Review of the Audion Sterling Stereo Plus

For me, vacuum tube electronics have always represented a compromise but probably not in the way you would think. I believe that solid state amplification can equal the sound of vacuum tubes, but usually with a significant consequence of price. Simply put, dollar for dollar, one can garner more music with tubes than with transistors. As always there is a downside and with tubes it is often manifested in a loss of power, at least relative to the majority of the solid state offerings of today.

Audion made their name in the high end some years back with a lovely 300B mono amp called the Silver Night. Its arrival in many ways pre echoed the single-ended mania wrought by our high end compatriots in Japan. Throughout the fervent SE era there were a thoughtful few who kept asking one very key question: Where are the loudspeakers that are well suited to these amplifiers offering but a single digit of wattage? There was no viable answer. Oh, there were a few audio psychos with VOTs and a few more with a pair of Klipsch out in their garage, but no one really wanted to hear those speakers. Later of course the Lowther name was hopefully revived, but again the result was usually disappointing.

The Audion Sterling Stereo Plus is perhaps something of response to a longing for more power from a very simple tube design, and at a reasonable price. Its 18 watts comes from a single EI KT90 per channel. There is a single 6922 shared as a common input tube and a single 5687 driver, again shared by both channels. Unusually, there’s a prominent volume pot in the center of the faceplate, though the Sterling offers but one pair of inputs. The chassis, like that of the Silver Night, is of a pleasingly low profile and is quite a bit deeper than it is wide. The transformers are happily hidden from view by a similarly low profile transformer cover that is emblazoned with the Audion logo plate. The amplifier is solidly built, if not overbuilt, with a clean and efficient look about it. The rear panel connections are well done. My only quibble would be over the binding posts which, though sturdy enough, offer no method to tighten them down other than by hand. All in all, the Audion Sterling Stereo Plus is an attractive, one would almost say elegant, amplifier that you will be proud to display in your living or listening room.
A look inside the cleverly executed chassis reveals excellent construction techniques and layout. The transformer leads are neatly soldered directly to the output taps, no crimped on ring terminals here! The power transformer is a fairly large toroidal while the outputs are conventional EI designs. All in all, the internal construction of the Sterling is superb.
Early in my listening, I encountered but a single problem with the Audion. Occasionally, I would notice a fairly high pitched fluttering sound. Sometimes it was only audible when there was no music playing, but often it could be heard riding the music during quieter passages. I immediately suspected the 6922. Since I wasn’t using my preamp with the Audion in the system, I popped the top and removed one of the RAM Labs SLN 6922s out of the phono stage. Amazing. Not only was the Audion Sterling far more quiet, I found that the entire performance of the amplifier was improved. The background was now solid state black and the amplifier had a much better sense of large and small scale dynamics. The amplifier went from pleasant to musical with the substitution of but one tube. Ah, the joys of tube amplification! To borrow a phrase from Joni Mitchell, the Audion now sounded unfettered and alive. To put it simply, designing tube gear is sometimes an art, but testing tubes is always a science…and a science known and understood by a very few.
Still, as with any low powered tube amp there is always the question of whether there is enough power for the music’s needs. And, there’s also the mercurial KT90. This is a tube with a checkered past, somewhat in keeping with what I like to call the vacuum tube’s Second Coming. The KT90 was initially developed and marketed as a rebirth of the classic Genelex KT88, often referred to as the Gold Lion. Early KT90s were far from this, or even up to the standard of the 6550A and other octal based beam tube variants available at the time. Yes, it was more reliable than the Chinese KT88, but that’s not saying much. Worst of all was the fact that the KT90 just didn’t sound very good, a fact that was hard learned by many a hapless tube gear makers from Audio Research to VTL. The why of its poor sound is beyond my knowledge but there are a few in our industry who have offered interesting and well reasoned explanations.
Even with all of my suspicions about the musicality of of the KT90 I was determined to give the Audion Sterling Stereo Plus the full measure of my attention, if for no other reason that to find out if it was the tube or if it was the circuits that led to the less than satisfying results of the KT90. For the impatient among you I can say that it must have been the circuits. The Audion was one of the most enjoyable amps that I have ever used, but that’s a little too simple at this point in the review.
I have yet to address the issue of power, so I shall do so here: First of all, a watt’s a watt and don’t ever believe otherwise. All this nonsense about tube watts sounding more powerful is just a lot of wishful thinking from a bunch of tube newbies who don’t know enough to heed the wise man who said: “I have been foolish enough to think such thoughts, but wise enough to avoid saying them.” So, the Audion’s 18 watts a side are just that, no less and no more. The fact is that in my listening, with speakers ranging from ancient electrostats to modern low sensitivity mini-monitors, I always found that I had enough power to avoid having the amp sound strained. On the contrary, I found the Audion was always able to sound graceful and well controlled. At the limits of the its power delivery, it just flattens its presentation somewhat. This is apt proof of a well done tube design that recovers from clipping both quickly and without undue dramatics.
In the heart of its power range the Audion is a fine performer, particularly well suited to music which relies on a sense of acoustic space and instrumental timbre. It is a joy on both acoustic jazz and female vocals. The amplifier has a quick and light quality that makes it perfectly suited to a small system or a main system in a small room. The soundstage is wide but not always very deep. This is perhaps an inherent compromise of every stereo amplifier, but may also be the result of the shared input and driver tube. Again, this is hardly a fault that would be voiced if the Audion was partnered with appropriate gear and a reasonably sized room. As music gets more complex, either large scale symphonic work or massed voices, the Audion merely shifts gears, again letting the music compress just slightly.
Despite its modest power, the Audion sounds quite full range. Again, this speaks of thoughtful transformer design that is so often missing from lesser designs. The more simple the music, the more pure the signal, the more musical the Audion becomes. It beckons the listener not just to listen, but to feel the music and learn its message. So, it would appear that the previously perceived failings of the KT90 were more a result of mistakes by the amplifier designers than attributable to the tube itself. That the folks at Audion have succeeded where others have failed speaks well for their ingenuity and rekindles my interest in this oft’ maligned tube.
What is it about tube amps that make us love them, sometimes more than they deserve? Is there something about seeing the light from the power tubes and the knowing in our hearts and minds that we are literally seeing our music being amplified? Is there merely a consonance to their presentation that is simply beyond the quantification of our measurements, or are we just too foolish to know what we should be measuring? I’ve wrestled with these issues for decades, but have always come away without a confident answer. In the case of the Audion Sterling Stereo Plus I can say that its charm is more than superficial. Not only does it look the part, it delivers the musical goods. It has been a model of reliability (save for the bad 6922) and would appear likely to be a trouble free & faithful musical partner for years to come. Owing to the cathode-bias that obviate any need to adjust the KT90s over their lifetime, the Audion will also be a very easy amp to maintain. So, if you have heard most of the solid state amps at or near the $2000 price point and been disappointed you need to hear the Audion. If it’s elegance and music that you seek, you will find it in the Audion Sterling Stereo Plus.
Manufacturer’s comment from Audion
The Sterling Stereo Plus, KT88 power amplifier, has undergone a few changes since Paul’s original review. There have since been three incarnations, which have included a new larger chassis design. The footprint has remained roughly the same however the chassis is now taller allowing for larger mains and output transformers (of which we now wind in house. The chassis is made from military grade aluminium to improve sonic performance and aesthetics. The circuit too has changed in as much as we now use a pair of 6H23N tubes in the front, which now gives a better frequency response, in real terms better lows, tighter mids and stronger highs.
Internally we use better quality components now and offer a good upgrade path, which has recently changed from a 5 tier path to just 3 new classes (Insignia, Excelsior and Signature Reference) which is now being phased in over the next few months.
Listening wise the KT88 is a good all round performer. We use JJ KT88’s which we have found to give the best performance/ price ratio. Sonically very detailed with good bass and top end. The 18 watts output remains unchanged, and in pure class A, we have found that this amp can be used with many speakers, even those with lower efficiencies.
We have recently launched a newer version of the Audion Sterling plus known as the Audion Super Sterling, using the KT120 tubes, delivering 24 watts per channel in class A. The KT120 is an interesting tube in that it is sonically a cross between the sweeter EL34 and the more durable power house of the KT88,
We will soon be celebrating our 30th Anniversary so look out for our new amps coming later this year in celebration of that.
Graeme Holland
Review of the Audion Sterling Stereo Plus