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Blue Circle Audio BC21.1 Stereo Tube Preamplifier

Part I

February, 2004

Sandy Bird

 

Specifications:

 

2 x 6922 based line stage
3 line level unbalanced inputs

1 tape loop

 

MSRP: $1650 (+$250 for Shallco)  

Blue Circle Audio

www.bluecircle.com

Introduction

Are vacuum tubes on their way in or out? One would have to wonder since they are old technology in terms of what is available today, but a quick walk through CES, CEDIA or any tradeshow concerning audio and you will find that some of the most exotic and expensive gear uses tubes.

The question becomes more complex when you consider computer motherboard manufacturers have put tube outputs on sound cards (I consider this to be a bad idea on many levels).

The one thing I can assure you, for the time being, is that tubes are not going away. I do think most tube equipment manufacturers need to step out of the past and consider finding ways to incorporate more ergonomics and user friendly features into their designs.

Of course, the main thing is the sound, and tubes sound wonderful, for a variety of reasons we have explained in several reviews. One reason is that tubes tend to have even-ordered harmonic distortion, and transistors (solid state) tend to have odd ordered harmonic distortion. Even sounds nicer than odd, if you have to listen to distortion at all, and all amplifiers have distortion. But, we are getting ahead of ourselves. First . . . .

Blue Circle, the Company

Some people in this world are known as being eccentric. Gilbert, owner of Blue Circle Audio, might be best described as exactly that . . . eccentric. After meeting Gilbert a few times, you will never have a problem picking him out of a crowd with his feathered hat and black suit. But more importantly, you will be able to pick Blue Circle Audio gear out of any hi-fi lineup. It is hand built, point-to-point wired (no circuit boards), and is finished with a distinctive fashion that I for one love. The polished stainless steel faceplates with large stained wooden control knobs give a distinctive statement that I would be proud to display in my equipment rack. Not everyone will like the styling which lends itself to a love or hate reaction (for instance, my wife hates it). Regardless of how you see Blue Circle’s artistic designs you will appreciate the minimalist approach Gilbert has taken to audio circuitry.

Gilbert’s company Blue Circle is a small audio equipment manufacture located in a small town called Innerkip just outside of Toronto, Canada. Their main focus is on two channel audio, but they also produce a fully balanced five-channel power amplifier. Their product line consists of a combination of tubed electronics, solid state and a couple of hybrid products. To finish up the ultimate audio system, Blue Circle also supplies balance power conditioners and other tweaks for the audiophile. Most of Blue Circle’s products carry their signature statement, a blue glowing circle enclosing a blue dot, typically located directly in the center of the component. Since I once considered swapping the green LEDs on my keyboard for blue ones, this blue glow appeals to me, although I wish I could shut it off in a dark room.

Gilbert’s eccentricity also extends into his audio gear since Blue Circle sells (and I have actually listened to these) a pair of 25-watt monoblock amplifiers that are housed in a pair of women’s high heel shoes and a matching preamplifier housed in a purse. Of course, you can get these in any color you wish. Do not think you are going to save some money by sending Gilbert a pair of your spouse's extra shoes, since he refuses to work on used shoes.

The BC21.1 Preamp

The BC21.1 is Blue Circle’s entry level tube preamp. It is a simple two-channel design with top notch sonics that could be the center of an audiophile's two-channel system. The design uses a pair of 6922 tubes, which are one of my favorite preamp tubes. The chassis is consistent with the Blue Circle signature designs (thank goodness no red shoes here) and is heavy for its size. The front is polished stainless steel, and the rest of the chassis is made of heavy gauge metal.

The BC21.1’s wooden knobs control volume, balance, and selection of three inputs, while the small toggle switches control the tape loop and power. To keep with the wood theme, instead of rubber feet, the BC21.1 sits on top of three wooden feet, which means you will never end up with the matchbook under the table leg scenario even if Gilbert’s feet are not cut to perfect tolerance. The single ended RCA inputs are gold plated and of high-quality.

The BC21.1 uses a standard IEC detachable power cord, which will make it easy to upgrade for those of you who believe in that sort of thing. Input labeling is silk screened both right-side up and upside down.  This can be particularly useful when looking over the top of the unit.  The large control knobs of the BC21.1 give a sense of very fine adjustment, somewhat similar to a large knob on an old tuner. 

For volume control, the 21.1 has three options. The base option is a standard pot which can be upgraded to an RF based remote control pot or a Shallco 31 point stepped attenuator. For those of you not familiar with stepped attenuators, they control volume by using a single resistor for each volume setting. This eliminates using a carbon or conductive plastic pot which may have less then desirable sonic properties. It also allows for almost perfect left and right channel tracking if high tolerance resistors are used. Both the standard pot and the Shallco version were tested during the review period.

Sonically, the standard pot was adequate, but had two issues in my setup. It was much too sensitive with amplifiers with both of my solid state amplifiers. Secondly, it did not track the left and right channels together at very low volume. Using my Sonic Frontiers Power 1, a tube amp, with a much lower power rating than the solid state amps I had no problems with the stock volume pot. However, using solid state amplifiers such as my B&K or Anthem, the pot was far too sensitive and usually in a location which exhibited poor linear tracking.  The problem is cause by the overall gain of the amp and preamp combo being substantially higher with the solid state amps. This problem is easily resolved by adding a resistor to Blue Circle’s point-to-point wired equipment. If a customer experiences this problem, Blue Circle will make the necessary circuit change.

The Shallco pot on the other hand worked perfectly with both solid state and tube amplification. Gilbert claims to have taken years to figure out the perfect resistor values to work optimally with all types of amplifiers. The Shallco is set up using a non-linear ramp such that the attenuation points near the bottom are more sensitive than the ones at the top. This works perfect in my situation where I need small adjustments for late night listening, but stretching a couple of dB in either direction will not make much difference at loud volumes.

Although there was a 2-3 week gap while the Shallco was installed, I do feel there was a sonic improvement. My personal recommendation is to buy the Shallco up front, you will not be disappointed. However, if you do purchase the stock pot it can be upgraded at a later date.

Blue Circle also offers a remote control option with the BC 21.1. This involves using a motorized conductive plastic pot, which has similar sonics and issues as the stock pot, but is controlled via an RF based remote control. Yes, I said RF based, so you can control the volume from another room. Blue Circle does not necessarily recommend this option as they believe the Shallco provides the best sonic performance, but they do realize some users, such as my wife, would rather have the remote than ultimate sonics.

On the Specifics of the Sound

The BC21.1 was supplied with Sovtek 6922 tubes. You will find Sovteks supplied with many products, as they are readily available and still being manufactured. One of the benefits of a tube design is the ability to use different tubes to achieve the sound most desirable to the end user. When looking for 6922 replacements you can also substitute 6DJ8 or ECC88 tubes.

My favorite tubes while using BC21.1 were Amperex 6DJ8s. This was not much of a surprise since they are also my favorite tubes in the Sonic Frontiers Line 1. The BC21.1 captured all of what makes this family of tubes my favorite preamp tube. Properly implemented 6DJ8, 6922, or ECC88 tubes have amazing detail and drive. The bottom end of the frequency range is fast and tight, showing no sign of definition loss even in the lowest frequencies. The upper end of the frequency spectrum paints a beautiful image with no sign of roll-off.

If you are a follower of the ‘lush warm mid-range’ sometimes associated with tubes, I recommend you stay away from 6922 tubes, because you will not find it. The 6922s in combination with the design implemented by Blue Circle represents a perfect balance of the smoothness of tubes and the unadulterated detail associated with the best solid state designs. With the BC21.1 in my system, I could listen to music for hours without any sign listener's fatigue, which is the acid test for a preamp to me. The only thing I found missing for the BC21.1 is the airiness I get from my Bottlehead Foreplay (a 12AU7 based preamp). Whether you would consider airiness to be an admirable quality that you miss, or a blessing of a design that does not add artificial artifacts to the sound, is a personal preference.

Most of my time with the BC21.1 was spent listing to modern jazz such as Holy Cole, Diana Krall, and Acoustic Alchemy. The BC21.1 held strong in punchy bass lines, defined vocals, and shimmering cymbals. The music was simply easy to listen to, even over long periods of time. I did use a variety of other music with the 21.1, and as with all good equipment, it sounded every bit as good with Rock and Classical as it did with Jazz.

Click HERE to go to Part II - On the Bench and Conclusions

 
Related to the article above, we recommend the following:

 

Nature of Equipment Reviews

What We Hear

Accuracy, Distortion, and the Audiophile

High Fidelity

 

 

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