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Jeff Rowland Design Group MC-606 Amplifier Review

Doug Schroeder reins in the power of the 6 channels of the Jeff Rowland Design Group MC-606

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Jeff Rowland Design Group MC-606 Amplifier


Late in 2007 Bill Dudleston, the owner and designer of Legacy Audio, was discussing with me on reviewing his flagship speaker, the Helix. This was no small matter as the Helix is a world-class speaker and I would be the first to review it. I knew that I needed superb electronics to pair with it, so I approached four manufacturers whose work I admire and had worked with previously. These manufacturers are Jeff Rowland Design Group, Ayon Audio and Wireworld Cables, and the Valve Amplification Company (VAC). I would like to thank these manufacturers for furnishing top-tier gear for the “maiden review” of the Helix.

Utilizing the additional components of these four manufacturers I have developed a “Super-review”, a suite of four separate reviews which integrate, highlighting the performance of each component with its counterparts. I encourage readers of this review to seek out the complimentary reviews of the following equipment: Legacy Audio Helix speaker system; Ayon Audio CD-3, Wireworld Cable Silver Electra line and VAC Renaissance Signature Preamplifier MkII.

The reader of these reviews will gain valuable insight into the complementary nature of the system far more than if these components were reviewed in isolation from each other. In the end, should an enthusiast find the descriptions of the synergy between the components compelling, then he would be encouraged to consider pursuit of them specifically for use with each other.

This review is going to have more technical detail than many I have written. The MC-606 Multi-Channel Amp was conceived by Jeff Rowland to be used in conjunction with extremely high-end passive speakers and active crossovers requiring multiple channels of the highest quality amplification. Those who are not interested in pursuing this particular speaker configuration may want to consider the amp for surround purposes.


Let us say that you are successful. No, scratch that; let’s say you are so successful that your work is legendary. You have built a sterling reputation for the quality and longevity of your components. You are lauded for your circuit design, admired for your build quality, appreciated for your customer service, and adored for the musicality of your equipment. But that does not mean so much to you; what means more to you is advancement, redefining what can be done with today’s technology. In this particular scenario, you would be Jeff Rowland, a name which resonates with audiophiles familiar with the High End.

If any manufacturer could rest on his laurels it would be Jeff. His amplifiers are sought on the secondary market more than a decade after they appear. When I told an audiophile acquaintance who is heavily into DIY audio about the Rowland review, he was reverent, “That mans’ a genius!” Evidently others think so too, as not many amplifier companies have had the staying power (pun!) of the Jeff Rowland Design Group.

Jeff has been at it long enough that he’s made his mark and (I presume) his money. Likely, he could pack it up and set sail or sit on his derriere and enjoy the fruits of his labor. Instead, he determined to put a chunk of his company’s assets on the line in the development of his own breed of Class D amplifiers. It seems that for Jeff it’s not good enough to produce a top notch amp; it’s only good enough to produce a top notch amp with new technology. When I converse with Jeff I get the distinct feeling that he’s most interested in advancing the art of making amps, not advancing merely by making more amps.

A big part what makes a Jeff Rowland amp special is his work ethic, which I couldn’t help but notice when I caught him on the phone at the shop well after business hours, while he was repairing older amps sent in for servicing. He had just recently lost a good tech, and most of the repairs requiring familiarity with his designs fell to him. There is a small tragedy for high-end audio in this. Jeff has committed himself to superb customer service; has made timeless designs, has built them to last and, if they have needed servicing, has been there to do it. Now he is being squeezed by time and resources. He has the means to employ the techs, but the techs nowadays don’t know classic amplifier design! They are not as skilled in repair of his amps, and the techs who are knowledgeable are far and few between. Jeff, committed to his ethos of excellence, spends long evenings laboring over old amps so that audiophiles who buy his gear second hand have the best he can give them. His 21-year-old son and 23-year-old daughter, though successful, are not going to follow in his footsteps. Thus, time is limited for those who want to own a component touched by Jeff Rowland himself.

This is the bane of any technology-based company founded by an entrepreneur without a clean line of succession. At some point the vision for the company either wanes or is altered. It seems Jeff is attempting to alter his vision and his amps so as to stay technologically current and reduce incidents of repair, meanwhile addressing the dearth of technicians.

Sharing the same aluminum “metallic wave” finish that his other offerings have, the MC-606 appears a uniform black. Substantial handles with smoothed edges protrude from the face of the unit. A solitary light amber power button completes the minimalist machined slab of a face plate. The top plate continues the wave influence on toward the back of the unit with uniform low rise ridges running parallel to the face plate, while the side heat dissipation fins undulate in thickness, recalling an illustration of an electronic wave. A thinner, more utilitarian set of handles in the rear allow for easy two person placement of the amp.

The Bang & Olufsen ICEPower® technology is at the heart of the MC-606, or shall I say hearts. Six of these electronically pulsing Class D (not true Digital) units “circulate” the power of the amp to the outputs. Internal Power Factor Correction (PFC) units set the pace, like the Sinoatrial Node of the heart, for the electrical supply to each module. The 501 monoblock amplifiers and Capri preamp which I reviewed previously both can accommodate external Rowland PFC devices known as the PC-1 model.

The joint effort of the high power modules and the PFC makes for an enthralling presentation. While it’s obvious to many what higher wattage can do, it’s not so commonly known what the Power Factor Correction does. The purpose is to crank up the voltage and keep it there. The PC-1 units or the Power Factor Correction used in the MC-606 converts 110V North American household current to 380V DC. What is the purpose of all this voltage? Traditional amps can only charge their capacitors at peak voltage during the short duration of peak voltage from the wall, which is grossly inefficient. (According to Jeff, Power Factor Correction utilizes 99% of the electrical power from the wall socket instead of the 65% maximum available in conventional power supplies. –Ed.)

The current drawn is out of phase with the voltage in creating an abnormal condition in which the power factor, that is defined as the ratio of apparent power to real power, is maximized to the point that at certain lower frequencies there is loss of control over the driver. Power Factor Correction, in general, aims to restore the control of the driver over the entire operational frequency range.

As Jeff explains it, Power Factor Correction makes the current consumed by the device in phase with the voltage at the wall. With PFC, the power drawn is in proportion to the supply from the mains. The spiking of current in the resulting higher harmonic noise that occurs with traditional designs is avoided on the AC mains. One literally hears quieter background due to cleaner AC lines with the PFC in the power supply.

Standard power schemes could be likened to a swimmer with a snorkel. When extra oxygen would be needed to dive deep, due to the temporary supply the swimmer would need to interface with the air, to resurface and “load up” again. The PFC acts like a direct line to the submerged swimmer, giving a continuous maximum feed and negating the trips to the surface. Elimination of the need to load up the current improves performance markedly.

Jeff has incorporated this technology since 1997 as it appeared in his Model 10 and Model 12 designs, as well as his 300 series. He is the first to have introduced it in conjunction with the ICEPower Class D amp, and it appears to be on the way to becoming a permanent fixture in his amps.

About external active crossovers

Let’s shift our attention from amps to speakers for a moment. Speakers can dictate the amplification used in a stereo. While that sounds obvious, I’m not referring to truisms such as single-ended triode SET amps mating well with high efficiency speakers, or high-power solid-state amps pairing up nicely with planar speakers. I am referring to the fact that the speaker in this Super-review series, the Legacy Audio Helix, is a passive speaker with an external active crossover. That necessitates an unusual amplification scheme.

There are variations on stereo speaker design which include their being “active” versus “passive”. An active speaker has the amplification “on board”, or inside the speaker, with the crossover either internal or external. Alternatively, most traditional passive speakers have internal passive crossovers. However, some of them are designed to be fully passive, in essence a cabinet housing drivers for use with an external or “outboard” crossover.

Such speakers must use an external crossover, usually powered or “Active”. In some cases, as with the Magneplanar line of speakers one may find owners who mod the speakers by opting for an outboard passive crossover. One cannot tell by looking at the number of binding posts on the rear baffle whether the speaker uses an external crossover. Familiarize yourself with the operations of a particular speaker prior to purchase, and if you hear terminology you do not understand, get answers before you hook things up and turn on the power!

In order from most common to least, the permutations are:

Dynamic speaker: the traditional speaker, with internal passive crossover requiring external amplification.

Passive speaker: Utilizes an external/outboard Active Crossover (external amplification).

Active speaker: Incorporates internal amplification, and often crossover.

2 Responses to Jeff Rowland Design Group MC-606 Amplifier Review

  1. Jay Chung says:

    hi Doug

    Very nice review. I am considering Soundlab speakers. How would this amp go with SL speakers? I don’t really need the home theater capability. People seem to prefer tubey sounding amps with SL. I would love to hear your thoughts. God bless.


  2. Jay,
    God’s peace,

    I would have no concerns about using this amp with Sound Lab speakers. It is a refined amp and I do not believe it would be strident with the speakers. It would have adequate power to control completely the electrostatic. I tend to run SS amps with the Kingsound King III electrostatic speaker as well. I think that the Rowland and Sound Lab could be excellent. You would definitely want to try some different power/interconnect and speaker cables to tune the system.

    Douglas Schroeder

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