February 2006

Welborne Laboratories 300B DRD SET Amplifiers
Falling off the SET and DIY wagon... and loving every minute of it!
Review By Scott Faller
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  To the tube crowd out there, the name Ron Welborne is almost a household name. Ron's name is synonymous with nicely affordable kits for the hardcore hobbyist interested in exploring the thermonic arts. Currently Ron has a bevy of different products to choose from. From the DRD's (direct reactance drive) in both 300B's and 45's to his Ultrapath battery powered preamps, to remote controlled stepped attenuators to power supplies for projects. Ron has a nice selection for the DIYer and enthusiast. If you aren't of the DIY ilk, Ron also offers fully assembled units.

A couple of years ago at Christmas I hosted a gathering for the local audio guys. We had loads of people show up that day. Between the four or five systems I had set up for people to hear, several of the guys brought their own gear to swap in and out of the many systems that were eating up the kWh's that day. As always, my Fleapowered system gets lots of listening time by the guys. There is something inherently inviting about its sound. I'm not sure if it's the Lowther PM2A's in the Medallion cabinets with my 15-inch Goodman's subs shouldering bass duties, or the Handmade Audio 2A3 amp that mates so well to these speakers, but something keeps people coming back to this system (me included).

This particular gathering brought people in from far and wide. One of the regulars drove down from Springfield Illinois with a couple of amps in tow. When Brad showed up, I helped him bring the amps inside. Upon first glance, I could tell that we were going to be in for a nice treat. Brad had bought and built a pair of the Welborne 300B DRD's. These were in the stock case that Ron offers with each kit.

After a couple of hours of listening to my single ended system, we decided to pull my 2A3 out so we could give the DRD's a whirl. We plugged them in and I wandered off to visit to some of the other guests. After about an hour or so I came back to give them a quick listen. I grabbed one of my favorite albums, Pat Metheny's Still Life Talking. I dropped the needle, cranked it up a bit, then went over and sat down in the sweet spot. About five minutes into side one, I looked at Brad, smirked and said "You know, those are going to cost me a years worth of my audio allowance!". Sure enough, two weeks later I was on the phone with Ron ordering a pair for myself.

A Little About The Amps & Kits

Lets talk briefly about the DRD design itself. The DRD (direct reactance drive) isn't a new concept. The Welborne DRD design is actually a derivation of an old Loftin-White direct coupled design. Granted, Jack Elliano of Electroprint and Ron have made some adaptations, but the basic design concept is still in tact. The DRD concept is to directly couple the driver tube to the output tube. This removes the sonic degradation and coloration of the coupling cap (or the resistor or transformer if it is a resistance or transformer coupled amplifier).

As you can see from the schematic, there is exactly one passive component in the signal path, one resistor on the input. After that, there are just two tubes (the driver and output tubes), then Jacks custom wound output transformer. This is about as close to  straight wire as you can get in an amplifier.

When it comes to power supply schemes, Ron offers you a choice, tube or solid state. The tube rectification runs a bit more money because of obvious reasons. The assembly will take you a bit longer too. Since my SET's have all had tube rectification, I decided to try the solid state version. I've heard good things about Ron's solid state power supply design but I've not tried it on something as revealing as an SET played through Lowthers. If there is one set of speakers that will tell you exactly what is going on in the electronics upstream, it's the Lowthers.

When it comes to parts and cases, Ron also offers a myriad of choices. At last count, he offers nine different choices in unfinished wood cases to house your new amps. Ron also offers a number of different electronics upgrades too. You can order silver hookup wire, resistor upgrades, transformer upgrades or if you want to go whole hog, you could order his latest offering, the Terraplane 300B (or the 45 version).

The Terraplane is the same basic design as the DRD with a few notable upgrades. Ron has (almost) completely redesigned the power supply adding more filtration for an even lower noise floor. He's also eliminated many of the electrolytics within the amplifier. The Terraplane does cost more than the standard DRD but by the looks of the improvements, it should well be worth the extra money.

Part of the fun of being a tube-head is the ability to roll tubes to fine tune the sounds of your amps and pre. The Welborne DRD 300B is somewhat limited when it comes to tube rolling. The 6N1P driver tube is of Russian manufacture and has very specific ratings. Unfortunately, there aren't any drop in replacements. Sure, there are a few that have ratings that are similar but none are exact drop ins. The fortunate part about this is the fact that (to my ears) the 6N1P is a great sounding choice for a driver tube. The data sheet shows us that it is very linear tube across the audio frequency band.

When it comes to tube rolling, you can always swap your output tube to change the sound. Here you have quite a few choices. Some of them require fairly deep pockets but most of them are still pretty reasonable. For me, I've got the TJ Meshplate's that Ron set with the kit and I'd also got really nice sounding a pair of Chinese no-name tubes. Each tube has their own flavor. I find the Chinese tubes a little more extended and revealing where the TJ's are a bit warmer with more midrange body. I enjoy them both and swap them regularly depending on my mood at the time.

The Assembly

Within a week or so of ordering my amps, I received several boxes filled with parts. Since woodworking is another hobby of mine, I decided to order mine ‘nude' or without the case. Ron can supply you a nicely finished case if you wish or you can do as I did and build your own. The parts came in neatly packed, well marked boxes and bags. Each bag has the corresponding part number to mate to the assembly instructions. The instructions are clear and concise. They leave no question as to how to fully assemble and test the amps. Ron walks you through, step by step with a full color assembly guide that takes you part by part and layer by layer.

The option I chose was the "Ultimate" upgrade. This came with solid silver hookup wire sporting a Teflon dielectric, Caddock power film resistors, Black Gate caps and the TJ Meshplate 300B tubes. Since the Black Gate caps are becoming quite scarce and may (or may not) actually cease production (if you believe the internet buzz), Ron no longer offers them as an upgrade. In turn he provides the very nice sounding JJ and Elna capacitors.

When it comes to the actual assembly, you are going to need a modest array of tools. Here's a quick list of what comes to mind that you will need; wire strippers, side cutters (dykes for those of us who are less politically correct than we should be), needle nose pliers, angled needle nose pliers, a set of soldering aid tools with reamer, angled and forked tips, a decent soldering station, temperature regulation is nice but not mandatory (read = not a soldering gun), a decent multi-meter and I strongly suggest that you invest in a variac.

Granted, Ron tells you how to test and start these without a variac but I personally don't feel comfortable building or modifying any piece of gear without one. Ten amp Variacs can be had on eBay for under $100 bucks, shipping included. If you are going to spend this much on a pair of amps, I feel the minimal investment in a variac is worth it.

Ron says that the total assembly will take about 8 hours per amp. That's probably a bit optimistic, but if you've built a number of projects, it's probably not far off. In my case, I got the parts in December of 2004 and I finally turned the amps on in October of 2005. Ten months, that's not too bad... considering.

Here's a few assembly tips mostly for the novice.

First lets talk about soldering. Soldering is as much an art as it is a skill. The trick to soldering is to apply just enough solder to make a good joint without flooding the terminal with excess solder. Last thing you want is this huge goober of a solder joint. As you can see from the pic, I didn't load the terminals up with solder. I took my soldering iron and pushed the wire down on the terminal, heating both the wire and the terminal equally, then I applied a minimal amount of solder. Again, it was just enough to make a clean joint. I held the iron on the joint until I saw the solder get a reflective sheen, then I used my angled reamer (OK... no penis jokes) to hold the wire down to make sure it not only made good contact with the terminal but also stayed at the bottom (or top) of the terminal so I could solder additional wires on the vacant terminal space. You really want to avoid soldering wires on top of wires if you can help it. I realize this isn't possible sometimes but whenever possible, try not to do it. (Editors note: no penis jokes, but you are talking about making good joints so my thoughts were elsewhere.)

The end result of using the proper amount of solder is you get a cleaner, purer joint which has better electrical conduction characteristics. Proper heating of both wire and terminal are critical to the operation. If you end up with what is called a cold joint (one that doesn't have that sheen when the iron is on the joint), these things can be extremely noisy. They tend to show up as grain and even audible distortion in the sound.

The basic assembly of these amps is done in two stages. First is the easiest, the top plates. This is where the terminal blocks and most of the parts reside. Once you have finished the top plates you have to mount the plates on the amp casings and begin the final portions of the assembly. This is where all of the large power supply caps, chokes and back plate are installed.

There are a couple of tricky spots during assembly. Since these are mirrored pairs, you need to assemble one of the pairs backwards. This can be a bit confusing for the novice. It is extremely easy to solder a part on the wrong terminal if you are not paying very close attention. Let me suggest this up front, number all of the terminals on all terminal blocks with a pencil before you start soldering so you don't make a mistake. Also remember that even the IEC connector for the power cord has to be wired backwards in the mirrored amp. I've been building and modifying stuff forever and I still goofed up one of the connections. It was the 6 volt supply voltage to the driver tube. Luckily, I didn't smoke anything. (Editors Note Part Deux: It is noted that audio guru and all around solder sniffing dude Scott Faller did not smoke anything. Um, we are still talking about joints, yes?).

When it comes to the hardwood cases that Ron supplies (or you build) remember, brass mounting screws and hardwoods don't work well together. Pre-drill your screw holes. If you don't, you may just twist off the head of a brass screw. If you do that, it's nearly impossible to get the old screw shaft out without destroying a part of the amp case.

And finally, read ahead in the assembly manual. Envision what parts are going to be installed in the next few steps. The final steps of assembly can be like a game of chess. Think ahead to make sure you don't block a future move.

This is what the first layer of the inside of my amp looks like. As you can see, I was pretty anal about the routing of the wires. Me, I make sure that everything is square to the world rather than running willy-nilly all over the place. I guess this comes from my years of doing power wiring in boxes and control panels. To me, there is nothing worse than sloppy wiring. It confuses me when I look at it and in turn I feel like I have more of a chance of connecting something wrong. Then again, my oldest daughter (23) claims I suffer from OCD (Obsessive Compulsive Disorder). Just because I have all my resistors and capacitors organized and neatly tucked away in their own little drawers which are sorted and cataloged by type, voltage (or wattage), size, and brand doesn't mean I have issues, does it?

Here's what the final product ended up looking like in my cases. I realize it seems a little menacing for the novice but it really wasn't a difficult build. As I mentioned before, Ron walks you through, part by part during the assembly and before you know it, you are saying a short prayer to the Gods of Thermonic Emissions and flipping the switch.

Loudspeakers

Before we start talking about how the amps sound, I'd like to take this opportunity to talk about SET's and speaker matching. For those of you that know this already, please feel free to skip down to the next section.

Low output Single Ended Triode amps are designed to be used with high efficiency speakers - period. In fact they work best when mated to speaker designs that do not use crossovers (read= actively crossed over or single driver speakers). SET's and many tube amps have very low damping factors. With SET's, the damping factor is usually less than 10. When you try to mate your (supposedly) high efficiency, multi-way speakers of (say) 92dB which also happen to be an EBS (extended bass shelf) design, you have a very strong likelihood that it will make any SET sound horrible. SET's need true high efficiency speakers to perform their best.

Personally, I wouldn't try to mate any speaker less than about 95dB/W/m at 8 Ohms to an SET. To take that thought one step further, I wouldn't use a multi-way speaker either unless it utilizes the simplest of crossovers (read = first or at most, second order crossover with minimal parts and absolutely no impedance compensation or Zobel network). When you start adding passive components between an SET amp and the raw driver, it can cause the SET some real problems. These problems manifest themselves as veiling, flabby bass, midrange bloat or any number of other sonic irregularities.

SET's by nature enjoy (and need) the purist route possible to have them perform at their best. When you look at a typical monkey coffins impedance curve you'll notice that you get huge impedance spike the speakers resonant frequency and minor spikes at (or near) their fundamentals. If these spikes reach much above (say) 50 ohms, this can spell disaster for an SET. The other issue is dips in the impedance curve. If your 8 Ohm speaker dips to (say) 3 Ohms in the bass region, this spells disaster too.

Many speaker designers try to put Zobel networks in the enclosure to level out those huge spikes and dips. Supposedly they make the speaker SET friendly. Trouble is those electronics usually end up choking the life right out of the sound. Honest to goodness, you are best off using high efficiency speakers that are specifically designed for low powered tube amps.

If you are wondering what speakers to use, let me direct you to the Welborne Labs website. At the bottom of Ron's front page is a link to many, many speaker manufacturers who build Hi-E speakers. Personally, I'd recommend Lowthers only from Jon VerHalen at Lowther America, John at Classic Audio Reproductions, any of the designs using Fostex speakers like Terry Cain at Cain and Cain or Louis at Omega Speakers, Tannoy's, Klipsch's, Audio Note any of the front or rear loaded horn designs or any number of vintage speakers on the market like the Altec A-7's or 19's. I've listen to each of the speakers mentioned. Although each have their own flavor, they are all very good mates to SET amps.

Oh, and while I have your attention I'd like to end this once and for all. Single ended amps and single driver speakers do complex music AND Rock and Roll just fine. You have not lived until you hear Rob Zombie, Metallica or Nine Inch Nails on a Fleapowered system (done right). I get a lot of grief from some of the hardcore SET guys for my choices in music since many seem to be classical fans but I'm here to tell you Rock sounds even better on an SET than on a high powered solid state rig with Low-E speakers. Again, it's all about the purity of the signal path and truly revealing speakers. Still don't believe me? Next time you are in St Louis, drop me a note, come by and I'll drop the needle on some Snoop Dog or Bubba Sparxxx for ya. You'll be amazed, I promise.

Listening

I've listened to quite a number of single ended triode amps over the past few years. I'm fortunate, where I live we've got more than a few people who are single ended freaks that hang out together. We have amps ranging from simple 45's to push pull 45's (my next project) to 2A3's, 300B's to 50's and 845's. After you play around with so many different SET designs you start to expect a certain sound from a particular tube. Our choices in speakers are pretty varied also. They range from back loaded horns to Voight Pipes (Cain and Cain Abbeys), to Fostex's in a bass reflex cabinet, to big honkin Altec A-19's to Klipsch Horns to Avant Garde's  to MLTL's.

For me, Ron's DRD broke the mold for the ‘typical' 300B sound. I have to say, I've never heard a cleaner sounding single ended amp (notice I didn't say 300B). The DRD design is so clean and simple it's as if the amplifier doesn't get in the way of the sound. Much like we all hope our preamps do, the DRD's don't impart any sonic signature to the music (other than the sound of the tube itself). Granted, as any self respecting SET guy will tell you, the output iron plays a huge part in the overall sound of the amp. Ron has paired up with Jack Elliano of Electraprint who provides all of the iron for these amps.

I can tell you positively, Jack knows how to wind a great sounding transformer. One of the local (gifted) amp builders (Willie Rivers) has brought his amps over before and after being retrofitted with some of Jacks iron. The differences were more than subtle. It was if the amp was transformed (no pun intended), almost as if it were a completely different design. That's how good his transformers are.

Now that said, quality always comes at a price. Sure, you can go to the Hammond website and buy an OK sounding 300B transformer for a reasonable amount of money, but there is no sonic comparison to a quality piece of iron. You may be thinking to yourself that Ron's kit is a bit costly, but it really isn't. One of the bigger chucks of money goes for the transformers. Again, quality costs money.

While I'm on the transformers, Ron is exactly right about the heat generated from his (or should I say Jack's) transformers. Unlike so many other tube amps I've run across, these transformers run very cool. They are just slightly warm to the touch. I've actually got a pair of amps that turn into space heaters when they are switched on, that's how hot they run.

Just as Ron mentions on his website, improperly designed solid state power supplies (vs. tube rectification) can make an amp sound hard and brittle. The treble quickly becomes very fatiguing. After listening to the DRD for a couple of months now full time, it now has me rethinking some of my future projects. The super fast HexFreds he has chosen live up to my sonic expectations completely. I don't hear any etching or hardness in the treble region at all. This makes power supply design and building much easier and considerably less expensive.

Every time I have higher wattage guest amps (SET's) at my house, I am constantly amazed at how much better my Lowthers respond to them. As great as they sound with the 2A3's and 45's, amp designs with more wattage always seem to really bring the PM2A's to life. I guess it's the headroom these higher wattage amps provide. I tend to listen (more than) a little bit loud at times. Loud to the point that I can run a Fleapowered amp into clipping. That isn't the case with the Welborne DRD. The whapping 7 watts produced by this design easily drives my Lowthers into the 110dB/W/m realm (actively crossed over of course).

As I sit hear and listen to Art Blakey and the Jazz Messengers Buhaina's Delight Backstage Sally, Freddie Hubbard is blowin' the horn, I can hear those leading edges of breath that comes out of the horn before it becomes the actual note. That is the type of resolution you get from this amplifier.

Moving on to something on the complete opposite end of the musical spectrum Van Halen's 1984 remastered release. This one I'm playing via the Squeeze Box and a cool little tubed DAC from MHdt Labs. If you remember "Hot For Teacher," Alex VH opens this with a wild drum solo. In the midst of the kick drum solo, he starts hitting the floor Toms with his hands. The accuracy and resolution of the Welborne DRD's let you hear that hollow sound of Alex's hand slapping the skin of the floor Tom plus the big room filling bass sound of the drum itself. Then you've got Diamond Dave standing just in front of the right speaker asking the question, What do you think the teacher is going to look like this year?. The DRD's did a marvelous job in conveying exactly what was recorded.

Another artist that amazes me is Poncho Sanchez. If you are into Latin Jazz, this guys albums should be on everyone's short list. These guys are a great test for those little dynamics like attack, decay and also clarity because of the percussive nature of the music. In turn, the Concord Picante label has done a great job with their recordings. As you would expect with such a pure signal path, all of the true dynamics of the congas and all of the other percussion instruments came through clean and crisp. The DRD's showed no signs of muting or more importantly, falsely enhancing the dynamics of the recorded sounds. As an aside, my wife and I and another couple  saw him on his last visit through St Louis and he literally had everybody up in their seats and in the isles dancing. This is music that moves your soul. Highly recommended.

I'm sure you are wondering about bass and treble extension, midrange milkyness and all that. Well not to let you down (but not to inundate you with flowery prose either), I'll give you a very brief description. I have to preface this first. I actively cross over my Lowthers in the Medallion cabinets which means I rely on my vintage 15-inch Goodman subs and a separate amp for the bass in my system. It just so happens my Goodmans are actually dual-concentric (a fancy way of saying coaxials). They easily hit 25Hz corner loaded in my room so I thought these would be fine for the demonstration. I used my Handmade Audio 2A3 complete with Teflon Sonicap coupling caps and Blackgates as a comparison.

After swapping the two amps in and out of the system, there really wasn't much of a comparison. The Welborne DRD's outperformed the super sweet 2A3's in the bass department pretty handily. The bass was firmer, deeper and there was just more of it. When it came to the midrange and treble, I went back to my bi-amplified setup and the Lowthers.

This is where things get really subjective. This now becomes, what sound do you like better. My 2A3 has always had (as do most 2A3's) a stellar midrange presentation and a super sweet treble. It's warm and absolutely lovely. Not quite a 45 or a 50 (tube) but damned close. Ron's 300B has the upper hand when it comes to clarity, resolution and treble extension. The DRD's are considerably cleaner and more detailed sounding without loosing touch with the music you are playing.

One last example about just how great sounding these amps are, over Christmas I have a bunch of the local audio freaks over at our house for our annual Christmas bash. They hadn't yet experienced the Welborne DRD's in my system, especially with vinyl. I decided to do the show stopper early in the event while everybody was still sober (almost). While I had everybody sitting in front of the DRD's, I popped on the new Pure Audiophile release of Art Blakey and the Jazz Messengers live album, Keystone 3. After side one, the guys actually erupted into applause... no BS. That's pretty telling all by itself.

So in the end...

As I mentioned earlier, any single ended guy will be happy to inform you that each tube has a slightly different sound and presentation. Some of that ‘tube sound' has to do with the particular design implemented in that amplifier. You pick up sonic signatures of caps, resistors, chokes, transformers, whatever happens to be in the signal path. I'm happy to report that most times it works very well. Such is the case with the Welborne DRD 300B.

This design has proven extremely reliable. Personally, I've had mine running for extended periods of better than a week straight without any issues (something I normally don't like doing to output tubes). I've yet to read about any failures regarding design issues on any of the boards.

As I mentioned earlier, Ron's kit might seem just a tad pricey at $1,700 (as tested) but when you start looking at the prices of the individual pieces parts, it's actually fairly reasonable. I will tell you this, this truly is one of the (if not the) best sounding 300B's that I've had the pleasure of listening to. So when you start to compare prices on amps, understand that you may find something less expensive out there but you won't necessarily find anything that sounds better.

Personally, the sound (or lack thereof) of this design is truly refreshing. It brings new levels of clarity to the realm of single ended designs. The stunning realism of the music gained by using the Welborne DRD 300B Monoblocks has been a welcome addition to my system. The DRD's ‘sound' hasn't been the least bit fatiguing or harsh. The DRD's have given me the ultimate in clarity which has allowed me to dig deeper into the music than ever I have before.

Another thing that I need to mention is the DRD's complete lack of hum or buzz. Those of us that play with low powered amps know all too well the 60Hz (and 120Hz) gremlins that live inside a misplaced transformer, untwisted wire or part placed too close to another. I'm happy to say, Ron's amp is dead quiet. The noise floor is lower than any SET I've had the pleasure of playing with.

So, are you ready to step up to the ultimate in clarity? Only your ears know for sure. The Welborne DRD 300B will definitely deliver if that is what you are looking for. If you are in the market for your first (or possibly last) SET amp, I'd strongly suggest Ron Welborne's DRD 300B. It is a stellar performer that will provide you with the ultimate in clarity without sacrificing the music in its quest.

Personally, I love these things but then again, I fell off the SET wagon a long time ago.

My Ratings

Please keep in mind this rating system is used to compare the Welborne DRD 300B's against absolute perfection, or a money no object SET design. If you see what you think may be a low(ish) score, it's because there are 300B designs that are even more refined but consequently cost considerably more. To top that off, if I assign 5's across the board, I've just painted myself into a corner leaving no room for that ‘ultimate' amplifier. You won't see me handing out many 5's. In turn, I feel I need to leave room in the ratings system to accommodate those amplifiers.

Specifications

Type: DIY single-ended tube monoblock amplifier

Output Power: 7 Watts

Frequency Response: 10Hz to 48kHz (-3dB)

Input Sensitivity: 1.5 volts

Tube Complement: One per monoblock, 6N1P and 300B (TJ Meshplates)

Weight: 25 Lbs.

Price: $1,732 USD (including tubes and upgrades, unassembled)

Company Information

Welborne Labs
971 Garden Drive
Highlands Ranch, CO 80126

Voice: (303) 470-6585
Website: www.welbornelabs.com