Maxon TBO-9 True Tube Booster/Overdrive Guitar Effects Pedal

The Maxon TBO-9 True Tube Booster is well designed, well constructed, and sounds great in virtually all settings and applications… and carries a big price tag to go with its big sound. But if you like this model as much as we do, perhaps it’s better to pay a little more for a product of quality rather than sacrifice your tone in favor of something cheaper.

Category Value Rating
Features 20% 4 stars
Usability 25% 3.5 stars
Sound 25% 4 stars
Documentation & Support 10% 3 Stars
Price 20% 2 Stars
3.6 stars or better: Outstanding, WIHO Award
3 stars or better: Worth considering
2 stars or better: Suited to specific needs
1 star or less: Not recommended


The TBO-9 is an overdrive pedal with a US military spec miniature tube at its core. The pedal contains both the aforementioned tube section as well as a solid state section, and by way of “cascading,” both sections work together in similar fashion to many tube amps.

The unit contains four knobs (Drive, Boost, Level, and Tone), which at first appear to be standard fare, but they react differently and are more interactive than any other overdrive we have used.

As with other Maxon pedals, the TBO-9 also features true bypass operation.

The Maxon TBO-9 pedal's circuit features a clean blend function built into the Drive control. For example, at zero drive, the TBO-9 passes clean signal only along to the tone and amplifier stages of the pedal. However, this clean signal is fed from the tube section of the pedal, whose gain can be adjusted via the Boost control. As the Drive control is increased, the solid-state distortion circuit is blended with the tube-driven clean signal. In this manner a wide variety of clean boost, semi-clean, overdriven, and fully distorted tones can be achieved simply by manipulating the pedal's Drive and Boost controls.

The unit also comes packed with Maxon’s proprietary AC2009 DC Power Adapter, a necessity since AC battery operation isn’t possible.

While this may all sound a bit too complicated for the layperson, you don’t need a degree in electronics to operate this unit — just let your ears do the work.


And let our ears do the work is exactly what we did! Before we even knew the technical mumbo jumbo in regards to subminiature tubes, gain stages and all that jazz (or even reading the manual), we were able to instinctively twiddle a few knobs and get some great sounds.

Because of its complex circuitry and high power requirements the pedal requires a unique power supply in the form of Maxon’s AC2009, which ensures a consistent regulated high (and noise free) current. Conveniently, the AC2009 is included with the TBO-9, but it deserves repeating that this is the sole power supply and there is no battery operation.

We were able to use a standard Boss 9-Volt adapter successfully with the unit with no perceivable loss in sound or increase in the noise floor, so compatibility with popular pedalboard power supplies shouldn’t be a problem if your system meets the power requirements of the pedal (with a Voodoo Labs PP2+ we would suggest using one of the Line 6-compatible power jacks, but note that using non-Maxon power supplies may invalidate the pedal’s warranty. Check with the pedal’s distributor before experimenting).


Overdrive pedals are typically used as either the sole source of overdrive into an otherwise clean amp, or as a clean boost to push an amp that is already distorting or breaking up. For those not familiar with the term, clean boost simply means setting the gain of an overdrive pedal to zero and the level to maximum (tone control set to taste). The idea is to boost the signal into the amplifier cleanly and without coloration to push the front end of the amp a little harder.

If there is an amp that responds better to clean boosting than the 50 Watt Marshall JCM800, we certainly don’t know about it! So it was this amp we turned to when we tested the TBO-9’s clean boost capabilities. As expected, the unit worked as anticipated, slamming the front end of the amp and also providing a slight volume boost — perfect for making solos jump out of the mix.

We heard minimal coloration to our base tone and the pedal remained fairly transparent. While we preferred this transparency, some players prefer the “mid hump” that pedals like a classic TS-9 provide, so your mileage may vary. In clean boost mode we began to dial in the Drive and Boost controls and our JCM800 transformed from light Marshall crunch to a fire-breathing high gain monster! Even better, the sound remained hiss, hum and feedback free (despite all the gain) and the overall tone took on a spongy/saggy feel in a pleasing way.

Unlike some overdrive pedals (such as the Ibanez TS-9 or Boss SD-1) the Maxon doesn’t suck the bottom end out of the tone when engaged. In fact, by dialing in the Boost control we were able to fatten up our tone, especially nice when playing through one of our single-coil equipped Strats.

Next we moved over to a Rivera Hundred Duo Twelve and dialed in a clean Fender-style tone. The goal here was to see how well the TBO-9 behaves as a pure overdrive. With the Gain up full, the Boost and Tone at about noon and the Level set to unity, we were able to go from clean to mean effortlessly by engaging/disengaging the pedal. As a pure overdrive the TBO-9 produces an overdriven sound similar to that of a classic Tube Screamer, but embellished in the sense that we could not perceive any obvious frequency spikes (especially in the midrange), and the overall sound was much smoother and fatter.

Like all Maxon pedals, the TBO-9 features mechanical true bypass switching which ensures silent operation and zero “tone suck” when the unit is between your guitar and amplifier.

Documentation and Product Support

As mentioned earlier, this unit is truly plug and play – just let you ears be your guide. The instruction manual provides a basic overview of the knobs and switches as well as a few sample settings to get you started.


The Maxon TBO-9 (MSRP $350) sells for approximately $260, which is high by anyone’s standards. Is it worth every penny? Perhaps, but many may find the high price tag hard to justify when comparable products are available at lower prices from both popular brand name manufacturers as well as some other boutique builders.

As we also concluded in our review of Maxon's spectacular PAC-9 Pure Analog Chorus, the price tag is the only gripe we have with this otherwise excellent pedal.

Contact Information

Godlyke Distributing Inc.

Evaluation Short-List
  • Maxon TOD-9
  • Maxon ROD881 Real Tube Overdrive
  • Hughes and Kettner Tube Factor Overdrive/Distortion

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