2020, Chapter 14
Measurements, Schmeasurements
So, we did an improved Vali 2.
Yes, our $149 tube hybrid amp. Yes, improved.
Improved, as in, now it has a driver stage, just like Magni 3+, so it offers higher performance than Vali 2. Higher performance as in higher power, lower noise floor, and lower distortion (well, a bit).
And that’s where, I expect, your responses bifurcate.
One half of you looks at the still-dismal distortion performance, and says, “Why bother? It’s still a turd in the measurement hierarchy. Why polish it?”
And the other half looks at the tube and the price and says, “Waitaminuit, you made a $149 hybrid sound even better? Sign me up!”
(And then both sides snipe at each other, safely behind keyboards.)
Sigh.
That’s just too 2020, isn’t it? Why don’t we extend a hand of friendship, and say “this is the amp for all audio enthusiasts, we don’t care what camp you camped in the month before?”
Or at least accept that other people have other perspectives, and when you’re talking a $149 amp, it’s not the end of the world if someone else’s perspective doesn’t match yours.
So yeah. I’ll just say it, so we can get past all of the yelling: Vali 2+, even with its improvements, still measures like ass. If you want measurements, we have Magni Heresy and Magnius.
But if you are even a little bit tube-curious, this is a great way to hear what the crazy’s all about.
Vali 2+ for the Uninitiated
For those who don’t know much about our previous inexpensive tube hybrid, I should probably make it clear what Vali 2+ is. So here you go. Vali 2+ is:
- A $149 tube hybrid amp—as in, it uses both a tube and transistors (tube for voltage gain, bipolar transistors for output stage, to be exact)
- Designed specifically to use one tube—so it’s easy to try different kinds without buying matched pairs
- Quiet and powerful for an inexpensive tube hybrid amp
- Also a preamp—it has preamp outputs suitable for use with powered monitors or speaker power amps
- Improved from Vali 2—it has a driver stage like a Magni 3+, which improves performance, but doesn’t make it a measurement darling
- Less powerful than Magni 3+ or Heresy, more powerful than Fulla 3
- Much less expensive than Lyr 3 or Mjolnir 2, our other hybrid amps
- Not a “full tube amp” like Valhalla 2, which means it can put out much more power because it can output more current
We think Vali 2+ is a really neat amp for people who want to try tubes for the first time, whether or not they stick with the stock tube, or if they want to try a bunch of different tubes. Vali 2+ is super-flexible, and can use tubes from 6DJ8 to 6CG7 and 6N1P, or you can use adapters to run crazy stuff like WE396As in there…
Oh wait, did I go too tube-nutso on you? Sorry about that. Like I said, the stock tube is fine. It’s just that some people like to try lots of different things. Which is totally fine.
But, Like, It’s Just Distortion, Man
Yeah, and maybe all uber-measurement amps sound the same and maybe we like distortion and maybe we actually like distortion sooooo much that
all of audiophilia is a search for the perfect distortion profile.
Ever think about that?
Yeah, I know, it’s a super disturbing thought, but what’s inherently wrong about it? If finding the right distortion is the way to audio nirvana, Vali 2+ is one path. You’re looking at 0.3% THD into 32 ohms at 1 VRMS out with the stock tube.
Or, to put it in simple terms, 1,000 to 10,000X the distortion of Magni Heresy and Magnius. Like -50dB THD+N, not -120dB.
Eeek!
Run away!
The world is ending!
You can sooooo totallyyyyy hear that, right?
Well, hmm. Here’s the weird thing. When we put Vali 2 (the old one) in as a ringer on a blind test of Magni Heresy and Magni 3+, it was very, very hard to pick out from measurement darlings! Check out the
Lighted By the Blind chapter for the full skinny.
“But how can this be?” someone cries.
Well, lots of things. Here’s a short list:
- We are listening, typically, at levels much less than 1V RMS output—that’s pretty damn loud on most headphones. So the distortion may be lower than the measurements suggest.
- Second harmonic distortion, which both Vali 2+ and Vali 2 have boatloads of, is pretty benign, sonically. Or at least some people think so.
- The transducer itself—the headphone—has its own distortion. Many are not much better than Vali 2+--as in, -50dB to -60dB. This will make it more difficult to hear the amp contribution.
- We are deaf.
In any case, Vali 2+ is not another clean, measurement-perfect amp. It has plenty of distortion. The distortion follows a typical triode progression (2nd most prominent, 3rd well down from that, 4th well down from 3rd, etc). And the distortion will change with tube type…so if you get into “tube rolling” (trying different tubes), it will affect the output of the amp.
Too technical? Cool, let’s move on to why we made Vali 2 better.
Whys and Wherefores
So why did we bother taking time out of our busy schedule to make Vali 2 better?
Well, first off, our schedule, as in, my schedule, really isn’t that crazy. I have time to play with stupid analog stuff that will probably never make it to being a product. And I do like to look at what we’ve done in the past to see if we can make it better. And Vali 2 had had a great run--it was introduced almost 5 years ago! (Time flies, right?)
So, when I was improving Magni 3, adding a driver stage and going to the newer matched transistors we use in the output stage of Magni 3+, I figured, “Let’s take a look at Vali 2.”
Vali 2 really wasn’t a bad amp. But the old-style output devices, and lack of drivers, meant that the transistor performance limited the tube performance. Adding a driver stage would fix that, and the new matched devices would increase performance. And, at the same time, adding more filtering to the power supply could take down the output noise level a bit.
Aside: output noise level is usually higher in tube and tube hybrid amps, especially when they use AC heaters. AC heaters are exactly what they sound like—you use AC to heat the tube filament, which is what drives the electrons off the cathode to make the whole megillah work. Problem is, AC might bleed a bit of 60Hz hum, which can mean audible noise on the output. Furthermore, Vali 2 and Vali 2+ both use out Coherence™ direct-coupled tube-to-transistor hybrid stage, which demands a super-quiet plate supply to keep noise down. Changing AC heaters to DC was out of the budget (though we did play with elevation and decoupling, and made some changes there), but filtering the plate supply was feasible, so that’s what we did. The result is 10dB less noise in Vali 2+.
Aside to the aside: adding a driver stage allowed us to better isolate the combobulated tube/VAS stage of Coherence™—which is fairly current limited—which means that the output stage wouldn’t load the voltage gain, even with difficult loads. The result is a distortion profile that is much more typical of a pure tube amp. Whether or not this sounds like a pure tube amp is an exercise we’ll leave to you.
Ergh. I should probably talk about Coherence™ a bit. This is covered in the Lyr 3 chapter and the Buzzword Bingo chapter, but it deserves some words.
Coherence is our unique way of combining a tube input and voltage gain stage with a transistor output stage—without using coupling capacitors. Most hybrids will capacitor couple the tube stage to the output stage. Lyr and Lyr 2 work that way. Mjolnir 2 still works that way. It’s one way to do it.
Coherence is another. It directly couples the tube to the transistor output stage, which eliminates the interstage coupling capacitor. This is super-cool in Lyr 3, which also uses an operational point servo to make it DC from input to output. That, in hybrid terms, is pretty nuts.
Vali 2+, like Vali 2, uses the basic Coherence topology to eliminate any interstage capacitor—but it does use output coupling capacitors.
“Well, that’s super-bizarre, why don’t you get rid of those, too?”
Simple: size and cost.
(Sigh, it’s fairly amazing how much in engineering boils down to those two words. Add “heat” and you may have literally ALL of engineering in three words.)
Vali 2+ is, to put it in
Better Off Ted terms, a cost- and size-constrained amplifier. It has exactly two voltage rails. Getting rid of the output coupling capacitors in Lyr took four MORE rails. Each rail needs rectification, filtering, etc. Each adds size and cost. And those four rails were primarily to run Lyr 3’s current-sourced, operational-point-servo scheme, which in itself added a whole lot more parts. Doing all that simply wasn’t in the cards for Vali 2+.
Beyond that, there are a just a couple of small visual tweaks to Vali 2+—we changed the top chassis perforations to better match our tube gear (as in, the perforations are on a circle rather than on a grid), and dropped the front LED. I mean, the tube is sticking all the way out of the amp, and the heaters glow a bright orange—no real need for an LED, right?
Development was pretty straightforward. Vali 2+ took just two prototypes—one to make sure the tweaks worked, and one to clean up a couple of bonehead mistakes.
Yet another aside: and this is one reason why Vali 2+ is Vali 2+ and not Vali 3. It’s an improvement to a current product. It adds no features. So it gets a plus rather than a full rev number. Yeah, I know, nobody really cares. But we promised no more silent tweaks, so there you go.
So how does it work? Very well, for an inexpensive tube hybrid headphone amp. It has plenty of power for most headphones, preamp outputs for powered monitors so you can create a whole desktop system around it, and it matches our Modi 3 and Modi Multibit products for a nice stack. And (to me) it sounds really good.
But then again, I might be deaf.
Similarly, the path to production was pretty simple: I gave Alex a BOM, and our metal guys a new top chassis drawing, and got the boards spun up for the board house. Then it was just “sit and wait until we were out of Vali 2.” This took about 8 months.
As in, yeah, we had lots of Vali 2s in the production pipeline. This included both stock on shelves and additional runs.
And, yeah, this is really how things work—we are scheduled out for 6-12 months on almost everything. Depending on the amount of metal we have in process, or the amount of older parts we have to use up, it can easily take this long after the design has been done, verified, and put to bed before the successor shows up. So don’t be surprised when I tell you I had this one sewn up before COVID was even a thing.
Crazy? Maybe not so much. Having lots of stuff in process—and having lots of parts on hand—allows us to keep our sanity when something completely bonkers happens, like AKM’s DAC fab burning down.
Yeah. It’s 2020 all right.
Peering Into the Future
So if you decide to pick up a Vali 2+ and get into the wonderfully retro world of tubes, is there anything you should know? I mean, tubes are ancient, right? And the tubes we use are old—as in, they are “new old stock” 6BZ7s. Is this a problem?
In short, yes and no.
Yes, because the stock of 6BZ7s is nearing its end. Or at least we can’t find any more. We have enough stock for a couple of years, but after that, there aren’t enough for us to continue using them.
So is it time to panic? No. When the 6BZ7s go away, we’ll just move to a new production tube from JJ or Electro-Harmonix. These tubes are gonna be more expensive, so we might have to bump the price of the amp up by $10 or $20, but Vali 2+ will go on just fine.
It also means you won’t have to worry about replacing the tube. When it starts getting noisy, or sounding funny, or whatever (tubes have a rated life of about 5,000 hours…Vali 2+ should comfortably exceed that, as the tubes are run very, very conservatively, but you never know), you can get 6BZ7, or 6922, or ECC88, or switch it up for 6N1P or 6CG7.
Aside: we have tons of 6N1Ps. We considered supplying it as a standard tube in Vali 2+. But 6N1Ps run pretty hot (they have higher heater current). Not hot enough to hurt the Vali, but it might get a bit ouchy for someone who is just getting used to the idea of a tube amp. So we didn’t go that way.
After all that, where does this leave us? With a super-affordable, reasonably powerful, quite versatile little tube hybrid amp that might just be the thing for playing with the weird and wacky world of tubes, without spending a ton of money…or it might be the amp you fall in love with, literally everything you ever need.
I mean, I had a Vali 2 on my desk since before they were available. Now it has been replaced by Vali 2+.
But again, my desk is small.
And I might be deaf.
Enjoy!
