Milbert Amplifiers

The Most Musical Amplifiers. Made in USA since 1986.

EEs At Fender Put Guitar Amps To Work

EE Times magazine, 13Mar2000, cover photo, pp.155+

Jamming on guitars is a big part of the workday for engineers at Fender as they determine the best circuitry to provide the right blend of swirl, bounce and crash--the magic that makes Fender a big name in the guitar world. After these jam sessions, they start working with some of the newest DSP chips, blending them with the same technology that's made Fender amps collectible items for 50 years: vacuum tubes.

No one's keeping records, but engineers at Fender Musical Instruments Corp. (Scottsdale, Ariz.) think they're the world's largest users of vacuum tubes, which are made mostly in countries that used to be behind the Iron Curtain. Though Fender amps are using DSPs for more and more functions, semiconductors just can't do everything musicians want.

"Guitar amps use vacuum tubes in ways that are absolutely noticeable," said Dale Curtis, vice president of R&D at Fender. "It's more about how they distort than how the operate in a linear mode. The thing about vacuum tubes is the way they distort gradually, compressing at the top of the waveform. If you play quietly, there's less distortion; as you play louder, there's more distortion. This lets the guitar player be expressive without adjusting the knobs. Tubes give them an infinite palette of sound simply by playing harder or softer. DSPs can model 60 to 70 percent of what tubes do, but the other 30 percent is where the magic is."

In the music world, amplifiers are as cherished as guitars. And like guitars, old Fender amps often increase in value as they age, an odd twist in an era of throwaway electronics. Before long, Fender will unveil what its marketers and designers think will be a big success, one that uses extensive DSP technology to mimic around 100 classic amplifiers in a single one.

The DSPs will let guitarists quickly shift from the unique sounds of, say, a Bassman, a Vibroverb or even an amp from a competitor like Marshall. Vacuum tubes are still a mainstay of the design, but the DSPs are what let it do many different things in an instant.

"One challenge of the DSP amp is to make it really flexible," said Chuck Adams, senior project engineer. "I made an operating system for the DSP that in 30 milliseconds completely reconfigures the system. When the musician steps on the foot switch, it immediately does what it wants."

These musicians often perform in an atmosphere where focused thoughts and technological awareness aren't possible. That means that the user interface must cater to a musician's mind, not a computer user's.

"The user interface has to be very simple. First and foremost, this is a guitar amp," said Matt Wilkens, principle engineer. "We kept all the knobs that we've used for years and displays and switches are as simple as we can make them, with some ways that let you program the changes that you normally use."

Adams, who joined Fender about a year ago, got a quick indoctrination into the world of guitar amps. To make an amp that mimics the sound of lots of old amplifiers, the engineers had to listen to them. Though the designers say that watching musicians user their amps is "one of the funnest things you can do," listening to amps nonstop took some of the edge off that pleasure.

"We wanted to get the sound of the old vintage amps, so the three of us and some marketing guys went to New York City where we know a collector who has vintage Fender amps and other vintage amps, probably about 75 classic collector amps," Curtis said. "We spent two days in his building in Manhattan, playing amp after amp at incredibly excruciating volume. At the end, I thought I'd be happy if I never heard another amp in my life."

After that trip, the engineers went back to designing circuits, happy that it's only occasionally that someone starts jamming at his desk to see how a circuit tweak changes the sound of the amp. "Critical listening" is one of the job skills Curtis looks for in an engineer. And most of them play an instrument, even though some are like Curtis, who plays piano everyday but says "lousy" describes his skills on the guitars made by his company's sister division.

Surprisingly, he says that finding engineers with vacuum tube experience is not such an odd thing. Wilkens, who studied solid state at Cal Poly at San Luis Obispo, worked with tubes in his audio hobby. Adams spent years working with tubes in broadcast audio before joining Fender about a year ago, but he's finding some significant changes in the way they're used.

"It takes a while to figure out what this guitar stuff is about. They want to hear distortion in ways we'd never do in broadcast audio," Adams said. "At a macro level, things are very similar; they're very subjective. But on an actual level, they're very different."

So different that Fender's team has a whole lingo written to describe the amp's performance. In an actual dictionary for terms, newcomers on the design team can learn that "crash" is the way that harmonies of the string cause clipping as the tones go from one hard limit to another. "Swirl" is what lets a guitarist hit a note and then stand there for seconds until the tubes finish their job. The marketing team, which includes people who have toured with the Rolling Stones and others, plays a big part in helping the designers figure out what musicians want in an amp.

"We know what it means when they say 'strident' and we know their definition of 'bounce' is way different from what EEs think of when someone says bounce," Curtis said. But when they say something like, 'It needs more shoulder,' we come back and try to decide if they're pulling our leg or whether we need to figure out what shoulder means."

Sometimes, big-time celebrities stop by to see how a program is progressing and to get a chance to try out some of the classic gear that's kept in a sound room where people go for serious jamming. In some ways, the star who fills huge stadiums is just another customer for the amp. If engineers are busy, they won't even try to drop in and listen to the big name play.

"When they do go to the sound room, they need to take their ear plugs. That's particularly important when they test some of the amps designed for stadium performances."

"We are designing the 1,200 watt unit," Curtis said. The first time we tried it with four speakers, we hit one note and the acoustic tiles started snowing; flakes just vibrated off them." He added, "The light covers came loose and started swinging. All of us were covering our heads with our arms."

Altogether, there are about 30 engineers in R&D for amplifiers. They need a diverse set of skills. Ease of use is a critical element and the appearance and durability of the cases are also big selling points. But the electronic engineering side has changed significantly in a short time.

"Five years ago, the only person who knew anything about digital electronics and DSPs was me," Curtis said. "Now, about a third of the department is here for digital signal development."

But even with all the new technology, the engineers have one big concern.

"Ten years ago, I thought tubes would be unavailable," Wilkens said. "But then the [Berlin] wall came down and we found we could get them from countries that had been behind the Iron Curtain. Now, I think we'll be using tubes as long as we can find somebody to make them. The only way we'll stop using them is if we can't get enough any longer."

Fender 'religion' impacts designers' efforts

Fender is as much a religion as a brand name, said Dale Curtis, vice president of R&D at Fender. "Some musicians won't buy a Fender, and others won't buy anything else."

This fervor means that products have lifetimes measured in decades -- something that still amazes the engineers.

"We still sell the 1959 Bassman, the '65 Delux and Vintage Twins," Curtis said. "If we were Ford, we'd still make the Model T and build new cars with the very latest technology."

Having a company name that's legendary in an industry as large as modern music is something of a double-edged sword. Though many of the Fender amps last a long time, Curtis is always reminded that any missteps also live a long time. He knows exactly where to find the record of such a blunder in a book that highlighted Fender's first 50 years.

"There's one product description that asks, 'What was Fender thinking when they designed this?' I'm always hoping that no one will ever say anything like that about something that from this design team," Curtis said.

However, he's also aware that the foundations of the company are derived from something of a misstep. One of the products that made the Fender sound a maintstay in the development of rock and roll was the Bassman amplifier. It was developed by Leo Fender, who founded the company in 1945.

"After Leo designed the first electric bass, he needed a bass amp. So he designed the Bassman. It was a terrible bass amp, but it was a great guitar amp," Curtis said. "That started kind of a funny cycle. Fender designed the product that people used to make music, to make the sound. That caused people to buy the product that makes that sound. Then more people want to mimic that, so they buy more of our equipment. The reason that Stratocaster and Telecaster guitars are so popular is because rock and roll was made on them, and people want to copy that sound. The same is true for the amps." -- Terry Costlow

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Last modified 21 Mar 2023

Milbert Amplifiers, The Most Musical Amplifiers. Made in USA since 1986.
Milbert Amplifiers
The Most Musical Amplifiers
Made in USA since 1986

8051 Citation Drive #C
Gaithersburg, MD 20877 USA
phone 202-558-5502