Korg Nutube B1
At the Burning Amp Festival in 2017 Nelson presented a pre-amp using the Korg Nutube dual triode. The latest revision of the circuit available is now available complete with Fairchild JFETs and all directly supplied by Nelson Pass.
Please check the following links for more information:
There are 4 elements to building a complete preamplifier. Purchase the elements separately, or all together as a "full kit" bundle for $299. To build a complete preamplifier you will need:
What's in the completion kit?
Everything else you need to complete the project other than 1, 2 and 3 above. It's an assortment of bits and pieces that joins the Nutube, PCB and Chassis together, turning the whole things into a "full kit", hence the name "completion kit".
The included "wall wart" style power adapter supports an input voltage of 90-264V and has a US style plug. If you don't live in the US you will need to obtain a suitable plug adapter.
Discussion threads / Links:
- Technical discussion: B1K main thread
- Build Guide: B1K Build Guide
- Pre-order Q&A (old news) in the B1K pre-order Q&A thread
- Prototype feedback (old news): B1K pioneer batch feedback
- Pre-order status (old news): B1K pre-order status page
What are the chassis specifications?
- Galaxy 230x170 full aluminum chassis, anodized black with white printing
- Internal dimensions 40x210x170mm
- LED hole ø2mm
- Left switch
- Hole ø6.5mm
- 15mm x 15mm square rear recess, 7mm deep
- Right switch
- Hole ø6.5mm
- 15mm x 24mm rectangular rear recess (allows for switch and LED), 7mm deep
- Potentiometer hole ø10mm, with ø32mm round recess in the front ø8mm deep
- Rear RCA holes ø10mm
- Rear power switch hole ø11mm
I couldn't have enjoyed building this more than I did. I am a big fan of the SP1 tube just because it is different. I have made several builds using the Korg tube, from preamps and amps to headphone amps and buffers. The first B1 that I got was already built but I wanted to hear what one sounded like with this design. I wasn't disappointed. The best description of the sound for me was that it was musical. I could go on about all of the aspects, but I got what I wanted here and that is plenty for me.
Kit build is very good and easy to do. Me being me, I upgraded the volume control to an EIZZ stepped attenuator, and opted to make my own power supply, using toroidal transformer and beefy circuits as well. Note that the photo of the power supply shows it in rough form, and the box was cleaned up afterward. I keep the B1 power switch on and just use a switch on the power supply in the front.... I used shielded silver plated copper wiring throughout the build. In other words I maxed out the component quality. The result rivals any other build that I have owned. I have been horse racing it with another preamp build of mine, but can't decide which I like best. They both have their merits.
The B1 chassis needs some help in the support of the top and bottom plates, since the SP1 will give no easement in handling any vibration. This is easily solved by using a bead of silicone for the bottom plate around the perimeter on the inside. I also opted to use additional damping in the form of Dynamat in strategic spots. The one piece of advice that I would give to anyone building this kit is to use silicone supports for the SP1 board! These are inexpensive and pop into place. They are used for the reduction of noise for computer fans. To get the board to be properly held, I used small O rings that took up the additional space left by the silicone support.
At the price I didn't expect too much. That is ok, since I had a general curiosity about the SP1 tube, even though I have worked with it in the past. This particular kit is easy, almost self explanatory. That's good, because there are many like myself that will get so far with something, but not all the way, and it is a PaiN to have research the crap out of something just to find a simple yes or no to a question.
So I got the kit assembled, and appreciated the quality parts choice along the way. Once done the result look s very good, and not something that resembles a kit. Finally it is the sound that makes me sigh in relief. It doesn't sound like a kit. It does however, sound like a tube circuit. In fact it sounds more tubey than most anything I have built in the past. For me, that was the goal, or at least one of the key points.
You will realize how positive this review is by the fact, I am building another one. This with a few upgrades... yes, because I can.
I enjoyed building this pre amp, it was not difficult especially with the instructions available at diy forum..... great job guys!
I made the top cover with my cnc laser in acrylic and painted the underside, I left a window to see the Nutube, I then laser etched the writing in mirror image on the bottom so it looks nice at night with the letters glowing with the Nutube lite....
And it sounds really nice, I liked it so much I built another one but this time with a different case and remote control volume and input selector with 3 inputs....
The kit is quite easy to set up, and the tuning too if you go smoothly. I encountered a microphonic issue that I solved by placing a small ball of Patafix under the Nutube. I think it could be useful to isolate the PCB from the chassis because I have a very slight ringing noise when I turn the potentiometer (audible through the headphones). Finally, I placed the switches behind the front panel for aesthetic reasons. I had some worries because the input wires are not shielded, but in reality there is no residual noise. Now I will probably connect it to an F5 (to be built) for two reasons: the simplicity of the schematic and the class A operation. Many thanks for the useful guide.
The Korg NuTube kit was a joy to assemble. An easy build, I spread it out over two days (through ps test on day 1). Everything powered up with all test points in spec and no problem setting a stable bias on the triode. The sound is a great complement to a DAC with a low noise and high dynamic range output. It seems to soften the edges but also gives it a fuller, more detailed but still bright sound. This preamp seems to make the rolled-off nature of vinyl at the high and low end as well as the midrange coloration more obvious. I am using this with Klipsch bookshelf speakers (RP-150M) and an ACA; I may compare this preamp to a passive preamp for playback of vinyl in future.
Nice kit. Enjoyed the build. Very decent sound. Only issue was to find manual for final adjustments.
Will build more of these 🤓
Yay! I finished my B1 Korg and a few days ago. Immediately I noticed the nuances in the music and maybe a slight echo. I am using it between a Schiit Modi Multibit and a Class D power amp driving Pioneer BS22LR. It fills out and smooths the Class D amp. I also built the ACP+ preamp, and with the Class D power amp, I feel the B1 Korg coloration sounds better. With the ACA amp, the sound is rich. The PCB/FETs, Korg Tube, and case from diyaudio.com. The rest of the parts were from Digikey, Mouser & Newark. I had the connectors, switches, pots, power supply, and miscellaneous parts as leftovers from other projects.
A couple of minor points.
• I encountered one small issue. My 270-ohm 3-watt resistor seemed to be running too hot for being enclosed. I checked, and both the 270-ohm and 9.1v Zener were at the far ends of their 20% tolerance. So, I swapped them out for a 270-ohm 1%, 5-watt (Vishay ALSR05270R0FE12), and 9.1v 1.3-watt 2% Zener (Vishay BZX85B9V1). I also raised them off of the PCB when I mounted them. The power supply now runs substantially cooler. All voltages are according to Nelson's article.
• The PCB has a slight change from Nelson's schematic. In the schematic, the input has the junction of the 332k resistors AFTER the 1k resistor. On the board, the junction of the 332k resistors is BEFORE the 1k resistors.
• The PCB parts were easy to order, except for the capacitors, which seem to have too many grades and choices. I need to learn more about why there are so many choices and grades. I checked around the Internet for what were the best grades for audio. Maybe I got it right, maybe not.
• I started with the build guide but ended up changing the wiring to maintain the twisting between the jacks and the selector switch. Basically Orange/Orange-stripe is #1 right input jack -> selector switch -> volume control -> right channel -> right output jack. Blue/Blue-stripe for the left channel all the way through. The Green and Brown pairs were used for connecting #2 jacks to the selector switch. I used black and green hook-up wire for the power jack wiring. The concept was to use the PCB ground trace as the center for my star ground.
Overall, it was a wonderful experience, and I enjoyed building the preamp. Plus, it looks nice. My next step is to move the preamp from my desk to my living room for other amps and other speakers.
Thank Nelson Pass and diyaudiostore team for having me a lifetime preamp.
This is hobby, so I deviated couple of parts from originals:
4 X 2200uf cap on power supply, 6 X 6.8 uf Wima cap for coupling, greyhill rotary switch for 4 input, and mono stepped volume controls, also added isodamp on nu tube and opposite side of pcb. I do know about level of distortion, but this amp just sound good and excellent.
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