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