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The NSI and NSI-G Integrated Amplifiers
Technically – and we mean that literally – the new NSI and NSI-G are integrated amplifiers, at least from an electrical point of view.
However, you are going to need to re-think just about everything you know about integrated amplifiers when it comes to the NSI and
NSI-G.

Let’s go back to late 2016…
Having completed the design of several “NS” series components, Gilbert started to think about building an ultimate integrated amplifier.
Essentially the project was going to combine the NSC preamp and NSL power amp. It was supposed to be a relatively simple project,
resulting in a single box version of these two superb components.

Two things you should know at this point: first, Gilbert started out by building the NSI as a personal project -- it was not initially I
ntended for public consumption. It was just supposed to be a unit for personal listening that would keep him happy for a while.
Second, the output limit of the NSL maxed out at 28 watts per channel. It is an amazing 28 watts per channel, but still only 28 watts
per channel. Definitely not enough in terms of sales and marketing, and more to the point, not quite enough to drive a pair of Gilbert’s f
avorite speakers. A new goal of over 50 watts per channel was set.

Unfortunately, 50 watts was a big problem in terms of utilizing the output stage of the NSL. The op-amps used in the NSL are I
ncredibly fast, incredibly transparent, and incredibly musical. They are just not incredibly muscular. So more power meant that a
completely new output stage was needed -- an output stage that would retain the clarity and agility of the NSL but with a considerable
increase in power.

The concept for the new output stage design took more than a year to come to life and then another three months of testing and
development, often late into the evening. The new output stage puts out 80 watts per channel into 8 ohms, the optimum bias point for
this new design. It certainly has the speed and agility of the NSL, but these virtues came at a cost of both money and space. It took
more room and cost to build a power supply that could supply enough energy quickly enough to satisfy a demanding speaker load…
and Gilbert’s picky ears.

With the new output stage design completed, the prototype NSI was built in mid 2018.  The result was a solid state integrated amplifier
that performs better than anything he has built to date. Mission accomplished, right? Not exactly.  Building the prototype spawned a
question and challenge: how much further could the NSI design be taken and how could he get it there.

First he added a 6SN7 tube. And because Gilbert has never been a huge fan of NOS tubes because of cost, reliability, quality control,
availability, etc.,  after adding the basic tube input stage, he decided to create a circuit that could make a standard tube sound as
NOS as any NOS tube. Then, he made it adjustable so that you can add just the right amount to any situation to get that “dream”
sound. The result is a “FUN” control that works more effectively than you would believe. And so, the basic NSI was born, which should
have been enough to keep Gilbert happy.  

That could have ended the story. The NSI at this stage was an amp good enough for all but a tiny few of us and an extraordinary
accomplishment.  But no… Gilbert still felt a need to scratch his creative itch, and things soon got out of hand. Simply put, as we all
know, everything Blue Circle relates to power supplies. With all the new circuitry came new power supply designs, and the question,
how far could he improve them? So, less than 3 months away from Toronto Audiofest 2018, he went back to work.

The search began for the largest chassis in the shop. In the end, one chassis wasn’t big enough, and the result is a two chassis unit
weighing over 110 lbs. All of the power circuits were heavily modified (maybe fortified is a better word). Then almost 12 more weeks of
testing and tweaking trying to find out how far the NSI design could be taken before performance improvements leveled off. And so was
born the NSI-G.

The NSI-G is not for everybody. It is the amp for the tiny few for whom the NSI is not enough. It is a very large component – the sheer
size of the power supplies demands a certain amount of space. Again, the prototype is a 135 lb. unit built into two chassis. It can be
built into a number of different chassis configurations. The NSI-G is, however, a testament to how far the simple concept of the
integrated amplifier can be taken. Performance-wise, it will compare favorably to equipment at 5 times the cost. It may literally not
have an equal. For those lucky enough to get a listen to it in your own home, you are welcome to be the judge of that.



Specifications
Output Power: 80 watts into 8 ohms.  120 watts into 4 ohms.
Frequency response:  Excellent. When you hear it, you won’t care. You really won’t.
THD:  From 0.05% to 1%. The more you turn up the tube, the more distortion you will get and they are all of the rich and warmth
second harmonic distortion.

Dimensions and weight:

NSI: Amplifier 17" wide x 6.5" high x 19" deep, 45 lbs.  Power Supply 5.25" wide x 5" high x 15" deep, 22 lbs.

NSI-G:  Irrelevant. We can build it to suit your needs.  What you see in the picture is not necessarily what you get.







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Picture shown NSI-G measured 17.5" wide x 15" high x 21.25" deep + binding posts.  Other dimensions may be available.
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Contact:  bcircle@bluecircle.com  /  519-469-3215