
Korg NuTube, vacuum tube for the 21st century - ChuckMcM
https://korgnutube.com/en/
======
i_am_proteus
Couple of notes from someone who has "designed" (adapted old schematics,
really) and built tube amps for both hifi and electric guitar:

\- These things run at low voltages (5-80VDC), which is _fantastic_ for a
designer, because 'real' vacuum tubes need several hundred volts DC, which
means a big power supply transformer/rectifier/filter network.

\- These things don't appear to be able to source a lot of current, which
makes them good for preamp and tone circuits, not so much for power amp
circuits. Classic tube guitar amps got a lot of their tone from the phase
splitter, power amp tubes, and power amp transformers. Don't expect an all-
nutube-amp.

\- Utility for guitar amps would be for "hybrid" amps with a tube preamp and
tone circuit feeding a solid-state power amp. There's certainly room for
experimentation by amp designers here, since most contemporary tube amps just
copy old circuits (mostly Fender and Vox) and use the same tubes they used
(12AX7 being the ubiquitous preamp tube). I doubt the NuTube sounds like a
12AX7 when dropped into the same circuit.

\- Utility for hifi is questionable. An all-tube design allows for a very
linear, low-parts-count amplifier. These will need to be mated to a solid-
state power amp, which nullifies the advantage of a tube amp and enters
"vacuum tube as marketing gimmick" territory.

~~~
jdietrich
_> Classic tube guitar amps got a lot of their tone from the phase splitter,
power amp tubes, and power amp transformers._

100% this. A tube gain stage in isolation isn't especially difficult to
imitate using solid-state electronics or DSP, but sounds nothing like a tube
amp.

 _> Utility for guitar amps would be for "hybrid" amps with a tube preamp and
tone circuit feeding a solid-state power amp._

The Vox MV50 amps make a decent attempt at this, pairing a Nutube with a class
D power stage. It's tiny, it's reasonably loud and it sounds pretty good.

I suspect the lack of interest from other manufacturers is mainly due to cost;
for the price of a single Nutube module, you could add a decent DSP chip and
gain a whole bunch of extra functionality. An ornamental 12AX7 and an orange
LED has better showroom appeal and costs significantly less. Purists will
still want real tubes and real transformers, budget-oriented players will want
an amp with all the DSP bells and whistles, leaving the Nutube caught in an
uncomfortably narrow niche.

~~~
WalterBright
I don't understand why a tube's profile cannot be emulated with a DSP and so
be indistinguishable.

~~~
Filligree
Oh, it absolutely can. The target market for tubes isn't people who do double
blind tests, though.

~~~
ehnto
They want tubes and the tube sound, not just the sound. I can understand, it's
a matter if authenticity rather than practicality. Just like a kit car replica
versus an original car. The original will always be more authentic, and there
will be some who care more than others.

------
al2o3cr
From the landing page:

    
    
        The real triode structure produces a warm, unique vacuum
        tube sound, delivering excellent linearity.
    

"Tube sound" _is_ nonlinearity. WTAF. See also the NuTube-powered headphone
amp here, which measures 1+% THD at all practical output levels:

[http://www.nutube.us](http://www.nutube.us)

Actually-linear headphone amps regularly achieve under 0.01% THD...

Beyond that, compared to a "classic" preamp tube like the 12AX7 (very popular
in guitar amps), the NuTube looks like it has:

* simplified structure: the 12AX7 has indirectly-heated cathodes (the filament heats the electrode). This permits the two triodes to be used more-or-less independently. OTOH, the NuTube has a shared directly-heated cathode (the filament IS the electrode). Not a huge problem, but it means some circuits are trickier. Not likely to be cloning a K2-W, ferinstance.

* lower anode voltage: the 12AX7 is specified down to 100V on the anode, but the datasheet considers 250V "typical". The NuTube has a maximum anode voltage of 80V, presumably due to the reduced size of the physical elements. This has the expected consequences for performance: lower gain (10 vs 100), lower transconductance (10uA/V vs 1250-1600uA/V) and higher plate resistance (300k vs 80k)

* considerably different grid characteristics: the 12AX7 specifies an absolute maximum grid voltage of 0V, because taking the grid positive causes it to conduct electrons from the cathode and heat up. The NuTube specs don't mention a maximum, but the anode curves are shown for up to +4V on the grid. AFAIK grid conduction is sometimes considered part of "tube sound" when it happens in power output stages, but it's definitely not "linear".

Other than the line from Vox (owned by Korg) it doesn't seem like the NuTube
has gotten much uptake in the industry until recently - 2018 reviews for the
Ibanez NTS mention it's the "first pedal with NuTube".

~~~
i_am_proteus
To a degree, "vacuum tubes" are like "machine learning" and "blockchain" in
that their presence in a product has a magical money-attracting quality that's
often divorced from their active role in the product's operation.

That said, comparing %THD between all-tube circuits and solid-state circuits
for hifi isn't entirely apples-to-apples, especially since "single-ended-
triode" type tube amps' distortion is predominantly in the second-order
harmonic, which listeners often perceive as loudness or "roundness" or
"warmth."

I've listened to 2% THD tube amps that sounded pretty good to my ears, whereas
a 2% THD solid state amp will generally sound like ass. Although, honestly, I
haven't spent much time listening to ass, so there's a chance I might just be
talking out of mine.

~~~
klodolph
The characteristics of a single-ended triode depends a huge amount on the
circuit around it. A simple cathode resistor acts as local negative feedback.
Bypassing it with a capacitor removes the local negative feedback for a range
of frequencies. Then there’s the choice of load, resistor or transformer. All
have different electrical characteristics, all fall under the “single-ended
triode” umbrella.

Personally, I’m quite skeptical about the idea that second-order harmonics are
“warm” or “round” sounding. Whether or not distortion is “musical” depends on
whether you are making music or adding noise to something that is already
music; if you are playing a guitar then the distortion is music, if you are
listening to a song, the distortion in your audio equipment is by definition
noise.

I understand that sometimes distortion is inevitable even when it’s not
desirable. Your microphone preamplifier will sometimes get overloaded, or you
might be listening to a song at high levels with transients beyond the power
capabilities of your system. So for microphone preamplifiers, go ahead and
stick a tube in there. But for listening, it is usually cheaper to fix your
distortion problems by buying a more powerful solid-state amplifier with more
headroom, and more expensive to fix your distortion problems by switching to a
tube amplifier with better distortion characteristics.

~~~
madengr
I’d think since 2nd order distortion produces harmonics at octaves (which are
naturally pleasing to the brain), vs 3rd order which produces IMD.

~~~
klodolph
That is simply incorrect. I think there’s a fundamental misconception about
what distortion is, and how it works, at play here.

Any distortion produces intermodulation distortion.

A sine wave will produce exactly an octave harmonic if you distort it with
only second-order distortion. However, nobody listens to pure sine waves. So
if you feed anything more complicated than a pure sine wave, you will get
something other than harmonics at octaves.

~~~
madengr
Perhaps I should have been more specific; 3rd order IMD. The IMD3 can’t be
produced by the ideal JFET drain current (Vgs-Vt)^2; tubes are the same. Of
course there are other distortion mechanisms too. This is in the RF power amp
world (been designing them for 20+ years), the IMD3 are the main concern as
those fall around the carrier; we generally don’t care about 2nd order since
those are easily filtered (but not in audio).

Maybe it’s a stretch to apply this to audio. If you play a flat on piano, and
IMD3 falls on a sharp, then that sounds bad. The distortion one octave higher
sound fine. Even the sharp one octave higher sounds better than the adjacent
sharp.

I bought a tube amp kit for Christmas, so it will be interesting to measure
the two-tone IMD3. I only have measured audio THD once, and that was using a
spectrum analyzer, so only looked at harmonics. Even if you used two-tones,
the IMD would fall within the RBW of the spectrum analyzer.

~~~
phasetransition
Single ended triodes of low to no degeneration are not the same current
profile as a JFET.

The Child Langmuir law has a 3/2's exponent, so you get 2nd and 3rd for the
single ended case. Further, virtually all guitar amps have a push pull
amplifier output (of questionable symmetry) operating into the speaker, so the
even order terms are cancelling to some degree here.

The general character of many tube amps is to make a smooth transition from
predominantly 2nd order distortion to a mixture of odd order harmonics. This
ends up as primarily the 3rd order as a guitar amp speaker makes a heck of an
underdamped lowpass filter.

Between the cathode bias bypass caps, the dc blocking caps, and the RC
behavior of grid stopper resistors combined with the Miller capacitance,
guitar amplifiers have a lot of internal bandwidth filtering that reduces IMD
amplitudes.

\---

JFET current behavior in the saturation range is as you say, but not
necessarily so in the ohmic region. Generally people using JFETs in these
circuits use at least some of their ohmic range behavior.

Since you have skill and experience in this area, and also have a tube amp
kit, I suggest googling for "Tubes 201." This is an excellent summary article
for the behavior of vacuum tubes.

Also, Aiken amplification website, and Merlin Blencowe's book I mentioned
yesterday you would find to be good reads.

------
jdietrich
If you think this is cool, wait until you see the Gamechanger Audio Plasma
distortion pedal. It uses a xenon discharge lamp as the main tone-shaping
element.

[https://www.gamechangeraudio.com/plasma/](https://www.gamechangeraudio.com/plasma/)

~~~
RileyJames
Just wow!! Lightning in pedal! And the sound is incredible.

Check out this video at around 3 minutes and you can see the lightning
triggering as he plays guitar:
[https://www.youtube.com/watch?v=_AZj5tc8EmA](https://www.youtube.com/watch?v=_AZj5tc8EmA)

~~~
jackhack
You'll love the tesla coil guitar amp, then:

[https://gizmodo.com/this-tesla-coil-guitar-amp-would-make-
sp...](https://gizmodo.com/this-tesla-coil-guitar-amp-would-make-spinal-tap-
weep-w-1795492685)

------
tlb
Here's a project using actual VF display tubes as an amplifier:
[http://www.hpfriedrichs.com/radioroom/vfd/rr-
vfd.htm](http://www.hpfriedrichs.com/radioroom/vfd/rr-vfd.htm) If you look at
the wiggly plate current curves he measured, there should be plenty of
harmonic distortion for tube audio enthusiasts.

My 1970s HP oscilloscope contains several Nuvistors
([https://en.wikipedia.org/wiki/Nuvistor](https://en.wikipedia.org/wiki/Nuvistor)),
which are nearly as small. 17mm x 10mm dia.

~~~
ChuckMcM
Wow, I think that first reference is going to put a crimp in Korg's patent
application :-)

~~~
bayindirh
I think it won't. Because it looks like there's even a magnet on the Korg's
tube. They might be leveraged that same research, and listed it as a prior art
or paid him as co-inventor.

~~~
ChuckMcM
The confusing bit for me, and realize I'm not a patent lawyer but have
patented a few things, the referenced articles first publication was in 2008.
I was told that in the US (but not in Europe) you have one year from public
disclosure to file for a patent. (In Europe you give up your patent rights if
you disclose first.) So to patent this you'd want to have filed in 2008. Here
it is 10 years later. So why hasn't a patent issued? I've seen them take 3 - 5
years but 10 years seems like a stretch.

------
anon1253
As an extreme tangent, but something that I was reminded of due to "tubes".

I recently bought my first audio upgrade (Cambridge DAC 100, Little Dot MK III
with Voshkod 6ZH1P-EV from the 70's on Beyerdynamic DT 1990 Pro headphones)
and honestly, the first time I listened to it I was in tears. Coming from just
plugging in some Sennheiser HD1 to my mobo audio out, the difference was
staggering. There were sounds in tracks I was quite familiar with that I had
never heard before. I bought a Schiit with a closed DT 1770 Pro for my office
... which wasn't nearly as good (and incidentally I think the filter caps
might not handle the el cheapo DC-AC converter on the solar panels all that
well which gives annoying (as in really audible) cracking and popping sounds
even after tube rolling). Now for the downside: "audiophile" is a horrible
niche to be in, there is so much cargo-culting and downright hostility that
makes it a very "toxic" place to be in (not to mention stupidly expensive if
you buy all the ahum "bs" ... a signal processing class would be a better
investment...). But, I find the toxicity to be a little bit sad as well. Since
it detracts people from a very real life improvement. Audio is one of the
primary modalities of our sensory system, and even with mediocre hearing (like
a male 30+ will likely have) you can, and do, hear an enjoyable difference for
a modest investment. The difference between some second-grade Bluetooth thing
and a nice "desktop" set /is/ real. My advice, get a nice open headphone
(400-600$ range, I /really/ recommend something with a detachable cable since
those fail first), something to replace your on board DAC for 150$, and an
headphone amp (I like tubes, but for no other reason than that I like the way
they look and "sound"). For something around 750-1000$ your life will be
better and it'll last you a heck of a lot longer than any AirPod will
(heirloom piece). That is, if you like listening to music, if not, disregard
everything. Yes it's an investment, but this is HN, where I feel recommending
1k is not that big of a deal.

Now for the more on topic part: apart from some high voltage DC applications
like transceivers or transmitters (like microwaves!) tubes have largely been
replaced by solid state. And with good reason, they last much longer, and are
less conductive to all sort of ailments ... so apart from /super/ specialized
applications they have no place. Apart from maybe providing that nice warm
glow on your desk, when you're lonely, at night, and just want to listen to
that "one song" while staring out of the window.

~~~
locusm
What Schitt DAC did you go with, I have the 1st gen Modi and are looking to
upgrade. There is some very well made, affordable audiophile level gear
available these days if you know where to look. Have you tried out anything in
the Raspi/DAC scene?

------
ZoomZoomZoom
First public reviews I saw note highly microphonic nature of these "tubes".
This is a big disadvantage for applying them in guitar/bass amplifiers or any
other live gear.

Guitologist has a nice video review that could be interested to tinkerers and
musicians:
[https://www.youtube.com/watch?v=raYGrKWSKRE](https://www.youtube.com/watch?v=raYGrKWSKRE)

------
m0zg
I wonder if these are any different to JFETs in blind auditions. People have
been basically taking old Marshall circuitry and turning it into pedals using
J201 JFET transistors. It's a bit of a bear to set up bias for, but the
results are impressive enough that there's an entire cottage industry around
this by now and some higher end manufacturers (e.g. Bogner Amplification) have
jumped on the bandwagon. Needless to say, a JFET is at least an order of
magnitude cheaper than this can ever be.

~~~
analog31
The JFET is at a disadvantage from a marketing standpoint, because it faces
the burden of proof, and is known to be cheaper. There's an automatic
presumption that someone is using it to save money while making compromises to
the audio quality. All it takes is one person to proclaim that it doesn't
sound _exactly_ like a tube.

In contrast, a 12AX7 is indisputably a tube.

~~~
m0zg
But this is not 12ax7. And nutube is a cold cathode tube. There have been
attempts to use low-power tubes called nuvistors before. Those are actually
more of a tube than nutube, and they failed to get any traction. It's a
notoriously fickle market, and tubes are still manufactured in China, Russia,
and even in the US, so it's arguable if they need to be "replaced" by some
newfangled thing.

~~~
analog31
Indeed, last I checked, a 12AX7 is like 5 bucks in quantity (and I'm no master
at low cost sourcing), so it's barely even an economic argument. The guitar
amp can't be made much smaller overall because it still needs a speaker.

------
vonseel
Have any professional audio products been released using this technology yet?
Guitar amps or similar.

Is this purely used in audio or is there a display (video) usecase for this as
well? The landing page seemed to imply the technology is coming from display
tubes.

~~~
droussel
Vox has released guitar amps with NuTube in them:
[https://www.voxamps.com/MV50](https://www.voxamps.com/MV50)

Ibanez has also released a Tub Screamer that uses them:
[https://www.ibanez.com/na/products/detail/nts_01.html](https://www.ibanez.com/na/products/detail/nts_01.html)

~~~
jeremymcanally
And the Vox amps at least sound really great IMO.

I had the "Clean" one for a while, which mimicks a Fender circuit. It sounded
pretty darned close to a "real" tube amp. The only reason I got rid of it was
I got a Fender Super Champ x2 with USB out for recording more easily.

------
ChuckMcM
These are pretty cool, it is a triode made out of vacuum fluorescent display
tech.

~~~
mrandish
Not much of a hardware guy... so what would this be useful for and better at?

~~~
ChuckMcM
The way the thermal constant works in a tube is unique to its construction. As
a result when you saturate an amplifier built with tubes rather than getting
square wave clipping (which is full of odd harmonics) you get a modulated
overtone. In Music systems this overtone has energy at musically compatible
harmonics and so it still sounds good. In radios it can be easier to filter
out the spurs (spurious overtones from non-linear operation) without swamping
the modulation on the signal.

~~~
jackhack
translation: "an amplifier that sounds pleasant and warm, not harsh like a
transistor."

~~~
blattimwind
Good transistor amplifiers (i.e. 70s technology) are sufficiently good
approximations of an ideal audio-band VCVS that they have no sound at all.

~~~
mark-r
I used to think that until I compared a couple. The most realistic sound I've
ever heard was from a tube-powered system.

~~~
ferongr
Post your statistically-significant double-blind testing logs.

~~~
Applejinx
You do understand that your point of view is only one among many valid
positions on the subject, some held by authoritative figures? (and I don't
mean me, I'm thinking the likes of JJ)

This isn't solely a defense of the position you challenged, more a call-out on
your tactic here. You're not exactly representative.

The talk of transistor amplifiers being perfect and having no sound at all is
of course nonsense: typically this kind of claim looks at frequency response
and outright ignores slew rate, crossover distortion, behavior as the amp
exits its passband on either extreme, and so on. There CAN be transistor
amplifiers, both simple and incredibly complex, that are so good that they've
got effectively no sound at all. It's even possible that it's easier to get
there with a transistor amplifier given enough money and resources. But that's
not the claim.

------
tubetime
for all the gory technical details, the datasheet is available here:
[http://korgnutube.com/pdf/Nutube_DatasheetV1E.pdf](http://korgnutube.com/pdf/Nutube_DatasheetV1E.pdf)

interesting that they break the typical vacuum tube naming convention--the
first number usually refers to the filament voltage. as a 6P1, i'd expect it
to have a 6.3V filament, but it actually has a 0.7V filament!

------
icanhackit
Interesting bit of trivia: The Noritake Group, the parent company behind
Noritake Itron who make the VFD module, specialise in ceramic products ranging
from circuit boards, dental materials, electronic paste to fine china. That's
what I love about Japanese companies - the utter complexity of their product
lines and exhaustive use of in-house talent. Though as Sony can attest, it can
be their undoing as well.

~~~
jmole
It's one reason that "lifetime employment" worked so well for them.

------
cordite
Assuming 8 hours of use a day, this would last at least 10 years. Does audio
equipment suffer less from the disposable electronics culture that we have
with computers?

~~~
anigbrowl
Yes. The secondary market for audio gear is very healthy, even for things that
have stopped working and may only be useful for parts. It's so healthy that
building modern clones of classic early innovations is a sustainable business
model.

Electronic music exists as it does because the advent of digital
synthesis/recording technology in the 1980s led to mass abandonment of analog
gear by rock and pop musicians, which was eagerly snapped up by broke hippies
and hip-hop DJs. Commercial musicians jumped on the digital bandwagon for
reliability, range, and repeatability (sounds stored as easily-recallable
software presents instead of requiring tedious rewiring and knob-twiddling or
having 10 keyboards on stage). Also, commercial musicians had mostly used
synthesizers to substitute for acoustic instruments; it's cheaper to hire a
keyboard player than a string or a brass section, and digital synthesis and
sampling offered more realistic imitations than was possible with analog gear.
Electronic musicians are more interested - no, obsessed = by the timbral
characteristics and weirdness of the instruments themselves. I know people who
have dedicated years of their lives to analysing and reproducing the
characteristics of discontinued instruments like the TB-303 bassline as if it
were a Stradivarius. Synth circuit engineers are venerated like stars at music
equipment trade shows, and the social hierarchy of electronic musicians is
ordered by their known propensity for experimenting or modifying their gear
rather than commercial success. It's an interesting ecosystem.

Anyway, rest assured that few if any of the products using this component will
end up in a landfill.

------
ElijahLynn
And... the site is down now. (504 Gateway Time-out)

------
kazinator
This is now in various products now, like a small amp Vox called the MV50 AC
(NuTube in preamp section, Class-D power amp). Lots of YouTube demos.

These Korg NuTubes were developed in conjunction with Noritake, the (only?)
company that makes vacuum fluorescent displays.

------
bashinator
Drop-in replacements for various common tubes used in audio applications (e.g.
the 12AX7) would be an enormous market success. I wonder if there are any
plans to make a higher wattage part that uses pentode design.

------
byron_fast
I want to believe. It may sound _exactly_ like tubes. But if it doesn't look
like a tube, and hurt when you touch it, it will probably be a market failure.

~~~
byron_fast
See also: the Nuvistor.
[https://en.wikipedia.org/wiki/Nuvistor](https://en.wikipedia.org/wiki/Nuvistor)

