The Tech 21 Formula 21 is a tube bass preamp from Tech 21, the maker best known for the SansAmp line. It uses four 12AX7 tubes in all-tube circuitry, and it grew out of a simple question: Tech 21 founder Andrew Barta was curious how the company's SansAmp Bass Driver would sound if he made it with tubes. The result, Tech 21 says, is a product with an old-school analog, vintage sound that is unique on its own.12
It is sold under the company's Private Stock banner, and Tech 21 notes it is available direct from Tech 21 only.1
Where it came from
The Formula 21 is based on the circuit concept of the SansAmp Bass Driver, Tech 21's long-running bass preamp pedal. Andrew Barta created it because he wanted to hear that circuit realized with tubes, and the maker describes the outcome as a lightweight tube-driven pre-amp that leaves the player free to choose the power amp and wattage that best suits their rig.1 Vintage Guitar announced it as "Tech 21's Formula 21 tube bass preamp" in February 2013.2
Controls
The control set follows the SansAmp Bass Driver concept, but because the circuit is tube based, the three-band EQ uses passive controls that cut up to approximately 6dB rather than boosting.1
| Control | What it does |
|---|---|
| Three-band EQ | Passive controls, cutting up to approx. 6dB, following the SansAmp Bass Driver concept1 |
| Drive | Determines the amount of drive; gives a saturated pre-amp tube sound with warm distortion in higher settings1 |
| Character | Switchable proprietary formula filter that warms up the bass, giving more bottom and more top end; disengaged, a more neutral, "Jaco-style" sound1 |
| Presence | Listed among the controls by Vintage Guitar2 |
| Bright switch | Listed among the controls by Vintage Guitar2 |
The Character switch is the tone-shaping heart of the preamp. Engaged, it applies Tech 21's proprietary formula filter for a warmer sound with more bottom and more top end; disengaged, the preamp stays out of the way for a more neutral, "Jaco-style" voice.1
Inputs and outputs
The Formula 21 has a 1 megOhm input. Tech 21 notes that for active basses, you can compensate the sensitivity by decreasing the Drive setting to eliminate any unwanted extra signal.1
On the output side there is a 1/4-inch output, plus an XLR output that is switchable between line and instrument level so the preamp can run direct to a mixing console. A ground lift is included for dealing with ground loop hum.1 Vintage Guitar's announcement describes the same connections as "a 1-meg input, 1/4-inch output, and switchable XLR output."2
The XLR output is switchable between line and instrument level, which is what lets the Formula 21 go straight into a mixing console without a separate direct box.1
How it compares
The Formula 21 sits apart from Tech 21's SansAmp bass pedals, such as the SansAmp Bass Driver DI V2 or the dUg Pinnick, by being all tube rather than analog solid state. Its three-band EQ deliberately follows the Bass Driver concept, so players familiar with that pedal will recognize the layout, but with passive, cut-only tube controls in place of the Bass Driver's approach.1 For players after a SansAmp-style direct output in a pedal format, the SansAmp RBI rack unit and the SansAmp XB Driver are related options in the company's bass line.34
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Questions
How many tubes does the Tech 21 Formula 21 use?
The Formula 21 uses four 12AX7 tubes in an all-tube circuit. Tech 21 describes the tubes as low noise and hand selected, and the whole preamp section is tube driven rather than a hybrid design with a solid-state front end.
Does the Formula 21 have an XLR output?
Yes. The Formula 21 has an XLR output that is switchable between line and instrument level, so it can run direct to a mixing console. It also has a ground lift, which helps with hum when connecting to a PA or recording desk, alongside its 1/4-inch output.
What does the Character control do on the Formula 21?
The Character switch engages a proprietary formula filter that Tech 21 says warms up the bass, giving more bottom and more top end. Disengaged, you get a more neutral sound that the maker describes as Jaco-style, after the famously clean, mid-focused bass tone.
What is the Bright switch on the Formula 21?
The Bright switch is one of the Formula 21's controls, listed by Vintage Guitar alongside the three-band EQ, Presence, Drive and Character controls. Tech 21's own product page for the Private Stock Formula 21 does not give a separate description of what the switch does.
Sources (4)
- Private Stock, Tech 21 NYC, 2019-09-11
- Tech 21 Offers Formula 21 Bass Preamp, Deluxe Blonde Pedal, Vintage Guitar magazine, 2013-02-04
- XB DRIVER, Tech 21 NYC, 2024-11-15
- Gear News: Tech 21 Announces SansAmp RBI Makeover, Bass Musician Magazine, 2022-10-04
