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rhing

Pass DIY B1 with Korg NuTube Triode Preamp

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I just built this kit offered through the diyAudio.com store and Nelson Pass. It is Nelson Pass’ JFET B1 buffer married with a Korg NuTube dual triode. The Korg NuTube dual triode is essentially a vacuum tube built on a Silicon wafer footprint. 

 

https://diyaudiostore.com/products/korg-nutube-b1

 

Having built several DIY projects, I assembled this kit over a weekend and used Duelund DCA20GA Tin-plated Copper wire for all signal connections and Kimber Kable TCSS Copper wire for DC power supply connections. The chassis fits very nicely together to make a very professional-looking preamp. The Korg NuTube provides gain, so this is an active preamp with two line-level inputs. 

 

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I brought this preamp with me to Northern California recently and tried this preamp in a couple systems at friends’ homes. The preamp was used with a Conrad-Johnson MV75-A1 tube power amp driving KEF Reference 101 monitors, and with a Texas Instruments TPA3255EVM Class D power amp driving a pair of Klipsch Forte II speakers. In both cases, this little gem performed very well creating a deep soundstage with holographic imaging as most tube preamps do. The detail and tonality are excellent and this preamp is really quiet. Even better is that this dual triode runs cool. Nelson Pass has even recommended leaving the preamp powered on all the time with the kit-supplied wall wart power supply. 

 

You can read this lengthy forum thread on this preamp where some people have installed film caps instead of the electrolytic caps that fit the PCB, installed stepped attenuators and tweaks for taming tube microphony. 

 

https://www.diyaudio.com/forums/pass-labs/313612-b1-korg-triode.html

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I've been thinking of building a 4 channel version for my K510 actives. Have you tried playing with the nutube plate bias to adjust the second harmonic component?

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Just a little bit with the pots. I still need to set up a distortion analyzer to measure harmonic distortion and phase. Setting the test points, T7 and T8, to 10 VDC works well for my ears. 

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Glad to hear good reviews of this preamp. I just got in on the preorder for the next batch. Long term plan is to have this paired with an F5 powering my Forte II’s.

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