Acurus 200X3 3-channel power amplifier
Starting out with the technical specs and those gathered from an email inquiry to Mondial designs, makers of the brand, here it is:
Power:
200 watts continuous into 8 ohms 20Hz to 20Khz at no more than 0.06% THD, 0.005% IM
300 watts continuous into 4 ohms 20Hz to 20Khz at no more than 0.03% THD
Power Consumption, all three channels driven at rated power: 1,200 watts
Quiescent Power Consumption, all three channels with no signal: 75 watts
Input sensitivity: 1.1 volts for full rated power
Input impedance: 20k ohms
Signal-to-noise (A-weighted): 110 db
Frequency Response:
20Hz - 20kHz +0/-0.1db
10Hz - 100kHz +0/-0.5db
1Hz – 130kHz +0/-1.0db
Channel Separation: 90db
Damping Factor at 8 ohms, 50 Hz: 500
Comments:
I bought this amp compelled to replace a defective Onkyo Integra whose main amps seem to work fine but whose preamp section is totally dead. I always had the suspicion different amps give differing sonic characters. But among well-designed amps, this shouldn't be very obvious. Hence, it came as a pleasant surprise to learn the Acurus is giving me more listening revelations and pleasures than I expected.
Amplifier circuit topologies, power reserves, feedback amount, damping factors, tolerance of parts, to mention some - all conspire to differentiate the linear responses of various amps when driving real reactive loads. I may not be able to say which is superior, but they do sound different. Between the amps of the TSV919THX Onkyo Integra flagship receiver of 1996 and the Acurus 200X3 amp of 1994 that I now have, the sonic differences are subtle but easily discernible.
Apart from a 3db- 4db increase in SPL for the same pre-amp volume setting, I notice a more distinct stereo separation and a more focused center imaging at the same listening levels. The improved separation manifests in a more expansive soundstage. The big bands behind Frank Sinatra, Buddy Greco and Michael Buble seem to be spread farther apart. At the same time, the center imaging gives the vocals a more precise position dead on. In most musical materials, shifting from phantom to 3-channel in prologic mode made absolutely no difference in localizing the center vocals. That's how well the center imaging is with the Acurus driving the MS914s. No change was made on the speaker placement.
The bass coming from my MS914 speakers seemed a bit more pronounced, better defined and deeper. It seems to drive the MS914 to depths I thought not possible with the older amp. I can only correlate this change to the improved damping factor (Onkyo only had 50) and a more linear and extended frequency response down to 1Hz.. Having deactivated the sub crossover function in the pre-amp, I soon found I needed no sub in most musical materials. Though a good sub does appear to extend the lows much farther down in some materials that have lows the MS can't reproduce anymore. I wasn't a strong believer in damping factor as a determinant in amplifier behaviour. But I guess with a damping factor 10 times what I used to know, the Acurus had a better control on the lows that made them even more prominent and musical.
It seems the burn-in needed for the Acurus revealed its improvements in the highs and mids as well as its dynamic abilities. Listening to some heavily orchestrated symphonies like Beethoven's 5th and 9th, the latter with full chorus and soloists, the lividness of the various musical textures seems to distinguish themselves with greater 3-dimensionality, detail and a lot less constraint and congestion at loud passages. While the MS speakers are revealing enough in the highs, matching it with the Acurus gives more body to what are revealed. The cymbals and church bells in Tchaikovsky's 1812 Overture now has greater presence that seems to float above the complex orchestral harmonies. I could hear them ofcourse with the old amp, but it seems the new amp makes them a lot easier to hear. The strings similarly stand apart from the horns with greater differentiation.
I never thought a mere 2-way speaker system, however competent, could provide such a level of definition complex musical signals demand. What is more pleasing is the absence of any strain during loud transient passages for which I thought the MS was incapable of delivering without some difficulty. It turns out that an amp with a more generous power headroom and a more extended linearity are all that is needed to bring the MS914 to greater sonic heights. This confirms what many audiophiles say, you can never go wrong with more audio power. The more power, the more dynamic headroom. One doesn't need to listen at high volumes to benefit from a higher rated amp. It's the headroom that matters - allowing transient peaks that can go twice that of normal listening levels to pass without clipping contraints. I was probably driving the Onkyo so that there was little headroom for transients to pass without difficulty. But that was was my preferred listening level. The Acurus gave me a 3db headroom.
One final test I made was to use the Sheffiled "My Disc" test track on the signal-to-noise ability of the amp. Playing a track recorded at -70db from 0 reference, very close to near silence, I could still hear the recording a good 6 inches from the speakers. With my previous amp, I couldn't hear anything at -60db with my ears burried into the speakers.
A brief description of its constuction: The acurus amp is designed for purists who prefer the minimalist approach. The facade is as stark as it goes with only an oversized power switch on the leftmost side. Weighing a hefty 36 lbs, a good 10 pounds lighter than the Onkyo Integra receiver, its construction felt solid, though not as tank-like or as bullet-proof as a Bryston or a Perraux which can be twice as heavy for the same power rating.
Without any warranty, I opened it up to reveal a couple of can-sized capacitors each rated at 95 volts and 23,000 mfarads. There are six power transistors in each massive heat sink, two at the sides and one at the back, all indentical. The circuit boards are of glass-epoxy material and the connection to the inputs and speaker outputs are all hard-wired using heavy gauge wires. The usual multi-way banana terminals are used for the three speakers and the absence of balanced XLR input terminals betray this amp is not exactly a high-end product. The transformer is a huge torroid sitting smack in the middle. And without any magnetic shielding from a metal cover typical of most transformer implementation, I couldn't detect any audible hum or spurious noise at full power with no signal. This is one of the first criteria of good amplifer design: with ears literally burried into the speakers, and the pre-amp set to max volume with no signal, there was nothing but dead silence from the speakers.
With no speaker protection relays or stand-by circuits, turning the amp on and off made absolutely no sound whatsoever. My only trifling caveat is that the amp will continue to sound the source after turning it off, sputtering to death only as the last charge on those huge capacitors expire - a good 10 seconds at normal listening levels, longer at lower volumes. Otherwise, I am crossing my fingers it will survive a good 10 years before I upgrade to another. Hopefully by then, I'd be rich enough to get a pre-owned Theta Dreadnaught III, pressumably the one amp to beat the Acurus according to one reviewer.
