Jeff Rowland Design Group 501 Monoblock Amplifier Reveiw

Jeff is one of the few designers to use input transformers with Class D. One of the practical benefits of this is that the amp becomes less sensitive to input from the source. Impedance mismatches are greatly diminished, and as a result the 501 is more compatible with passive preamps. Rowland amps are also designed for 4 Ohm loads, which makes them ideal for less-than-efficient speakers.

Looking inside the 501, what can be called a transformer is absolutely puny! It is only marginally larger than a man’s thumb! Of course, when working with a chassis a fraction of the size of older amps, one can see why Jeff has to eliminate anything bulky. Transformers certainly have become diminutive; the ones used inside the McIntosh MA 6300 and the Audio by Van Alstine Ultra Dac (link to avahifi.com product page) were physically smaller than I anticipated, though not nearly as diminutive as those in the 501’s.

What about less efficient loads, did they cause any consternation for these amps? Not in the least, as planar speakers like the Eminent Technology LFT-8B’s fairly sprang to life! I had never previously experienced the pleasure of magnetic planar speakers driven by so much power, although the Eminents are technically known as Linear Field Transducers, which are technically push-pull magnetic planar. Many are familiar with the gravitational-like draw of the planar speaker. Add the extra dimension of extreme power driving them and their effect is much like a black hole – there is nothing you can do or say, you can’t escape their pull.

I didn’t want to escape the other-worldly grip of Mars Lasar’s “Escape”, as the panels seemed even faster than their normally speedy sound. With that much power, the smaller 8” woofer in its own enclosure was very taut and melded with the planar elements as well as I have heard it. Power can actually soften the LFT-8b’s presentation, and one can turn down the level while still experiencing the intensity of the planar technology. I thrilled to the exceptional spatial relations in this synthesized music.

Sometimes synthesized music sounds like a test disc because of all the “hidden” nuances and effects from the separation between the Left and Right channels. As tracks like “Escape” ramp up they get complicated, with several themes or effects bouncing at times from speaker to speaker. With lower-powered amps, they can easily get smothered by the bottom frequencies and sheer quantity of information being produced. It was refreshing to hear a moderately priced speaker handle retrieval of not only cymbal strikes but mid-tone squawks and beeps, and synthesized stuff cleanly. It made a strong case for an individual with the LFT’s to upgrade not the speakers but the amplification!

“Soundstage and scale we expect from high-power amps, but the 501’s floated whisper soft passages to me as delicately as the Melody and Eastern Electric single-ended triode gear that I have used.”

Turning down the lights in the listening room, I enjoyed the dazzling blue, star-like LEDs glinting off the silver façade-like supernovas. The music usually seemed to shine just as brightly. Up to this point, I had not particularly associated solid-state power amps with micro-dynamics on the order of low-power SET amps. Soundstage and scale we expect from high-power amps, but the 501’s floated whisper soft passages to me as delicately as the Melody and Eastern Electric single-ended triode gear that I have used. That was a surprise I was not expecting. However, in my Tannoy Glenair review I commented that the combination of high-efficiency and high-power were very captivating. In this particular instance, though the efficiency was lower, the power was much higher, offsetting the variance and retrieving the intimacy which almost assuredly would have been lost on most amps of less than 200Wpc.

A good example of this effect was on sustained piano notes. Bob Mamet’s Adventures in Jazz is a delightfully upbeat Smooth Jazz disc. It is a treat to hear planars being fed high power reproducing piano. It gave me an excellent feel for the spatial relation of the keyboard work and the intensity of each note. In terms of tonality, the 501’s are not absolutely correct, they suffer a lack of warmth that the finest tube amps can deliver. Conversely, they presented the energy of the piano better than any of the SET amps I have reviewed. Hammer strikes were especially exciting; one could readily get a sense of the amount of force Mamet used upon each key!

I mentioned that the 501’s were not as rich as the Pathos integrateds, so I would like to clarify. While Class D is not yet the equivalent of Class A, I would place this amp solidly in the upper echelon of Class A/B category in terms of performance. Thinking back over the years to names I have used in my system, Threshold and Parasound come to mind immediately, and amps which I have reviewed including more recently McIntosh, I feel the 501’s compare favorably to all of them. The naturalness is such that I would be content to use them for solid-state reference amps.

One of the reasons I can say this is because I have a superb means of offsetting any harshness or bite by use of Wireworld cabling. One thing that you will immediately appreciate with the power generated by the 501’s is the amplification of characteristics native to the cables. Wireworld cables are as lively and “dynamically alterable” as any I have ever used. I have at times produced no less than four distinct system presentations as I have moved about the power cords and interconnects from Wireworld’s Electra and Silver Eclipse sets. With terrifically sensitive speakers like the 96 dB Legacy Focus HD, it becomes an art form to arrange the cabling in the most pleasing fashion. I consistently heard the Silver Eclipse speaker cables as superior on the speakers. However, even though I had two of the silver coated copper Eclipse, I preferred taking a smidgen of that Class D sound away by using the solid-copper Electra power cords.

Other Factors

Jeff has been working on another development, the PFC-1, which stands for Power Factor Correction. This is an outboard “add on” transformer-power supply which converts 110v signal to 220v. In the creation of the PFC-1, Jeff is addressing the fact that typically inconsistent amounts of voltage are utilized by an amp depending on its load. The PFC-1 obviates the need to draw more current from the wall, as it is supplied to the max continually! The anticipation is that there will be a holistic improvement in the amp’s capability.

Jeff sent me three of these units for the Capri and 501’s. It should be noted carefully that this is NOT a universal transformer solution. These are designed to work with Rowland units with switchable power supplies. The Capri has an auto-sensing power supply, but the 501’s do not. The owner needs to open them up and reposition the fuse 90 degrees, into the 220v slot.

Jeff indicated that the PFC-1 could be used with other equipment, but that one should take extreme care and contact that equipment manufacturer to see if the unit has any special needs when switching to 220v operation. A screw on one amp was fairly welded to the unit; I wrecked two screw drivers in the attempt to remove it. Of course, the screw head stripped and I found myself taking a drill and bit extractor to it. It is not a comfortable feeling taking a power drill to a $3,500 amp on loan, but with deft touch and plenty of patience the patient was saved without a scratch.

Jeff indicated that I should hear a marked improvement across the board with the three units. But, I didn’t hear it. In fact, I felt the sound was a bit hampered by them. The sheer grunt and visceral nature of the resultant sound was improved, the impetus of the presentation improved, but I also heard a more veiled result. The cloudless sky that was the Capri and 501’s began to become a bit overcast. Jeff was at a loss as to how this could be, as he was receiving universal praise for the PFC-1. It took quite a bit of sleuthing on my part, but I finally established a plausible explanation. I say plausible since I have not yet been able to conduct definitive tests to affirm my theory – but I’m pretty sure of it.

I believe the issue was due to the use of the Wireworld power cables. Don’t jump to contusions, and think, “Oh, those cables are not that good…” No, no, no! Erase that thought, dear reader. Here is the issue as I see it: With the Wireworld cabling and the PFC-1, I had two power conditioning systems in play simultaneously. That may sound incorrect, but I point out clearly in my Wire World review that these cables are, in fact, power conditioners. They are designed to filter out unwanted anomalies without the use of passive electronics. They do so fabulously, but they react with other power conditioning/treatment equipment in a manner which shadows or veils the sound a bit. I ran into it squarely when I used the Wireworld product with the Tice Audio Solo conditioner. I heard a similar effect again and I’m fairly certain this was the case with the PFC-1.

The other variable I would change with this device is to upgrade the pigtail link between the PFC-1 and the destination component. There is supplied a proprietary link which has one male and one female plug, so it is impossible to simply switch to an aftermarket power cord. Jeff had mentioned to me his goal to have a cable manufacturer build one, but it was not available at the time of my review. I look forward to resuming analysis of the 501’s and the PFC-1 combo as time permits after the “Super-Review” I am conducting. That will be several months from now, so you will need to bid your time on it.

How did the 501’s sound with different sources? I am a CD user; however, lately I have added the Sonos Digital Music System to my listening room. A review is forthcoming. The Sonos system allows two primary sources, a Network Attached Storage drive and streaming audio from music services such as Rhapsody. I shall cover these sources in detail in the Sonos review, so I will not linger over them now.

The two most utilized players for this review were the Cambridge Audio 840C and the Ayon CD-1. I found it a particular pleasure to have both of these units on hand, as I was in the hunt for a new reference. I found the Cambridge and the Ayon to be like planets orbiting the same sonic distance from the amp, yet one was more “airy” and the other more “solid.” Consider the Cambridge player as the airy one, since it opened up the recording in a manner not unlike an actively crossed speaker system using very high efficiency speakers. In such speaker systems, there is often a quiet “Ahhhhhhhh” noise coming from the speakers even when there is no signal. While not emitting this particular “sonic sigh”, the 840C was open-throated as though it had an active crossover.

In a different orbit around the 501’s, the Ayon CD-1 was very pleasantly solid sounding. For those who have complained that the 840C was not solid enough, the Ayon CD-1 would do the trick. It seemed to have all the resilience, timing and detail of the 840C with a slightly more solid foundation. I would be reticent to select one over the other, and the 501’s made them both sound tremendously engaging.

Conclusion

Let me finally comment on the outstanding capabilities of the 501 to render the music as though it were cut from an acoustic fabric.

Three-dimensional projection and positioning of singers and instruments were exceptional, again on the level of better SET amps. In every parameter, laterally, vertically, and in depth, the spatial clues were placed impeccably. This was possibly the strongest suit with the 501’s. I spent much time listening to them for their “wide open spaces” feel, which conferred a sense of movement from a portal toward a large expanse. The power, no doubt, had much to do with this. When one is accustomed to 200 or so watts and only so much “spatial power” is given, it is a joy to hear just how vast the sound stage can become!

I see clear skies and unlimited upside for Class D amplification. When such illustrious designers as Jeff put their focus on the technology, it will not be long until Class D is solid-state amplification! In the meantime, if you want to work with the thrill of practically unlimited power in a design that has the Hallmark of the Jeff Rowland Design Group, go ahead – you will be impressed.