Welborne Labs Apollo Amplifiers


Single ended amplifier. Based on either the KR300BXLS or VV52BX. Many upgrades available.

User Reviews (2)

Showing 1-2 of 2  
pangl   AudioPhile [May 19, 2007]

Displaying some addictive characteristics of lower powered SET sound yet this amp would allow you to drive more inefficient speakers with better frequency range.


Quality of assembly is at the mercy of the kit builder. Does not quite sound like an pure SET amp.

Let me cut to the chase. The Apollo parts quality is simply top notch - so top notch that Welborne stop selling it due to its slim profit margin. At least it's the story on the ethers.

There are some reports that the Apollo lacks reliability somewhat, and that's the real reason for its demise. I am not so sure about that one. People do have to keep in mind, however, any kit form item is at the mercy of its builder. My pair - purchased from the original builder, for example, has hum that I could never get rid of. Solders simply got loose during transit. And changing the impedance between 4ohm and 8ohm is much more involving (even it looks like some simple re-wiring). When you buy a pair of this, make sure you are knowledgable somewhat in dealing with kit form stuff, or you may be in for some nasty surprises.

BTW I am not a believer of high output SET amps. They just don't sound the same like 45 and 300B, which IMHO my all time favourte tubes for SET. 805, 211, 845, the KRs, I have tried them all. They sound great, but they are not the reasons people get addicted to SET like I did.

So I see Apollo more like a product you experience with, much like staying in long lines to see the Statue of Liberty. The only high power SET amps that I would recommend buying is the Gamma Acoustics 211 (which has a bad rap for reliability, but boy that amp SINGS!) and KR 6000 monoblocks (that's an $9000 pair monoblocks).

(The Audio Note Conquest is an parallel single-ended so I don't count it)

Similar Products Used: Bel Canto SET40, KR 6000, Audio Note Conquest, Ming Da MC845, Gamma Acoustics Rhythm (an 211 based SET), Welborne Laurel 300B.
Bryan F.   an Audiophile [Mar 10, 1999]

Welborne Labs Apollo II SET's
I was suppose to have this written and out the door a month ago. However I
have been tweaking and trying to get a grasp on the sound of my system. As many changes have occurred. Yet alone I wanted everything to be run in. So here I am with keyboard in hand. I apologize to all who asked some time ago. In all honesty I was unable to comment until I had spent more time with them. Thanks once again for your patience.

The Apollo II's are point to point wired single ended triode amplifiers (monoblocks to be precise) with an output of 25 watts of class A power and no more than 1.5% THD at clipping. Utilizing the KR Enterprises VV52BX output tubes, and parts that are of the highest quality. Including Black Gate Muse capacitors, Jenson Copper in Foil capacitors, Caddock and Mills resistors, Teflon tube sockets, Swiss made milliampere meters, ElectraPrint output transformers, 6EM7 driver tubes (NOS of course) and Cardas rhodinium connectors (inputs and outputs included) to name a few. For more information please contact Ron Welborne at:

Welborne Labs voice; (303)470-6585 FAX; (303)791-5783
P.O. Box 260198
Littleton, CO USA 80126

Well, lets get down to business. I found the Apollo's while trying to fill the need of finding a single ended amplifier that would work with less efficient
speakers. However, I didn't want to loose the refinement that draws me to lower
power SET's to begin with. OUCH, big problem. As while the Cary CAD-805C, Bel
Canto SET 80, and the likes offer power. They seem to lack refinement as opposed
to their lower powered siblings. Also I didn't want or need this much power (As
they offered 40-80 watts). As my Merlin VSM SE's are 89db in the efficiency
arena and easy to drive. However I did want to reach volumes in excess of 100db.
So there was a need for double digit wattage.

So I looked for other companies that could meet my needs. I looked towards the Wavelegnth KIR and Art Audio Jota but their price tag was a little out of my budget. Then I ran into the Welborne Labs Apollo II's and they looked promising. Being able to meet my needs of high(er) refinement while offering power to meet my application, and most importantly offering the highest bang for the buck. As I couldn't find any other amplifier that offered the parts and build quality for under $9000-13,000. Believe me I looked.

They arrived at my door in two large white boxes. Packed in those boxes were
smaller white boxes and even in some of the smaller boxes were even smaller
white boxes. Each layer of boxes having packing material between each other as
to not damage them during shipping. Upon unpacking the boxes everything was
very orderly packed. With all capacitors, screws, resistors....ect. packed in
individually labeled bags. Assembly proved to be time consuming but easy. As the
instructions are clearly written and Ron will be glad to answer any question via
phone or e-mail.

Now is where I have to say a few things about some options I decided to go
with. First of all everything in my Apollo's is stock with two exceptions. One
being that I wired the whole signal path with Kimber AGSS including grounds.
This added an extra $400-500 to the price. The second upgrade I also opted for
was the silver wound version of the modified version of the ElectraPrint VT2-KB
output transformer that Ron Welborne has made especially for the Apollo II. This
added another hefty $1200 to the final cost. The end result is that the whole
signal path is wired in silver. Please remember that returns do diminish and at
this point one needs to weigh the pluses heavily against the price of the

How do they sound is the magic question that many ask. Well, this is a very
hard question as Ron Welborne and Alan Kimmel have done their homework. As not
only have they been able to exploit the current potential of the KR
VV52BX (which Dr.Harvey "Gizmo" Rosenberg told me the Apollo's could do) but they have also been able to savor the refinement of lower powered SET's.

The first thing that one notices upon listening to these amplifiers is that
they are very well balanced from top to bottom. However let's explore the world
that is the Apollo a little more in depth. Now different virtues come to mind
however are dependent on the listening material. So I am going to start at the
bottom and work my way up. On material that goes low one realizes why Ron says,
"they excel in the bass department." They go low. Not only with authority, but
with accuracy, control, and also the bass is very natural sounding. With bass
being tight as well as deep. However not overbearing as it blends perfectly and
never seems like too much of a good thing.

Now it's time to talk about the midrange in general. From bottom to top as
what a single ended amplification device is suppose to excel in is the midrange.
However, most feel that if an amplifier excels in the midrange it can't in the
bass department. And we know that these things sure excel in the lower depths
but what about in the lower and upper midrange. Isn't it overwhelmed by the
lower extremes? In all honesty it is not. For some reason the overall
presentation is well balanced. Including that of bass vs. midrange purity. As the
midrange seems to be at home. With the lower midrange being very smooth and
taught. Following the characteristics of the bass to a " T ". While the upper
midrange has a rightness and naturalness about it that is very hard to overlook.
Icing on the cake is treble that is smooth as butter. I will address treble
extension further down.

In my system there is a little midrange bloom. Complements of the Joule
Electra LA100. To limit "bloom" one could use a passive. As the Apollo's are
designed to work with passives which may be a problem with some actives. As if
going active I would recommend a low gain pre amp like that of the Joule. That
offers only 8db of gain. I would be leery of any high gain pre and the

For comparison sake I wish to make a little comparison comparing the
Apollo's to two of my favorite SET's. Those being the Cary CAD-300SE Signatures
and the Wavelegnth Cardinals. Both of which I could have lived with but needed
more power. The Apollos present music both like the 300Sigs and the Cardinals.
Now I know this is where you may be thinking that I am going to state that the
Apollo's have the best virtues of both. However I am not as they all present
music in a different way. I am only using them as comparisons so that others who
cannot audition the Apollo II's may get a feel for their sound.

I have always liked the Cary CAD-300SE Signatures. Finding them highly
musical, offering a palapable liquid presentation. Oh, so smooth and warm.
However they do have a rolled of bottom end, lack extension in the treble
regions, and don't offer a high level of detail/resolution. With all this said
they are highly musical. Making me forget amplification and allowing me a window
into the world of musicality and a very big one at that.

I have also always liked the Wavelegnth Cardinals. However as far as SET's go
they are on a different plane then that of the Cary CAD-300SE Signatures. In
that they are extremely detailed/resolved, have well extended bass, and boast
some of the best extension in the treble region that I have experienced with any
SET. Though the Cardinal XS seems to even better the regular Cardinal somehow
in term of treble extension. Actually the Cardinals sometimes don't seem as if
they are SET's but the feeling of being there, depth/width of sound stage and the
glowing output tubes say in every way possible that yes these are SET's and no
stereotypical SET at that. Even though they are on the analytical side of the
SET phenomenon they are most enjoyable. Offering a different window but a
definite window into the realm music reproduction.

So how does all this relate to the Apollo's. HMMMMMM.....well the Apollo's
like I said offer a little of both and also something else. As they are like the
300 SIGs in that they are highly musical. The Apollo's aren't as warm and lush
but still retain a high level of musicality like that of the 300 SIGs. At the
same time the Apollo's offer a resolution level that one would be hard pressed
in determining whether the Cardinal was champ or the Apollo. The Cardinal does
however boast better treble extension. On the other hand I find that the Apollo
II's only lack the very very last breath. With most not even noticing this fact
at all.

Summing up the Apollo II's is no easy task. As they are more neutral sounding
and not as colored as many SET's in general. They boast smooth, detailed treble
that is well extended. Yet, they are far from cold. As they offer a touch of
warmth and are very smooth. Allowing one to hear the detail that recordings have
to offer. While boasting bass that may knock your socks off. Bass that may
actually make some solid-state and push-pull fans nervous. As Ron said, "They
sound as dynamic as a 100 watt amplifier." That being no exaggeration. Believe
me on this one. Oh, and the treble extension may make them (ss and pp fans that
is) think the same. As the Apollo's are far from having rolled of bass and lack
of treble extension. However, they don't present music like that of PP or SS and
I think we all know what the audible differences that are apparent of
each design. With all three designs offering different

In the end the Apollo's achieve a high dynamic level and offer a most
righteous natural sounding balance from top to bottom. While also offering a
touch of warmth. Offering an analytical window yet retaining a high level of
musicality. All this in a a pair of mono blocks that are flawlessly finished and
attention to detail of the highest. Offering 25 watts of Class A power at a
bargain of a price. Are they for everyone? Of course not. However in all my
years of hi-end audio I have yet to be as happy as I have been with my time
spent with the Apollo II's thus far. They are that good and I am the type of
person who has sold equipment in as little as a week. Yet, I feel as if I have
found another piece of my Audio Heaven puzzle and at far less than one would
think. The Apollo's are far from cheap but in the world of Hi-Fi one could and
should consider them a bargain.

Happy Listening to all!
Bryan A. Freese

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