Dave Clarke of VOX R&D Talks Handwired Guitar Amps

For the past 13 years Dave Clarke has headed up R&D for legendary British amp builder, VOX Amplification. With new handwired tributes to the hallowed AC15 and AC30 plus a return to UK production stirring up interest, we spoke to VOX R&D Manager Dave Clarke to get the rundown on these amps. In our wide-ranging conversation we also talked about the new VOX MV amps with their innovative Nutube front ends as well as the VX Series and Adio series.

The HUB: Hey Dave - how's things at VOX R&D? You guys are celebrating a big birthday this year, right?

Dave Clarke: This year is VOX’s 60th anniversary and the company obviously has had a very interesting past. In the ‘60s, VOX amps were made famous by the artists who played them—like The Beatles as well as important artists today. Something special we’ve done for our 60th anniversary, that we haven’t done since 2002, is making amps in the UK again. The amps we are making here are tributes to two of our most classic and famous amplifiers: a 1957 AC15 and a 1964 AC30. The Hand-Wired AC30 is the one with the Top Boost on the Brilliant channel and the Hand-Wired AC15 has the EF86 on the normal channel, which isn’t used as much as it once was, but it’s a really, really sweet-sounding tube.

The HUB: What was the impetus behind the decision to build again in the UK?

Dave Clarke: This is something we’ve been talking about for some time. With the 60th anniversary coming up, it made absolute sense to tie these special amps in with the anniversary. We had the time to get the factory sorted out as well as take our time with the product to make sure we were one-hundred percent happy with what was coming out of it. It needed to be good enough to represent the 60 years that VOX has been around.

The HUB: So, other than obviously the country of origin, how does that affect materials, the build process, etc?

Dave Clarke: These amps are completely hand-wired, so there are no printed circuit boards inside. They don’t use tag strip boards—everything is of the highest quality. Parts like high-quality carbon comp resistors, high-grade capacitors, UK-made mains (power) and output transformers. Cabinets are made in our factory, so the wood is cut on-site; the cabinets are covered by expert workers—it’s amazing what they can do. It’s the same painstaking attention to detail that went into designing these amps.

The key thing is, we have, as close as we can, recreated those vintage circuits so you’re going to get all of that vintage sound, which isn’t necessarily what people are going to expect. With the components we’re using, it will not respond like a modern amplifier.

The HUB: Can you explain that a bit further? Are you referring hum or noise in the circuit? Or how the older amps produced “ghost notes”?

Dave Clarke: Not so much hum; it’s things like those interesting ghost notes you get that really enhance the vintage vibe. You’ll get those subharmonics that you don’t really get with modern amplifiers.

The HUB: Got it! A few years ago on YouTube, I stumbled upon “Bohemian Rhapsody” with the guitar part isolated and you hear a lot of subharmonic ghost notes in the solo. When you hear the full mix, those ghost notes are pretty masked.

Dave Clarke: You’ll get those ghost notes with these amplifiers. In developing them, it was this whole thing, ‘Do we modernize them or do we keep them like they used to be?’ It was a little bit like “you’re damned if you do or damned if you don’t.” In the end, though, we said let’s make a recreation that’s as close as we can to the originals, and that’s what we went and did.

The HUB: When you’re resurrecting a vintage circuit that you’re trying to present as faithfully as possible, do you just look at the original schematics or are you getting five vintage units, listening and building it to a certain spec from there?

Dave Clarke: We do look at the original schematics; we use them as a start point for the design. But we also have a reference ‘57 AC15 and a reference ‘64 AC30 in our sound room. We use them as the tonal basis because we know they sound really good. We also have access to other amps from the same era, but the starting point is always going to be those vintage schematics.

Now the interesting thing is, in going through those old designs, there are component values that just don’t exist today. A perfect example: one of the most common smoothing components was an 8 microfarad smoothing capacitor. You can’t get them anymore, they just don’t exist. What’s happened over the last 60 years is that components have become standardized in ways that are different from back in the day. So we have had to use the modern-day equivalents that don’t have the old, strange values.

The HUB: Speaking to that, you can look at a component value on paper and that means one thing on a math level. But with your experience with vintage units, that specific original value and how it may have drifted over time is going to have a major impact on the sound. If you can’t get a specific vintage component value are you compensating elsewhere?

Dave Clarke: Exactly. People may find some tweaked capacitors and resistors along the way. As I’ve said in one of our videos, we’re using modern components in a sort of vintage way. What we’re trying to do is compensate for those changes. There are certain cap values in the vintage tremolo circuit that are just not available, so we’ve had to create our own values by paralleling the output series capacitors.

The HUB: In developing these new amps, did you have a team of people you were out to please? Did you say, ‘If we’re able to please this artist or this player, then we’ve done it.’?

Dave Clarke: We have a global voicing team—we’ve got guys and girls in the US, Japan, and Europe. We go to all of them to make sure everyone is 100 percent happy. We want them to be completely behind these products. There are a lot of people on the European team who have a lot of experience with vintage products. So obviously, it was important to be sure they were happy. Like I said, we were taking our time, wanting the end user to have something as close to a vintage VOX as possible.

The HUB: What is your prototyping process? Do you get the circuit built first, or do you build the head and cab together since they affect each other? What comes first?

Dave Clarke: Well, the electronics and the cabinet, they all get done kind of at the same time. You want that perfect relationship between the chassis and head, the cabinet and the baffle and speakers, and so on. Building them in the factory, they were building entire [prototype] units for us. There’s a significant amount of electronics to fit within the chassis and they need to fit perfectly. One of the key differences in the originals is that they have those tag strip boards that were incredibly untidy and a nightmare to service—very messy inside.

Everything inside these new models is very nicely laid out in rows using turret boards. So we took all that into account in designing it. And then we had a variety of things manufactured: output transformers, mains transformers.

We tried to make the cabinet as close to the original as possible. With modern-day safety testing and standards, there are certain things that we are not allowed to do anymore. One of the key difference there are the vents above the tubes, for example. The old ones were metal and get far too hot.

The HUB: You don’t want to brand people's’ hands when they touch the vents!

Dave Clarke: No. We want the product to be incredibly robust and safe. So again, it’s treading that fine line between vintage and modern. We’ve kept as much as we’re allowed to be vintage and made changes as discretely as possible.

The HUB: Would you touch on the modeling processes you use in developing gear like the new ACs?

Dave Clarke: We may be designing vintage things, but we do it in a very cutting-edge way. We use 3-D printing for prototyping. Currently we have three 3-D printers; each does a different job. Everything is modeled in 3-D software so we effectively have digital prototypes. We’re finding that with more and more integration between ECAD and MCAD—electrical CAD and mechanical CAD—they’re starting to get stitched together and communicate, and it’s brilliant.

The prototyping process is much more streamlined. In the 1960s, when everything was hand-drawn and hand designed, if something didn’t fit properly it all had to be redone. Today we iron out all those issues in the virtual space. It’s certainly chopped down our development time.

The HUB: Do you share these 3-D models with other VOX offices or the factories? I.E. ‘Here’s a new knob we designed, print it and tell us what you think.’

Dave Clarke: Absolutely. We’ll print things out and send them around. We’ll also sometimes just send the virtual file as a way of sharing over the web, allowing them to see what’s going on in near realtime. The way "The Cloud" is now, seas and continents nearly disappear, so we can work much closer together.

The HUB: It also must have effectively expanded your R&D team of three there in the UK to bring in the the worldwide manufacturing and voicing teams you’ve already mentioned.

Dave Clarke: This is one of those times new technology is good.

The HUB: Changing gears a bit, players buying an amp at the level of the new ACs are going to have their own opinions and likely swap in their own tubes, if not speakers. So, let’s talk about the tubes and speakers. What was the QC process for them? Was there something specific about how the Celestion speakers were selected? They’re not blue!

Dave Clarke: We began talking to Celestion years and years ago as we first began thinking about this UK project. We said to them, ‘Look, all 1964 AC30s have silver AlNiCo Blues. What is the deal with these silver AlNiCos?’ They went back to the archives and found that there was a two-week period when they couldn't get the blue paint and they sprayed them silver. These silver speakers are generally found in old boxes. We thought it would be a cool thing to have silver as well—another tip of the cap to the original. So what we have are UK-made AlNiCos in silver that you won’t find anywhere else. If you want an original silver AlNiCo, they cost a fortune.

The HUB: So they’re sonically the same—it’s just a nice aesthetic touch?

Dave Clarke: Yeah, sonically they’re going to be the same as standard Blue AlNiCos.

The HUB: About tubes, you’re using Rubys—the same as with the standard Handwired amps?

Dave Clarke: We swung with Ruby to make sure we had the highest quality we could get. Ruby worked really closely with us, selecting and grading not only the power tubes—the EL84s—but also the 12AX7s. So again, we ended up with a product that is as close to the original as we can get without resorting to incredibly expensive (and hard to source) new old stock tubes.

The HUB: VOX has touched on certain circuit permutations in the past. Obviously, you can’t make a VOX AC30 without a Top Boost, but you had a different variation on the EF86 for your 50th anniversary hand-wireds. So, did you learn something new in that particular circuit? How do you approach it freshly but still deliver that vintage sound?

Dave Clarke: What we wanted to do was recreate as closely as possible what existed 60 years ago. For the 50th anniversary there was a different ethos—we wanted to have one amp with two unique things from the past. The AC15 and the AC30 for the 50th anniversary shared the same preamp sections, an EF86 channel and a Top Boost Channel; and obviously two different power stages reflecting the wattage differences. Comparatively, the 60th anniversary AC15 and AC30 are basically completely different beasts from each other. We wanted to bring those vintage amps into the modern age.

The HUB: Moving to some more modern designs, can you speak a little about the germination of the VOX MV50 series and Nutube.

Dave Clarke: Right. For anyone who doesn’t know what the MV50 is, it’s a tiny but mighty amp head. The key thing: it’s 50 watts. You’d never think that in a million years looking at it. That’s not 50 “BS” watts—they’re 50 proper watts! The other really crucial thing about the MV50 is that it's our first product with the Nutube in it. The Nutube was something that was designed by our extremely large-brained Japanese colleagues at Noritake Itron and it’s effectively the first innovation in vacuum-tube technology in probably the last 30 - 40 years. And it sounds incredible. There are some rumors going around that it’s not really a tube, it’s some gimmicky thing. But it is not. It is a vacuum valve.

The HUB: Do I remember reading that this was also Fumio Mieda’s brainchild?

Dave Clarke: Exactly. The biggest brain in the world.

The HUB: For context, he also designed the original Uni-Vibe and worked on the KORG MS-20, right? Those are some major innovations. Other than aesthetically, how does Nutube differ from standard tubes as guitarists know them?

Dave Clarke: The first thing guitarists will notice is that it doesn’t look like a tube. It’s not cylindrical like tubes of old. It looks more akin to an LCD display. The technology it’s based on is the VFD, which is a vacuum fluorescent display. They were used in industrial applications and things like ovens, microwaves, and clocks as display devices. Since they already had a vacuum, Mieda-san thought to himself, ‘Could this be repurposed as a direct-heating triode?

Five years and considerable sums of money and R&D later, what we’ve come up with is exactly that: It is a direct-heated triode that’s happy to run on low voltages without running in a starvation mode, and reliability is extremely good. For all intents and purposes, the Nutube has an infinite lifetime. Its mean time between failures is about 20,000 hours, which is probably going to outlive the product itself.

The process for making the Nutube is highly mechanized compared to tubes of old that involve a very hands-on process that’s also fairly grubby and dirty, and the cost is still high. Whereas with Nutube, the process is highly automated. You put raw materials in one end and out comes a completely working Nutube on the other side.

This is no technical exercise; one of the reasons we’ve produced Nutube is as a way of preserving tube power for future generations. Because who knows, vacuum tube production may not be viable any more. Or a government regulation comes along that says you can’t use a certain ingredient.

The HUB: Right, and at this point, vacuum tubes are only coming from two or three factories now.

Dave Clarke: That’s right. No matter what brand you buy, it came from one of three factories. You’re either in Russia, the former Yugoslavia, or China, and that’s pretty much it.

The HUB: And when you have limited sources, local conditions — political, economic, regulatory or otherwise—can have a major impact on the world of guitar amplification.

Getting back to the MV amps, they definitely look like VOX products. The VU meter is a nice touch, although it might aesthetically be more what bassists are used to than guitarists. Can you talk about the three models — MV50 AC, MV50 Clean, and MV50 Rock—and how you got to them.

Dave Clarke: The AC is voiced heavily on the AC30 obviously—our classic signature tone; the Clean is based on a very well known American amp that does clean very well [chuckles]. The Rock is based on another British brand that is also very famous.

The HUB: It’s pretty flexible, so it’s a little different from a standard tube amp in how you can set it up. Can you speak to that?

Dave Clarke: The thing is, the Nutube sits in the preamp—it’s a preamp tube. The power stage is 50 watts, but it’s Class D and it’s happy to work with a multitude of cabinets and impedances without the need of an output transformer like a standard tube amp. For maximum output, though, the MV50 needs to be run through a 4-ohm cabinet. If you’re running into a 16-ohm cabinet, you’re only getting 12-½ watts.

The HUB: That’s still not quiet by any stretch of the imagination...

Dave Clarke: It’s got an excellent emulated line out, so if you go into a desk or headphones, it sounds really good. And I want to be clear, it’s absolutely analog. The whole preamp — everything but the Class D is completely analog.

The HUB: The MV50s seem like strong gigging options. But if I’m a recording guitarist or a studio owner, I could see getting all three so you’re getting true amp sound rather than something that’s modeled in software. Which in itself is not bad, but it isn’t quite the same vibe.

Dave Clarke: We are seeing people buying one or two to have a couple different flavors. Another thing we’re seeing, especially with the Clean, is it’s ending up on pedalboards because it’s small enough to do that. A guitarist going into a rehearsal studio or whatever can just plug their pedalboard with the MV50 on it into the house cabinet and they’re ready to go.

The HUB: Speaking to that, do you see a future in which there is a more pedal-friendly layout?

Dave Clarke: Watch this space. [laughs]

The HUB: Fair enough! Let’s talk about the VX Series amps and the Adio—they’re both pretty recent arrivals in the VOX world.

Dave Clarke: The ethos we started from on the Adio was a guitar amp with tons of tweakability and tons of sounds. We then added Bluetooth, which adds connectivity to your cell phone, letting you deep-edit effects within the amplifier itself. So there’s tons of stuff you can do under the hood that you can’t do with its contemporaries. And the sound it produces is quite extraordinary for its size.

The HUB: So you can hook it up to an iPhone or an Android phone, and I assume to an iPad too?

Dave Clarke: Any iOS device running, I think, iOS 8 or higher. The Android version is a little trickier, but there’s a full list of compatible Android handsets.

The HUB: The Adio has four user programs — can you recall them from the app itself?

Dave Clarke: Yes. You can set the user programs from within the app then store them locally on the amp so they’ll always be there, even if the app isn’t loaded. You can also use them as a kind of a scratch pad so you can control it within the app.

The HUB: Historically, when you talk about these big programmable rigs, guitarists tend to have one modeling unit like as a ToneLab or the Kemper Profiling Amp—which is a little different from keyboardists. Keyboardists over the years have kind of gotten with the MainStage approach—they seem a little more accepting of apps. But for guitarists, especially playing a gig, if you have an iPad mounted on a mic stand and all the knobs are right there, that’s pretty convenient… It seems like we’re getting to the tipping point where apps and modeling products for gigging guitarists are a bit more socially acceptable, if that’s even the right term.

Dave Clarke: There is a sort of a paradigm shift there. Guitarists are being dragged kicking and screaming into the future. It’s quite interesting, and this time we’ve done it wirelessly. Another cool technology inside is our proprietary Acoustage, which is a virtual surround sound function. It makes everything sound enormous. And it not only works on the guitar effects, it works on the streaming Bluetooth audio.

The HUB: So, in addition to being a practice or gigging amp, it can also double as a home stereo?

Dave Clarke: Exactly. You can easily see it on a kitchen table or tucked away in a corner to play any media while letting you jam along if you want.

The HUB: And it doesn’t have an aesthetic that screams “guitar amp,” so it comfortably sits in the background. Let’s talk about the new VX amps.

Dave Clarke: What we wanted to do with the new VXs was to expand on the existing VX1 and VX2 and branch out beyond just guitarists. With Nutube we’re able to integrate tube tone without a reliability issue into products that wouldn’t otherwise have it. And the VXs are super-portable. The sound is amazing from such a tiny little thing. The VXI and VXII are modeling amplifiers, whereas the new VX50, VX Bass, VX Keyboard and VX Acoustic Guitar amps have all-analog preamp front ends. So everything other than the effects are analog.

The HUB: They all have that VOX look through and through, though I noticed you are using some slightly different logos. 

Looking at your range these days that includes the Custom and HandWired, which are both going strong, it seems that VOX is a lot more than just the AC15, AC30, and a wah pedal. With all these new products, where do you go from here?

Dave Clarke: It’s an interesting question. VOX has always been an innovator — all sorts of weird and wonderful inventions were created by Jennings Musical Instruments, the original company name. Things like the VOX Guitar Organ that Dick Denney made and demonstrated on American TV.

This legacy is something we’re very aware of today. So being paired up with KORG [Ed. Note: Korg is VOX’s parent company], who’s a technology company, we’re really able to balance those things. Though we’re always ready to drive forward, we’re also aware of our core heritage, which is our ACs. But we are very willing to push the boundaries and try new things.

The HUB: How about the new Continental Organ?

Dave Clarke:  It is a product that has been dormant since the mid-’60s, but it’s still strikes a chord with VOX fans. Plus, it’s got the Nutube technology as well as effects that hearken back to the guitar pedals of the era. Keyboards of the ‘60s and ‘70s didn’t have effects and people would throw on guitar pedals behind them. Bringing back the Continental seems to be a nice blending of the two. Suddenly VOX is not just a guitarist’s company, it’s a keyboard-friendly company again.

Back in the ‘60s we were always pushing the boundaries. We made guitars, keyboards, and PAs, and it’s nice to be expanding beyond what VOX has recently been known for.

Check out our VOX Continental overview.

The HUB: Well, you’re covering a lot of ground for every player out there. Thanks for taking the time to chat with us today, Dave!