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The BC-107 Solid-State Line stage Preamplifier
Gilbert really doesn’t care what the marketing folks have to say. Actually, he really doesn’t care what just about anyone else has to say
either. He has his own ideas and is constantly investigating and discovering new things. Many of our finest components are the result
of Gilbert wandering off into one of his explorations, just to satisfy his own curiosity. The NSL power amps are two very good
examples. Another example is the BC-307 cross-hybrid preamp. Fortunately for our customers, and not so fortunately for the marketing
department, the 307 design was just being completed when Gilbert started work on the BC-107.
The History
The BC-307 has three signal paths, one of which is pure solid
state. Gilbert learned some new SS circuit techniques during the
307 design phase, and of course, he decided to incorporate them
into the BC-107. And then, while developing the 107 design he
came up with a few more design tweaks. The BC-107 has turned
out to be much more than just a BC-109 with a conventional
power supply. And much to the dismay of the marketing
department, it is not much cheaper than a 109 either. It may
even sound almost as good, and perhaps in some ways, even
better than the 109. The marketing folks are not very happy and
Gilbert couldn’t care less.
Tech Stuff
The BC-107 is a pure solid-state line stage preamp. It has a fully differential input stage and is DC-coupled from input to output. The supposedly
“more conventional” power supply is nothing short of massive. There is more than 750,000 ìF of power supply filtering. That is more than three-
quarters of a Farad and more than most 200 W power amps! And for those who may want even more in the future, there is a GBC jack installed
on the back panel so that you can add one of our GBC outboard power supplies without sending the unit back to the factory for an upgrade. All
you have to do is simply plug the GBC outboard into the jack… plug-and-play.

The BC-107 does not have a power switch. It is designed to be powered up continuously. At idle it draws only about 1.5 W (less than
an LED bulb) so don’t worry about your power bill. As in all Blue Circle preamps, volume is controlled by a hand-built Shallco
attenuator. There are four standard inputs and the customer can specify what mix of single-ended and XLR that they want. The mix
can be 4 SE, 3 SE and 1 balanced, or 2 SE and 2 balanced. Additional inputs are available upon request. Both balanced and single-
ended outputs are standard issue.
Music
The bottom line of course is the sound of the 107. As many of you may know, we never speak directly about how our gear sounds. We
leave that up to the reviewers and our customers. This preamp is so new we do not have any reviews nor have many people had the
pleasure of owning one yet, but here is what one of the first owners of a BC-107 had to say on our online forum:
“…out of the box and stone cold it demonstrated superior detail without harshness, a substantial soundstage but what impressed me
the most was the separation of the instruments. I found the bass a bit too thin until 3 hours into the testing when the bottom end
decided to show up for work. Needless to say my better half and I stayed up late unable to stop listening to the awesomeness of
this system.

It should be noted that with this massive a power supply, the 107 will continue to improve in performance for a very long time to come
as the caps break in.

From what we are hearing from those few who have lived with this preamp for some time, the verdict seems to be that this may be the
most neutral, organic preamp that Gilbert has built to date. It does not sound solid-state nor does it sound tubey. One professional
reviewer, who listened to it for a very brief time, said that it compared very favourably with his $25,000.00 reference preamp. The 107
sells for about one fifth the price. He has since ordered one for himself. If you would like us to build one for you, contact your local
Blue Circle dealer.
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The BC-107 did not turn out to be the component that many of us
thought it would. In fact, for the marketing department, it is a bit of a
problem. Originally, the 107 was supposed to be a BC-109 with a
conventional power supply. For those of you who are not familiar with
the BC-109, it is a dual-mono solid-state preamp built around a
Supercap-based power supply. The idea behind the 109 was to produce
a preamp that was as quiet as we could make it. Since even the
chemical reaction of a battery produces some noise, the solution was
to use discharging Supercaps to power the preamp. Those who
listened to the 109 were very impressed with the sound, but a number
said that they would like a more conventional power supply and asked
if we could make one. That was supposed to be the design
criteria for the BC-107. But this is Blue Circle Audio and Gilbert Yeung
is our designer, so...  here is what happened:
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Features and Options
*Several cosmetic options available at additional cost.
The BC-107PH Solid-State Preamplifier (with phonostage)
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The BC107 preamp with internal phonostage based on the BC Li'l703.
Illustrated with optional walnut/curly maple faceplate
(Standard faceplate is stainless steel on main unit and black plexiglass on the power supply)
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The BC-107PH is available on a special order basis only.
Standard features......
*Single Stereo - 31 position Shallco attenuators with 2 level gain switches for a total of 62 settings.
*Gold contacts roatary selector switch.
Optional features...
*Dual decks balanced 47 postion Shallco attenuators with 2 level gain switches for a total of 94 settings.
*Processor bypass loop.
*Remote volume control.
*Wide range of faceplate and cover options.
*Headphone amp and jack output

Measurements
Pre-amplifier
-Residue noise reference to full rated output: >- 100 dB or < 60 uV non weighted
-Residue noise reference to full rated output: >- 110 dB or < 20 uV within audio band
-Tracking error: < +/- 0.05 dB
-Hum below 400Hz: <1.0 uV
-Frequency response at 5V output: 10Hz to 55K Hz +0.00db, - 0.00 dB; -1db, -1db at >100 kHz
-Distortion at 5V output: < 0.0028 %
-Voltage gain: 20 dB
-Maximum output: 8.5 V
-volume control range: -95dB to 0db in 62 steps standard in Shallco attenuators
-input impedance: 100K ohms
-output impedance: 2.5 ohms
Dimensions: 17.5" wide x 3.5" height x 15.5" deep.
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Contact:  bcircle@bluecircle.com  /  519-469-3215