Stepping up to a Classic

GUITAR TOOLBOX BASICS: The BK Butler 911 Tube Driver with Bias Mod


Have you ever had one of those guitar items that you always wanted to try but never seemed to get around to? The BK Butler 911 Tube Driver has been one of those items for me. This is a pedal that has been around for over thirty years and has become a long-standing favorite amongst some of the most elite players in the business for its smooth distortion and boost capabilities. During its long life the Tube Driver has appeared in many forms. Being hand-built for most of its life and priced accordingly, it was also one of the very first boutique pedals. I finally got around to trying one out and here is what I found:

This pedal has been around long enough to have accrued multiple pages worth of history so I'll condense it down for you. Surprisingly, the Tube Driver has experienced a bit of a nomadic life: Thanks a heapin’ helpin’ to Kit Rae for his excellent Tube Driver Page where you should go for far more in-depth info on the Driver's development and its various circuits over time. It is like sipping from a fire hose.


As stated before, the BK Butler Tube Driver is available once again directly from B.K. Butler. There are a couple of ways to get your grubby paws on one of these boxes: Firstly, you can go to BK Butler's website HERE and order one. He hand-builds each pedal to order so there can be a slight wait (one to two weeks is advertised). Secondly, you can go to BK Butler's eBay store where he sells his products. He has even been known to run an occasional sale on his eBay store with reduced prices and/or free shipping. Hmmm... Once again the pedals are made up to order so delivery times may vary. Whatever the case, the result will be that a package will arrive in the mail for you. That alone means you can take a short break from mailing yourself things just so you can get something in the mail... The pedal arrives in a USPS flat rate shipping box. Inside that box is Butler's signed shipping/storage box containing the pedal, instructions, and your invoice:

The Tube Driver pedal lives in a substantial, custom steel pedal housing with its power transformer mounted inside the front panel. It measures 7.25”L x 4”W x 3.5”D (with the bias mod knob) and weights 2.5 pounds. Frankly, it big, and is built like a tank. But when you think about it, the package needs to be as large as it is in order to give the tube enough air to cool. There are three ventilation slits midway along the right-hand side to aid the cooling as well. As a result, the pedal feels only a shade warmer than the ambient temperature. The tube itself is a "Ruby" branded tube. It is also worth mentioning that the Tube Driver requires its own 120 volt AC mains power. Those who prefer micro pedals may find the package a little too big for their liking and may want to run for a solid state pedal. There is a video below that points out that some of the tone of the pedal may be found in a solid state pedal but the playing feel of a tube overdrive just isn't available on a solid state unit. Solid state pedals simply don't compress the same way. That has been my experience as well.

On the Driver’s top panel there are five controls: Output Level, EQ Hi and Low, Tube Drive, and the effect in and out footswitch. All the pots have fine, soft detents as you rotate them. There are two LEDs on the top panel, a green one on the left that lights up when the pedal has power and a red one on the right that lights up when the Driver is engaged. On the back panel there are input and output jacks and a power cord trailing out through a strain relief. The optional bias adjustment mod adds a Bias knob on the back panel with a hand-lettered legend. BK typically sets these into the region where Eric Johnson sets them before shipping them out. On the bottom panel are your serial number, BK's electro-pencil engraved signature, and the four sturdy feet. The pedal has no power switch because Butler believes that it is fine to leave it idling and that it actually benefits from burning in. Sure enough, I began with mine the evening it arrive and it felt a bit bright and bratty but, whether because I learned how to use the pedal or because the tube began to burn in, within a few hours and days it smoothed out considerably and felt far more musical.

Photo Courtesy BK Butler Website

From the input, the signal goes through an opamp gain stage into a 12AX7 tube in “starved plate” configuration and thence into a passive, two-band EQ and buffer amp to the output. The hard clipping comes from the opamp and is then tamed by the tube. Interestingly, the EQ is set up so that its response is flat with both controls at the zero or hard left positions. From there, the controls boost their set frequencies as you raise the controls. As Charles Dickenson said in Stave One of A Christmas Carol,

”This must be distinctly understood, or nothing wonderful can come of the story I am going to relate.”

On my first encounter with a rather heavily road-worn example in a dealer's used section, I wrongly thought the pedal must have been trashed and out of spec because I started out with the EQ knobs in the center position and everything felt boomy and harsh. It didn't start feeling right until I turned the knobs over to the left-hand side. As it turns out, that is all part of the plan, so it is a good idea to start your adventures on a Driver with both of those little guys turned… um... far left. Hard to look at, counter-intuitive, but that's the way it works. Start there.

There are so many things you can do with this pedal. There are few tube amps in the world that don’t sound better with a clean boost out front. With the Tube Drive near the bottom of its range and the Output Level cranked up you can use it exactly that way. As you move up into the range of the "Tube Drive" control you can begin to use it as a tone shaper, a gain stage, and/or a third channel. As a tone shaper it can serve as a dose of "Marshall in a can" when you pair it with a clean Fender amp. I've always found the Mesa Boogie amps to have just a little more aggressive "grindy" sound to them than I liked when I've kicked them up to medium gain. Instead, using one Mesa channel as a clean sound and another as your crunch, you can kick in the Tube Driver over the crunch as your lead channel, making for a much smoother sound. As the gain goes up, so does the girth and complexity of the sound. When played through a clean, muscular amp with a pinch of bass rolled in on the pedal it can give you that 4x12 cab woof or thump sound as well. If you are going to be playing lead high on the upper strings it can fatten up the sound incredibly. It thickens the sound to a lovely "in your face" presence. Oh, my.

When run into a compressed, crunchy amp with some drive dialed up it rounds off the pick attack entirely and leaves you with a saturated, pillowy-smooth lead tone. I even found that a judicious application of the pedal smoothed and rounded out the Deluxe-based lead sound on my modeler. Didn't see that one coming but I'll be taking advantage of it in the studio. As I mentioned, the pedal offers a really nice pillowy sustain that is different from the feel of the solid-state pedals I've tried. It makes your guitar feel different - very much like it feels when played through a wound-out, loud tube amp. That playing feel is vital to me, something I've sought since I played with bands in the '70s and wound out my amp. Another application that I found really cool was placing it in front of a little 1963 Gretsch 6150T Compact Tremolo amp. With a pinch of Output Level and a tiny bit of Tube Drive, the classic little amp moved right into the lovely, nasty sound Joe Walsh used for the pretty James Gang's ballad, "Midnight Man." Also, see the mention of David Gilmour's song, "5 A.M." below for nearly-clean uses. The pedal can be used to thicken things in gain situations from low to high. So you see, this isn't a one trick pony.

Eric Johnson uses the 911 Tube Driver for his "violin tone" lead sound by running it into a driven Marshall Plexi. The result is that attack-less, smooth sweet sound such as you hear on "Cliffs of Dover."

David Gilmour sends the output of his Drivers into a clean-ish Hiwatt amp. He uses as many as three Tube Drivers on his boards to pull off the various levels of gain in the many lead sounds he generates live. He’ll use one for crunchy sounds and another one to create his lead sounds. Even the ostensibly clean lead sounds such as the lead part in "5 A.M.," played with a Les Paul featuring P-90 pickups, will often utilize a little pinch of Tube Driver to fatten them up. By combining the Driver with a Muff Fuzz he is able to generate several different tones from light drive to the crushed, sustained lead sound on Pink Floyd's “Sorrow.” He also uses the Tube Driver for his driven lap steel sounds such as we hear on the leads parts from “High Hopes.”

Billy Gibbons has used the Driver for years and has become known for giving away dozens of Butler and Real Tube units as gifts. Hilariously, back in the early '90s BK designed the black Real Tube unit using the chords from ZZ Top’s song, "Tush" to tune the EQ. A short while later Butler was astonished to receive a call from Billy after he tried the Real Tube in a guitar shop and fell in love with the sound of it. Billy's current stage rig includes a custom chrome-plated Driver.

Joe Satriani - Remember Surfing With the Alien? The Tube Driver was all over that album. I've always loved that lead sound on "Always With You, Always With Me." Got it.

As we all know by now, there is no perfect pedal. The Tube Driver wants to see relatively high input and output impedances so it won’t necessarily play fair with all you other toys. So far I've had good results with a buffered compressor plugged into the front end. If you are willing to take the time, the boys from That Pedal Show have put together an episode of their hilarious and entertaining show about tube preamp pedals. They spend a good percentage of their time focused on the Tube Driver and discuss it's glories and (few) vices in detail. This ends up being the most comprehensive demo of the pedal I've seen and quite entertaining. I don't think I could compete with it. Note their impression of Dean Markley’s Overlord Pedal (a knock-off of the Tube Driver):

Check out the middle of the screen

I haven't talked to BK about mods, but I would assume any damage caused by modification would void his three-year warranty. With that disclaimer, it is possible to substitute other tubes for the 12AX7 the Driver is delivered with. A 12AY7 will drop the gain by 55% and a 12AU7 can pull down the gain by nearly 80%. Both will also reduce the midrange and give the pedal a more vintage sound when the gain is backed off. Remember that much of the distortion is generated within the opamp chip. That chip is mounted on a socket so it is possible to experiment with others. Kit Rae reports smoother sound with a Burr Brown chip. You can look that up on his website, HERE.

I really shouldn't have waited so long to try out the Tube Driver. This is one of those definitive items that has a wonderful, unique character and offers many neat benefits when it is in your signal chain. Like many of the really useful tools out there there is a little bit of a learning curve but when you get over the hump the investment pays off smartly. Having tried several solid state drivers I can really feel the difference the tube stage makes... and I definitely prefer it. Now I'm wondering how I ever got alng without it.