KingTone’s The Duellist is currently Ariel Posen’s most-used pedal. One side of the dual drive (the Bluesbreaker voicing) is always on. But there’s another duality at play when Posen plugs in—the balance between songwriter and guitarist.
“These days, I like listening to songs and the story and the total package,” Posen told PG back in 2019, when talking about his solo debut, How Long, after departing from his sideman slot for the Bros. Landreth. “Obviously, I’m known as a guitar player, but my music and the music I write is not guitar music. It’s songs, and it goes back to the Beatles. I love songs, and I love story and melody and singing, and there was a lot of detail and attention put into the guitar sound and the playing and the parts—almost more than I’ve ever done.”
And in 2021, he found himself equally expressing his yin-and-yang artistry by releasing two albums that represented both sides of his musicality. First, Headway continued the sultry sizzle of songwriting featured on How Long. Then he surprised everyone, especially guitarists, by dropping Mile End, which is a 6-string buffet of solo dishes with nothing but Ariel and his instrument of choice.
But what should fans expect when they see him perform live? “I just trust my gut. I can reach more people by playing songs, and I get moved more by a story and lyrics and harmony, so that’s where I naturally go. The live show is a lot more guitar centric. If you want to hear me stretch out on some solos, come see a show. I want the record and the live show to be two separate things.”
The afternoon ahead of Posen’s headlining performance at Nashville’s Basement East, the guitar-playing musical force invited PG’s Chris Kies on stage for a robust chat about gear. The 30-minute conversation covers Posen’s potent pair of moody blue bombshells—a hollow, metal-bodied Mule Resophonic and a Fender Custom Shop Jazzmaster—and why any Two-Rock is his go-to amp. He also shares his reasoning behind avoiding effects loops and volume pedals.
Brought to you by D’Addario XPND Pedalboard.
Blue the Mule III
If you’ve spent any time with Ariel Posen’s first solo record, How Long, you know that the ripping, raunchy slide solo packed within “Get You Back” is an aural high mark. As explained in a 2019 PG interview, Posen’s pairing for that song were two cheapos: a $50 Teisco Del Rey into a Kay combo. However, when he took the pawnshop prize onstage, the magic was gone. “It wouldn’t stay in tune and wouldn’t stop feeding back—it was unbearable [laughs].”
Posen was familiar with Matt Eich of Mule Resophonic—who specializes in building metal-body resonators—so he approached the luthier to construct him a steel-bodied, Strat-style baritone. Eich was reluctant at first (he typically builds roundneck resos and T-style baritones), but after seeing a clip of Posen playing live, the partnership was started.
The above steel-bodied Strat-style guitar is Posen’s third custom 25"-scale baritone. (On Mule Resophonic’s website, it’s affectionately named the “Posencaster.”) The gold-foil-looking pickups are handwound by Eich, and are actually mini humbuckers. He employs a custom Stringjoy set (.017–.064 with a wound G) and typically tunes to B standard. The massive strings allow the shorter-scale baritone to maintain a regular-tension feel. And when he gigs, he tours light (usually with two guitars), so he’ll use a capo to morph into D or E standard.
Moody Blue
Another one that saw recording time for Headway and Mile End was the above Fender Custom Shop Masterbuilt ’60s Jazzmaster, made by Carlos Lopez. To make it work better for him, he had the treble-bleed circuit removed, so that when the guitar’s volume is lowered it actually gets warmer.
"Clean and Loud"
Last time we spoke with Posen, he plugged into a Two-Rock Classic Reverb Signature. It’s typically his live amp. However, since this winter’s U.S. run was a batch of fly dates, he packed light and rented backlines. Being in Music City, he didn’t need to go too deep into his phone’s contacts to find a guitar-playing friend that owned a Two-Rock. This Bloomfield Drive was loaned to Ariel by occasional PG contributor Corey Congilio. On the brand’s consistent tone monsters, Posen said, “To be honest, put a blindfold on me and make one of Two-Rock’s amps clean and loud—I don’t care what one it is.”
Stacked Speakers
The loaner vertical 2x12 cab was stocked with a pair of Two-Rock 12-65B speakers made by Warehouse Guitar Speakers.
Ariel Posen’s Pedalboard
There are a handful of carryovers from Ariel’s previous pedalboard that was featured in our 2021 tone talk: a TC Electronic PolyTune 3 Noir, a Morningstar MC3 MIDI Controller, an Eventide H9, a Mythos Pedals Argonaut Mini Octave Up, and a KingTone miniFUZZ Ge. His additions include a custom edition Keeley Hydra Stereo Reverb & Tremolo (featuring Headway artwork), an Old Blood Noise Endeavors Black Fountain oil can delay, Chase Bliss Audio Thermae Analog Delay and Pitch Shifter, and a KingTone The Duellist overdrive.
Another big piece of the tonal pie for Posen is his signature brass Rock Slide. He worked alongside Rock Slide’s Danny Songhurst to develop his namesake slide that features a round-tip end that helps Posen avoid dead spots or unwanted scratching. While he prefers polished brass, you can see above that it’s also available in a nickel-plated finish and an aged brass.
The Victorilux comes in the 3x10 configuration discussed by our columnist, plus 2x12 and 1x15 combos.
Victoria has had great success with their point-to-point-wired amps based on classic designs—with a twist. Their long customer list of influential musicians and weekend players proves they’ve done something right. Who doesn’t want a new, robust, high-quality amp that looks and sounds vintage?
My love of the Victorilux started in 2011, when I got to try one for the first time. It was my brother’s, and he showed me a long email thread with company founder Mark Baier discussing different speaker and tube options. I was impressed. My brother’s amp was a 3x10 combo loaded with Jensen P10R speakers. It had dual 6L6GC power tubes and a 230V power transformer. Other speaker configurations were also offered by the company including 2x10, 2x12, and 1x15. Today, Victoria offers Eminence speakers instead of Jensens, according to the company’s website. I really like Eminence Legend 1058 10s and Legend 1518 15s because of their full tone and ability to handle high power without losing touch-sensitivity.
I describe the Victorilux as a Fender-black-panel-style amp in a tweed enclosure with brown-panel charm.
I describe the Victorilux as a Fender-black-panel-style amp in a tweed enclosure with brown-panel charm. As with Fender tweed amps, the chassis is placed vertically in the cabinet, which is robustly constructed with finger-jointed solid pine. The speaker baffle board is Baltic plywood. The controls consist of two 1/4" inputs, volume, treble, mid, bass, reverb, and speed and intensity for the tremolo. With just a single channel, there are fewer things that can fail. The circuit component layout is tidy and takes no shortcuts, and everything is coupled and fitted tightly.
For me, the Victorilux was love at first sight. And that deepened when I heard it. I expected the amp to sound something like a Super Reverb: good and clean. But I was surprised by how fine it sounded at low volumes. It had a sparkling clean-yet-lush-and-warm voice even at the quietest bedroom levels. The EQ spectrum seemed wider than I was used to with older Fender amps—especially for the mid control. I have seen a few Victoriluxes without mid knobs, and I strongly recommend trying one with mid control, since that dial can change the amp’s character between a mid-based British voice and an American scooped tone. With the mid knob set high, the Victorilux starts breaking up surprisingly soon for a dual 6L6GC amp. Lowering the mids will take you back into Fender-black-panel land.
At that first meeting, I was quickly able to dial in a nice tone—as can be done with a vintage Fender. But when I turned up the volume, it didn’t sound Fender black-panel at all. The amp broke up earlier and was more aggressive, with more sag and compression—thanks to the Victorilux’s cathode bias design, which reduces clean headroom. I guess Baier was inspired by the early breakup characteristics of small Fender tweed amps when he chose cathode bias for the relatively high-powered Victorilux. Cathode bias is a less efficient power-amp design compared to fixed bias. All black-panel-era amps and the bigger tweed amps had fixed bias, to maximize clean headroom.
The original Jensen speakers in this amp have been replaced with a trio of Webers for a more powerful and chunky sound, with firm, well-defined bass response.
I also expected the reverb to be lush, but I particularly liked the smooth and gradual knob response. The tremolo could nicely sweep deep and slow or very fast. To summarize, I found the Victorilux to be a brilliantly designed amp that contains the best inspirations from Fender’s tweed and black-panel eras.
I later tried a set of Weber speakers in the amp: two alnico 10A150s in the bottom row and a 10A125 on top. That made it much more powerful and chunky, with firm, well-defined bass response. For those who play in power trios with a loud drummer, I recommend this speaker setup. You will fill the stage completely with massive guitar tone. Those are my favorite Webers, though the ceramic 10F150 or 10F125 will also do the job.
I hope my experience will encourage the vintage Fender fellowship to try out various amp brands. There are ambitious alternatives out there, and my experience with the Victorilux proves that classic tone can be crafted using well-built modern amps.
Kemper Profiler Stage, Nueral DSP Quad Cortex & Line 6 HX Stomp (clockwise from top)
That democratization of pro-level workflows has opened new and exciting paths for guitarists to explore. Barry O’ Neal, who is the chief puzzle solver for Xact Tone Solutions in Nashville, has built rigs for some of the biggest acts in the world, including Taylor Swift, Bon Iver, and Peter Frampton. “In the beginning, all gear was pro gear, to an extent,” he says. “There is a line of demarcation between pro-grade gear and consumer gear. And there used to be a lot clustered around that line. Now, they are all either way above or way below.”
At this point, the difference between modeling technology mainly has to do with features. Do you need more inputs and outputs? Is direct recording via USB a priority? Are there certain one-off effects or sounds you need on a gig? All the top-level units have a somewhat similar set of core features, but each one also branches off into more specialized realms. Let’s dig in and discuss choosing a modeler, break down some myths that surround these units, and help novice users get just a little bit more out of their chosen processor.
Which One is For You?
Kemper Profiler Stage
Ah, the eternal question—as a guitar journalist, this might be one of the most frequent questions I get asked. There are many ways to tackle this. One element of this puzzle that I’ll leave for others to debate is how these different units compare in terms of tone. From my perspective, you need to figure out what you’re missing in your current setup and how a digital rig would make your life easier. As we’ve seen in literally hundreds of Rig Rundowns over the years, these units have passed the test both onstage and in the studio. Even when you have Dumbles and vintage high-powered tweed Twins at your disposal, having a modeler in the rack can still be useful. (Hi, Keith Urban!) “Go online and watch videos on how you program and use the unit. If those don't make immediate and visceral sense to you, bail,” says O’Neal.
Fractal Audio FM9
I usually point people to two different camps: the all-in-one units (Line 6 Helix, Fractal Axe-Fx, Neural DSP Quad Cortex, Kemper, etc.) or the smaller stomp-sized boxes that have a narrower focus on amp, cab, and mic emulation (Strymon Iridium, Walrus ACS1, or the Boss IR-200). This is an important fork in the road because both types of units offer their own solutions. Plus, price can vary widely. Although there will be some overlap, this article will focus mostly on the all-in-one units. However, the stomp-sized amp emulators have their place. Simply place one at the end of your board for an easy analog-digital hybrid setup or keep one within arm’s reach in case a tube goes out on the gig.
Neural DSP Quad Cortex
One of the bigger conceptual things to think about when choosing a modeler is the difference between an open ecosystem and a closed one. The Line 6 Helix and Fractal Axe-Fx units (and their various spinoffs) are what I consider closed systems, because you can’t create an entirely new amp model within their space. (The Axe-Fx III has an incredibly powerful ToneMatch feature, but that’s more based on deep customization of a pre-existing amp.) Both offer regular firmware updates with new amps, cabs, effects, and features. On the other side of things, you have Kemper and Neural’s Quad Cortex, which allow you to “profile” or“capture” digital versions of your amps and effects. This is really the defining feature of these units. With a simple recording setup, you can get extremely accurate versions of your prized—and fragile—tube amp and leave the original at home. The one caveat is that the quality of the result is only as good as your engineering skills, which is why a cottage industry of purchasable, professionally made profiles has popped up.
Start With What You Know
A piece of advice that I always recommend to anyone getting into modeling is to create your own presets. Yeah, it might take more time than just tweaking a factory or purchased preset, but in the end, you will learn much more about the features of your unit, as well as how the various elements of your signal chain interact with each other. For example, let’s say you’re a country-rock player who prefers a Vox-style amp.
With a simple recording setup, you can get extremely accurate versions your prized—and fragile—tube amp and leave the original at home.
Put aside the bells and whistles for the moment and focus on how to create a good base tone. Carter suggests a similar route: “Start simple with just an amp and cab. Get used to the interface and GUI [graphical user interface]. If you’re a Bassman player, it doesn’t make sense to just jump in and start tweaking a Mesa/Boogie.” Depending on your modeler, the various parameters for amps and effects might be different—or nonexistent—but at least you will have a point of reference before jumping into the deep end with experimentation.
Once you have the basics down, a prime place to start branching out is in routing. Gone are the days of needing a huge amount of rack gear to experiment with pre- and post-effects, parallel solutions, and MIDI. With a virtual playground, you can emulate nearly any imaginable signal flow and even design some that would be impossible in the analog realm.
Fig. 1
Most of the digital “boards” that guitarist and PG contributor Joe Gore designs are subversive, inspiring, and far from the mainstream. (He offers 13 different meticulously crafted Helix presets through the Line 6 marketplace.) Gore’s presets taught me invaluable lessons about using expression pedals when I tried to reverse-engineer them. Each scene or snapshot change has up to 60 different parameter changes, which alone is quite the feat. I would highly recommend his Blood & Pasta and Psych presets—they are simply mind-blowingly creative. In Fig. 1 you can see an example of how extensive this can get. Don’t be afraid to push the limits and reverse-engineer something from a more complicated setup.
“This is really the first time in a while where you can have bar bands playing the exact same gear as stadium acts.” —Cooper Carter
If you’re at least considering a digital unit, you likely don’t get the cold sweats when you think about learning your way around various menus and options. Each of us has our own specific tolerance of those, but in my experience the better you learn the ins and outs of your gear, the better you will sound. Although these are very, very tech-heavy units, you can get incredible results with simple setups. Going “digital” isn’t an all-or-nothing proposal. If you really dig your amp or pedals you can easily integrate those with any digital modeler. Let’s look at a few options that allow you to hold on to a bit of the analog.
4 Cables or 7?
Fig. 2
The easiest way to combine digital control with analog pedals is to take advantage of the effects loop. Here’s a scenario: You want to use your modeler simply for effects alongside your trusty tube amp, but you don’t want to run everything in front. This is where the “4-Cable Method” comes in. In this arrangement, you’re able to run all your compression and drive pedals directly into the preamp and move all your modulation and time-based effects to after the preamp. In Fig. 2 you can see a diagram of how to hook everything up. Here are the steps:
- Arrange you signal chain in your modeler so that the effects loop insert is at the point where everything before it will go in front of your amp and everything after will go directly to the power amp.
- Connect your guitar to the input of your modeler (cable 1).
- Connect the effects send of your modeler to the input of your amp (cable 2).
- Connect the effects send of your amp to the effects return of your modeler (cable 3).
- Connect the output of your modeler to the effects return of your amp (cable 4).
This results in a hybrid setup that allows an incredible amount of flexibility with routing your digital effects within a traditional tube amp. (One tip: Check the global settings on your unit and make sure the effects loop is set to instrument level rather than line level.) Not sure if a certain effect works better before or after the preamp? Simply move them around in your modeler.
In Clip 1 you can hear what it sounds like with distortion, delay, and reverb running directly into the front of the amp.
And in Clip 2 I used the 4-cable method to clean things up.
Fig. 3
But what if you’re running a stereo rig? That’s where the 7-cable method comes in. There are a few more things you’ll need (other than cables) to pull this off. First, your modeler must have two effects loops and dual outputs. Let’s pretend that the 4-cable setup described above is for amp #1 via output 1 of your modeler (Fig. 3). Now, follow the steps below for the second amp:
- Connect effects send 2 from your modeler to the input of amp #2 (cable 5).
- Connect the effects send from amp #2 to effects return 2 of the modeler (cable 6).
- Connect the main right output of the modeler to the effects return of amp #2 (cable 7).
It always helps me to sketch out how I envision everything working before diving into editing a patch.
The signal flow in the modeler will also become a bit more complicated. It always helps me to sketch out how I envision everything working before diving into editing a patch. If you think of these two as simply two parallel signal paths that come from a single source, it helps to keep everything straight.
Monitor This!
Fig. 4
On major tours, there’s an army of talented engineers that help craft the best sound possible, both onstage and out front. For most of us, that’s a real luxury. One routing setup that Carter suggests helps with both your monitor mix and getting a bit of that amp-in-the-room feel onstage. “The most practical application would be to run your fully processed signal to FOH and then a separate signal to a powered cabinet on stage,” he says. “From there, you can insert a split before the delay and reverb and feed that to your monitor or in-ears.” In Fig. 4 you can see an example of how to feed FOH, an onstage cabinet, and your in-ears. Tweaking the level of delay and reverb in your ears separately from FOH will allow you to better shape the reverb for the room without affecting what you’re hearing. “Whatever sounds best to you will make you play better,” says Carter.
Impulses Galore
One of the easiest ways to level up the realism of a preset is to use an impulse response (IR). This is where the all-in-one units and smaller stomp-sized modelers cross paths. Remember, the speaker and cab configuration in a traditional setup is basically an EQ—different cabinets and speakers treat the signal differently and therefore match better with certain amps and guitars. An impulse response is a digital version of everything after the amp, which would include the mic pre, mic, cab, and speaker. With a digital modeler, these would run in place of a cabinet block and before any time-based effects or reverbs.
Creating an impulse response isn’t too complicated. There is a wealth of tutorial videos on YouTube detailing the process, and some DAWs come with a built-in IR creator. In short, you sample ambient sound around a core tone and then the modeler uses that to treat your guitar tone.
In Clip 3 you can hear a Vox-style amp with a closed 2x12 cab IR.
And in Clip 4 you can hear that exact same tone with a larger 4x12 cab IR.
There are a host of ways to use IRs in your signal chain, but often it can be a somewhat paralyzing notion to try and wade through dozens of options to find the right one. Most IR packs come with loads of different WAV files that that can be separated by either cab, mic, or, for acoustic settings, guitar type. One way to quickly parse through them would be to set up a simple template with your preferred signal chain and then insert a split after the amp block to two separate IR blocks. Then map those IR blocks to different footswitches. This allows you to A/B a pair of IRs without taking your hands off the guitar.
Acoustic amplification can be a tougher road. Brian Wahl and Bradford Mitchell are behind Worship Tutorials, a website that offers various presets and IRs for many types of modelers including Helix, Kemper, and Axe-Fx. A few years ago, Wahl purchased a few acoustic IRs but never really connected with them. So, he decided to make his own. “One of the big myths I see is that people think you need to get an IR pack that closely matches their guitar type. That’s not true,” he says. “It’s like thinking you can’t put Telecaster pickups in a different guitar,” adds Mitchell. The purpose of the IR is to help shape the tone of your instrument in ways that EQ can’t quite reach since there’s a bit of reverb and possibly delay packed into each one. Another myth that Wahl hears is that if you have a really good pickup system, you don’t need an IR. “My response to that is we’ve found that guitars with higher-end pickup systems actually benefit more by using an IR,” he says.
“One of the big myths I see is that people think you need to get an IR pack that closely matches their guitar type. That’s not true.” —Brian Wahl
The process for Wahl and Mitchell starts with making a high-quality recording of the miked acoustic. Then, they will match the recording across six different pickup systems and 10 different mic options. Once you factor in different sample rates and WAV lengths, the process can become quite intense. “When deciding which IR is for you, I typically recommend staring with a mic you’re familiar with and cycle through the different pickup options,” says Wahl. Trust your ears at this point in the process above all else. “Most of them actually might sound bad,” he adds, “but once the correct IR clicks, you’ll know it.”
Talking with Wahl and Mitchell inspired me to dig up a few acoustic IRs and test his theory. I plugged my Córdoba Acero straight into my HX Stomp and recorded into Logic Pro X via USB.
In Clip 5 you can hear my completely unaffected signal. The Acero’s pickup system combines a piezo and under-saddle mic, so I kept the blend at noon. It’s not a bad tone, but enough of the piezo quack is coming through to warrant a better solution.
For Clip 6 I loaded up an AKG C12 dreadnought IR. The result sounds better. There’s more air around the sound, but the high end is a bit thin.
Clip 7 is an IR from the same mic, but I chose a different pickup option. It’s not as good as Clip 6, but still has that ambience that I dig.
Finally, we have Clip 8, which is a combo of a piezo pickup and a Neumann U67-style microphone. It’s kind of gross and thin but could serve a purpose in the right mix. I think recording examples like this is essential to finding the right IR match. Taking an objective listen will help you decide between options that could be quite subtle.
State of Expression
One of the most fun—and interactive—parts of using a modeler is exploring the absolutely endless options that expression pedals can offer. In most units, nearly any parameter you can think of can be assigned to an expression pedal for real-time tweaking. One player who really opened my eyes to what’s possible with expression pedals is John Nathan Cordy, a British guitarist who specializes in jazz-fusion styles and has a YouTube channel that explores most of the modern modelers. One of his favorite expression pedal tricks was inspired by the ambient pads Eric Johnson would play on the intro to live versions of “Cliffs of Dover.”
Fig. 5 shows the diagram, but here’s how you set it up:
- Arrange a basic signal path and then add a parallel path.
- Place a digital delay on the parallel path. Digital works better because with analog emulations you can dip into self-oscillation, and we don’t want that.
- Within the delay, assign your expression pedal to the feedback control so that when the heel is down you’re at about 10 percent and toe down is 100 percent.
- Put a volume pedal block before the delay and assign the expression pedal so when the toe is down it mutes the input.
- Add reverb to taste after the delay.
- Connect the parallel path back to the main path after the amp and cab block.
I’d recommend saving this as a template and then experimenting with loopers, compression, multiple outputs, and more.
Next Steps
Ultimately, the better you know any piece of gear, the better it will sound. Once you find a modeler that you connect with, invest the time to learn and explore the features and effects that you can put into practice. Understand its strengths and weaknesses and make sure those align with the goals you have for your rig. And don’t be too bashful to ask questions online—each of these units has a robust community of users, which means there’s a ton of info out there. Chances are if you run into a roadblock, someone else has too.
Finally, do what inspires you. Don’t overthink things or get distracted from the big picture, which is to enjoy making music.
Once we plug in our guitars, all sorts of electrical processes happen as our signal makes its way from the input jack on through the unique set of electrical components that give each amp its signature sound and on through to the speaker. What goes on inside of our amp once we've plugged in our guitar? And what makes one amp louder than the next?
Although there's much, much more to cool amp tones than could possibly be discussed in an introductory piece like this, there are a lot of basics in common between the various brands and types of circuits, particularly with regard to how tubes (preamp and power), watt ratings, and speakers work. Because of this, we can learn a lot from a more specific example. To that end, let me tell you a little story about one of my favorite amps.
Dan Formosa found his 1960 Vox AC15's international voltage selector was incorrectly rated, and avoided overloading the amp's original tubes after doing an extensive online search and calculations.
I recently had a revelation about a beautiful, fawn-Tolex-covered, circa 1960 Vox AC15 that I bought from a dealer in the U.K. (full disclosure: many years ago) and finally got around to restoring. That meant replacing the electrolytic capacitors before daring to turn it on, since they have a life span. The AC15's international voltage selector on the far right of the control panel has settings for 115, 160, 205, 225 and 245 volts. I expected my U.S. wall voltage to be a few volts higher than its nominal 120, but still within reason for powering the amp at the 115 setting. However, the readings I got when checking the internal voltages were sky high. Its original Mullard EL84 power tubes were being overloaded at almost 17 watts, while 12 watts is the designated maximum and 14 watts would be pushing my luck. A few Variac voltage experiments over the next few days, along with some obsessively created Excel calculations and charts, verified that a wall voltage of 105 would be more appropriate. A week of deep Google searches and an eventual exclamation of "Thank you online discussion boards!" uncovered the problem. While there were no markings on my AC15's power transformer, chassis photos of two exact same amps and transformers showed the power transformer input terminals labeled as 105, 145 (not connected, like on mine), 160, 205 and 245. Despite the control panel's graphics, the amp never had a 115 volt option. That setting connects to the power transformer's 105 volt terminal. Furthermore, the 225 and 245 selections were both connected to the 245 terminal. Apparently when Vox printed that panel in 1960, they were just kidding.
My near-miss chance of seeing the power tubes glow like it's Christmas led me to think about the journey electrons take through an amp, combining forces emanating from your wall and your guitar to power the speaker. And what it means to overload a tube, as I came close to doing. Did you ever wonder why a single EL84 tube is rated at 12 watts, but powers a 5 watt amp? Or why two EL84s power a 15 watt amp? And why, when adding two more to the set, four will produce 30 watts? Let's explore watts and electrons, and investigate how exactly they travel in your amp, from power tube to speaker.
Identifying the limit of a tube or a speaker in watts means defining the maximum amount of energy per second it can safely handle.
Power In Vs. Power Out
When discussing power and watts, keep in mind that your tube amp isn't primarily functioning as a guitar amplifier. It's more of a space heater that produces sound. Here's a question that Steven Fryette, of Fryette Amplification and Sound City Amps, is frequently asked: "How is this a 30-watt amp when it says 100 watts on the back?" The short answer: An amplifier is filled with components that consume power that never gets to the speaker. Power transformers get warm, the pilot light and heating filaments within the tubes suck up a lot of juice—the preamp tubes and power tubes are approximately only 50 percent efficient— and there's heat being produced by the output transformer. Power-wise, the speaker operates mostly as a heat sink. A tube amp is therefore far less efficient than you might guess. More than 99 percent of the incoming power ends up as heat. Less than 1 percent exits as sound. To help understand how all that power turns into hardly any sound, we'll discuss EL84 tubes—although any power tube could serve as an example, since all are guided by the same physics.
At the center of the tube, preamp tubes included, is a cathode, a small tube that emits a cloud of electrons when heated. The plate—that's the gray or silver metal wall that you see when looking through the tube's glass—contains a high-voltage, electron-attracting DC charge. The signal from your pickups is sent to the preamp tube's grid, and eventually to the power tube's grid. The grid is a wrap of wires within the tube surrounding the cathode. The grid regulates the flow of electrons traveling from the cloud to the plate. In a class A or class AB amplifier (more on that to come), the grid allows electrons to flow even when at rest, or "idle," meaning electrons are on the move even with no guitar signal on the grid. Start to play and an increase and decrease of electron flow perfectly mirrors the guitar's signal. Electron flow is also known as current.
An RCA 6BQ5, aka EL84, tube consumes 12 watts, but like all power tubes it produces about half of that in power. The EL84 is a staple in the world of power tubes, typically associated with Vox and Marshall amps.
So, what's a watt? A watt is a rate of power—one joule per second, with a joule being a unit of energy—and can be calculated by multiplying volts times amps. Therefore, a watt is a measure of energy per second. Identifying the limit of a tube or a speaker in watts means defining the maximum amount of energy per second it can safely handle. Given the calculation for wattage (volts x amps = watts), you can see that increasing voltage, amps, or both will increase wattage.
Defining that power relationship one step further, what's an amp? It's short for "ampere" (not, in this case, "amplifier"). An amp holds the "per second" dimension of time seen in watts. In a classic plumbing analogy, volts are equivalent to water pressure, while amps measure the flow rate of that water. Too much of either will electrically flood your tube or speaker.
Water flow and pressure may not be a great analogy, because what really results when a tube or speaker becomes overloaded with watts is too much heat. But to complete the water analogy, resistance (or the related term "impedance" … we'll get to that, too) is like reducing the diameter of the water pipe. It's therefore fair to think of a tube as an electron pump, continually circulating electrons.
The Secret Life of Watts and Tubes
Electrons bombarding the plate too quickly will cause it to glow red and radically shorten the life of your tubes.
Receiving the up-and-down voltage waves of a guitar signal, the grid controls the flow of electrons, holding some back or unleashing them in accordance with whether you're delicately picking or bashing. The high level of positive, electron-attracting DC voltage on the screen grid and plate elements determines the amount of electrons pulled from the cathode. (Essentially determining how loud your amp gets.) Tubes, however, have limits, both on the rate at which the cathode can produce electrons and on the rate at which the plate will accept them.
Try to attract more electrons than the cathode can emit and you'll reach saturation. Flood the plate with too many electrons and you'll exceed its maximum dissipation level, overheating the tube. Set the grid's bias voltage too negative and you'll reach cutoff, a point where the negative swing of the guitar signal's sine wave will suddenly prevent any further electron flow from the cathode.
Picture your guitar's signal as a simple sine wave—a pure A440, for instance. Turning the volume up high can produce too much voltage swing on the tube's grid, and then on the plate, to be handled cleanly. The result you hear will be the sound of a sine wave being abruptly flattened at the high and low points of the wave. You may be perfectly happy with that level of distortion. But what if we overload a tube in a less friendly manner?
Class Acts
Amplifier circuits are designed to use tubes in different ways. The circuits we are primarily concerned with in tube amplifiers are class A and class AB. However understanding classes A and B helps to explain class AB, a hybrid of the two. So….
How Class A Circuits Catch a Wave
In a class A amp circuit, the power tube constantly carries the entire signal. So, a tube operating in a class A design is always conducting at maximum dissipation—full on—whether you're playing guitar or not.
Amplifiers with one power tube—single-ended amplifiers—operate in class A. That one power tube carries the entire 360-degree span of the sine wave, measured along a horizontal axis in degrees. The bias is set so that the amp idles along the vertical (Y-axis) center of the sine wave, evenly positioned between the peaks and valleys. That means the tube is always conducting at maximum dissipation—that it's always on full whether you're playing or not. When playing, the guitar signal creates peaks and valleys in the sine wave. Many, actually. The peak of the sine wave increases current flow; the valley of the wave reduces it.
This flow diagram shows how an EL84's power comes from electrons flowing from ground, through the tube, through the output transformer, and back to ground. It's a cycle.
An EL84 power tube can produce approximately 5 watts in a single-ended amp. Therefore, you would think two EL84 tubes would produce 10 watts. And that's true: Power tubes can be configured in parallel to double the output power. Consider, for instance a Gibson GA-9 amp, which puts two 6V6 tubes in parallel. It's done, but not often. Why? Because a class AB configuration can produce more than double the power output from two power tubes. But before we get to that….
Make Some Noise, Class B
In a class B amp, each tube carries exactly half of the signal. Because the transfer of the signal from one tube to the other is never perfect, it creates crossover distortion.
In a class B amp, two power tubes share the sine wave. One conducts the first 180 degrees of the wave, and the other conducts the second. It's a push-pull arrangement. Unlike in a class A amp, each tube is at work only half the time. This allows each tube to be pushed further, into higher amplification, during the time it's conducting. To take advantage of that rest time, voltages at the plates can be higher, as can the signals going into the power tubes' grids. If a single EL84 tube can deliver 5 watts in class A, it can deliver twice that in class B during its half of the sine wave. Two tubes, therefore, will deliver four times the power, in theory. In practice, it may be less. Another advantage of a class B circuit is that at idle, neither tube is conducting, so it's a very efficient configuration for power consumption and for tube life.
All of that would be great for a guitar amplifier if the transition from one tube to the other occurred instantaneously. It doesn't. As the sine wave moves from positive to negative and back to positive, there's a delay—a misalignment in the transition between the tubes. The delay creates crossover distortion. Steven Fryette's description: "Crossover distortion can create a fizzy sound in the amplifier, [because] one tube is turned off before the other is fully turned on." And that, in a nutshell, is why class B isn't a common option for guitar amps. Enter class AB.
Class AB—Double the Fun
A class AB circuit solves the crossover distortion problem by having two (or four) tubes overlap responsibilities. Each tube, or each pair of tubes, carries more than half of the 360-degree signal of the sine wave.
In a class AB circuit, two power tubes share the responsibility of conducting the sine wave, similar to class B, but with some overlap. The tubes are set up so that one starts conducting before the other finishes, so each tube conducts for more than 180 degrees of the sine wave. This eliminates issues with the transition from one tube to the other. While not as powerful or efficient as a class B circuit, it's close—and the reason two EL84 tubes can deliver 15 watts in class AB amplifiers.
But if one EL84 delivers 5 watts and two can boost that to 15 watts, why do four only deliver 30 watts? Because in an AB amplifier with four power tubes, the tubes work together in two pairs, with each set delivering exactly twice the power of one tube. In a Vox AC30, for example, each pair of parallel EL84s creates 10 watts. It then puts the pairs in class AB configuration, doubling the output of a two-power-tube-amplifier, like the Vox AC15, from 15 to 30 watts. The diagram here explains that in greater detail.
In a class AB circuit, each power tube get a chance to rest half the time an amp is operating. Because of that, power tubes can be pushed harder when they are conducting.
The Output Transformer Takes Sides
The output transformer converts high voltage and low current on the primary side—which is to say, the tube side—of the circuit to enough low voltage and high current on the secondary—or speaker—side to drive a speaker. An output transformer's primary side is rated in ohms, but ohms in impedance, not resistance. The difference is that impedance takes into account that an AC signal is involved, since resistance will vary significantly depending on the frequency. (Frequency is the number of oscillations per second in the AC signal.) The impedance determines the rate of flow of electrons, with higher impedance being more restrictive.
The Alliance: Speakers and Transformers
It's important to match a speaker's impedance rating with the output transformer, because, interestingly (and maybe somewhat surprising), the impedance on the primary side of the output transformer will change based on the impedance of the speaker you connect on the secondary side. If you connect a speaker rated at half the impedance—for example, put a 4-ohm speaker in place of an 8-ohm speaker—the impedance seen by the tubes will be cut in half. Twice the current will flow on both the tube side and the primary side. The 4-ohm speaker will be louder but can lead to trouble. Your power tubes or output transformer can overheat. It's not risky, however, to put a 16-ohm speaker in place of an 8-ohm speaker, although it won't sound as loud. In discussing this with John Paice at speaker manufacturer Celestion in Ipswich England, he had some simple advice: "Don't do it." Best practice is to match the speaker with the output transformer.
Doubling the wattage of a 15-watt amplifier will increase perceived loudness by 23 percent, not double it. And so, a 5-watt amp would sound 71 percent as loud as a 15-watt amp.
In terms of guitar amplification, we measure—and hear—power and loudness along a logarithmic curve. Doubling the wattage going into a speaker results in a 3 dB increase. At 3 dB more, we're not doubling loudness. It's approximately a 23 percent increase in volume. You can therefore expect a 30-watt amplifier to sound 23 percent louder than a 15 watt amplifier. And a 5-watt amplifier will be 71 percent as loud as a 15-watter.
If mixing speakers in a multi-speaker cabinet, be conscious of each speaker's impedance rating (they should match) and also of each speaker's sensitivity rating, found on its spec sheet. (Sensitivity is usually determined with a microphone connected to a sound level meter placed one meter in front of the speaker. The result is expressed in dB.) Advice from Celestion's Paice: "If mixing speakers, try to keep their sensitivity rating within 3 dB of each other, because any more than that will become noticeable. The more sensitive speaker will dominate the blend."
What’s with Speaker Wattage
A large speaker magnet does double-duty. It will hold the voice coil more firmly, producing more bass. It also acts as a larger heat sink. A Celestion G12M rated at 25 watts incorporates a 35-ounce magnet. A G12H at 30 watts incorporates a 50-ounce magnet. "A bigger lump of metal is better at dissipating heat, so you can put more power into it," explains Paice. In addition to heat, too much power into a speaker can potentially result in too much cone movement, damaging the cone and its surround, and possibly resulting in failure. Nonetheless, a 50- or 100-watt Marshall amp pushing a set of four Celestion 25-watt speakers is a classic sound, employed by Hendrix, Clapton, Page, Slash, and many other guitar heroes. Running multiple speakers in a cab reduces the punishment any single speaker must take. And, of course, using a high-power-rated speaker with a low-power amp can also net good sonic results. "Some people think that you have to put as much power into a speaker as it will take," says Paice, "but you can get lots of breakup with a high-power speaker using just a lunchbox-size amp."
Bactrian Amps, Anyone?
You may be thinking, okay, if doubling watts into a speaker doesn't double the loudness, I'll just use two amplifiers. No, no, no—the same principles apply. Since we hear logarithmically, two 15-watt amplifiers will give you the same output as a single 30-watt amplifier. It's an increase, but not double.
I like going back to the classic 1959 publication on sound and amplification, Basic Audio, Vol 1. by Norman H. Crowhurst. He shows an illustration of two crying babies in a twin stroller, comparing their loudness with one crying baby in a stroller. Two babies are louder, but not twice as loud. So while that physics phenomenon may not work to your advantage as a guitar player, think of how grateful you would be if you were the parent of twins.
Peeling the Onion
Let's take a deeper look inside tubes, output transformers, and speakers.
This diagram shows the ve components within an EL84 tube. Note the minute distance between the grid and cathode. That's the open range for negative-charged electrons.
Under the Glass
Ever wonder what's behind the glass of your amp's tubes? Well, there's a lot going on in your average pentode or triode—electrons charging around, hitting walls, held at bay. Let's examine an EL84, which is a pentode, as is an EL34 and many other power tubes. That means five elements are at work within the tube (not counting the filament, the heating element tucked inside the cathode). Schematic diagrams like the one below portray tubes as if the cathode is on one side of the glass and electrons flow in a straight line through the tube, with all elements evenly spaced.
In reality, the cathode sits vertically in the center of the tube, and its electrons flow outward. When the cathode is heated, a "space charge" of electrons—a cloud of negative-charged particles—form around it like swarming microscopic bees. Because opposites attract, they are instantly drawn to the high positive-DC voltage of the plate. But the grid stops them. The grid is a wrap of thin wires encircling the cathode that carry your guitar's signal. The grid's at-rest charge appears negative to the cathode, slowing the electron flow. There are two ways for the grid to assume that negative appearance, depending on an amplifier's design: Either the grid is connected to a small negative charge or the cathode has a small positive charge. Electrons don't care which method is used. Just ask 'em.
The cathode, grid, and plate are elements common to triodes (three-element preamp tubes, like a 12AX7) and pentodes. The two additional elements inside the pentode are the screen grid and the suppressor grid. Like the guitar-signal grid, they are wraps of thin wire with mostly open areas that allow flying electrons to reach the plate without being blocked. And like the plate, the screen grid carries a high electron-attracting DC voltage, but its voltage, unlike the plate, is consistent, whereas plate voltage will vary with the signal.
The suppressor grid, the outermost wrap of wire closest to the plate, is connected to the cathode and its job is to repel electrons, which hit the plate and bounce off. The suppressor grid sends them back to the plate to avoid power loss. Beam tetrode tubes like the 6V6, which have four elements, incorporate metal plates that serve a function similar to a pentode's suppressor grid, working to keep the electrons in place.
This illustration shows the three grids plus the cathode and plate in a typical pentode tube.
Are Your Tubes Biased?
Sure, you've heard the term bias, but what is it and what does it do for your amplifier? Bias refers to the amount of negative charge the cathode detects on the grid, and it is set to keep the electron flow in check at a happy, medium level. Too negative and not enough electrons will flow when you're playing, so your amp won't produce enough volume and will sound anemic. Too positive you'll be bombarding the plate with too many electrons and overheating it, producing a warm red glow that you don't ever want to see in a tube. At that point, its lifespan could be measured in minutes.
The wattage a tube's plate receives can be determined by multiplying the rate at which electrons flow from the cathode to the plate times the voltage at the plate. The former is measured in amps, and in a cathode-biased amplifier can be calculated by knowing the value of the resistor connected between the cathode and ground, and the voltage drop across the resistor (the "drop" is the voltage measured between one end of the resistor and the other). An EL84 is designed to receive up to 12 watts maximum, and this or just below becomes the target when adjusting the tube's bias. So there you go.
The Many Tasks of Output Transformers
In the main story, we talked about how the output transformer wrangles voltage and works to impede and control the flow of electrons toward the speaker. That's not all it does, but in the process of doing that, it also blocks high voltage DC from streaming through the circuit, which is why you won't get electrocuted touching your speaker connections.
On the primary, or tube, side, the output transformer's impedance rating should more or less match the required impedance for the power tube or tubes being used. That impedance is measured in ohms, on the order of 4,500 ohms for a single EL84 tube, and 8,000 for two in class AB. An output transformer designed for an impedance lower than what the tubes want will lead to too much current flow, overloading the transformer, the tubes, or both. And soon they're kaput.
High voltage on the power tubes' plates also comes from the output transformer, via the rectifier tube or circuit. And that DC voltage is regulated by a large filter capacitor to help smooth out any ripples in voltage.
Yes, Speakers Are Sensitive
There's a rating for how reactive a speaker is to a signal that's typically called sensitivity. Awwww…. A speaker's sensitivity is measured by sending a 1-watt, 1-kHz signal into the speaker and measuring the loudness at 1 meter away.
If 1 watt sounds low, remember that power efficiency of a speaker is also surprisingly low. Most of the power going into a speaker is dissipated as heat. According to Celestion's John Paige, 97 percent of input power becomes heat, and only 2 to 3 percent converts to sound. Years ago, regulations required that speaker voice coils include a fire retardant, because occasionally they'd ignite onstage.
Since speaker sensitivity varies, an easy way to increase or decrease the loudness of an amplifier is to simply change speakers. But here's a quick lesson in sound physics. We measure loudness in decibels, or dB, a unit of sound pressure level, or SPL. Similar to the way we rate the magnitude of earthquakes, decibels are based on a logarithmic scale. So, check out this chart. It illustrates the perceived loudness you might expect for speakers of varying decibels.
And remember, our ears work in a surprising way. To perceive sound as being twice as loud requires an increase of 10 times the sound pressure, or 10 dB. Therefore 70 dB will sound twice as loud as 60 dB, and 80 dB will sound four times as loud as 60 dB. For reference, casual conversation is around 60 dB and 120 dB is jackhammer painful.