The M520 Integrated: 7-month Customer Review

By Jonathan Horner:

Time flies and it is now seven months since I purchased the M520 integrated. During this time, because I work out of my home, the M520 has often been in use eight or more hours a day. The only exception is on weekends or when I go out of town on business. The unit has therefore been powered up for many hundreds of hours, perhaps more than a thousand. It has been absolutely reliable without even a hint of a problem.

The layout of the tubes and the transformers in three parallel rows, flanked by two handles to facilitate lifting and moving the heavy unit, exemplifies the old maxim that form should follow function. I don’t know if it was intentional, but the M520 evokes memories of the fabled Radford valve amplifiers that I once hopelessly dreamt of owning as a schoolboy in England. The combination of aluminum and stainless steel along with the complete absence of visible screws creates the impression that this is a deluxe product. It certainly draws many positive comments from visitors to my home. Most of them have never even seen equipment that uses tubes. The superior construction and superb industrial design of the M520 is quite different from the endless variation on flimsy anonymous black boxes that they identify with audio. The M520 is a conversation starter even before visitors experience its sound reproduction abilities.

The M520 is, of course, shipped with current production tubes. However, good as the unit is in stock form, it is transformed by the use of great tubes from the 1950’s and 1960’s. Perhaps it seems slightly mad to install a complement of tubes that could cost as much as the amplifier itself, a huge bargain incidentally, but the results are easily heard if one has other great system components. An owner can never claim, in my humble opinion, to know how good the M520 is until the best possible tubes are utilized. This speaks volumes about the quality of the original Mullard 520 circuit that designer Alex Yeung adopted, updated, and implemented so brilliantly in the Eastern Electric M520. Incidentally, Mullard named the circuit, which was released as what we would now call “freeware,” because it consists of five tubes per channel rated at twenty watts each.

I found that the best place to start with tube experimentation is with the rectifier. The 5AR4/GZ34 is a legendary tube with a reputation for transforming an amplifier’s sound. That was certainly the case with the M520. Here’s where I’d advise sparing no expense. The British manufactured Mullard “fat base” rectifiers are still to be found in used but superior condition. Since they can last up to thirty years in use, it is an excellent choice. So far, I’ve only found one that was actually NOS. The other great rectifier tube that I use is the Dutch made metal base 5AR4/GZ34. It may even be slightly superior to the Mullard although that is system and taste dependent. NOS examples are still to be found at premium prices. Third choice would be subsequent Mullard, Amperex, or Philips manufactured rectifiers with as early a production date as possible. They were labeled with many company logos but were manufactured in Britain or Holland. Philips was the parent company of Mullard and Amperex (among others). The Sylvania 5AR4 is also a fine sounding tube but does not have the reputation for longevity of the early Dutch and British rectifiers. The importance of the smooth power delivery of the 5AR4/GZ34 cannot be understated. There is inherently no switching noise. Looking at some of the “golden age” amplifiers, including the Radford amplifiers with which I am familiar, it’s noticeable that many of them use just one rectifier in stereo circuits. The M520 uses one per channel which is a superior implementation.

The next place to go in the quest for improvement is the initial tube in the circuit, the EF-86. My unit was shipped with Sovteks that weren’t very good, in fact one failed immediately. Bill O’Connell now ships the M520 with an excellent Philips E80F. There are many other possibilities. After upgrading the rectifier tube, this appears to be the place where the largest differences in sound improvement can be made. The EF86 has the distinction of being one of the few tubes expressly designed for audio use. Most tubes were designed for other applications and then later employed in audio circuits. I have Telefunken EF806S and EF86, Genelex Gold Lion and Marconi Z729, Amperex EF86, Mullard EF86, Tungsram EF86 as well as Philips and Amperex E80F and E80F PQ. All of them have a unique sound signature.

Moving on to the phase splitter, the 12AU7 tube, there is an incredible array of choices, many or most of which I have yet to sample. Among those that I have on hand are the RCA “clear top” 12AU7, RCA 5814A d-getter, RCA Command series 5814A, Telefunken ECC802S, Telefunken ECC82, Valvo 6189, Tektronix select Amperex orange globe 12AU7, Raytheon 5814, CBS-Hytron 5814WA, and GE 5814WA black plate with inclined circular and with inclined square getters. The 12AU7 and its many variants could take a lifetime to discover with just one circuit and one system. However, it is not hard, with practice, to discern what works best in a particular system and conforms to one’s particular tastes. In the case of this type, it is important that both halves of the tube are matched so that the phase splitting is equally balanced.

There is a tremendous amount of hyperbole and myth surrounding the great tubes of the past. At least in the case of the M520, I found that NOS tubes take an already excellent sounding unit into another dimension. It’s a sign of a great product when subtle nuances in the musical presentation are audible by the simple act of exchanging tubes. With the additional ability of switching between pentode and ultralinear operation, and having three negative feedback setting choices, the M520 is a highly adaptable audio device. Experimentation with those controls, in combination with the vast array of tube choices, allows an owner to fine tune their audio system. Despite the sometimes frustrating search for genuine NOS tubes, there are many rewards from persevering in that quest.

Since I always strive to minimize the electromechanical aspects of music reproduction, nothing pleases me more than to observe visitors to my home, most of whom have no interest in audio technology, being dumbfounded that my system's sound reproduction seems so natural. The Eastern Electric M520 is clearly, first and foremost, all about communicating the emotion and humanity of the performers along with the soul and the art of music. At times, with the very best recordings, its performance borders on the uncanny. It combines the best of electronic and mechanical design into a high value package that, all importantly, liberates the best tubes to deliver the musical message in a way that even the finest transistor designs can’t quite manage. Am I pleased with my purchase, yes! Is the M520 something special, yes! Would I strongly recommend it, yes! Is tube swapping both fun and fascinating, yes indeed!