The Secrets Behind UAFX Guitar Amp Emulators

Learn how Universal Audio captures the world’s greatest guitar amps in a pedal.

Putting the sonic majesty of the world's greatest tube amps into a stompbox isn't easy, especially if you're striving to capture the elusive tonal magic that's not found in a schematic.

Universal Audio's Chief Scientist Dave Berners and Senior Product Designer James Santiago have made it their mission to not only emulate these landmark amps, but to go deeper, giving guitarists the exact tone and feel of vintage "golden unit" tube amps.

Here, they reveal what goes into developing UAFX amp emulators, and uncover what they do differently that makes these award-winning "amp-in-a-box" pedals sound so good.

 

Guitarists often say UAFX amp emulators sound and feel like a real miked up amp. How did you achieve this?

Dave Berners: James can set the amps, mics, and recording chain up so they sound true to the source right out of the gate. But to make these emulations exceptional, we look at more than the amp's schematic.

 

Can you explain?

Dave Berners: It's the way the amp's components interact that is key. For example, component tolerances vary, so two amps can sound subtly different just because the resistors or capacitors aren’t precisely the same.

Then there’s parasitic capacitance — the interactions created simply by components and wires being near each other. James helps us pinpoint these subtleties, and we add them into the emulations. It’s those tiny, schematic-defying details that set UAFX amp emulators apart.

 

A stripped, vintage Marshall 4x12 miked up with a vintage Neumann during the emulation of UAFX Lion '68 Super Lead Amp pedal.

 

James Santiago: Right. You’d think I could just give Dave a schematic and say, “Let’s go.” But it’s never that simple. Small details like whether a wire is cloth or shielded really affect tone. That’s the level of authenticity we aim for.

Dave Berners: We go to great lengths to do this work, but it takes a combination of people who are technically skilled, and who know what exactly needs to be captured.

 

“We’ve done the work to choose the right amp and mic up the cabinet so that you can just focus on playing and trust it’ll sound like a record.”

James Santiago, UA Sr. Product Designer

 

Can you detail how UA's Dynamic Speaker Modeling differs from more traditional modeling techniques like impulse responses?

Dave Berners: In a technical sense, an impulse response (IR) captures a system’s characteristics. It’s a quick disturbance — like a spike that helps us understand how linear systems behave. IRs are often used to model guitar cabs because they’re relatively linear.

But guitar amps themselves aren’t linear. They’re inherently nonlinear because they distort, and speakers add to this complexity. With our amp emulations, we go to extremes — capturing temperature, humidity, and other factors to reflect the real non-linearity of the amp.

 

The guts of a vintage 1955 tweed Fender Deluxe and an array of classic speaker swaps, set to be captured in painstaking detail.

 

James Santiago: The thing is, even the simplest amplifiers have infinite levels of variance. We’re measuring things as small as the different voltages coming out of the wall outlet and the effect that has on the output of the amp.

Even the infinite number of combinations between the guitar volume and how hard you’re playing. We take all of that into account when we develop these algorithms.

 

Watch James Santiago, Dweezil Zappa, Phil X, Angela Petrilli, and John Notto talk rock guitar tone and the inspiring range of sounds available in the UAFX Lion ’68 Super Lead Amp pedal.

 

How do you choose the “golden units” for UAFX amp emulators?

James Santiago: You’d think a “golden unit” would be a mint-condition, pristine piece of gear. But often, the amps with the most character aren’t in perfect shape. I’ve compared ten plexi Marshalls side-by-side, and each sounded different. Some looked amazing but sounded flat, others were battered but had magical tones.

 

Sometimes there is a "golden unit," and other times a single emulation can be an amalgam of killer sounding amps — a Marshall Super Lead and Super Tremolo wired up and ready.

 

And to go a bit deeper, I’ve always put together classic setups during development. For Tweed Deluxe tones, I had to nail the sound of a Gibson 335 with humbuckers straight into the amp cranked — essentially the Larry Carlton rig on those great Steely Dan records.

I also explored an old Korg SDD-3000 delay paired with an Edge model Stratocaster and the “scratchy side” of a Herdim guitar pick. The Korg’s unique buffer and the Herdim’s sharp attack make the AC30 compress perfectly without losing percussiveness.

 

“Modeling the environment is as important as modeling the amp itself.”

James Santiago, UA Sr. Product Designer

 

On the heavier end, we’ve tested modern high-output active pickups in my 7-string Jackson guitar for palm-muted chugging tones. I had to match the aggression in Knuckles and ANTI while ensuring the amp’s response was as accurate as what I hear from our pedals. I even flipped the process to see if the pedals replicated the quirks of real-world setups. Sometimes, the results reveal as much about the hardware as the software.

 

In your mind, what separates UAFX amp emulators from others on the market?

James Santiago: Our emulations are built for scalability, meaning other modelers capture a single snapshot of a tone, which works fine for some, but UAFX models scale with the player’s touch and style.

 

Rear panel of serial number S/LA 10343 — one of the legendary 100-watt Marshall Super Leads.

 

So if you’re looking for a tone that’s as dynamic as you are, that’s where UAFX comes in. Our goal is to create a piece of gear that players can trust to get their style and dynamics across to the listener.

Plus, it’s more important than ever to have album-quality sounds, whether you’re making a YouTube video or playing gigs on the weekend.  We want guitarists to plug into a UAFX amp emulator and trust that it's going to sound great, right from the get go.

 

“It’s the tiny, schematic-defying details that set UAFX amp emulators apart.”

Dave Berners, UA Chief Scientist

 

After all the time you've put into capturing these amps in a pedal, what are you most proud of?

Dave Berners: There are a million different nuances a guitarist can change with their playing and a tube amp will react in all kinds of amazingly musical ways. The fact that we’re able to capture that is really exciting.

I think that’s only possible with James and I working together, creating what’s happening in these circuits in a technical sense, but also at a sensory level. We’re all players on the algo team too, so it’s just as exciting for us! I think that’s really important — we know what it’s like to have a favorite amp and a favorite setting because we have those too.

 

Start to finish, how long does it take to emulate an amp for a UAFX pedal?

James Santiago: This is not an 8-hour day, 40-hour per week thing. Every waking moment goes into recreating this gear. It doesn’t happen in a week — or a month. In reality, there are countless hours, weekends, and overtime involved.

Usually, it takes a few months of research, then gathering and evaluating different units, listening and examining circuits with Dave, and diving deep into every detail.

The fun part? I can destroy something for hours, and Dave does the math to rebuild it. It’s a team effort through and through.

 

— UA Staff