Introduction
The B1 with Korg Triode was introduced by Nelson Pass in 2017 at the Burning Amp Festival. The B1 is an established design which is as about as easy as it gets - a buffered passive preamp.
The Nutube from Korg is a vacuum fluorescent display that operates similarly to a triode vacuum tube. The green glow reminds me of the old computer monitor that came with my cousin's Apple II computer ages ago. This also gives this kit a cool factor that only audiophiles are able to appreciate. The rest of the world probably just thinks that we are dorks!
Why not just use a vacuum tube? Vacuum tubes use considerably more power and have short operating lives. The typical vacuum triode would have a lifespan between 2000 to 5000 hours. In comparison, the Nutube has a continuous life expectancy of 30000 hours (about 3.4 years) and 2% of the power consumption of a vacuum tube.
Korg's Nutube website would be a great place to read up more on this device - https://korgnutube.com/en/
This is an ideal kit for a beginner that has some experience in building a kit or two, and comfortable with a soldering iron. The kit as supplied from diyAudio is powered by a 24V wall-wart which makes this a safe project too - no messing around with mains voltage.
Put simply, there is an input buffer, followed by the Nutube, and an output buffer. The input buffer is required to lower the output impedance of the potentiometer used, while the output buffer lowers the output impedance of the Nutube, which is necessary to drive a typical power amplifier load.
You can read the following links for more information about the technical design.
The kit from diyAudio Store is priced at USD 299 for the full kit with all parts you need. The enclosure is well made, with a thick solid aluminum face plate. There are only two inputs, although this should be enough for most users.
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| The complete kit |
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| The chassis |
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| Sorting out the resistors |
Assembly
This is pretty straightforward and you should be able to get everything done in an evening or two, depending on how fast you are. The build instructions are very clear and the PCB is easy to work with. In fact, the most challenging part of this kit is getting your hands on one. They are made in limited quantities, and disappear in a flash when available. Otherwise, the hardest part for most people would be soldering the transistors and Nutube. The latter in particular requires very precise soldering as the pins are very close together.
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| Stuffing the resistors |
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| Setting the plate voltage |
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| The comforting green glow from the Nutube |
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| All wired up |
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| The completed product |
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| Back panel |
Adjustment of the two voltage pots at T7 and T8 adjust the plate voltage, which affect the level and phase of 2nd order distortion to suit your taste.
Audiophiles have experimented with boutique parts with varying degrees of success. The coupling capacitor pads are spaced for electrolytic capacitors, so you will need to be creative if you want to use film capacitors instead.
The Nutube is microphonic and some builders I know have encountered problems with ringing. I damped the gap between the Nutube and PCB, and also used silicon spacers to damp the PCB standoffs. My unit is well-behaved, even when flipping switches or tapping on the chassis.
Unlike most of my DIY projects, this worked fine from the start. I imagine that most builders with an intermediate level of experience would have similar success.
I kept this build as stock as possible, although I did use some solid silver wiring and KLEI RCA jacks just to satisfy the audiophile in me.
Sonics
Tonally, the B1 Korg is neutral, with a slightly soft edge. Music flows with a fluid and noticeable warmth. The effect is not overdone, and detail, speed and dynamics are still delivered intact. Where the B1 Korg stands above its competition, is the dimensionality imparted to the soundstage. Instruments and vocals are able to glow and occupy acoustic space. Many preamps are able to provide sharp and precise imaging and staging, but in a flat and 2-D manner. The subtle flavour of romance offered will not suit the cold, hard and clinical listeners out there though.
From a quality point of view, I would be comfortable recommending the B1 Korg for use even in entry-level high end systems.
Conclusion
This is an excellent kit to start off your DIY journey. The build is easy, and you end up with a simple preamp that sounds really good too - Best Buy
B1 with Korg Triode - USD 299
https://diyaudiostore.com/products/korg-nutube-b1?variant=39438124482633
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