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Korg NuTube, vacuum tube for the 21st century (korgnutube.com)
168 points by ChuckMcM 57 days ago | hide | past | web | favorite | 88 comments

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.

>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.

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

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

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.

Indistinguishable is a mighty strong word. We haven't completely mastered digital audio and to think we have is foolish (I do DSP for digital audio for a living, I'm Chris from Airwindows)

Also, a tube has absolutely no latency.

> a tube has absolutely no latency

I think that's the primary key here. We can decently emulate a tube amp in software even (and that can improve indefinitely as our knowledge improves), but we'll never create drop-in circuit element emulators either in silicon or software without adding latency.

As far as guitar tube amps go - check out a Kemper Profiler or Fractal Audio system, it's pretty much there. That said, I'd take the pure simplicity of a nice tube amp any day.

> 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.

Subjectively, the one effect often missing from preamp-only tube amps I've tried is power stage sag[1]. I've seen DSP software with it (or rather, a knob for it). In that respect, I'm not sure the solid state / preamp tube / all-tube segmentation can be justified anymore: modern modelling amps sound terrific (subjectively, to my ears), offer sonic variety (because why not), and have a completely different idea of value (comfort, power and size); With that, the NuTube just feels like it's going after an audience who won't be convinced that electrons flowing through a DSP are made of the same quantum stuff, which is unfortunate.

[1] Demo: https://www.youtube.com/watch?v=INi6lepBZt0

Frankly I think the world is (rightly) going the way of DSP + objective (probably class D more and more) power amp. If there is something nice about tubes, it is probably captured in somebody's software by now.

I don't know about the dynamics of tubes, but I have yet to hear a credible replication of the sound of a trumpet with a synthesizer.

The problem of synthesizing a believable trumpet sound is way harder than creating a believable tube distortion. The trumpet is a complex system consisting of the the interplay between the horn and the lips, tongue, throat and lungs of player. Also, the way you interact with the trumpet is widely different from the way you play a piano, resulting in different musical expression.

Compared to that, the dynamic of a tube are pretty simple, though creating a truthful emulation of a full amplifier is still a hard.

I don't think tubes will help much for synthesising a trumpet. You can get pretty good results with physical modeling, though. https://youtu.be/nRkT2PyH3kg

Hell, you're not going to get a credible replication of the sound of a trumpet off a CD… not compared to real life. Trumpets are among the few sorts of instruments that produce an overtone sequence going WAY beyond human hearing. It might not take that much more to cover those bases (I personally think 24/96 is more than enough and as such ought to be considered the baseline) and the heavy lifting will definitely be done by the amplification and speakers, but even a compact disc is going to fall short, much less a synthesizer.

I well know that any playback of recorded sound is hopelessly inadequate compared to live sound (I don't know why).

But listen to any Herb Alpert recording, and then listen to any synthesized trumpet. The gulf is as wide as the Atlantic. (Part of the reason is that Alpert plays with the notes and the transitions, while a synthesizer just emits a note.)

> while a synthesizer just emits a note

Well, maybe a crap one, or one not designed for that. Trumpets have some convenient physics that are (comparatively) simple to model, the problem you're thinking of may have more to do with the control system (i.e. not based on actuation of valves, but skipping right to the oscillators) than some inherent weakness of synthesis.

I've heard a lot of synthetic trumpet sounds on various popular songs. None sound much like a trumpet, so I am skeptical it is a "simple to model" problem.

(I played a trumpet as a kid, so I suppose my ear for it is more discerning than most. My talent proved elusive, but the lasting value was I can appreciate how incredibly good Herb Alpert was. He could play like Fred Astaire could dance and Ernst Udet could fly.)

By the way, I totally understand why almost all guitar amps that marketed as hybrid use preamp tube stages and solid-state power amps. However, the reasons are almost all are from the standpoint of engineering, not sound quality.

From my experience, overdriven guitar signal formed by ubiquitous FET-based approach driving a saturated tube power amp can sound gorgeous, tight and punchy, and feel very "natural" and responsive. 12AX7s into your ordinary solid-state power amps - not so much.

A FET preamp feeding a tube power section, pushed into clipping is at the heart of the Dumble tube amps. The Overtone Special (OTS) and Steel String Singer (SSS) are among the most desirable and most expensive guitar amplifiers in the world with models selling for $50,000 to $100,000+

Also the tube pre-amp stage in the Dean Markley RM 80 DR is absolutely gorgeous sounding, as corroborated by its intricate tone-shaping in the schematic. My friend and I use it with keys and synths without even touching the transistor output stage.

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:


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".

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.

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.

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

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.

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.

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.

> 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.

Do the math, your distorted spectrum will contain sum and difference frequencies. (For me, what makes the math easy is breaking a real sine wave into a sum of its complex components, which are easier to work with.)

This is, as you say, what makes 3rd order bad in RF, because if I have two frequencies F1 and F2, F1+F2 or F1-F2 can be filtered out no problem, but 2F1-F2 or 2F2-F1 is a problem. But this intuition about distortion does not extend to music.

In music, it is not so much the individual frequencies that are relevant, but the harmonic spectra, and the spectrum is within spitting distance of baseband, so filtering won’t do you any good (at least not in eliminating distortion).

And since music contains harmonic spectra to begin with, for a given F in the signal, you probably already have 2F, 3F, 4F. So when you calculate the spectrum for 2nd order or 3rd order distortion, you get the SAME frequencies in the output either way, just in different quantities.

As a result, as electric guitarists know, you have to be very careful about what harmonic content you feed into distortion. If you feed in a note, you get the same note out with different texture. If you feed an octave, it sounds good. Perfect fifth, great, the distortion adds overtones of the octave below the root. A major third is iffy and something you’d use with less distortion. As you get farther away from simple intervals, like octave 2:1, fifth 3:2, fourth 4:3, or major third 5:4, it gets worse and worse. (Eddie Van Halen reportedly retuned his guitar, tuning the second string down 14 cents, to get the major third closer to a harmonic third.)

And this is why distortion for a single instrument sounds good, but distortion for an entire song with multiple instruments (some of which are usually inharmonic) sounds bad. Even with 2nd order distortion, do you really want sum and difference frequencies between overtones of the guitar and overtones of the snare drum? No.

A 2% THD solid state amp would be pretty hard to design today, unless it's an effect you were trying to achieve. In that case, you can simulate the transfer function of one device with another.

Other questions I have:

What is the change in input Z of the grid above 0V? Does it come crashing out of the megaohm range like a typical triode?

(To the general reader: The grid conduction and the bias shift that it triggers is definitely a part of a "real" amp sound. If you've heard anything that sounds like a swirling sound out of an overdriven guitar amp, this is bias shift brought on by grid conduction)

Do you need to continuously source current to the grid like most low voltage tube cases

What are Cgk and Cga?

What are the curves like near cutoff, and are the slopes different due to a different grid geometry relative to a traditional triode?


PS, if tube amps for music are interesting to readers of HN, but you have no background, there is an exceptionally lucid book on the topic: "Designing Tube Amps for Guitar and Bass" by Merlin Blencowe.

>"Tube sound" is nonlinearity.

In balance. Too much nonlinearity is just noise. You want to have good balance, nonlinearity for warmth and linearity for fidelity.

If the filament is the cathode, you’re going to have to feed it DC for heater voltage.

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.


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

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


Here's a project using actual VF display tubes as an amplifier: 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), which are nearly as small. 17mm x 10mm dia.

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

BTW, the VFD used on the first link happens to be Noritake, that is, the same brand associated with work for the NuTube project, and the inventors of the VFDs, so this might not me new for them at all.

And also, by the way, almost the only brand still manufacturing VFDs that are easy to find on the market (at least buying one by one).

And also, they make pretty tableware :D

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.

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.

HP used a 8058 (iirc) as the first stage amplifier in some of my RMS voltmeters; they're from the 60s though.

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.

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?

Even more budget, a Behringer UCA202, and Sony MDR-7506. Total cost is about $110 for a huge upgrade in sound from where you start.

I'll second your recommendation to invest a bit in headphones and a DAC/amp. Even something like the $200 Sennheiser HD6XX headphones and a $75 FiiO E10K will be miles above AirPods/Beats/etc.

> There were sounds in tracks I was quite familiar with that I had never heard before.

That's technically true :)

Any recommendations for an easy to buy one in uk ?

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

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.

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.

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.

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.

Which Bogner products are you referring to?

Bogner Ecstasy Red and Blue pedals, which aim to duplicate the Red and Blue channels (and the various sub-modes) of the corresponding amps, and do a pretty good job.

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.

Vox has released guitar amps with NuTube in them: 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

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.

Seems like you can also buy them (nut very cheap) and make a DIY project.


Aside from the Vox MV50, I've never seen this in the wild. I hope someone proves me wrong, since the MV50 sounds great and I'd like to see what else is out there.

for audio, Korg has a gallery of examples: https://korgnutube.com/en/gallery/

the tech uses the same manufacturing line as a traditional vacuum fluorescent display. VFDs are technically vacuum triodes where the plate has been painted with a phosphor.

the device is probably not fast enough to be used as a video amplifier.

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

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

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.

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

The thing to note is that (good) tube amplifiers can be designed to be very linear until they're driven too hard - the audiophile community often overlooks this detail when they're shopping for "warm" tube amps for general power amp duties. The big differences between tubes and other kinds of amplifiers appear when they're driven at, and especially past, their design limits.

In an application like a guitar amplifier, some kind of effect/distortion pedal, etc the tube circuit is typically overdriven by design to get all of those warm harmonics. A tube that isn't being overdriven is every bit as capable of being a "wire with gain" as any kind of transistor or more modern circuit.

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

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

Liking tube sound or, more generally, the defects/characteristics of a particular amplifier (, headphones, speaker, room, ...) is perfectly fine with me.

I get easily annoyed though when people start spewing pseudo-scientific BS justifying that deviations are objectively better than no deviations or that there are significant (or "obvious with good ears") differences between amplifiers where there simply are no such differences.

Post your statistically-significant double-blind testing logs.

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.

eventually you do get a square wave (similar to a transistor) but with less overdrive, you get a "soft clip" waveform that is rich in second harmonics. these harmonics are an octave above the fundamental, and can also create a psychoacoustic effect where you hear another sound that is an octave below. bass players LOVE using tube amplifiers for this reason--it really fattens up the sound without making it sound crunchy.

A tube amplifier sounds very different when clipping (i.e. try to amplify the signal past the maximum the amplifier can produce), and this is used to create distortion, most notably for electric guitars.

There are DSP effects that can simulate this as well, of course.

Music uses vacuum tubes due to the sounds that they produce.

it works with a regular VFD as well! see https://twitter.com/TubeTimeUS/status/1061797427991068672 for a photo and the resulting waveform.

for all the gory technical details, the datasheet is available here: 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!

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.

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

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?

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.

I have an AKAI AM-2850 amplifer older than me. Its VU meters a bit lazy, but otherwise it's still shaking the house.

I'm no way getting rid of it!

P.S.: I generally dispose any of my devices when they let their magic smoke out. Computers stay at least five years and upcycled. Mine -> Family -> Extended family -> so on.

Computers generally become obsolete at some point. Most audio equipment doesn't - newer equipment might be cheaper, more reliable or more convenient to use, but it probably doesn't sound any better. The cachet and mystique surrounding vintage equipment means that it often appreciates in value with age.

Vacuum tubes are considered obsolete in pretty much any other field, but they're still the gold standard for guitar amplifiers. Despite huge advances in digital modelling, many guitarists still strongly prefer traditional tube amplifiers. Tube amplifiers are fragile, finicky, incredibly heavy and frequently too loud for domestic use, but they sound superb. The NuTube is by no means the first product to promise the sound of tubes in a lighter and more reliable package, nor will it be the last.

It is difficult to make audio equipment disposable. There's no Moore's Law-driven metric and anything low durability is obvious enough.

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

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.

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.

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.

See also: the Nuvistor. https://en.wikipedia.org/wiki/Nuvistor

Also known as the Audiophile Economic Effect. :)

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