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March 2009
Enjoy the Music.com
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Blue Circle Audio SB90T Hybrid Stereo Amplifier
A hybrid marvel priced to sell.
Review By Anthony Nicosia

Click here to e-mail reviewer


Blue Circle Audio SB90T Hybrid Stereo Amplifier  At this stage of the audio game I figure most of you have seen some products having a round blue circle with a dot in the middle and recognize it as the Blue Circle logo. The founder and designer of Blue Circle Audio is Gilbert Yeung. If you want to get a little insight into his truly creative mind, please look at his companyís website. Once there you can see the many wonderful products he has created such as power amplifiers, preamplifiers, phono stages, DACs, powerline conditioners, cables (interconnect & speaker), power cords, cones, isolation pucks, speakers and even something called the "USB Thingee" (I will let you check that out on the website yourself). What he does not offer though are SET (single ended triode) amplifiers. Quoting from his website, "I donít do SET". He does however make hybrid power and integrated amplifiers as well as tube preamplifiers. When it comes to SET amplifiers his feelings are that he just does not like the complete sound it produces. As he told me in an email, different people like different things, and SET does not have the sound he is looking to create. So just what is the sound that Gilbert Yeung is seeking with his new amplifier the SB90T? Well read on and lets explore this together as I tell you what I heard.

I have had the pleasure to spend some time reviewing Blue Circle Audio products in the past, although not yet their power amplifiers. In my system I personally own two Blue Circle BC86 MKIII Power Line Pillows, purchased before I started writing reviews. Most recently I wrote a review on those same BC86 Power Line Pillows along with a Blue Circle BC86 Pug and BC 86PC (which are variations of the Power Line Pillows), as well as a BC86PC Power Cord. To sum it up, I was very impressed with them all. Blue Circle Audio is located to the north of the US within our friendly neighbor Canada, in the city of Innerkip, in Ontario, to be exact. Gilbert Yeung started his business in 1988 working out of his parentís basement and has now graduated to a separate-dedicated facility located on a few acres of land. Even though he now has workers that help him with production he still has a hand in making some of the products himself. Chances are if you buy a Blue Circle product Gilbert Yeung would have had his magically creative hands actually helping out somewhere in the process.


Want To Personalize Your Product? Try Asking.
The warranty on most Blue Circle products is up to three years, as always please check the website for complete details. It is always refreshing to see this longer warranty rather than a one-year guarantee. I like it when manufacturers feel comfortable enough to take a strong stand behind the products they build as it gives me that little extra confidence in it. Another nice thing is that Blue Circle offers both cosmetic and functional upgrade options. Not to overlook anything or perhaps miss a potential customer the website states, "If you donít find what you are looking for contact us. We might be able to do it any way". If you think that is just some sales hype, think again. Gilbert Yeung, from my personal experience, is a no nonsense straight shooting; tell it like it is type of guy who does not throw words around without thinking. Again check the full story out on his website which explains about a time when a customer called asking him to make a 15 to 20 watt amplifier and preamplifier to replace his SET integrated setup. The SET was placed right next to him giving off too much heat so he sought Gilbert Yeungís help in making him something solid-state in design. Apparently he talked him into it and the rest is Blue Circle Audio history as the SBP preamplifier and SBS stereo power amplifier was born. Now that is a classic example of listening to your customers and tailoring to their needs.


In Comes The New SB90T
Blue Circle makes amplifiers that cost all the way up to $28995 (the BC208 pair of power amplifiers) while the SB90T is the next to lowest priced power amplifier costing only $3295. The lowest price power amplifier is the also new SB100S at $3195. So what is the difference between the two amplifiers, besides the $100 in price? Well first they both are housed in the same sized audio chassis and weight in equally at 40lbs. Without going into too many details, the SB100S is a solid-state amplifier putting out 100-watts into 8 Ohms and 150-watts into 4 Ohms. The SB90T though is a hybrid power amplifier, using one 6SN7 tube, rated at 90-watts into 8 Ohms and 135-watts into 4 Ohms. Both were introduced to the public at the RMAF (Rocky Mountain Audio Fest) show this year in Denver. Unfortunately I could not get away from the San Francisco Bay area, and my day job, to attend. Many years ago I lived for a short time in Boulder Colorado a gorgeous suburb just outside of Denver and would have loved a return trip to this beautiful state.. Shortly after the show Gilbert Yeung and I contacted each other via email when he offered to let me take the SB90T for a "test drive" saying that he thought it would be a good match for my Legacy Focus 20/20 loudspeakers. Well who was I to refuse a Blue Circle product and so that is how this review got underway.


The Setup
The SB90T came well packed and included a thoroughly informative owner's manual as well as a standard power cord and one spare 6SN7 Electro-Harmonix tube. I did not do any official tube rolling for this review being that I did not want to detract from the stock amplifier on hand. I will tell you though that I did try different NOS 6SN7 tubes which did change, ever so slightly, the sound even more so to me liking. Tube rolling of course opens up a whole different ballgame and which tube you choose will depend on the type of music you listen to, associated equipment in your system and of course personal taste. The supplied Electro-Harmonix tubes though were an excellent choice as they are as of now readily available, inexpensive to replace and a wonderful all around sounding tube. Getting back to the review, please read the manual before attempting to use this unit in your system because there are actually a few things that make the SM90T just a little different. First there is a ground lift switch the company recommends you keep in the down position for initial set up and secondly instructions about how to connect the speaker wire to the amplifier. The SB90T is phase non-inverted and so instructions are supplied as how to connect the speaker cables depending on your preamplifier and whether or not it is also absolute phase non-inverted or absolute phase inverted.

I would also like to note that the SB90T is for use with RCA cables as no XLR inputs are present. If you desire XLR inputs they must be factory ordered at an additional cost of $300 and includes the conversion circuit inside at the inputs. As for speaker cables, connections are provided for use with spade rather than banana plugs. This limited my choice of cables for this review and I wound up using a set of AntiCables to connect the SB90T to my speakers while connections to the Placette Passive preamplifier from the SB90T was done via a set of Acoustic Revive RCA interconnects. If you want to use an adapter for banana plugs Blue Circle can supply you some for only $35 for a set of four. I was informed that the reason for the binding posts that come with the SB90T is that the EU market does not accept banana plugs. As for the factory supplied power cord, I did most of my listening with it in to review the SB90T. There was nothing special about it and on a side note I do believe that purchasing something a little more upscale would benefit this amplifier.

Someone spending this type of money for a power amplifier will probably replace the stock cord. Which power cord you choose will of course be system dependent as well as a matter of choice and budget. I for one remember doing a review on the Blue Circle BC62 power cord and getting marvelous results from it. The good news is that the BC62 costs only $280 for six feet. There is something to be said for synergy and when purchasing this amplifier I would not hesitate to send the factory an email asking which of their power cords to purchase with the SB90T and to get both at once right from the start. After experimenting with various cords that I had on hand, I decided to use the Acoustic Revive six foot Power Reference cord at $750. After I did this I would take what I say in this review and add an extra dimension of depth to the music, more texture to the sound and even some extra lower level bass.

Also of note is the size and shape of the amplifier. It was quite large left to right and front to back yet not very tall. These are of course subjective terms and you should look at the bottom of this review for the actual dimensions of the amplifier, but I rather liked its shape and size. It fit perfectly on my Salamander audio shelf and its compact height left me plenty of room for the amplifier to stay cool. I ran it for hours at a time and actually never felt it heat up which I think is a big plus as some amplifiers get very hot over even a short span of time after being turned on. The only minor quibble I had with the amplifier was that it did produce a "thump" when turned off. Gilbert Yeung explained to me that they were aware of this but that it was nothing to be concerned about and depending on the sensitivity of the speakers and size of the woofer (mine are both large and sensitive) it would either be louder or softer. I had an amplifier that did this before so this was not the first time I had encountered this. After listening to the "thump" a few times it never bothered me and the sound emanating from the SB90T more than outweighed any minor sound issue at turnoff time. Aside from this, the noise the unit itself produced was negligible and I was quite impressed with its silence throughout its stay in my review system. I just wish I could say that about other amplifiers I have had in the past, especially tube units. This really was one quiet amplifier.

Like tube amplifiers in general, they take a little time to warm up and sound at their best. I would think that after forty minutes it was sounding at or very near its best. Quite honestly though it surprised me in that it did sound good even right at turn on and still "cold". Because of this I never felt that I needed to wait to play music and instead jumped in right away to listened as it just keep getting better as the minutes passed. One nice thing about the SB90T was that it would sound great even at very low level volume, although I did prefer listening to it at louder levels. This made it ideal for those late night listening sessions where I did not want to turn off the music yet, but I also wanted to respect my families resting time. Listening with headphones is not an option yet as my preamplifier does not have a headphone jack. Having played around with different cables I can say that this amplifier does respond to better cables so if you have already invested in some or want to in the future, the SB90T should respond in kind.


Listening Session
Starting with Mary Chap Carpenter's CD, Party Dolls And Other Favorites [Columbia CK 68751] I should tell you that I was impressed with how smooth it sounded. Perhaps partially because it has tubes the SB90T sounded smoother than many solid-state amplifiers. Yet even with the tubes its bass impact was strong, forceful and quite dynamic. Of course it is a hybrid design and this is where its solid-state roots seemed to flex its muscles. On the song "I Feel Lucky" not only does the SB90T show what it can do with a strong base presence but the decay of notes  when Mary Carpenter sings is a joy to hear. Her piano work is also defined quite nicely as the SB90T captures the piano notes as they come across both quick and distinct with a good sense of spaciousness. Moving on now to The Beatles CD, "Revolver" [ParlophoneCDP 7 464412] I just had to hear "Eleanor Rigby" and "For No One". With "Eleanor Rigby" I hear Paul McCartney's voice in all its original glory as well as a very soft display of violins, nothing too high pitched and shrill here as the SB90T seems to tame them quite nicely. "For No One" features Alan Civil on the French horn obligato as he chimes in during certain passages within the song. My ears are very sensitive when it comes to the sound of horns and violins, and the SB90T did a very good job of easing my fears in both cases as I thoroughly enjoyed the way they were represented.

Now to listen to one of my favorite Rolling Stones songs for review we have the song "Sympathy For The Devil" from the CD Beggars Banquet [ABKCO 95392]. Here the SB90T gives us a wide and deep soundscape presence. It was more than wide enough, just not quite as wide (filling the distance between the speaker and the wall nearest it) as some tube amplifiers I have heard. What it did do exceptionally well was to lay before me a soundscape that was very deep, front to back, that I found quite striking. Not all amplifiers do this as well and the SB90T was a pleasure to hear. The soundstage it produced was also noteworthy in its ability to let the listener hear the individual performers within it with great distinction and clarity. When playing Led Zeppelin's "Black Dog" from Led Zeppelin [Atlantic 92638 2] I tried pushing the loudness level of the amplifier. Yet it did not fail to impress me with its smoothness and ability not to break up with volume levels that bordered on making me feel uncomfortable.


A Meeting Of Tube Hybrid Amplifier And Tube Tuner
I could not resist pairing up the SB90T with my McIntosh MR67 all tube tuner (made between 1963-1968). My MR67 is in excellent physical condition and comes with an original wooden McIntosh case. It also has very recently been serviced from an authorized McIntosh service center. Just as I thought, pairing these two tube products together produced some wonderfully musical listening sessions. Listening at night with the SB90T and its nicely lit Blue Circle logo coupled with the McIntosh's beautifully lit face plate and meters was an extra added bonus not to be missed. Together they produced a little wider soundscape than when listening with a solid-state CD player. It did this while still maintaining the depth of soundscape that I heard before. Vocals were full, beautifully transparent and had a sense of ease about them. I like violins and cellos which the combination of Blue Circle and McIntosh gear reproduced with a true sense of timbre to these instruments. This was indeed a good match in my system.


Final Thoughts
After living with the Blue Circle Audio SB90T hybrid amplifier in my review system for a while there was no doubt in my mind that I thoroughly enjoyed this product from Gilbert Yeung at Blue Circle Audio. I often found myself coming home to listen to music rather than trying to write a review. During these times I had to stop and remind myself to concentrate on reviewing rather than let the music carry me away. I liked the fact that it had 90 hybrid watts and was pleased with its ability to produce quality bass as well as handle the inner details of music as it showed me a thoroughly deep soundscape The fact that Gilbert Yeung can bring such an amplifier to market for only $3295 makes the SB90T just that much more appealing. As for the Blue Circle logo which lit up so nicely whenever I turned on the amplifier, what can I say, I loved it. This really was an amplifier that I was glad to have in my system, if even for a short time.

My ratings: Please take into consideration that the equipment under review is being measured in my room, with my equipment and heard through my ears. As always you should be the final judge as to what works for you in your environment and measured against what traits you value most. The following was how I rated the equipment based on a rating system that does not take in to consideration the cost of the product, until the very last question, "Value For The Money". Before that all products are rated against others in its category, regardless of financial considerations.



Sub-bass (10Hz - 60Hz)

Mid-bass (80Hz - 200Hz)

Midrange (200Hz - 3,000Hz)

High Frequencies (3,000Hz On Up)



Inner Resolution

Soundscape Width Front

Soundscape Width Rear  
Soundscape Depth Behind Speakers

Soundscape Extension Into Room


Fit And Finish

Self Noise

Value For The Money


Type: Hybrid stereo amplifier
Frequency Response: 10 Hz to 25 kHz
Power Output: 90watts into 8 Ohms, 135 watts into 4 Ohms
Residue Noise @ Full Output: > -105dB audio band weighted
Distortion @ 10W into 8 Ohms: < 0.25%
Voltage Gain: 23.5 dB
Input Sensitivity: 1.8 Vrms
Input Impedance: 47.5K ohms
Tube: One 6SN7 tube 
Dimensions: 17.5 x 3.5 x 15.5 (WxHxD in inches)
Weight: 40 Lbs
Price: $3295
XLR Input option: $300
Banana plug adapter for speaker cables: $35 for a set of four


Company Information
Blue Circle Audio
Innerkip, Ontario, Canada















































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