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Product Review

ME 550 Series II Two-Channel Power Amplifier
July, 2002

David Wurtz

 

Specifications:

2 x 100 watts RMS 8 ohms DC-20 KHZ
2 x 150 watts RMS 4 ohms DC-20 KHZ
1 x 300 watts RMS 8 ohms DC-20 KHZ
Voltage Gain - 30 dB (33dB Bridge Mode) Maximum Output Voltage - 50 Volts (100 Volts Bridge Mode) 
Maximum Output Current - 40 Amps peak Input Impedance - 100k Ohms (unbalanced) Phase Non Inverting - 0 degrees 
Rise Time - < 1 Microsecond 
THD & IMD - < 0.1% 
Dynamic Headroom - 1.5 dB 
Hum & Noise - 99 dB below rated output Frequency Response - DC - 150KHZ +/- 2dB 
Energy Storage Matrix - 66,000 uF Transformer - 500VA Toroid
Options - High Capacitance option - this brings the total Energy Storage Matrix capacity to 160,000 micro Farads. It is suggested for larger speaker systems and those with multiple bass drivers or impedances of 4 ohms or less.
RRP - $1995AUS (+$425AUS for Hi-cap option)

ME Sound Pty Ltd
727 Wang Wauk Road,
Dyers Crossing, NSW, 2429 Australia.
info@me-au.com
http://www.me-au.com

Introduction

Recently, Peter Stein from ME Amplifiers did a re-evaluation of his range of power amplifiers from six models to three. In doing this, he has also kept the cost down to AUS$1995 (+$425 for the Hi Cap option, described below) for his base range of dedicated power amplifiers. This is really not a lot of money for an amplifier, especially one that can be upgraded (as all ME products are). I reviewed the ME 240 integrated amplifier last year with a very glowing outcome, so please read on and we will have a look at the new ME 550 series II with the Hi-Capacitance option (+$425) and see how it performed.

The Hardware - Outside

Externally, the ME 550 has classic gold lettering on gloss black background (on a brushed aluminum chassis) and four gold feet. A really great look in my opinion. The two grates (with accompanying filter pads) on the front are cooling ducts. The 550 has a huge 4” fan that is thermostatically controlled and draws air through the front two grates and exits out the back through the purple heatsinks. Yes, purple . . . . I have heard this referred to as a “gawdy” color on an amplifier, but I quite like it. Anyway, if you don’t like it, you don’t have to look at it as it is on the back.

There are also four lights arranged around the “Soft Touch” power switch. They are; “Operating Temp”, “On”, “Overtemp Cutout”, and “Standby”. I found the power switch took time for me to get used to, as there is virtually no movement when you press it, and the amp actually switches on about 1.5 seconds after you touch the switch. Occasionally, I pressed it again, thinking it was not turned on. The ME 850 (the bigger more expensive brother) does not have the same switch, feeling like I have actually pressed it.

The layout on the back is quite simple, with a toggle bridging switch, a remote “Power On” terminal, two pairs of RCA inputs (I’ll explain in a minute…), two pairs of high quality (5 way) banana plug speaker outputs, and an IEC grounded AC socket.

The two pairs of input RCAs are labeled “DC direct” and “AC coupled”. Essentially, you use the “DC direct” for connection to a servo-controlled preamp (an ME24 preamp for example), and the “AC coupled” for connection to other more typical products (CD players, valve or passive preamps, surround sound receivers etc.)

The bridging toggle switch converts the ME 550 into a 300 WRMS (into 8 Ohms) (400WRMS into 4 Ohms), brutish monoblock. Bridge mode is easily achieved by simply flicking the switch, inserting the input RCA in to the right input, and connecting the plus and minus of your speaker to the two positive speaker terminals, leaving the two black (negative) terminals disconnected.

The owners’ manual is very, very good and comes complete with trouble shooting charts to help isolate problems.

The Hardware - Under the hood . . .

Internally we see a modular construction for future upgrades if required. This idea has been used by ME (which stands for Modular Electronics by the way) since its arrival into the marketplace in1977, and now we see several other manufacturers using this idea to try to future-proof their products. No wonder, with today’s multi-format, multifunction audio society. The power supply is based around the ME Energy Storage Matrix, which uses dozen of smaller capacitors wired in parallel instead of one or two large ones. The PC board layout is very well organized, especially the layout of the output transistors. They are mounted on the heat sink and attached to the main PCB in a way that the transistor can be removed in a matter of minutes without removing the main PCB. This is in keeping with the modular design of all ME products.

The main PCB is quite crowded with primarily state-of-the-art electronic components. Many of these (capacitors, for example) are built especially for ME Sound, and labeled with the ME logo.

The ME 550 Series II has doubled the number of bipolar transistors (2SC3281 and 2SA1302) in the output stage from 8 to 16, compared with the Series I ME 550. They have also changed the types of transistors it uses, with Peter Stein saying, “The new ones are faster and more linear and have lower measurable distortion”.

The internal fan draws a huge amount of air through the system, and I noticed the air flow is a little noisy. With the amount of air moving, I would doubt the unit would stay hot for long after the fan kicks in.

Protection System

Essentially, the protection system is designed around disconnecting the power to the amplifier circuitry when a fault condition exists. Examples of this are High Frequency Oscillation, DC on the input of the amplifier, High level - Ultra low Frequency, and excessive internal temperatures (above about 80 degrees Celsius. If you have a particular problem with one or more of these conditions happening under normal operating conditions, the ME 550 can be modified to overcome or change the protection criterion.

The High Capacitance Option

This option is suggested for lower sensitivity speaker systems, ESL loudspeakers, or speakers with impedances lower than 5 Ohms. This option increases the total capacitance in the power supply to over 160,000 microfarads (it comes standard with approx. 66,000 µF). This in theory should give your ME 550 a better bass reproduction (increased bass integrity) and better transient response (or peak output capability). Considering it is about a 1/5 increase in price, it is in my opinion well worth it under any circumstances. Larger power supplies do make a sonic difference.

The Sound

The manual states the ME 550 should be at operating temperature (or about 90% of its potential sound quality) within a few minutes. I ran it for about an hour before doing any critical listening sessions or writing any notes.

I connected the 550 to my Osborn Reference Epitomes, Consonance Reference R1.1 tube preamp, Perpetual Technologies P1A- P3A combo DAC and DCE, and Redgum DVD Player as my transport. Cables were from Analysis Plus, Osborn, Eichmann, and some self designed.

I will start out by saying the overall sound of the ME 550 is very clinical (I’ll explain in a minute). Speaking in absolutes, I found that it very much gave me exactly what I put in, very tightly detailed and extremely transient. Not highly musical like a valve or MOSFET design, more rather sharp and somewhat aggressive.

This is not necessarily a bad thing, mind you. It is just the sonic signature of this amp, probably because it uses bipolar output devices, which have this characteristic.

Nothing musically lagged when being driven by the ME. Every note was quickly delivered, starting and stopping effortlessly and maintaining the integrity of even the most massive bass notes. This tightness was so-much-so, that I actually noted a little sibilance from time to time that I had not really noticed before when using valve or MOSFET designs. Again, bipolars have this characteristic.

Sound staging was good, and while not exceeding my Redgum Reference Monoblocks ($12,000 odd), it was more than acceptable.

Male vocals were handled well, with a nice, deep richness and no chestiness. Female vocals were equally well presented and accurate, while slightly missing some of the three-dimensional qualities than can be associated with them.

Acoustic guitars really shone through on the 550. The accurate and transient nature of the 550 and the recording of Australian guitar legend Tommy Emanuel provided extremely pleasing results.

The ME handled all high-energy music that I threw at it with ease, powering through everything from big drum sounds to hard and fast guitar riffs and heavy cymbal work.

Classical music was well presented and very energetic, though I thought it slightly lacked in bringing out the emotion in some of the more classic of classical pieces.

Conclusion

The high current capability of the ME 550 makes it an excellent choice for practically any speaker system. I really enjoyed my time with it. Its clinical ways gave me a new perspective in amplifier accuracy and detail.

The 550 is perfect for the user with an idea to greatly upgrade the two-channel side of their hi-fi/home theater system. Additionally, for the user getting into the hi-fi market for the first time and looking for a quality-sounding unit in a very affordable price bracket that can drive any speaker system you throw at it with the utmost precision, the ME550 should be on your short list.

- David Wurtz -

Related to the article above, we recommend the following:

Amplifier Primer
The Importance of the Power Supply (by Nelson Pass) Negative Feedback
Nature of Equipment Reviews What we Hear
High Fidelity Accuracy, Distortion, and the Audiophile
 

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