Blue Circle Audio BC307 Preamplifier
by Marc Mickelson | September 3, 2015
© www.theaudiobeat.comI'm used to Blue Circle products being unusual, even unique. After all, Gilbert Yeung of Blue Circle is the fashionista who brought the audio world the Music Pumps and Music Purse -- a pair of mono amps fitted into women's high heels with a matching preamp-in-a-purse. Gilbert has also created power amps that use hundreds of paralleled op-amps in place of output transistors, and he has re-engineered the venerable Technics SL-1200 Mk II turntable to accept an outboard power supply of his own creation -- and of course that power supply uses batteries. Gilbert has gone green as well, fashioning solar power for one of his phono stages. That he has been able to experiment and create these products is one thing; that he has done so while building a successful business and brand is another -- and one that's even more impressive.
But even within the Blue Circle product line, the BC307 preamp stands out. It cleverly scratches an itch that many audiophiles can't identify but know exists: the desire to tailor the sound to taste or recording quality or type of music. It does this not with tone controls that contour the preamp's frequency response. Rather, it allows the user to dial in the effect of three different gain stages, balancing each against the others to add a bit more presence here or a touch more linearity there. The BC307 is fully balanced and available with various user options, including an MM/MC phono stage and headphone amp, making it the true functional and sonic centerpiece of an audio system.
The BC307 is a two-box affair, with a separate power supply housed in a shoebox-shaped chassis. Both the preamp and power supply can be ordered in different matching finishes, including all stainless steel, my preferred look for Blue Circle equipment. No matter the finish, the glowing Blue Circle logo has a central spot on the front panel.
The power supply is characteristically stout and connects to the main unit via two detachable umbilicals that you can't connect improperly because they have a different number of pins. It's within the audio chassis where things get interesting. Gilbert Yeung calls the BC307's circuit a "cross hybrid." A "specially designed splitter circuit" sends the signal down separate gain paths that use two tubes -- 6922 and 6SN7 -- along with a third that's completely solid state. On the BC307's front panel, in addition to the normal input and volume controls, there are potentiometers for each of the three gain stages, the output of which "a special adder circuit" combines.
When you begin fiddling with the three gain controls -- and "fiddling" is accurate until you understand just how they affect the sound of the BC307 -- you begin to discover the real heart of this preamp. The BC307 has a fixed 23.5dB of gain, and the 6922, 6SN7 and solid-state circuits are unity gain, so they don't increase or decrease that 23.5dB figure. The BC307's main volume control, a Shallco attenuator, governs the preamp's output, reducing the signal more or less, depending on its setting. This is the theory anyway. In practice, when you increase or decrease one of the gain controls, you also increase or decrease loudness. But this is the wrong way to think of it. Instead of thinking of those controls as influencing the amount of audio stew you'll make with the BC307, they are instead spices added to the recipe. More or less of any of them doesn't appreciably change the portion but does affect the final flavor. Blue Circle also stresses that the BC307's ability to "make the marriage between your preamp and amp much happier." It doesn't do this because those gain pots alter the preamp's electrical properties -- its output impedance, for instance. Rather, they allow for the tailoring of the sound, matching it better to that of your amp -- "better," in this instance, being something that you and you alone decide.
As with many Blue Circle products, you are able to add options to the stock, line-stage-only BC307 that can increase its usefulness. Such customization represents a good amount of Blue Circle's business and is mostly limited by your imagination and budget -- and Blue Circle's ability to design and implement your requests. The phono-stage options for the BC307 range in price from $750 to $3500, while the headphone amps begin at $500 and go all the way to $3750. Contact Blue Circle for particulars. RF remote volume control of the BC307 is yet another option, and it costs $350.
Any preamp other than the BC307 requires very little in the way of setup -- unboxing it, placing it on your equipment rack, plugging it in, connecting the sources and amplifier. All of this applies to the BC307 too, but the work only begins there and can lead to some interesting, surprising, frustrating and fulfilling results, all boiling down to those three gain controls. How you adjust them, the proportion of each to the other two, can lead to sound that is okay, pretty good or transcendent -- with many stops along the way. And while I'd like to provide you with absolutes -- a magical combination of settings that represents the sweet spot for the BC307 -- I can't. So much of what will define your experience with this preamp depends on the rest of the system in which it is used and, moreover, your own tastes and goals.
In other words, more than with any other preamp, context matters with the Blue Circle BC307. Therefore, what I recommend is a systematic approach that includes some way of repeating results. Hansel and Gretel dropped white pebbles to find their way out of the forest, and you should do the same with the BC307, keeping track of all adjustments you make and recording the important ones in some way. The BC307's volume control is a stepped attenuator, so there are distinct settings, making it easy to reproduce overall volume levels. This is not the case with the gain controls, which are non-detented potentiometers, so there is no way to reproduce settings exactly without a bit of forethought and work.
What I did was a trick I learned from John Giolas of Wilson Audio, who used it for setting up a Thor's Hammer subwoofer in my system. A subwoofer controller is even more complicated than the BC307, and in order to mark settings, John used small wedges of painter's tape affixed to the front panel, the tip corresponding to each knob's marking spot. These allowed quick visual indication of each setting as well as the ability to dial in past settings with precision.
I began my listening by leaving the gain pots where they had been set when the BC307 was shipped to me. I figured that this was as good a place as any begin. I then put each at 12:00, roughly 2:00, and then at points clockwise and counter clockwise from there, noting the sonic differences for each. With the Jeff Rowland 825 stereo amp, I preferred different settings than with my Lamm M1.1 monoblocks. Then, when the Wilson Sasha 2 speakers were swapped for the Sabrinas, another round of readjustment ensued.
While I could tell you exactly where the knobs were set for each combination of equipment, I don't think that information would be very useful, given that you won't be using the BC307 with the same equipment -- and same set of ears -- as I had. What is useful is knowing what each control seems to do to the BC307's sound, so you can effectively combine the outputs. Frankly, I would rather like to know all of that too -- even after months of use, I was discovering new facets of the BC307 as I adjusted and readjusted the controls for the three gain stages.
In general, the two tube gain stages effect just what you think they would: presence, midrange roundness, tonal color and midbass weight. However, even all of this is adjustable, because there are two parallel tube gain stages. The 6922 seemed slightly more warm and plush, more traditionally tubey, than the 6SN7, but I really came to think of the both of them as one adjustment, playing their cumulative effect off that of the solid-state stage, which tended to even out some of the excesses of the tube stages -- tended, as in most of the time but not always. You actually can have too much of a good thing, and that goes for the sound of tubes, at least where the BC307 is concerned.
In the end, the goal -- as far as I could discern -- was to reach a balancing point with all three gain stages, where even very slight adjustment of one clearly affected the overall sonic balance of the preamp. At that point, I reasoned, the BC307 was at its truest performance, its most level point among all of the sonic characteristics that the three gain stages influenced. When one dominated, I needed to dial in more of the others to not only change but improve the sound; but when all three were in balance, Grasshopper, harmony and balance reigned and all was well. And if all was not quite well, a small adjustment could make it so.
Yes, getting to this point of equilibrium required a lot of work -- listening, adjusting, relistening, readjusting, repeating -- but it was worth it. So let's assume at this point, following this long preamble, that I have adjusted the BC307 optimally -- that I can make no further changes without hurting the sound. Just what, then, is the BC307's sound? For the most part (always a relevant statement when describing the BC307), it's one of smoothness, palpability, tonal saturation, midbass weight and overall musical naturalness. It was impossible to make the BC307 sound lean, colorless or edgy, no matter how its three gain stages were set. I've reviewed a few of Gilbert Yeung's amplifiers in the past, and they sounded the same way -- full of body and musical ease without hardness, glare or any other destructive musical force.
I listened to a lot of well-recorded vocal music with the BC307; its portrayal of corporeality and dimension was enthralling. Two recent discoveries, the soundtracks for the movies Inside Llewyn Davis and Vicky Christina Barcelona, were very instructive. The first movie is about a good musician who will never achieve greatness, while the other is a philosophical treatise on the nature of love. The Inside Llewyn Davis soundtrack [Nonesuch 534867-2] is heavy on '60s-era folk and features spare music that's well recorded. Vicky Christina Barcelona [Telarc CD-85001] features what director Woody Allen calls "mostly Spanish [music] . . . reflecting the feeling of Spain or certainly Barcelona as I portrayed it." The BC307 served both CDs well, especially the buoyant title track, "Barcelona," for Woody Allen's film. This is a typical Telarc recording -- smooth, dusky, slightly lacking in air, more about in-room presence than conveying the personality of the recording venue. It reminded me greatly of the optimally tuned BC307 -- the copious tonal color, image roundness and heft.
You may be wondering, as I was before I went through the elaborate adjustment process I outline above, if the BC307 can be readjusted in order to sound completely different, to effect some other set of sonic traits, especially for different-sounding recordings. The answer is to some extent. Redialing the gain stages, especially if done radically -- to the opposite end of the range from where they are -- can certainly change the sound of the BC307 but not necessarily improve it. That is, balance among all characteristics instead of maximizing a few of them made for the best sound, at least to my ears. So, in my case, turning the solid-stage knob from roughly 1:00 to as far counter-clockwise as it will go certainly lessened its sonic effect, but doing so consequently increased the effect of both tube stages. Small adjustments were audible, but again falling into the realm of different, not better.
And, in fact, there really wasn't any good reason to readjust the BC307 once I'd determined the optimal settings. It was muscular with rock, suave with classical, and delicate with jazz. It was always itself, more about "they are here" than "you are there," meaning it put the musicians in the room, put meat on the bones, rather than dissecting the recording, venue and all. This has come to define the Blue Circle sound for me, a combination of dimension, weight and tonal density that to my ears is far more like live music than the airy leanness of so many other components. Even if you could tune the BC307 to sound this way, why would you want to?
Audio Research's SP20 ($9000) would be the obvious comparison product for the BC307: It's a tube preamp with phono stage and headphone amp built in. Unfortunately, what I had in-house during the BC307's extended stay was the next step up in the Audio Research line, the Reference 5 SE line stage ($13,000), which is more conventional than the BC307 in function -- it's a standard remote-controlled line-stage preamp -- and sound. Whereas the BC307 is weighty, lovely and languid, the Reference 5 SE sounds faster and more open, as much about the space in which the recording was made as the three-dimensionality of the performers within it. This also gives the Reference 5 SE a lighter disposition, both in terms of the images it portrays and its tonal balance.
With the Vicky Christina Barcelona soundtrack, the Reference 5 SE highlighted the pluck of strings more than the presence of the vocals, as the BC307 did, although both made it plain that I was hearing nylon and not steel guitar strings. It's not as simple to say that one of these preamps is more detailed than the other, for instance, because they both sound detailed. Rather, their tendencies are not the same, with the well-adjusted BC307 sounding more like dusk than the dawn of the Reference 5 SE. No matter the music, the BC307 sounded more palpable, put more meat on the bones, than the Reference 5 SE.
It is true, as Roy Gregory likes to say, that there's nothing new under the audio sun. But this doesn't mean that innovation is dead in audio design. In fact, it's everywhere, from amplifiers with newly devised digital output modules, speakers with high-tech cabinet and driver materials, DACs with new schemes for decoding digital data, even turntables with novel drive approaches.
However, one product segment that seems devoid of even the most basic innovation is preamps -- except for the Blue Circle BC307. With it, Gilbert Yeung has pushed the boundaries of preamp design, giving listeners control over the experience of hearing reproduced music and not a way that recalls audio's distant past. The BC307's innovation is not mere novelty; those three gain stages offer real differences and their judicious use leads to real improvement. While the more obsessive audiophiles among us may rue the day they met the BC307, because of its ready adjustability -- its all sizes fit someone approach -- there is no questioning its value, especially if you believe, as I do, that listening to music is a human endeavor, governed more by taste than the fundamentalism of a one-correct-way approach.
While choice can be a dual-edged sword, there's no denying that the Blue Circle BC307 represents a stark alternative to every preamp on the market today -- and probably tomorrow as well. Whether having three parallel gain stages is your thing or not, the BC307 will please many listeners and its performance is in the upper crust here and now.
Warranty: Three years parts and labor.
Blue Circle Audio
Canada N0J 1M0
Analog: TW-Acustic Raven AC turntable; Graham B-44 Phantom Series II Supreme and Tri-Planar Ultimate U12 tonearms; Denon DL-103R and Dynavector XV-1s (stereo and mono) cartridges; Nordost Frey 2 and Valhalla 2 phono cables; Audio Research Reference Phono 2 SE and Lamm Industries LP2.1 phono stages.
Preamplifiers: Audio Research Reference 5 SE, Lamm Industries LL1 Signature.
Power amplifiers: Lamm Industries M1.2 Reference, VTL Siegfried Series II Reference and MB-450 Series III Signature monoblocks, Jeff Rowland Design Group Model 825 stereo amp.
Loudspeakers: Wilson Audio Sasha W/P Series 2 and Sabrina, Venture Audio Ultimate Reference.
Interconnects: AudioQuest William E. Low Signature, Nordost Frey 2 and Valhalla 2, Shunyata Research Zi-Tron Cobra and Anaconda.
Speaker cables: AudioQuest William E. Low Signature, Nordost Frey 2 and Valhalla 2, Shunyata Research Zi-Tron Cobra and Anaconda.
Power conditioners: Essential Sound Products The Essence Reference, Quantum QB4 and QB8, Quantum Qx4, Shunyata Research Hydra Triton.
Power cords: Essential Sound Products The Essence Reference and MusicCord-Pro ES, Nordost Frey 2 and Valhalla 2, Shunyata Research Zi-Tron Cobra.
Equipment rack and platforms: Silent Running Audio Craz² 8 equipment rack and Ohio Class XL Plus² platforms (under Lamm M1.2 amps), Harmonic Resolution Systems M3 isolation bases.