MPS-1 Overview and Setup
The Emotiva MPS-1 sports some very unusual attributes for a product in its price class. Close inspection of the PCB boards of the amplifier modules revealed doubled sided, plate through, glass epoxy, FR4 PCBs used throughout with 2 ounce poured copper on all power sections and ground planes. You can never have enough copper for power and ground and it's nice to see Emotiva spared no expense and did it right. The choice of all 105 degree C rated capacitors is a rarity for consumer audio products at any price point, but the Emotiva flaunts them both in their power supply and individual bypass caps sprinkled throughout the entire design. 1% metal film resistors were also used though out this design. I found it refreshing for a company to use such tight tolerance and robust parts in their design which, in my opinion, speaks volumes for their sense of pride in design. Another costly feature implemented is the active anti-clipping circuitry which is basically inactive in all but the most demanding operating conditions. This is a very thoughtful feature that, although garnering a slight penalty in measured performance (particularly SNR and distortion), it yields invaluable protection for overload conditions which typically fry the tweeters in loudspeakers. Once an amp runs out of headroom it enters a mode commonly referred to as "clipping". When an amplifier clips it essentially sends a square wave response or DC voltage to the speaker which after only a few short cycles can fry the tweeters voice coil or burn out series inductors in the crossover sections. The MPS-1 doesn't allow this to occur since it not only limits the output signal when overdriven, but also smoothes out the waveform to prevent the dreaded square wave response of clipping. The neat thing about the soft clipping circuit is how unobtrusive it is under normal listening conditions. This is a feature I wish more companies would execute this intelligently in their designs.
Editorial Note on the MPS-1 Amplifier Design
The MPS-1 utilizes a class H design. Similar to class G, but potentially more efficient, it modulates the power supply rail voltage just slightly higher than the output signal, keeping the voltage across the transistors small and the output transistors cool. This results in a very efficient and cool running design, commonly referred to as a'tracking amp' because the power supply tracks the input voltage and supplies the correct output current. The modulating power supply rail voltage is created by similar circuitry that you would find in a simple power amplifier. In terms of complexity, this type of amplifier could be thought of as multiple power amplifiers driving a class AB amplifier and is therefore fairly complex and expensive to properly manufacture and execute.The amp has four high current complementary output power BJTs per channel. Paralleling multiple BJTs is a good method of ensuring amplifier output impedance is low enough to deliver high current while driving low impedance loads. It's also an effective way of minimizing frequency response variations which can occur when driving highly reactive speaker loads or exotic cabling.
The MPS-1 has multiple high voltage (50V) capacitors in series, yielding 100V (2 x 20,000uF = 40,000uF per channel). In order to do 200wpc a minimum recommended cap voltage of sqrt(2)*40 + 5 = 62V should be used. Using 100V gives them plenty of design margin and added headroom since the rails can swing much higher. Individual large 350VA toroidal transformers for each amplifier module ensures that this amp can drive 4-ohm loads with no problems, while also providing excellent channel-to-channel crosstalk immunization, especially at high power levels.
While the Emotiva literature on the AV123.com website states 48,000uF of power supply
capacitance per channel (4 x 12,000uF) for a grand total of 336,000uF total power supply capacitance,
it is a bit misleading since these capacitors are actually wired in series and yield an effective power
supply capacitance of 12,000uF or ¼ stated in the literature for each channel for a total of
84,000uF.
In order to meet the height profile of the card cage, Emotiva had no choice but to use
lower voltage caps in series to achieve a higher capacitance working voltage to meet the maximum rail
voltage requirements for achieving the rated power.
Though a clever design approach, series
connecting capacitors cuts the available storage down by ¼ and also doubles the Effective Series
Resistance (ESR) as opposed to parallel connecting.
Considering this was perhaps the best way of
meeting the design profile, I would say this was a good compromise.
However, my only gripe is the
overstated literature which I am hopeful the manufacturer will change after reading this
review.
One of the biggest advantages of the Class H amplifier topology employed in the MPS-1 is its much higher efficiency when compared to typical linear Class A/B amp designs. I asked Emotiva to furnish some efficiency numbers on their amp under various load conditions to demonstrate this in action.
From Emotiva Engineering Labs
My test set-up for this is pretty basic. I set the Variac to 120 VAC, measure the AC current draw on my Fluke meter; multiply the two and divide it into the power output of the amplifier. Although expected; it is always interesting to see the efficiency change around the area of transition for the amplifier.
|
AC Vrms input V |
AC Irms input A |
Power in (V x I) W |
Power out W |
%EFF |
|
120 |
3.73 |
447.6 |
300 |
67 |
|
120 |
1.8 |
216 |
100 |
46 |
|
120 |
1.59 |
190.8 |
90 |
47 |
|
120 |
1.22 |
146.4 |
80 |
55 |
|
120 |
1.15 |
138 |
70 |
51 |
As you can see this is pretty close to the theoretical. Also note the 4-ohm load represents a worst case scenario as the I2 losses are compounded in the higher current mode.
These are some impressive numbers for sure. In comparison, classic linear Class A/B designs typically run between 35-40% efficient. Thus the Class H design topology of the MPS-1 allows the end user to tap 27-32% more power (At full load) from the wall outlet to their speakers.
Inputs and Outputs
The Emotiva MPS-1 comes with all of the connections any audiophile would need as
far as amplifiers are concerned.
It is important to note that very few 7CH amplifiers in this
price class sport both balanced and unbalanced line level connections, not to mention a fully
functional trigger that is selectable for music or 12V detection.
The power receptacle is a two
prong job, which will likely suffer less ill effects of ground loops when installed in systems with a
poor earth grounds or miscellaneous components that utilize earth ground reference.
I was a bit stunned when the UPS guy showed up with three boxes labeled
Emotiva.
How could this be?
Well, one box was for the card cage, another for five amplifier modules
and one smaller box for the remaining two amplifier modules.
All of the amplifier modules were individually packaged in their own
boxes (total of 11 boxes) and sealed with plastic wrapping.
Talk about careful packaging!
Emotiva spared no expenses here.
I soon found my way through all the packaging and quickly pulled one of
the amplifier modules out for a closer look.
What an impressive sight it was.
An oversized toroid power transformer, a big capacitor bank, and well
laid out circuit topology seemed apparent.
I noticed a thin plastic film over the front of the card that connects
to the chassis.
This was meant to protect the contacts from dust or debris.
Make sure you remove this thin plastic film from each amplifier module
before installing them into the card cage otherwise none of the LED
logic will work and you will be stuck with an amp with only a yellow
illumination from the Emotiva power button to give you visual
indication that the unit is working.
You don't want to make this mistake after loading up all seven modules,
cabling and placing this 115lb monster into your rack.
The Emotiva MPS-1 is certainly the most unusual amplifier I have
had the pleasure of reviewing.
Its card cage design brought me back to my telcom days when I was
designing DSL modem cards that were to be inserted into huge DSLAM
cages at the telephone companies.
The advantage here was having all of your technology in one location as
a central demarcation point for control and configurability, while at
the same time being more space and energy efficient.
I never really considered applying this type of solution into a
multi-channel amp, but after doing some thinking, I was glad somebody
did.
Too bad it wasn't me
The MPS-1 card cage housing was manufactured as a sturdy metal case with a backplate
that connects power and logic to each mono block amplifier.
The power supply and circuitry to the right is for maintaining the front panel display and supporting the LED logic. Blue LEDs indicate normal operation for each amplifier module, while red indicates failure. Each amplifier module is optically isolated with 5 opto-coupled relays per module, making a grand total of 35 opto-coupled relays to ensure no ground loops or stray signal paths are present between each of the seven channels. Not since my telcom days of designing secure audio systems for NAOC and Air Force One have I seen such attention noise mitigation and ensuring the best possible channel to channel isolation.
Sliding in each amplifier module proved to be relatively easy thanks to the inclusion of slick nylon rails, but care must be observed while doing so.
Here are some guidelines to follow that I highly recommend:
- Do not apply any pressure or stack any gear on the empty card chassis housing until all of the amplifier modules are loaded.
- Guide each module into the chassis with two hands to ensure they install smoothly and uniformly.
- Push each card into the chassis until you feel it lock into the power receptacle and then install the supplied mounting screws to keep them locked down.
After I had all of the power modules installed it was time to place the MPS-1 into my component rack. It was interesting to note that the individual models and card cage weight was very manageable. But, when the card cage was fully loaded, it became a bear to lift, topping my UPS shipping scale at 115lbs. If at all possible, installing the empty card cage in your rack before loading it with the amplifier modules would be most ideal. After making all of the necessary speaker level and line level connections, I was ready to roll.
