Product Review - Acurus DIA-150 Stereo Integrated Amplifier - July, 2001

Arvind Kohli

Specifications: Power: 150 Watts RMS per Channel into 8 Ohms, 200 Watts RMS per Channel into 4 Ohms Input Impedance: 10 kOhms THD: 0.06% Size: 5" H x 17" W x 14" D Weight: 35 Pounds MSRP:   $1,599  USA

In some ways, being an audiophile is like being an economist. You are forever perplexed by trying to maximize what you have: power, component quality, design quality, construction, aesthetics, etc. Meanwhile, you only have a limited amount of resources, those being money, space and time.

There are many products that have taken a stab at providing an alternative to satisfy audiophile needs. Perhaps one of the most successful is the Two Channel Integrated Amplifier. It incorporates the source switching, volume control, and other functions, with the power amplifier all in one box. Let us take a quick look at the pros and cons:

Pros:

- Cheaper. You will save a substantial amount compared to the cost of the same separate pre and power units. Many manufacturers offer the same pre and power sections in integrated and separate units, and they do cost more.
- Fewer connections. You do not need the set of interconnects between the pre and power sections. Besides the money saved, you have also just reduced the total degradation of that dainty analog signal.
- Fewer boxes. My wife has not stopped thanking me. Though I would consider many models for my primary system, integrated products are the perfect solution for second systems in bedrooms, offices, studies, etc.

Cons:

- Limited power ratings. Most models are below 100 wpc into 8 ohms, and very few models are capable of driving low-efficiency power hungry speakers.
- You cannot experiment with combinations of different pre and power units.
- Home theater integration is only possible in some models that have a bypass feature for the preamplifier section. Arcam has models that provide surround decoding, but only two channels of amplification.

The only real argument against the the two-channel integrated amplifier, I feel, is when you may be hooked on speakers that demand more power. Otherwise, hands down, I feel integrated is the way to go.

Company Profile

Acurus was founded in 1992 as the value brand of Mondial Designs. Mondial was started with the Aragon brand, well know for its high end electronics in audiophile circles. Mondial was founded in 1986 by Paul Rosenberg and Anthony Federici, the latter of whom has since left the business. In December of 2000 Mondial was bought out by Klipsch of speaker fame. Paul Rosenberg is still with Mondial as the Director of Marketing and New Product Development.

The initial Aragon products were actually designed by Dan D'Agostino of Krell. About 11 years ago, Mike Kusiak joined Mondial as Chief Designer and is responsible for all products since, including the DIA150. All Mondial amplifiers have the same design philosophy, i.e., no integrated circuits, motorized volume pots, glass-epoxy circuit boards, large transformers, lots of capacitance and bipolar output devices.

Product Introduction

The DIA-150 was actually preceded by an earlier model, the DIA-100. The original DIA-100 took six months to design. It was designed because the passive preamp concept was getting to be quite popular, but they are very finicky as to which power amps they can be mated with.

A passive preamp by definition does not add any gain to the signal from the source components. Normal preamps will increase the incoming source signal, and usually add some tone controls and other features before sending the signal to the amplifier. The purist approach avoids all that circuitry in a passive preamp; it is basically a straight wire with source switching, attenuation (volume control), and balance. At the maximum setting on the volume knob, a passive preamp will theoretically let through 100% of the source signal, and lower settings are just a fraction of full strength (or "unity gain" in techie). This is the purist solution to the audiophile rule for analog signal: "First do no harm".

The problem with passive preamps is, most amplifiers are designed with the expectation of seeing an amplified signal from a preamp, thus the need for careful amp matching. In my experience, only a small percentage of power amplifiers cannot be satisfactorily used with a passive preamp. Another, major consideration is that you have to keep the cable between the preamp and amp short and use cables with low capacitance.

Enter the DIA-100. It was the prefect package for the purist audiophile. It featured a passive preamp section, mated to an amplifier with high input sensitivity, i.e., designed specifically for a passive preamp (higher sensitivity meaning a low level of input can drive it to full output). Of course, with an integrated product you also do not have to worry about interconnects. Brilliant!

The DIA-150 takes a great idea and makes it better. They added a full function remote control and beefed up the amplifier. At this point, I should decipher the model names. "DIA" stands for Direct Input Amplifier, i.e., an integrated amp with passive preamp section. The "100" in the original model stood for the 100 WPC into 8 ohms it was rated at, and you can guess what the "150" in the new model stands for.

Setup

My primary listening room is 16' by 16' by 8'. For casual listening, the speakers were placed so that there were 70" between the tweeters, and 128" from the tweeters to the listening position. For critical listening sessions, all three points were about 70" from each other, and well away from room boundaries.

The Outside

The DIA-150 features a steel chassis and brushed aluminum front panel. The front panel sports two dials for volume and balance control, and eight buttons for power, mute, and selecting from the six inputs. The rear panel features five- way binding posts for the left and right speakers; thankfully these are placed at opposite ends of the panel. There also are six line level inputs as well as a pre-out and tape out, and these are all of the gold plated RCA variety.

The remote control is very neat and easy to use. It offers power, mute, input selection, volume, and balance. The buttons are neatly laid out and easy to use. I may not find myself welcome in purist circles, but I really do need a remote control. And, Acurus does it right.

Technicals

The preamp section is a passive design, and all functions can be controlled by front panel as well as remote. In keeping with purist expectations, the remote functions have their own circuit board, and the volume and balance functions have motorized pots.
The DIA-150 has a generous amplifier section, featuring a transformer rated at 1.0 kVA. Total capacitance is rated at 36,000 microfarads. An article on their website by co-founder Anthony Federici talks about current ratings for amps and suggests that if you read the values on the fuses located on the power rails, it will give you the continuous current the amp can handle. Using this method, the DIA-150 would be rated at a total of 10 amps per channel.

Most CD or DVD players are capable of outputs up to 2 volts, but with normally recorded music levels, that value is much lower. The amp section of the DIA-150 is designed so that it will run full output (i.e., 150 WPC into 8 ohms) with only a 200 millivolt signal from the source component.

Continuous power ratings per channel are 150W into 8 ohms, 200W into 4 ohms. Co-founder Paul Rosenberg states that though it is not rated into 2 ohms, it will operate that low. One of the test speakers at the Mondial facilities is the Apogee Stages with impedance lows of 2.8 ohms, and according to Paul, the DIA150 will drive it all day with no hint of trouble.

The Sound

Luckily, I had several speakers and amps on hand for listening comparisons. The DIA-150 easily drove all speakers louder than my comfort level without a hint of distortion or compression. That includes the Dynaudio Contour 1.1 with an impedance low of 3.6 ohms and sensitivity of 86 dB/W/M, which is not exactly an easy load.

The DIA-150 easily is a superior product to the NAD 912, in my opinion, which is rated into 2 ohms but only puts out a meager 30 WPC into 8 ohms. The "soft clipping" feature on the NAD seemed to kick in often with the Dynaudio, making peaks sound compressed. The NAD also did not have the same control or extension on bass as the Acurus.

Of course, the ultimate in bass performance is delivered by my Bryston 4B, both in terms of extension and control. This is hardly a fair comparison to the Acurus considering the power ratings and price points. When mated with my PS Audio passive preamp, the Bryston did improve a smidgen. I cannot put my finger on it but it seemed like the background was quieter. I would characterize the overall quality of the DIA-150 the same, quiet background and clean sound, with ample power for most sane applications.

Conclusion

For those of you whose system does not require more than the considerable power the DIA-50 puts out, this is a combination to consider. Additionally, if you have a purist streak, this is a unit for very serious consideration. If you also need a remote, then you really need to check it out. Now $1,599 is nothing to sneeze at for most of us, but that is pretty much right smack dab in the middle of the competition for high-end integrated amps. And considering the power ratings and remote, it does justify as value for your dollar too.


Associated Equipment:
Speakers: Dynaudio Contour 1.1
Monitor Audio Bronze 3
Triangle Electroacoustique Titus xs
Amplifiers: Bryston 4B
NAD 912
Preamps: PS Audio IV
NAD 917
DVD: Panasonic A-320
Pioneer 414
Connectors: Self designed

- Arvind Kohli - 

© Copyright 2001 Secrets of Home Theater & High Fidelity
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