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Positive Feedback ISSUE45
TU-879S integrated amplifier with the VH Audio V-Cap upgrade
as reviewed by John Hoffman
During the 1950s and 60s, assembling a kit audio component could have been considered a rite of passage for many an audio hobbyist. There are fond memories of young men building a tube amplifier with their father during the evenings, or possibly as a weekend project. During this era, there was a wide array of manufacturers offering their products in kit form, and this allowed the hobbyist a chance to own a premium piece of electronics at a reasonable price. While many of these companies have long since vanished from the audio landscape, their names live on in the memories and stories told by audio enthusiasts. When a group of DIY hobbyists get together, the conversation will eventually turn to discussions about the merits of products from EICO, Heathkit, Knight, or Dynakit. While the majority of companies from the golden age of audio are gone, there are current production kits available that allow the audio hobbyist the opportunity to assemble their own equipment.
Elekit of Japan formed in 1973, and produces a wide array of electronics kits for the Japanese market. Even though Elekit amplifiers are highly regarded by the domestic DIY crowd, audio electronics are only a small potion of their overall product line. The Elekit vacuum tube line of electronics is designed by Yoshitsugu Fujita, who has a life long obsession with the reproduction of music. The TU series contains two tube amplifiers, a head phone amplifier, a tube pre-amplifier, and even a tube output CD player. These kits are quite affordable; yet still offer a level of sound quality that belies their modest price.
Victor Kung of VK Music is the North American importer of the Elekit products. VK Music is located in British Columbia, which has become quite a hotbed for small, innovative audio companies. Victor not only brings in complete kits, he also sources the proper transformers needed to work with the 120V/60Hz power grid. The part substitution adds a few dollars to the cost of the kit, but eliminates the need for a step down transformer to run the amplifier. Victor also translates the assembly manual from Japanese to English, which is straightforward and easy to follow. The VK Music website has a visual tutorial on the assembly of the kits, which is another tool that will allow the hobbyist to be successful completion of this project. One other point that should be made is that Victor is a passionate audiophile, and the importation of these products is about finding a way to bring affordable high-end audio reproduction to the adventurous audio hobbyist.
The Elekit TU-879S is an 8.5-wpc single ended integrated amplifier that utilizes pentode output tubes. This amplifier employs an automatic bias system that allows for the use 6L6GC, 6550, KT88.and EL34 output tubes. The pre-driver tube is a single 12ax7, and has a solid-state tube rectification circuit. Mr. Fujita has modified the TU-879R circuit, which results in the S designation for this amplifier. The Elekit has a small footprint, but is stuffed with high quality parts. The power supply contains a Kitamura KidenR-core transformer, which is an unusual component that normally isn't found in a modestly priced amplifier. The other parts contained in the amplifier exemplify the balancing act of cost versus sonic performance. For instance, the volume pot is a plastic film Alps unit, while the capacitors are standard grade electrolytic from Panasonic. The kit contains a fairly non-descript mix of carbon and metal film resistors; at this price point exotic parts are not going to be within the cost structure of this kit. The Elekit TU-879S sells for $595, and not only offers the audio hobbyist superior sound, but the challenge of assembling their own amplifier.
It is important to state this up front; I have no DIY experience prior to this review. My soldering skills are basically non-existent, and I maintain only a lay-mans understanding of electrical theory. In short, I am a DIY novice of the first rank. Victor Kung challenged me to complete this kit, and offered his support throughout the build process. One of my goals in this hobby is to assemble a component, and I was determined to successfully build this amplifier. I decided to place a call to a good friend who is a process technician, and recruited him as a tutor for this project. The assembly took approximately 14 hours, including the time needed to resolve a few small mistakes. The only meaningful error was reversing the negative feedback circuit, which resulted in a great deal of hum in the amplifier. The troubleshooting section of the assembly instructions helped identify the problem, and this issue was easily remedied. Not only did I end up with a nice sounding amplifier from this undertaking, I gained an education on how our audio components are produced. A whole range of skills were acquired, such as proper soldering technique, the orientation of polarized capacitors, spacing of large value wire wound resistors from the board, and the proper heat sinking of transistors. While this kit is relatively straightforward to build, I would recommend to a novice DIY hobbyist to find a mentor with electronics experience to offer some guidance with this project.
The Elekit TU-879S comes with a pair of Electro Harmonix 6L6GC output tubes, and an Audio Classic 12AX7 pre-driver tube. The sound quality of the Audio Classics tube is really quite poor, and I gained significant sonic improvements by replacing it. I have on hand a RCA12AX7, Sovtek 12AX7, GE12ax7, and Sylvania 5751 tubes. While the amplifier can use a wide variety of output tubes, Victor believes that the 6L6GC family of tubes provides the highest sound quality. After a bit of searching, I acquired a pair of Sylvania and RCA 6L6GC tubes. After a couple of sessions of tube rolling I settled on a full compliment of RCA tubes for this review. The Sylvania 5751 pre-driver tube ran a close second, and I could see where it would be the tube of choice in a system that has a warm presentation. The sound of the TU-879S can be greatly influenced by the brand of tube that is installed, which is typical of all the single ended tube amplifiers I have encountered.
Low powered tube amplifiers benefit from being used with high efficiency speakers. Full range single driver speakers are prime candidates, as are horn speakers. Even though the TU-879S has 8.5-wpc of output, this is a gusty little amplifier. The listening sessions of this review were conducted with a pair of Audio Nirvana Super 12 drivers that are mounted in a pair of Cain & Cain cabinets. These drivers are 95dB efficient, and have a usable frequency range of 38Hz to 18kHz. One evening I did substitute a pair of Mordaunt Short Performance 880 speakers for the Audio Nirvana. These speakers are a traditional multi-driver design, with a efficiency rating of 90dB. The crossover network has a 6dB per octave slope on the midrange and tweeters, and has a benign impedance curve. The Elekit amplifier drove these floor-standing speakers quite nicely. I would not say the Performance 880 were an optimum match for the Elekit, but the combination works better than one might expect. From my experience, I believe the TU-879S can be used with a moderately efficient speaker, as long as the crossover network is simple and the speaker has a stable impedance curve.
The TU-879S is a Single Ended Pentode, and has a different sonic flavor than other low powered amplifiers based on triode output tubes. This amplifier is free from coloration or excessive bloom in the midrange region, although it does have a slightly lean presentation. Clarity, detail, and accuracy are timely descriptors for the TU-879S, and this makes for a reasonably accurate rendition of the music. "Flying Red Horse" by John Gorka [Out of The Valley; High Street Records 72902 10325-2] exemplifies the strengths of this amplifier. Acoustic guitar notes flow beautifully, while the resonant character of a stringed bass is easily discerned. Mary Chapin Carpenter sings harmony on this track; her dark and introspective vocal style complements Gorkas' in a distinctive fashion. Single ended tube amplifiers are noted for excelling in the reproduction of vocals, and the Elekit amplifier turns in a fine performance. The two performers are clearly separated, although the blending of harmonies sounds natural. Music is about the synthesis of a wide array of instruments to achieve a desired effect, and this amplifier is capable of presenting a finished work of art without making significant alterations to the recording.
The spatial characteristics of the Elekit are on par with any $2000 SET amplifier I have encountered. I have no issues with placement of instruments, or any dimension of the sound stage. While the TU-879S will not keep pace with a multi kilo-buck SET amplifier, it does exceed the expectations one would have from a $600 amplifier. One evening I listened to "Sweet Sorrow" by the Joshua Redman Quartet. [Mood Swing; Warner Bros. 9 45643-2] The Elekit placed the saxophone dead center in between the speakers, and well out into the room. The drum kit could be heard behind and slightly to the left of the saxophone. The piano was in the back right hand corner of the soundstage, and was tightly focused instead of being splashed across the back wall. Finally the acoustic bass could be heard in front of the piano, although slightly behind the saxophone. In short, all was right with this song, and the Elekit faithfully reproduced the location of performers. High quality midrange reproduction and a fully developed soundstage is a template for good sound, and this amplifier fulfilled these criteria as well as can be expected from a modestly priced amp.
When evaluating inexpensive audio components, perhaps the most important question to be answered is this: what are the limiting factors of this piece, and do they interfere with my enjoyment of the music? In stock form, the bass region of the TU-879S is slightly diminished, which may be a concern to the hobbyist who values the lower registers. The opening electric bass notes on "Shoot the Moon" by Hugh Blumenfeld [Rocket Science; Prime PCD 43] has excellent speed, clarity and detail. While these are all valuable attributes, the overall quantity of bass is deficient, and this contributes to the feeling of a lean tonal balance to the TU-879S. One evening I installed a set of Audiokinesis Swarm subwoofers in order to add a bit of lower end reinforcement. The Elekit does not have low-level output jacks, and this necessitated the use of speaker level inputs on the Swarm amplifier. With a 50-hertz cut off dialed in, the subwoofers added just enough bass energy to bring the system into balance. While adding a subwoofer is one solution, I was determined to find out if there was an alternative course of action that could solve this issue.
One benefit gained from assembling a kit is that I am now qualified to install any upgrades to the TU-879S. The Japanese DIY community has developed a wide array of modifications for this amplifier. Adventurous owners can upgrade select parts within the amp, convert the tubes to triode operation, or even bypass the negative feedback circuit. It is important to mention that none of these modifications have factory approval, and the hobbyist pursues these changes at their own risk. The course of action I chose to pursue is a simple parts upgrade to the amplifier. I decided to place an order with Parts Connection for a Mundorf Mylitic capacitor to be installed in the amplifiers power supply. A set of first generation Jupiter beeswax capacitors replaced the Panasonics located in the signal path. An ACME EIC plug has been added in order to allow for the swapping of after market power cords. In an email I relayed my plans for the TU-879S to Victor Kung, who upped the ante to this experiment in a meaningful way. Victor reports that several customers have had positive results from installing V-Caps in the signal path of the Elekit. Arrangements were made for a set of these highly regarded capacitors to be added to this review.
An afternoon of work results in the installation of the IEC connector, Mundorf Mylitic power supply capacitor, and the Jupiter capacitors. The R-Core transformer takes up a lot of room in the Elekit, although enough space can be found to shoe horn the IEC connector into the back panel. The Mundorf is a two-section capacitor, and needed to be relocated due to its large size. There is enough room to mount a bracket on the inside of the transformer cover, and this allows for a neat installation. Pins are attached to the bottom side of the board to facilitate an easy soldering of the coupling capacitors. With this arrangement capacitors can be quickly soldered in, and it is now possible to quickly evaluate the performance of alternative components.
The reputation of the first generation Jupiter beeswax capacitor is that midrange performance is reminiscent of a paper and oil design, while high frequencies are on par with a good Teflon capacitor. The first round of upgrades effectively deals with the shortcomings that the stock Elekit amplifier has. The lower midrange fills in, yet still maintains the subtle shadings that were present in the original configuration. The lower registers are improved, and now music has greater output and extension. Since the TU-879S had issues on "Shoot the Moon”, I decided to revisit this song in order to discern what changes the new parts are responsible for. The bass guitar has fleshed out, and the guitar notes have excellent definition. When a crescendo is reached in the song, the Elekit can reproduce volume without any compression or strain to the music. Finally, Hugh Blumenfield's voice takes on a richer and deeper character, which is in line with how this piece should sound. The combination of these parts' upgrades addresses the issues that I have with the stock Elekit TU-879S, yet is still retains an affordable price tag that can be appreciated by the frugal hobbyist. 
The V-Cap TFTF is a high-end capacitor, and has the reputation of being one of the elite components in the market place. The Elekit requires four .1 uf coupling capacitors, and the V-Cap sells for $69.99 apiece. A $280 upgrade would not be considered expensive for many audio hobbyists, although one might question the appropriateness of installing them into a $595 kit amplifier. Coupling capacitors play a critical role in this amplifier, and significant changes to the sonic character of this amp can be achieved with this simple alteration. The installation of the capacitors took only a few minutes, and when placed back into service the TU-879S showed signs of improvement within a dozen hours. The V-Cap is reputed to have a 400 to 500 hour break in curve, although I experienced improvements far earlier than the aforementioned time frame. The enthusiastic praise for this capacitor by the DIY crowd appears to be true, and I can wholeheartedly recommend them as an upgrade. Every attribute of the music is touched by the V-Cap, and the level of improvement justifies the effort of installing them. Once again returning to "Shoot the Moon" as an evaluation piece, the Elekit Tu-879S now comes into its own. Every instrument has a natural presentation, while vocals have an improved texture and vibrancy. The spatial characteristics of the recording also benefit from the use of V-Caps. Not only does the soundstage grow in terms of depth and width, also the instruments have an improved presence within the stage. Dynamic contrasts within the song are easier to notice, and the feeling of a live performance is achievable. The V-Cap is not inexpensive, although audio hobbyists routinely spend more on peripherals for their system then what these capacitors cost. For those looking to unlock the true potential of the TU-879S, these capacitors are the avenue for doing so.
Pride of ownership and cost are perhaps the two leading reasons to consider building an Elekit amplifier. While these two points may be the most obvious, there are other considerations for undertaking this project. The satisfaction and knowledge gained from assembling this amplifier is invaluable, and provides a completely different perspective on this hobby. Envision this scenario if you will. After a couple of evenings of work at the bench, this compact silver faced amplifier gets gently placed into the system. After a bit of warm up, the seductive sounds produced by single ended tubes cascades into the listening room. You accomplished all of this, possibly for the first time. Perhaps you are a hobbyist that wants to enter the world of tubes without breaking the bank. For $600 the Elekit TU-879 represents an uncommon value in the hi-fi world. Choosing this amplifier is the frugal decision, and allows a person to allocate the funds towards other areas in the system. Of course there is more to this amplifier than just low cost, it offers a pathway to experience high-performance music reproduction. The Elekit TU-879S is built on an elegantly modified Williamson circuit, and will accept a myriad of upgrades. The stock unit sounds quite nice, however there are upgrade avenues that can be explored. Common modifications include replacing coupling and power supply capacitors, upgrading the volume pot, adding an IEC connector, or converting the amp to triode mode. In my experience, replacing the power supply capacitor with a Mundorf Mylitic, and installing the V-Caps at the coupling capacitor position resulted in a significant improvement in sound. A few sentences cannot adequately convey the metamorphosis the Elekit underwent with the V-Caps. These capacitors are worth every dollar, and owners of the TU-879S would be well advised to install a set; they will put a smile on your face every time you turn the amp on. John Hoffman
 I recommend viewing the website tutorial first, and then reading through the manual thoroughly before assembling the kit. Doing this should minimize any mistakes that might be made. If in doubt Victor is quite accessible through email, and will quickly answer any questions.
 The Gini Systems LS/3/5a would be a prime candidate for use with the Elekit amplifier. The strengths of each product should compliment each other, and offer a lot of performance for a modest outlay of cash.
 Do remember that the TU-879S is only 8.5 wpc, and high efficiency speakers are needed to realistically reproduce macro-dynamics in music.
 The Jupiter caps made strides towards improving the TU-879S, but did not dramatically change its character. For those pleased with the stock voicing, this is an avenue to improving the amplifier. If you require more body, consider an alternative capacitor.
 The strong suit of high efficiency speakers is the presentation of macro and micro dynamics. This characteristic is essential to getting reproduced music to sound like a live performance. The combination of HE speakers and low powered tubes are appreciated for these attributes.
 There are two other upgrade options that should be considered. There are two 100uf electrolytic capacitors in the negative feedback circuit that should be replaced. Also the internal wiring for between the board and output transformers is a candidate for upgrade. A run of shielded Cardas litz wire would do nicely. Both options are on a short list for experimentation.