Jeff Rowland Design Group MC-606 Amplifier Review

It should be noted that with the advent of the Class D amplifier, which is compact and cool running, active speakers are more feasible. However, with an active speaker one loses the ability to match amps. There is a difference of opinion in the audiophile community as to the pros and cons of active speakers. Some feel the advantage of a unitized speaker is superior, others that amp matching to speakers is significant enough to avoid such designs. As usual, there are passionate voices on both sides.

Active crossovers are highly complex, even if they offer the user preset choices, using computer software to make an equalization curve for each driver or “driver set” if an array is used. The Helix has four midrange drivers in each speaker, and the set of four utilizes one signal/curve from the crossover. On the use of the active crossover in the Helix speaker, please refer to the review. For our purposes let it be recognized that when a stereo signal (L/R) is sent to an active crossover each is divided into the proper signals necessary to drive the specified drivers. Each new signal moves to the corresponding amp channel, then to the proper passive driver or driver array in each speaker cabinet.

If this sounds oppressive, just think of spark plugs and cylinders of a car. Imagine a V-6 with six cylinders, where the electronics send each signal to the cylinders at the proper time. So also, an active processor sends the signals at the right time to the correct “cylinders”, the drivers. Just like your smooth running car engine, it works very well!

The Helix is an unusual “hybrid”: a passive speaker in the treble, midrange and bass, but having a built-in 750-watt ICEPower amp handling the amplification for the subwoofer. This makes the subwoofer the “active” element to the otherwise passive speaker.

Putting it all together, the left and right channels each from the preamp are digitally split by the processor into four separate signals with their own frequency curves. The Rowland MC-606 receives three signals from the Left output and three from the right (bass, midrange and treble). The last two signals coming out from the processor, the L/R subwoofer signals, bypass the MC-606 and go right into the speakers (remember, the amps for the subwoofers are inside the speakers).

The MC-606 was designed specifically for speakers like the Helix – remember the Helix needs six channels of amps. It is the perfect complement to the Helix’s internal 750w ICEPower supplied subwoofer. It should say something to audiophiles that designers like Jeff Rowland and Bill Dudleston are implementing ICEPower in their designs. All channels of the MC-606 are the equivalent of using Jeff’s mono block Class D amps with his Power Factor Correction technology, which I covered briefly in the Jeff Rowland 501 Mono Block review. This is a “no compromise” design sonically.

One of the decisions Jeff and I discussed thoroughly was the configuration of the MC-606 to be used in this review. We did not want a stock unit, but rather one with enough “firepower” to take the speakers to their threshold of performance. While the Helix has lower impedance at 4 Ohms, the sensitivity is outstanding, right at 102 dB! Legacy’s recommendation is 300 wpc. I would have been comfortable with the stock MC-606 and its six channels of 250W at 8 Ohms and 500W at 4 Ohms, but why stop there? The vast majority of true full-range dynamic speakers in the world are benefited in sound stage and transients by the move from a 500W amp to a 1,000W amp. To cook up the best sound possible Jeff and I agreed that we needed 1,000wpc each on the bass and mid, and 500wpc on the treble. This would yield a speaker with extended frequency capabilities and the amplification to take it to those extremes with ease!

Maybe you wouldn’t necessarily think of a multi-channel power amp with a collective 5,000 Watts as easy, but in many ways the amp is just that – easy. Start with the façade, so elegant and bright, which is easy on the eyes. Rowland equipment is so gorgeous that I find myself staring at it, zoning out as my peepers are plastered to it.

Despite the seemingly daunting description of the passive speaker/amp relationship, set up is fairly easy. Though the amp is busy in back it is clearly marked and laid out in a logical fashion. One aid to the owner is that on the backside the odd and even numbered channel connections are offset vertically so as to make cable connections easier. The ICEPower modules do not require tremendous amounts of space, so the amp can be squeezed into a more diminutive casing. While a 100 lb amp may not seem diminutive, consider the space and weight it would require to house 5,000 total watts among six channels with class A/B solid state amps!

I was very happy to have taken a close look at those binding posts prior to sending my request for the Wireworld Silver Electra speaker cables used in this review. The posts are very closely grouped, and it was much to my benefit to request banana connectors on the amp end of the speaker cables. I believe that an individual can use spade connectors, but it would be more of a hassle scrunching them into their places. Frankly, the specter of spades of different channels touching crosses my mind – what a nightmare that would be! I assert that the distinction sonically between the spade and banana connector is not significant enough to warrant the risk and hassle; go with the bananas. I will put in a plug here for the lowly binding post wrench. This device which was sent by Jeff is a plastic tube with socket ends appropriate to the posts. It was invaluable in cinching down the spades.

Still looking at the backside, each channel has a “BALANCED/UNBALANCED” switch, then the expected balanced input. An unusual problem presented itself upon start up as all the channels had been established, yet there was an easily perceptible hum emanating from the right channel of the Helix. I was quite sure this was not a ground loop as I have never had any issues with ground loops previously. As Bill Dudleston continued setup he began muting each of the four inputs to the Helix speakers, allowing us to hear that only the midrange was affected. I surmised that potentially one of the switches on the MC-606 had not been toggled to the “Balanced” position. Once changed, the hum vanished.

The next grouping of switches found in sets of three corresponds to the set of left channels and right channels. These allow for configuration of the amp from two to six channels. Any of the channels can be defeated, allowing for ultimate flexibility.

If one was going to repurpose the amp from a surround or passive speaker application to a stereo speaker having two or three sets of inputs, you bet I’d put all of the channels to work! While the benefits of passive bi-amping may be limited, doing so with enormous power is the best way to try it. The MC-606 arrived a few weeks prior to the Helix speakers, so I had a chance to use it with the disarmingly humble looking Eminent Technology LFT-8B speakers on hand. Oh my, oh my! I had never heard them sound anything like that!

Four thousand watts coursing through them was a real attention getter (I had previously used the Rowland 501 Mono Blocks with them, bi-wired at a substantial 1,000wpc). It’s been said numerous times that inefficient planars need power. You’ll never know just how amazing they can sound until you give them prodigious power. Every time I have upped the power with the LFT-8B it has become noticeably more coherent. The seam between the dynamic and planar drivers all but disappeared as I used the four channels of the MC-606.

It also affirmed that smaller bass drivers on the order of 8” can have surprising depth, but you need to pump kilowatts into them. Even 200-300 watts doesn’t command the cones nearly enough to stifle the “popping” effect from woofer excursion. One thousand watts does so nicely. Comparing the transient response improvement from the added power was easy; I just reverted to the MC-606’s 500-watt channels on the bass and I got what I expected, less grip and definition and more “pop” than “pow”. Comparisons like this reveal why class D amps are becoming darlings of audiophiles, as the precision and punch in the bass are addicting.

For the first weeks I have been using first the 501 Mono Block amps, and henceforth the MC-606, I have grown accustomed to the Rowland sound. I have also come to appreciate it a great deal. While it does not have the warmth of tube amplification, it does some things in such a superior way that it merits its own acceptance.

Chiefly, power is the calling card of Class D amps. Try to imagine the dynamism of a huge dynamic speaker with 102 dB sensitivity coursing with 5,000 watts! Even 200 watt amps sound puny and listless in comparison, no matter how warm or smooth. Enthusiasts who have been using lower powered amps for years might never be aware of how radically changed the sound stage can be with extremely high power. Audibly, the change sounds exponential; the expansiveness brought to speakers is breathtaking.

Enthusiasts speak of hearing “deep into” the music. Power generated by the MC-606 allows such depth. Consider that a smallish LED flashlight can project a beam for several feet, while a hefty D battery flashlight can shoot a beam possibly a few hundred feet. Now, let’s bring in the Arc-Light, which is the Rowland! Just like the gazillion candlepower Arc-Light shines like a mini-sun, so also the sheer wattage of the Rowland blazes a path into all the nooks and crannies in the music which lay unrevealed with lower power. Mind you, the person who wants moodiness, pockets of undifferentiated sound, or a presentation with only so much verve or precision will possibly not care for the Class D high power scheme. As an alternative to lower power amps, I love it!

In describing the ability of the MC-606 to flood the music with insight even into the recesses of the recording, consider for a moment not the music, but the crowds at the venue where the music was recorded. One live recording I enjoy is Al Jarreau’s Tenderness, which picks up the crowd within arms reach. Al’s mic is right there; you can reach out and touch it! People swoon, cheer, and sing along. Whereas this is masked more with lower power, the MC-606 brings it all to the speakers. Also the stage Al performs on is well defined, not vaguely alluded to, allowing for the acoustic instruments to be precisely located, which aids in a visualization of them.

One of the criticisms of class D amps is that they are cool, or clinical sounding. I will not argue that assertion generally, however I will speak to the MC-606 and Jeff’s Class D design in general. I agree that with the improper amp one can end up with too “white” a sound, too sapped of the feel of flesh and blood performers. However, I also found that the selection of preamp and cabling can largely offset this effect.