April 2000Assemblage SET-300B Amplifier
by Bill Cowen
What it is
The SET-300B, as you've correctly guessed by the model name, is a 300B-based single-ended-triode stereo amplifier. Power output is a whopping 8 (or maybe 9) watts per channel with no global negative feedback; the amp can also be wired for double-the-power mono operation. The base price of the amplifier does not include the 300B tubes themselves. This keeps the selling price as low as possible and allows the purchaser to select the best output tube that his or her budget (or tastes) will allow. For you tube-rolling types, this means that you dont pay an additional price up front for factory-supplied tubes that youre probably going to replace anyway. The rest of the requisite tubes are included, which consist of a Sovtek 6SN7, a pair of NOS GE 6BX7GTs, and a pair of NOS Mullard CV378s for rectifiers. The Parts Connection (TPC for short) supplied a pair of Sovtek 300Bs for this review.
There are three additional options that can be purchased either at the outset or added at a later time if desired: a parts upgrade kit, a Black Gate power-supply cap upgrade, and a volume control. Priced at $299, the upgrade kit includes a veritable whos who of audiophile-grade parts. Vishay resistors, Rubycon Black Gate electrolytic and Multicap RTX polystyrene capacitors, silver input wiring, Kimber RCA jacks, Cardas binding posts, E.A.R. isolation feet -- the list goes on. A quick tally from the price sheet of another parts supplier I use indicated a total of over $350 for the same parts, so its apparent TPC isnt getting rich on sales of the upgrade kit. The $174 Black Gate power-supply capacitor option upgrades a pair of the standard power-supply caps to the higher quality Rubycons.
The volume-control option, priced at $29.95, provides the parts necessary for volume attenuation right on the amplifier. Those with a single source (at a line-level output) can install this option and obviate the need for a preamp. The parts upgrade kit was supplied with the review unit, and listening impressions were done with all parts installed. The Black Gate cap option and the volume control were not supplied, and so were not auditioned.
The main man behind the SET-300B is one Glenn Dolick. Being a certifiable audio lunatic since his high school days, Dolick spent 15 years in industrial electronics, tweaking and repairing audio components in his spare time. Since his move to Sonic Frontiers almost ten years ago, he has been involved in the design or redesign of over two dozen Sonic Frontiers, Anthem, and Assemblage products. His main emphasis with every project is tonal balance, circuit simplicity, and sonic and economic value. In Dolicks own words, "Buy something that is of a good solid design and modify it! You will get the most for your dollar this way." Any tweakers listening out there?
From nuts to soup
The SET-300B assemblage (!) of parts arrived in a single large, heavy box. As I started unpacking, I was immediately impressed with the packaging of the individual parts. Each part type (resistor, capacitor, etc.) was grouped together, enclosed in a plastic ziplock bag, and labeled with multiple tags denoting the part value and quantity contained within. Slick. As the chassis became visible in the bottom of the box, however, I discovered that the shipping gorillas had left their mark. Both output transformers were sitting crooked, and the internally mounted choke had been ripped from its mounting posts and was flopping around inside. Removing and straightening the mounting straps proved sufficient to restore the transformers, but the choke was beyond help, and a new one was dispatched from TPC. Although the packaging was reasonable, perhaps the transformers could be shipped unattached to prevent this problem, as they have to be removed during assembly anyway.
As the parts were laid out and sorted, there were two items conspicuous by their absence: the Panasonic capacitors for the upgrade kit and...the instruction manual. At first I thought this was just a test by TPC to determine how intuitive the kit really was. But Im not that good. Fortunately, the entire manual is posted on TPCs website, and after a short download and printout, the necessary information was at hand. TPC shipped the missing capacitors out the next day.
There is very little point-to-point wiring to be done. Most of the components are installed on five separate circuit boards. Many decry circuit boards as falling short in the department of absolute sonic abilities, but it really all comes down to the final sound. Glenn Dolick offered the fact that the final production unit (with circuit boards) sounded better than the point-to-point wired prototypes, as much attention was paid to component placement and grounding schemes in the design of the boards. From a kit standpoint, it makes things much easier to assemble, and has the potential for a better outcome for the novice or even intermediate assembler.
Once finally started, the kit went together easily and nearly intuitively. I am not an experienced kit assembler, this being the third kit Ive put together in the last 20 years. The instructions are mostly text, but they provide a very logical sequence and enough detail that I was never left guessing how to install a part or where to place it. The TPC guys dont mind sharing their sense of humor either -- theres just enough of it in the manual to keep things interesting, yet not to the point of sounding hokey or unprofessional. I found only one incorrect reference in the entire manual, and this was apparently correct in the printed version but had missed the update in the website version.
TPC suggests that the kit requires eight to ten hours assembly time. Either Im slow (probably), or theyre optimistic. Total time spent was about 14 hours, which is still a very reasonable time frame for assembling anything of this magnitude. Perhaps others can meet the suggested time, and Ill bet that the factory people can do it in half that time. The only advice Ill offer to a novice is to quit when you get tired or when you catch yourself placing something in the wrong spot. Most mistakes are made when you try to push too hard to get things done. Take your time, and youll have a much better chance at a good outcome.
All in all, Id have to rate this kit as quite easy to assemble. If you possess reasonable soldering skills and know which end of the screwdriver goes in the slot, you should have no problem putting this amplifier together, and the reward of listening to something crafted of your own hands adds a lot of fun and pleasure to the experience. If you stumble, help is only an e-mail or phone call away, and if you really stumble, the entire amplifier can be sent back to TPC for troubleshooting and/or completion of assembly.
Close your eyes and pray
The moment of truth (or consequences) had arrived. After completion of the final assembly steps, it was now time for the start-up procedure. First, the 6SN7 and 6BX7s were installed, powered-up, and observed for that warm amber glow. No problem. Next, the 300Bs were installed and observed. Again, no problem. Finally, the CV378 rectifiers were installed and powered up. At this point, the manual warns that high voltage is now involved, and if there are problems, they will likely occur here. Fortunately, no smoke plumes erupted, but as the soft-start high voltage kicked in, one of the 300Bs started popping and snapping. Swapping the 300Bs left-for-right revealed the problem to be with the tube itself. A quick e-mail to Glenn Dolick initiated the shipment of a replacement pair.
In the meantime, a pair of AVVT 300Bs arrived that TPC had shipped for sonic evaluation with the amp. Both were dead on arrival. The plate structure within the tube had apparently shifted during shipment, and both tubes had dead shorts between the filament pins. Unfortunately, the tube problems didnt end there. The 6SN7 developed noise problems, and one of the 6BX7s developed a leak. Due to the number of tube problems encountered, Dolick suggested that we go through a complete voltage check on the amplifier to ensure that something wasnt amiss. Other than marginally higher voltages at each test point due to the steady (but unusual) 123 volts at my wall outlets, the amplifier tested out just fine.
Although it is my responsibility to note the problems, it is important that they are considered in the proper context. Understand that tube failures can occur with any tube component, regardless of the manufacturer. Secondly, in each instance, replacements were sent expediently. Those with many years of tube-equipment experience know that the quality of the tube source is just as critical as the quality of the tube itself. I never had any operational problems with the amplifier, only the tubes.
Was it worth the effort?
In a word, yes. But maybe thats not sufficient. How about YES! After allowing approximately 100 hours of break-in with different music at various volume settings, I sat down to put the SET-300B through its paces. The 92dB-efficient, 14-ohm-nominal-impedance Coincident Super Eclipse speakers (reviewed here in December, 99) were used for all listening evaluations.
The first thing I noticed was the bloom and sense of space that seem to be a trademark of most SET amplifiers was abundantly in attendance. Plopping Buddy Guys Damn Right, Ive Got The Blues [Silvertone 1462-2-J] in the CD player and selecting my fave track, "Black Night," elicited the same goosebumps that I get when listening through the Cary 805s. The brushed cymbals were properly positioned at the back of the stage, and Guys voice had the same hint of rasp and guttural tone to it. Bass notes were perhaps a touch rounded, but not to an extreme, and the extension was impressive -- more than I expected, actually.
The SET-300B proved to be a champ in the microdynamics department. Subtle volume shifts were really first-rate, as was the slow decay and fade of notes into silence. On Joan Armatradings "Always" (Hearts and Flowers, [A&M 75021 5298 2]), I literally melted into the listening seat with the beauty of the reproduction. Armatradings vocal range and inflection were presented with such believability that I had a hard time focusing on any critical evaluation. Its difficult to pick a product apart when the overall presentation just seems to transport you to another world. Yet I found the same thing happening time and again while listening to this amplifier. But switching back to ugly reality, if I have to find a fault in the area of dynamics, it would be in the macro sense. Played at levels within the scope of the amplifiers power and synergy with the speaker, macrodynamics were just slightly curtailed. Understand, however, that 8 watts per channel is borderline in adequacy for the Coincidents. I was actually surprised that the SET-300B played the Coincidents as well as it did. But I would guess that the macrodynamic issue would likely not exist with a more sensitive loudspeaker.
Switching to "She" (from the James Newton Howard and Friends CD by the same title [Sheffield Labs, 10055-2-G]) revealed treble reproduction that was sparkly, airy, and realistically (if not ultimately) extended. The SET-300B was always in control here, and never once uttered an edgy or fatiguing portrayal of the recording. It was on this particular piece, however, that I noticed a slight lack of speed. Dont take this to mean plodding or challenged, but more of a polite than explosive presentation. But once again, I got stuck just listening, and after several hours, I noticed that my note pad was still blank. Oh well. Life should be so hard.
Saving the midrange for last, this particular frequency range is where SET amps shine their brightest, and the SET-300B is no exception. Tonal balance and accuracy were spot-on, a clear testament to the priorities Glenn Dolick places on this aspect. Tonal color and shading were simply excellent, unraveling the intricate complexities of harmonic information on each note. I did notice a slight but perceptible haze in the midrange and lower treble. This was not grit or hash, but more of a restriction in absolute clarity. It was not enough to stand out as bothersome, but noticeable nonetheless. Overall, the midrange presentation (and the presentation as a whole) was incredibly addictive. Id even consider describing it as romantic, except that some may infer that to mean syrupy or lush, which its not. Lets just stay with addictive.
With output power in the 8-9 watt range, proper speaker selection and synergy is of utmost importance. Don't expect this amplifier to drive low-sensitivity or low-impedance speakers. If you do, dont blame the amp for the sonic deficiencies. But you already knew that. The Coincident Super Eclipses worked quite well, as there were only a few pieces of music that taxed the amplifier into audible distortion at normal listening levels.
As the 300B output tubes are not supplied as part of the base kit, I decided to borrow the Western Electric 300Bs from my Cary amps to see what difference they made in the overall sound. The results were a bit surprising in that the WE tubes provided less of a performance improvement over the Sovteks than I was expecting. I was tuned-in for a transformation and ended up with a definite but less-than-earth-shattering difference. The WEs provided more detail, more finesse and refinement, and added some definition and contrast to the bass. Tonal color was a bit lighter and brighter, revealing the Sovteks to be a darker-sounding tube overall. The most appreciable quality the WEs provided was a widening of the soundstage and near-holographic rendering of the space and place of the instruments. Although the WEs were undoubtedly superior to the Sovteks to my ears, the retail price of $900 per pair has to be factored into the equation. I cant say with confidence that the level of improvement was commensurate with the cost, as thats a judgment best left to you.
I also tried a late-manufacture NOS Philips 6SN7 input tube to see what differences existed, just for fun. The Philips would not be my first choice in the NOS Absolute Sonics contest, but it, like the Sovtek tube, is readily available, reliable, and inexpensive. Result? The midrange haze I referred to earlier was completely gone. The Philips tube provided a bit brighter overall perspective (not a bad thing with the Sovtek 300Bs in circuit), but most noticeably offered greatly improved clarity and finesse to the midrange. The cost/performance ratio here was not even a question. I would consider replacement of the Sovtek 6SN7 input tube as a must.
The only other SET amps on hand at the time were the Cary 805C monoblocks. Enough has been written about these amps over the years that further detail isnt necessary here. While it is irrelevant to compare a $9k product with a roughly $1k product in absolute terms, the Cary amps provided a benchmark for some perspective on the performance of the SET-300B. I could probably write several paragraphs about the differences between the two amps, but to what end? Id rather just get to the punch line: the SET-300B offers an overall sound quality that belies its price. The Carys offer more transparency, refinement, resolution, and power, and reinforce the often-diluted concept of "you get what you pay for." The SET-300B, on the other hand, introduces a new concept: you get more than you pay for. Nuff said.
The SET-300B is a fine-sounding amplifier regardless of price. If the price is taken into consideration, it has to be considered a bargain in the realm of high-performance audio. (Sorry, I hate the term "high-end.") While certainly giving up some ground to its much higher-priced competition, the sound quality contained in its less-than-a-kilobuck chassis need make no apologies. The SET-300B has a musical rightness that allows the listener to become immersed and involved in whatever music is played through it -- all for about the same money as a fancy pair of interconnects.
If youre looking for the ultimate in speed and rafter-cracking bass, then youd be better served with another amplifier. If, however, youre looking for an amplifier that lets you see into the music and expose the grace and harmonic beauty within, the SET-300B needs to be on your list.
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