a movie too.  (Just nod and smile condescendingly, and we can be sensible among ourselves.)

Then again, most people don't day dream about XLR, RCA, and BNC connectors, figure out the step-down ratio of the transformer used in a particular power supply, consider their favorite album or film somewhat half-baked or a moderate success purely because of the sound track or video quality, nor get indignant when a “knowledgeable expert” mentions the Yamaha NS-10 as a recording industry standard for near-field monitors (they're really just an industry standard for mediocre consumer speakers.)

The Meridian 558 was not created for most people.  It was created for those who are absolutely obsessive about sound.  I like to believe that the 558 was created for people like me.

And she says, “Why do you need so many amps? and  “Why do we have so many speakers?” and “Pickup your socks!”  Ah, the tyranny of love.  And I do love my wife, but when a sleek, sexy, 115 pound British bombshell lays down on my desk and asks for an examination, what am I supposed to do, say no?  Yeah, right.

Most audiophiles steeped in their own culture know Meridian as specialists of digital audio.  Many consider the Meridian 508.24 CD player one of the best available at any price.  Other products, including their surround processors and digital loudspeakers, have earned a distinguished reputation for advancing the state of the art application of DSP to the audio field.  By upsampling, noise shaping, matrix decoding, phase compensation, or other processes in the digital domain, many owners of Meridian products have become that much cozier with their audio blankie.  Mention digital audio among those in the industry, and Meridian will probably come up in conversation.

I sometimes wonder if the people at Meridian ever mind having the image of a primarily digital company.  I mean, digital is good.  Digital is the most potent future of technological advances in audio reproduction.  Anyone who disagrees with that has either got a serious case of denial, their head in a hole, the other way around, or all three.  Still, what many people don't realize is that creating good digital products requires a thorough understanding of analog realities.  Good digital without good analog is squat.

The 558 five-channel power amplifier is Meridian's newest flex of analog muscle.  Balanced XLR and unbalanced RCA inputs all the way around, two large toroids feeding five sets of capacitors, the capability to run bridged as a two-channel beast, beefy gold-plated binding posts for speaker hookup, a brushed, heavy face-plate finished in satin black, and enough girth to fill a hefty girdle . . . these things make the 558 an amplifier that just asks to be held.  Add a voltage trigger input to allow turning it on without unparking le butt, and we're good for a squeeze!  I feel lucky for not being slapped!

Each of the five channels has 20,000 µF of storage capacitance, for a total of um… math… um… 100,000 µF.  That's not obscene, but it leans toward the generous side, and with a rail voltage of ± 72 volts, provided by twin 1.2 kVA transformers (about 260 Joules total), the 558 was meant to swing baby!

The 558 is not just a fancy box with a lot of space inside.  What space isn't occupied by the power supply gives way to circuit boards and heat sinks, much to my fawning delight.

The main fuse in the rear is rated at 12 amps on the 120 volt model.  Assuming that you've got 120 volts at the wall socket, that breaks down to 1440 VA, more or less watts, that it can pull from the plug for the purpose of amplification, and the fuse value isn't just for show.

While messing around with the amplifier, loaded with enough resistors to supply all five channels with 4 ohms, I sent a full-scale continuous tone to all five channels to see if I had enough voltage output from the test device to overdrive the amp into clipping.  Indeed I did, and the amp mysteriously shut off.  Turns out I blew that 12 amp fuse right quick.  What, a review sample is supposed to get a vacation?  After replacing the fuse, and slowly inching the signal level up incrementally, I found that my output was more than 8 dB above the level required to make the amplifier clip, defined as THD of 1%.

And what was I doing messing around?  I was mildly interested in a little S&M, but what I really wanted to know was how my previous listening experience would relate to the distortion spectrum of the amplifier.  I figured a good place to start would be –10dB below that clipping point, where most critical listening would probably occur.

To look at the distortion spectrum (above) of this solid-state muscle amplifier makes you wonder about all that talk about the lower-order distortion of tube amplifiers sporting output limitations in the single digits.  Not only were the 2nd and 3rd harmonics extremely low in absolute terms, there was NOTHING else above the noise floor.  Either they just got lucky, or those Meridian guys really know what they're doing. I suspect the latter.

Just to allow an appreciation of what the harmonic spectrum means when we refer to lower order distortion vs. higher order distortion, see below the FFT at THD 1%, when the majority of the distortion is caused from exhausting the power supply.  The circuit itself is the same.  When clipping, you can see, and hear substantial higher-order distortion products.

I also ran a noise floor FFT with the unbalanced input shorted.  I didn't think to try the balanced input shorted, but since there's no cable to pick up noise, and the inputs are shorted, essentially shunting any spurious noise at the input, I don't think that it was necessary.

The largest components in the noise floor were powerline harmonics at 60 Hz, 180 Hz, and 300 Hz, all of which are easily below levels to meet the 100 dB Signal to Noise Ratio spec provided by the manufacturer.  If maximum output were determined as the clipping point that I measured, it would be at -8.36 on the graph.  Even the highest peak in the noise floor, at 180 Hz, is lower than -108dB compared to the point of clipping (at 4 ohms.)

The 10 kHz, ± 10 volts square wave results are shown left.  While the 558 doesn't swing voltage quite as quickly as some other amps available, due in part to the moderate bandwidth limits of 90 kHz (-3dB), more importantly, it doesn't overshoot or ring.  This implies responsible engineering, indicating not only that the design probably doesn't abuse negative feedback for the sake of arbitrary specs, but that the amplifier will most likely be stable, even in the presence of RF or loads such as electrostatic panels, which become  more difficult to handle as frequency rises, due to falling impedance and increasing phase shift.




Strapped into the rest of my audio machine, the 558 fit right in.

In a theatrical application, the 558 acquitted itself with sometimes frightening confidence.  When the foot came down, the house quivered, and I squealed inside like a little kid.  "Toy Story", and "Toy Story II" recently made the family DVD collection, and with the 558 harnessed to the MPS-2510s, entrances had a bang, splash, and sizzle, with a dash of aplomb to boot.  I cranked up, and the 558 leaned in with a pearly grin.  Mmmmm

Musical material, rendered by the Meridian 508.24 that I had tricked Stacey into letting me borrow, was just plain juicy from the lower mid-range on up.  Sweet, wet, vivacious and pumped, sometimes with a hint of steam or spittle, but never to the point of syrup, I enjoyed chaperoned meetings with Sarah McLaughlin's “Witness,” Sinead O'Connors' “Red Football,” and Dave Brubeck's “Take Five” with guilty intimacy.  Were I prompted for more adjectives to characterize the performance potential of the 558, I would add smooth, rich, and graceful.  Shall I risk, even pleasant?

I say performance potential because although I think that the 558 leans towards the direction of well-mannered, and is certainly no shrew, it is at heart an honest amplifier, as opposed to a euphonic one that makes almost everything sound “nice.”  In this way, it reminded me much of my Aragon amps, particularly in the mid-bass and midrange.  There is a clarity and definition of depth available that render recordings more naked than not, for better or worse.  While it doesn't necessarily prevent me from enjoying them, most of the albums I choose to listen to aren't recorded as well as I would have liked.  In such a situation, the 558 isn't coy in letting you know about it.  It may be a little less blatant about it in the very top-end than the Aragon counterparts, but not much.

As much as I'd like to appear as sophisticated and discerning as the next hack by coming up with some minor complaint about the sonic performance of the 558, I can't really do so in good conscience.  I guess that there are a few amps out there that have a bit more muscle into lower impedances, but I'd wager the 558 refinement and poise in league with the brute force it does possess more than makes up the difference.

I suppose one could argue that no amplifier is perfect, and I sure wouldn't take up the argument against that statement.

Still, even though I like the variety of more amps than necessary at any given time, if I had to settle down in audio land, and commit to a monogamous relationship, I can't see not being happy ending up with the 558.  It's a true beauty, inside and out.

Perfection is impossible.  Watch out impossible, the 558's comin'.

- Colin Miller -

Equipment used for comparison, reference and pleasure:

Meridian 508.24 CD Player
M&K MPS-2510 (LCR) Studio Monitors
M&K S-85 & S-80 (Rear) "Satellite" speakers
Sunfire Stereo Power Amplifier
Aragon 8008BB Dual-Mono Power Amplifier
Aragon 8008X3 Three-Channel Power Amplifier
Onkyo TX-DS989 Digital Receiver
Yamaha RX-V995 Digital Receiver
Toshiba SD-2109 DVD Player
Audio Control Rialto EQ providing EQ and X-over to...
Dynaco ST-400mkII 2-channel amplifier driving...
NHT 1259-based subwoofers (only 2 for now)

© Copyright 2001 Secrets of Home Theater & High Fidelity
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