Amplifier project by Nutube, a new vacuum tube!

You know VFD, but may not know this VFD. It can amplify signal!! Yes, it is a TRIODE!!

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VFD is well known as digit display but not a amplifying device. A Japanese company Noritake and KORG made a incredible device by VFD technology. It looks like VFD but it works as a TRIODE. I cannot avoid it and quickly designed a headphone amplifier. As same as another project in, I will sell the headphone amplifier kit at Stay tune!

Noritake is a famous for making china-ware "Setomono" but also for VFD (Noritake Ise denshi). I've known VFD is just a device showing digit but they made a incredible device. A triode by VFD technology!!!

Most of vacuum tune requires high voltage but VFD is just around 12V. Moreover it is quite compact compared to general vacuum tube! They have already nice website and referring to data sheet ( You can ask KORG to get it on the website ), I quickly design a headphone amplifier!!

As same as general vacuum tube, Nutube has high input and output impedance. For driving headphone, some impedance converter is required and I simply added voltage follower. As a place holder, I used TL072 but in the real device I will use NJM8920 (MUSES8920), which is also very famous ( in Japan only?) good operational amplifier.

Not as same as general vacuum tube, minimum anode voltage of Nutube is just 8 V! (working up to 50 V from data sheet). As another voltage, GRID bias is needed, just around 3.3V. Anyway it is quite handy and safety compared to general vacuum tube circuit!

As same as another my recent project on, I have a plan to sell the full kit including this wonderful Nutube! A brief review of Nutube can be found in the following movie... Have fun!

  • New Nutube with Class-D 15W x 2 amplifier is born!

    kodera2t12/06/2018 at 06:36 0 comments

    I've released several Nutube related kit but all of them are "bare PCB". I surely noticed the importance of enclosure for casual and daily use of it, and this time I prepared enclosure!

  • Can we make PURE vacuum tube amplifier by Nutube?

    kodera2t08/10/2017 at 06:00 0 comments

    As written, output impedance of Nutube is very high (several hundreds k-Ohms) and very far from driving headphone and speaker. This time I just connect "output transformer for vacuum tube" to Nutube as shown in the picture below.

    The signal is taken from input to op-amp and the sound is through "pure non-semiconductor". I've confirmed it can drive well for general headphone but I cannot make youtube video by headphone and the output is connected tiny powered speaker.

    The actual result can be found in the movie below. The answer is "YES we can make pure vacuum tube headphone amplifier but not power amplifier for speaker driving".

  • Nutube amplifier has an evolution with Class-D technology

    kodera2t10/24/2016 at 01:14 1 comment

    Now my Nutube amplifier has an evolution. My previous one was a headphone-driving application but it will be very fun if we can have "Nutube sound" through speaker!!! Here comes the next one! Nutube Pre/Main amplifier!

    Here is the schematic. Basic design concept is, "as much as, as is from Nutube". The sound from Nutube is transfer to speaker out as is, and additional component would not have additional "coluor" to sound. It consists of three stage. The first stage is made of Nutube, working as a kind of "analogue signal processor", generating rich "vacuum tube second harmonics sound". The second one is an impedance converter by JRC MUSES 8920. We may omit this stage if input impedance of the next stage is enough high (it requires more than 100 kOhm) but the next stage amp has that of tens of kilo-ohm so I inserted as well. The third one is Class-D amplifier by Texas TPA3110. This tiny chip provides 15W x 2 output. By nature, class-D produces a wonderful sound by very simple circuit. As a whole, it is working a "21st century amplifier supported by lots of modern technology".

    Actual operation can be found at following movie. As same as my recent creation, I have a plan to sell this kit at tindie. Stay tune!~

  • Now my Nutube headphone amplifier kit on-sale

    kodera2t09/26/2016 at 21:54 0 comments

    Now the kit including all parts are on sale at, please don't miss it if you have some interest for it! Initial 4-unit will be shipped immediately and another 4 unit will be shipped in a few days.

  • Now Nutube headphone amp kit prepared!

    kodera2t09/24/2016 at 08:48 1 comment

    Now the total parts kit of Nutube headphone amplifier is prepared as above picture. Here I would explain some adjustment point for completion.

    I put 2.0 mm pitch 17 pin connector but this connector is quite tight and a bit hard to insert all pin of Nutube (in addition, pins are very soft). After inserting before power-on, please confirm all pin connection by tester.

    A barrel connector for AC adaptor connection is prepared on board. BUT general AC adaptor generates lots of HAM noise. If you cannot prepare high-quality 9V power supply, please use 006P (9V) battery as power supply. Battery driven state is quite good from viewpoint of noise.

    One caution is,,,, A silk on board says "12V centre +" but adding 12V will break 3.3 V regulator (NJM2884), which maximum input is 10V. Please never add more than 10 V as a power supply.

    Again I can say, 006P is the best (or 6-seriesed AA or AAA). I recommend battery drive.

    After completion, please prepare your favourite music and add to the amp, also prepare headphone. In the initial power-on, you may be surprised unusual noise but this amplifier requires adjustment because it is "fragile" vacuum tube circuit. Adjust right and left grid voltage by wiper and set them for the best sound state. You may notice Nutube will have some light. It seems, both brightness are the same, R and L channel will be balanced.

    Once proper grid voltages are set, you don't need any adjustment except for volume control. Enjoy Nutube amplifier!!!

    (As noticed, I will sell this kit just for 4-unit. Preparation for 4-unit costs a lots (more than $200 just for four Nutube), and I cannot prepare more than one because I need to avoid financial loss in the worse case, no one will order....!!)

  • My Nutube amplifier quick review

    kodera2t09/24/2016 at 00:51 0 comments

    Here I would put a quick review regarding my headphone amplifier. As same as general VFD, fluorescent material is prepared in Nutube and we can enjoy small light during operation. (This is just light-on, not sound indicator such as magic-eye)

    Actually This amplifier can be battery driven. In my design NJM2884 is used for 3.3 V regulator and its maximum input is 10 V so around 10 V is the maximum DC power source. As for the current, I confirmed,

    45.8 mA

    which is really small for the case of vacuum tube amplifier!!!

    Actual operation can be found in the following movie. As same as another project, I have a plan to sell this kit at around $90 (sorry so expensive, but Nutube alone costs $50 and MUSES 8920, capacitor, PCB fabrication accumulates the total costs...!)

  • Now my Nutube headphone amplifier is working!!!

    kodera2t09/23/2016 at 13:16 0 comments

    So my Nutube headphone amplifier begins to work!!!

    I am not heavy audio maniac but even me I can hear some "warmful vacuum tube sound" by this incredible VFD Triode!!!!!! Wonderful device!

View all 7 project logs

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perillamint wrote 07/13/2017 at 02:08 point

I ordered this on Tindie and it arrived yesterday. Little complain is, this amp is very sensitive to power noise. I read schematics today and noticed OP-Amp is plugged directly on barral jack.

IMHO, It would lot more better if OP-Amp sources its power from regulator rather then directly from PSU to prevent switching noise ruining output.

Anyway, thanks for this great project!

  Are you sure? yes | no

kodera2t wrote 07/13/2017 at 10:36 point

Hello and thanks comment. Indeed the power noise is directly received by Nutube itself since it is vacuum tube and raw electrons flies on free space and very sensitive to external electromagnetic field. The power source of operational amplifier does not matter to noise sensitivity. Anyway thank you!!

  Are you sure? yes | no

mxmora wrote 06/27/2017 at 00:32 point

Why a class D amplifier? If you want to promote vacuum tube sound you should be using class A amp or something similar. 

  Are you sure? yes | no

bootdsc wrote 05/11/2017 at 23:02 point

Just ordered one of your kits, i plan on using the nutube side of things and couple it to one of my own headphone amp designs. Are there any traces running inside the pcb? ill need to cut away some of the board to acomodate the small footprint of my case.

  Are you sure? yes | no

kodera2t wrote 05/11/2017 at 23:07 point

Hello and thank you for ordering. PCB trace (top: RED, bottom: BLUE) is presented in the above (in this page) picture ! Thank you!

  Are you sure? yes | no

Marcelo Daher wrote 09/24/2016 at 21:22 point

Keep it up, man! Looks very good! I had seen some on the nutube when they were anounced but had seen nothing about it since. Did you have a hard time sourcing the components? Are the tubes available for purchase?

  Are you sure? yes | no

kodera2t wrote 09/25/2016 at 05:19 point

Hello. Just a few days ago, KORG/Noritake started to sell this tube for consumer. I've got them just before consumer sale but we (at least in Japan) can buy it by 5400JPY. I am not sure they will start international sale but I hope they will soon for spreading this excitement!!

  Are you sure? yes | no

NFM wrote 09/27/2016 at 05:46 point

I just bought one for ¥5400 in Akihabara just now.

I almost squealed like a girl when I saw it finally on sale.

  Are you sure? yes | no

Martin wrote 09/22/2016 at 13:53 point

Perhaps you can use real tube symbols in the schematic instead of the connector symbol. I was looking a while for the tube in the schematic. 

For example something like the middle one of this:

  Are you sure? yes | no

kodera2t wrote 09/23/2016 at 13:18 point

Yeah you are right. Actually this time I rush to design but I guess this wonderful vacuum tube will be explored by lots of people and some people will make Eagle library, I think ! 

  Are you sure? yes | no

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