Korg Nutube

[tim273]

Hey Everyone,

I'm sure some people on here have heard of the Korg Nutube: https://korgnutube.com/en I was just wondering what everyone's thoughts are on it?  Is it the future of tubes or just another fad?

Tim

[Doc B.]

330K Rp, really low transconductance (going to be noisy for low signal applications), plate current measured in microamps (1.7mW dissipation). Needs to draw grid current at low plate voltages. Needs buffers at the input and the output.

[tim273]

So, in other words, not so good for the types of amps you have here?

[Paul Birkeland]

It is technically a functional vacuum tube.

As Dan points out, it's completely useless, especially for audio.

Pete Millet has made a board or two that use them.  He uses a fet at the input to be able to drive the grid of the Nutube and a fet at the output to drive whatever his module is feeding.  That is the only real approach that will yield success. 

[EricS]

As Doc points out, it clearly needs a pre- and post-buffer.  It also provides 16dB of gain and you can fine-tune the distortion profile to dial up or down the magnitude of the second harmonic relative to the third harmonic as well as the phase of that distortion.  All in all, it's a very nice sounding preamp that provides quite a bit of flexibility for experimentation and learning!  I've been using mine for about a year and really enjoy it!  It sounds quite nice when driving a variety of Class-A mosfet amps that I have. 

[Paul Birkeland]

Ah yes, I also forgot to mention something else that bothered me.  When the cathode is exhausted and you need to replace the Nutube...

[tim273]

Yeah, that makes sense!  If they are going to do this, they should really make them easily replaceable!

[Paul Birkeland]

Yeah, that makes sense!  If they are going to do this, they should really make them easily replaceable!

Yes, like using, oh, I don't know, maybe a tube socket?

[EricS]

A form factor that fits a socket would be a nice feature - I didn't try before I soldered it in, but wonder if it would fit an IC socket?  I'm thinking I remember a 30,000 hr service life, but I might be wrong, its been a while since I've looked at the spec sheet. 

At a total cost of about $120-150 for a completed unit (tube, board, components, chassis, etc), its a heckofa nice little preamp with a noise floor somewhere near -110dB.  The circuit that I used is here: http://www.firstwatt.com/articles.html

[Deke609]

It's cool that a present day electronics manufacturer is producing a new take on audio tube technology. I hope the Nutube is a success and that this success motivates the manufacturer to do more r&d and release different nutube variants.

There's a very lengthy build thread "B1 with Korg Nutube" over on diyAudio. People seem pretty happy with it.

I hope to build one too after learning a bit about solid state devices - BJTs, FETs, OPAMPs and the like (which I'm trying to get the basics to understand how regulator ICs and CCS circuits work).