Back in the Dark Ages when the first issue of Sound Practices hit the streets, single ended triode amplifiers were the exclusive province of the intrepid DIYer. If you wanted it, you had to build it.
Yeah it was fun back in the old days (last year), but it was a bit lonely. If you were interested in triodes and single-ended stuff back then you were likely to have enormous phone bills because the only two people who understood what you were talking about lived in Montana and Florida.
Two years ago, you could still find N.I.B. Western Electric 300Bs for $75 and only exporters were buying them since only a few crazed builders and Western Electric collectors had amps to plug them into. Over the past year, single-ended audio moved from being an exclusively DPI' pursuit to a legitimate conceptual suburb of high-end audio. Mention that you have a triode amp down at the audiophile society meeting these days and you are more likely to get a request for an audition than the traditional blank stare.
Sure the tired hi-end market was ready for something novel and fun beyond new digital formats and the SE explosion gave audio journalists something to discuss besides ABX testing. Nonetheless, the enthusiastic reception of SE triodes in the established press points also to the sonic merits of this technology. This stuff does all the Official Audiophile things well: Image, detail, back wall, yak, yak, yak. But a good triode amp also plays with a breath of soul that is rare in the usual run of commercial gear.
Fortunately, the prospect of listening to triodes is becoming more and more realistic as small to medium sized manufacturers arise to meet the burgeoning demand for store-bought products at various price levels. A niche industry catering to the special needs of adventurous DIYers rose up out of nowhere simultaneously. It's getting to the point where we hear about new tubes, transformers, amps, kits, etc., several times a week! Things are really starting to get interesting. As good press on triode amps accumulates in the mainstream magazines, the market can only get better.
One particularly heartening development in the prevailing audio revolution is the resurgence of kits. Kits are a cool idea, once popular before they started building electronic gear with giant robots. Kits can help us recover the lost "hands-on" aspect of our hobby that many of us need in an era when you can't even tinker with your car without a 32-bit protocol analyzer. Everything in sight these days is a soulless "No User Repairable Parts Inside" black box appliance.
The kit is the great leveler. You can be a total novice at electronics and still jump right in. You'll be less of a novice at the other end. Most of what you learn is basic soldering and assembly technique, but you will also catch on to the idea that, on one level, any amp is simply a pile of parts. This can do a lot to demystify electronics. It's more like plumbing than audiophile journalism suggests. Every reviewer should build at least one kit in his or her life, I say.
Novices take heart A service manager for former kit giant Heathkit wrote in QST magazine back in the 50s that sometimes knowledge and experience could even be a bit dangerous in kit building. While beginners tended to cling to every word of the instruction manual, old hands at building would often invent "shortcuts" and skip sections of the manual, typically leading to unforeseen disaster or at least lots of extra work.
If you are ready, willing, and able to follow directions, the probability of making some weird mistake you never even thought about is greatly lessened with a kit. Most problems can be traced to failure to follow instructions. And if you do screw up you can get somebody to help. If you can't get your scratch-built triode-wired single-ended cathode-coupled 6ARSamp to work, light a candle and pray for divine inspiration.
In addition to providing a clear program of action and a complete collection of parts, kits usually offer a sound economic rationale as well. Often a kit sells as a turnkey package for less than you would spend to buy equivalent parts and materials yourself; especially when you factor in phone bills, time, and shipping charges. Sourcing non-standard power resistors and other obscure parts is the kitmaker's job, not yours. Rescues you from dozens of phone calls and $30 minimum orders when all you need is two 880 ohm resistors.
Furthermore, no investment in specialized tools like chassis punches and rattail files is required for kit assembly. You can get by with a soldering iron, standard hand tools, and perhaps a basic digital meter. You won't have to do any metalwork on the kitchen counter, so you don't wind up with razor-sharp metal filings stuck in the carpet, just little blobs of solder and lost nuts and bolts. As far as I am concerned, learning how to solder and do routine electronics assembly isn't a big thing. The ability to do decent looking metalwork, on the other hand, requires patience, skill, LOTS of practice, and a serious workshop. I don't have any of the above.
The question "How do I build an amp?" is like the question "How do I fix a car?" It's not that hard, if you know how. Unfortunately, learning how is a medium-to-long-term project and everybody wants to get building NOW, if not sooner. If this sounds familiar, whip out your credit card and call a kit dealer.
The psychic payoff of kit building is enormous. After a few nights of interesting and engaging work, you can be listening to an amplifier YOU built. Impress your next date: ‘Yeah, baby, I built that amplifier. Like that midrange?" Rediscover the rewards of actually doing something tangible in a push-button world.
The psychological rewards and economic advantages of kits are certainly considerable. However, the reason hobbyists build kits is to get the equipment at the other end of the process. Right now, there are some very interesting products on the kit market Even though I'm a notorious trashpickin' cheapskate scratch builder myself I was anxious to hear some of the current crop of SE kit amps because on paper they seemed to offer potential for high performance at a level of investment many hobbyists can tolerate.
Welborne Labs Laurel
At $1600 and up, the Welborne Laurel stereo and mono amplifiers are the higher-priced entries in the US kit market. With the Welborne kits, you can get into a serious triode based system for the cost of an Adcom-555 and a pair of Vandersteen 2C. You probably need to have gone though the 555/2C phase yourself to recognize how far ahead you would be with this 300B kit and a pair of efficient two ways.
Since Welborne's in the audiophile parts business, this amp is loaded with fancy designer parts. Outputs are Magnequest FS-030s on the stereo amp ($1600), DS-025s or FS-030s on the monoblocks ($1620 or $1900/pr). A "stock" Laurel comes with Golden Dragon 300Bs, 6SL7s, and GZ-34, and a pair of new old stock 6AG7s. Kimber Kaps are used in the audio circuit and as bypasses for the 5CR polypropylene filter caps.
Welborne is receptive to the idea of working with the buyer on parts selection, a refreshing alternative to a common high-end manufacturers' stance — "We auditioned eveiy fuse holder on the market and this one is the most transparent" and so on. As a symbol of kit building freedom of choice, Welborne packs each unit with both Allen Bradley carbon composition resistors and fancy Roederstein metal films. "Have it your way," is the order of the day.
The Laurel I got my hands on was an assembled stereo unit. Quite nicely assembled at that. I almost bated to dive in with a soldering iron and really get into checking out the amp. Now, if it were a borrowed Audio Research, I wouldn't even want to open it because I might mess up the paint on the screws and lower the resale value by $300. But this is after all a KIT amp. Kits don't have to stop being built I saw it as a project waiting to happen.
I called Ron Welborne and asked, "Say, you wouldn't mind if I tried an experiment or two with the amp, would you?' Heck, Ron not only didn't mind, he encouraged my experiments. Got the same response from Dennis Had over at Cary about the SE-I. Both kit designers were actually eager for hot tweak tips to pass along to builders to try. I really appreciate that attitude.
Since I'm used to spray painted Bud chassis homebrew monstrosities, it was a bit of a shock to my listening mom anti-decor to have the extremely handsome Laurel on my mantel. If I ever build an amp as nice looking as the Laurel, Joyce might finally stop moaning about the fact that I gave her Akai mini-system away five years ago. With its polished brass and walnut enclosure, the Laurel looks handcrafted rather than manufactured. It would be at home in a mahogany paneled den with green leather armchairs. Got that exclusive men's club thing going on. The entire assembly fits on a compact 14 x 17 x 2" chassis. With all those burning Class A tubes on one and a half square feet of zeal estate, the Laurel would be nice to cozy up with during a snowy evening. (Right now its 105 degrees in Texas, by the way).
All versions of the Welborne SE amps use a mu stage driver stage designed by Alan Kimmel. This circuit is a variation on the popular mu follower circuit optimized for use in power amps. A general idea of the circuit implementation is given above. The complete schematic and other relevant engineering data is available in Welborne Labs' latest design manual and catalog, a thick book of schematics and useful data worth every bit of the $10 asking price. Further insight on the mu stage is also provided in Alan Kirnmel's 1993:2 article on the topic in Glass Audio.
The assembly manual and layout are logical and should be easy to follow for the builder. Most of the parts are attached to a few epoxy terminal strips that sun the length of the amplifier. Basically you mount the transformers, tube sockets, and terminal board in the amp, then install the parts in layers as instructed by pictorial diagrams. Once you get everything in there isn't too much leftover space, so forget about strapping a bank of oil filter caps rescued from an old radar console underneath.
Out of the box, with less than 50 hours burn-in time at Seth Goldwin's pad, the Laurel bad a touch of zing, as I expected based on Seth's comments and my previous experience with freshly built gear.
The last few amps I built used Magnequest transformers and I found that they require up to two weeks of nearly constant play before they fully settle down. Poly filter caps also take a few days to mellow out. Same probably goes for everything in the amp. I don't remember such dramatic burn-in effects with store-bought gear. I suppose most manufacturers put some hours on a factory unit before it ships.
Like everything else in audio, the whole question of break-in is under dispute. Psychologists often attribute such effects to perceptual recalibration, where the perceived break-in is actually a by-product of the listener getting used to the particular sonic character of a given device. Although I agree that man has a high capacity for self-delusion, I believe that break in is real. Fooled me, anyway.
The Gauss 1502 compression driver tweeters I use for the top end in my Edgarhorn/Onken system are a mixed blessing. With the right amp these tweeters really sing but with some otherwise respectable equipment they turn into audio-frequency death beams. Over the years, I have developed a liking for systems with mildly sharp speakers and slightly soft amps, or at least amps that have a musical rather than a clinical top end. Altec 755C or Lowther PM-6s in my 4" throat Edgar horns also give me a squeaky clean sound, but they are far more forgiving than the pro-sound tweets.
I usually bi-amp with a triode amp on the mids and tweeter's. Accordingly, most of my Laurel listening was done with the amp on the mids and highs, 350 Hz up, but I also wired up the system with the Laurel playing full range. Until I get a chance to build a PP triode bass amp, I am using a Dynaco ST-35 I borrowed from a friend as a bass amp on the Onken/Altec 416. Even with a wimpy Dyna bass amp, the bi-amp setup sounds better overall because I don't have to pad down the mid horn to match output levels. The bass was actually much more natural with the Laurel but I couldn't take the midrange quality losses with an attenuator in line, so I mainly listened bi-amp. Anyway, after a week of nonstop listening, I decided that the Laurel still had a pinch too much lower treble information for my system. A subtle thing and probably as much to do with my speakers as the amp. Anyway, I was looking for an excuse to start heavy tweaking.
My first experiment was to unbypass the poly filter caps. The 0.1 mF Kimber Kaps shunted across the filter might offer lower impedance at high frequencies but the 5CR caps are okay by themselves. With a film bypass cap, they can get a bit too lively sounding — an advantage in some cases but not what I needed. After I yanked the bypass caps, the amp smoothed out enough that I was happy. Power supply components have major sonic effects in SE amps because the PS is in series with the audio stage in SE.
Continuing to experiment, I installed four Audio Note paper in oil caps for coupling. The Audio Note caps, while a touch on the laid back side, are free of the melodramatic quality some people don't like in classic oil caps like Vitamin Qs. They offer a polite tonal balance and poise without squashing dynamics. A tiny bit soft on the leading edge but the overall effect is very natural and involving. They provide just enough bite for a convincing illusion of reality. A friend once suggested that a good system is one you can fall asleep listening to, but not one that puts you to sleep. The Audio Note caps will give you a comfortable sound that is still exciting and very engaging.
Another capacitor I have been interested in lately is the Hovland MusiCap, a polypropylene and foil type. I have always been partial to
a nice oil/paper cap for power amp interstage coupling, but after a week of living with
Wavelength Audio's superb MusiCapped Cardinal amplifiers, I began to reconsider my position. I
tried an SRPP driver stage in a 300B amp with Magnequest FS-030s, but it didn't sound like
this. The Cardinals gave a lot of overused review-speak terms new meaning for me. Want
transparency, detail, and accuracy that doesn't singe your mustache? Here it is. I figured the
Hovland caps played a part in the Cardinal sound so I wanted to try ‘em in the
Basically, I had the Laurel for three weeks and during that time I had three different sets of caps in the amplifier. All I can say is, you folks who find cable swapping and resonance tweaks engaging should look in to cap swapping as a new hobby. In these simple no-feedback amplifiers, each "passive" component has a truly radical effect on the sound. Sure, you can hear parts changes in push-pull feedback amps too, but here it is a different order of magnitude. I had a real blast experimenting. The range of possible sounds you can craft by swapping low cost parts is mind bending. The Laurel can assume many guises.
Throughout my experiments, the Laurel maintained a sense of tight control and focus. This amp is very fast and punchy. It had the snap for Buddy Guy and just the right amount of richness and color to give female vocals the appropriate emotional twist. The bass performance of the Laurel was highly controlled for a SE 300B. It would be a good choice to run appropriate speakers flu range. If you think SE amps can only sound "old fashioned" or hopelessly tubey, you haven't heard the Laurel — or most other modern SE amps, for that matter.
Additionally, the Laurel has the vivid 3-D presentation that instantly lets you know you are listening to an SE triode. This is one of the main things you are paying for when you invest in triode amps. With a good SE amp, the music just floats in the air — a pleasant, almost psychedelic illusion that never wears away.
Don't mistake this little essay for a serious review. I mainly used the Laurel as a midrange amp with a non-standard speaker system. If anything was matched to +/-1dB, I'd be very surprised. I just wanted to "check it out" in my natural listening and tweaking mode to see if it would give me the level of musical impact I expect from a 300B SE. It sure does. It is a really nice amp.
After playing with the Laurel and the Cary SE-I, I am even more excited about kits. Both products were like "fun in a box" and each gave up some real good music for the money (and high perceived value overall) in their respective price classes. A kit can give you most of the fun stuff of scratch building without any of the dog work and tedium. Since I grew up in a silicon universe, I missed out on tube amp kits the first time around. I'm sure glad they're back!
NOTE: There have been reports that Welborne
Labs is not filling orders.
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