Amplifier project by Nutube, a new vacuum tube!

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!

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".

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 the kit including all parts are on sale at tindie.com, 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 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....!!)

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 tindie.com around $90 (sorry so expensive, but Nutube alone costs $50 and MUSES 8920, capacitor, PCB fabrication accumulates the total costs...!)

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!