ULTRA AUDIO -- Archived Article

July 15, 2003

Blue Circle Audio BC24 Stereo Amplifier

In many ways, Blue Circle Audio is a classic North American success story. Its founder and proprietor, Gilbert Yeung, immigrated to Canada, completed his post-secondary education, defied his parents wish that he enter a professional career, and started his own high-end audio manufacturing business in 1990. Today, that business has grown to become a major boutique manufacturer of amplifiers, preamplifiers, power conditioners, cables, and accessories, shipping hundreds of units per year. Blue Circle has established an international reputation for quality and reliability, and has a devoted following of audiophiles who will buy nothing else.

I had the pleasure of entertaining Gilbert at my home the night he dropped off his latest brainchild, the BC24 power amplifier. The man himself is quirky and funny. He pulls no punches with the truth, and gets very little sleep. Many of his designs, I was told, come to him in the middle of the night, causing him to leap out of bed at all hours and scribble down schematics. The results are musically satisfying and what’s more, according to SoundStage! consulting engineer, Bascom King, his experience is that Blue Circle produces original topologies with impressive performance measurements.

The BC24 is Gilbert’s attempt to recreate the sonic characteristics of one of his first designs, the BC2, in a physically smaller and less costly form. The BC24 is a stereo tube/solid-state hybrid design in which the first stage uses dual 6922 vacuum tubes for voltage gain, and the second stage uses transistors of an undisclosed type to provide the necessary current to drive the speakers. The design follows the basic plan of most amplifiers in which a gain stage is followed by a driver stage. Gilbert’s logic, with which I can find no fault, is that tubes are voltage-gain devices and therefore best suited to this function, while transistors excel in the current domain and therefore work best as output devices.

The unveiling of the BC24

In keeping with Blue Circle’s consistent styling conventions, the BC24 has a brushed stainless-steel faceplate with a rounded bend along the top and bottom edges. It is adorned with the company’s trademark blue circle with a central dot, which is illuminated from behind by a recessed lamp. The trick to the logo is that the glow of the lamp appears in the part of the circle nearest the observer, and seems to follow you around the circle as you move. The chassis, which is also made of stainless steel in a black finish, is a low-profile 3.75" high, about 14" deep, and 17.5" wide -- perfect for conventional rack shelving systems. The unit is unusually heavy for its size, no doubt because of the stainless steel; I would estimate about 30 pounds.

Inside the unit, two nicely machined aluminum heatsinks lie against the left and right sides, the larger components are glued to the stainless-steel base plate using silicon, and the two 6922 tubes are readily accessible. The wiring is mostly done in what Gilbert calls his "fly-wire" technique: Semi-rigid bare wires act like rails between major components, while branching connections are made by point-to-point soldering of more flexible wires to these rails. I was struck by the similarity of this arrangement to the one currently used by Jadis in their well-regarded amplifiers. Either one company is following the other’s lead or both have arrived at the same solution through a kind of convergent evolution.

The power output of the BC24 is rated by the manufacturer at 100Wpc into 4 ohms and 80Wpc into 8 ohms. Controls are characteristically simple: there is an on/off toggle on the front panel and a ground-lifting toggle at the back. Two RCA connectors for the inputs and a set of WBT-like binding posts for speaker cables are provided at the rear, together with an IEC-standard power socket that allows the user to experiment with after-market power cords.

Setup and ancillary equipment

I installed the review unit with a Transparent Super power cord plugged directly into the wall. The unit had some break-in time before I received it and was in my system for several months. A Sony 777ES CD/SACD player acted as a transport with its digital output running through a dCS Purcell/Delius combination set at maximum upsampling. My digital cable is the MIT Digital Reference, while interconnects were MIT 350s. Speaker cables were Cardas Neutral Reference, and both JMlab Electra 315.1 and a pair of Acapella Audio Arts High Violon speakers were used. My reference amplifier is the KR Enterprise 32bsi, which is a single-ended-triode tube amp.

First impressions

One of the first things I did with the BC24 was yoke it up to my Electras and throw on Dave Matthews Band’s breakthrough CD Crash [RCA 07863]. First impressions? Big sound, big soundstage, great bass control, and driving rhythm. This amp is fun, I thought. The characteristically heavy bass lines on "So Much to Say" were amply supported by BC24, more so than through my usual triode tube amp, and the pace was good and fast. High frequencies and incidental percussion were also admirably resolved and well placed within a room-filling sonic landscape. Through the Electras, a bit of midbass emphasis was noticeable, giving the amp a satisfying tendency to "rock."

As most of us know, some amps rock and some don’t. Part of that quality comes from the midbass power, and another part comes from dynamic range -- the ability of an amp to convey the difference in volume between loud and soft sounds. In this regard, the BC24 was much more advanced than most solid-state amplifiers, which I feel tend to homogenize dynamics. Soft sounds such as incidental percussion or the clicking of saxophone keys were soft but clearly articulated, while loud sounds exploded forth without running out of gas.

Further, the bite and bounce on the leading-edge transients that often goes missing in solid-state amps was there on the BC24. In fact, the BC24 had a generous helping of the good qualities of tubes, but with more solidity to the presentation as a whole, and the bass in particular. The bass, in fact, was the only part of the BC24’s sound that I could identify as having a transistor signature. It was a little too solid for a tube amp, and less rounded, with a trace -- but only a trace -- of fine grain. The fatiguing whitish sheen in the upper mids and treble that I associate with many solid-state amplifiers was quite absent. Very nice.

Voices of fire

On the whole, I was quite satisfied with the reproduction of voices through the BC24. The bell-like tenor of Steven Page has been a key ingredient in the success of the pop band Barenaked Ladies. On "Brian Wilson," from their coming-out album Gordon [Reprise 26956], Page’s whimsical lyrics rang out, conveying the mysterious emotional content of the song nicely. I would describe the tonal color of the amp as slightly cool, but not dry. Page’s voice was full, with a certain degree of bloom. Again, there was a feeling of more solidity to the presentation than I am used to from my KR. The tonal accuracy was not at the level of my tubes, however, which excel in that area. The KR is also around four times the price of the BC24.

In general, comparing the BC24 with the KR on my Electra speakers, the KR was the clear winner. The KR had more detail, more image solidity, and a "wetter" sound, with a more even frequency response. If I were a dedicated pop listener, however, I might be tempted to save the money I invested in the KR and go for the BC24. Though the KR can be frighteningly realistic on well-recorded material, it also resolves every post-production artifact in pop recordings, making many of them near unlistenable. Try listening to The Tragically Hip on a hyper-resolving system sometime. There are days when even my dog whines.

The BC24 is in many ways easier on the ears for pop recordings, and its tendency to rock and its ability to play loud on demand will be well suited to the listening habits of many audiophiles. As for the reliability factor, the BC24 never failed to deliver consistent sound quality through several hundred combinations of cables, sources, and speakers while in residence in my system. By contrast, I find it helps to put the fire department on speed dial and have my fingers crossed each time I flip on the KR’s 600V power supply.

The BC24 meets the High Violons

Since I happened to have a pair of highly exotic and highly expensive Acapella Audio Arts High Violon speakers in for review, and since my 25Wpc KR was insufficiently powerful to drive them properly, I called on the trusty BC24. I certainly didn’t expect miracles. Given the huge disparity in price between these speakers and the Blue Circle, it was a bit like asking David to drive Goliath. As it turns out I was pleasantly surprised.

Through the Acapellas, a number of non-linearities in the BC24’s sound that were evident on the Electras just disappeared. In particular the midbass emphasis was gone (admittedly, I found the Acapellas recessed in that region), and the realism of voices and instruments increased, as did image solidity and palpability. If there were ever a case study in matching speakers to amplifiers, this would be it. The differences were so pronounced that it made me wonder about the validity of any amplifier review (and there are many) which does not involve an effort to find the best possible match between the amp reviewed and the speakers used to review it.

A panoply of non-pop material came through with flying colors on this amplifier-speaker combination. Rebecca Pidgeon, Holly Cole, Hugh Masekela, Bill Evans, and even Verdi’s Rigoletto were rendered at extremely high levels of realism and emotional vividness by the BC24. Top-flight performance was heard even on the very complex and dissonant tracks of Tom Waits’ Swordfishtrombones [Island CIDM 90095]. The anti-classic "Frank’s Wild Years," for example, starts with a heavy washboard-bass-xylophone introduction that just doesn’t sound right unless your amp has the right balance of neutrality, detail, and bloom. The BC24 had it. I was engrossed by the music and laughing at the humor all the way through.

I happen to know that Gilbert himself has a pair of MartinLogan Statements at home, so it stands to reason that those highly regarded speakers may have some things in common sonically with the Acapellas. Whatever the cause, the BC24 really came into its own here. I had much more expensive solid-state amps in my living room at various times for comparison, including the Chord 64 and the pure-class-A Sugden Masterclass monoblocks. The BC24 smoked them all, particularly the Chord. Very impressive.

Tube rolling, anyone?

The Sovtek 6922s that come with the BC24 are competent, current production models, and they do a good job. As described above, the soundstage is generous, the high frequencies are well resolved, and the bass is full. The Sovteks’ failings are a certain degree of hardness in the top frequencies, with a touch of electronic hash in the midrange. I would estimate the replacement cost for these tubes at around $20 for a pair. In a well-designed topology such as I think this one is, and assuming that the amp is not left on continuously, I wouldn’t be surprised if these tubes never had to be replaced. The reader should be aware, however, that a universe of compatible tubes of this type is widely available at prices ranging from $20 to more than $500.

Interested in the potential of this amp with more exotic tubes on board, I called up a friend with a collection of vintage 6922-compatible tubes from Amperex, Telefunken, Phillips, and Siemens, and started rolling. Remembering to unplug the amp before changing tubes, my friend and I went through a succession of matched new-old-stock (NOS) gems, each pair more expensive than the one before. The BC24 improved markedly with each. First the hash was gone, then the bass became rounder and more detailed, then the highs took on extra sparkle, and finally the midrange blossomed to triode-like levels. I finally settled on a pair of rare Siemens and Halski CCa’s (around $450 for a pair, if you can find a pair), which brought the BC24 to an astonishingly high level of sonic performance; much higher than I would have had any right to expect in this price range, even when factoring in the cost of the tubes.

Though Gilbert might prefer that I confine my comments to the stock tubes, I think the potential of this amplifier when fitted with aftermarket glass is a strong selling feature. Here is an amp with the reliability and versatility of solid state, and the upgradability of tubes. Ready for a change in your system? Just pop in a different set of tubes.

Winding down

I was very favorably impressed with the BC24. For a reasonable price, you get a hand-built product from a high-end boutique manufacturer, which delivers sound quality sufficient to impress even a hardened tubeophile like myself. Further, the hybrid nature of the BC24 delivers the better qualities of both tubes and solid state in a maintenance-free package.

This is an amp I would recommend to friends who want superior sound, but don’t share my enthusiasm for trucking a ridiculously expensive 100-pound tube amp to the repairman every few months. The BC24’s neatest trick is that it can satisfy both those who love rockin’ old-fashioned tube glory and those who prefer the cooler neutrality of good solid state. The generous headroom on this amplifier allows you to match it to just about any speaker on the market. My advice is to buy it, match it to that special speaker your heart desires, and forget it’s there.

…Ross Mantle

Blue Circle Audio BC24 Stereo Amplifier
Price: $2450 USD.
Warranty: Three years parts and labor.

Blue Circle Audio, Inc.
Innerkip, Ontario
Canada N0J 1M0
Phone: (519) 469-3215
Fax: (519) 469-3782

Email: bcircle@bluecircle.com
Website: www.bluecircle.com   


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