Aguilar OBP-3TK Pre-amp/Rack Amplifier

The Aguilar OBP-3TK Onboard Bass Preamp Sculpt Your Tone From the Bass

The Aguilar OBP-3TK is a three-band boost and cut onboard preamp built for bassists who want dedicated EQ control without reaching for an outboard unit. Marketed by Aguilar as the most flexible onboard preamp design in their catalog, it gives you serious tone-shaping power directly on the instrument, with high headroom, low distortion, and the ability to reproduce the full dynamic range of your bass. With 18 dB of cut and boost at 40 Hz, 16 dB at a switchable 400 or 800 Hz midrange, and 16 dB of treble cut and boost at 6.5 kHz, the circuit covers the full musical spectrum of low-B rumble, midrange growl, and top-end definition. This model is the right choice for players who want to upgrade a stock instrument or build a custom bass that travels with stage-ready EQ.

Switchable Midrange Center and Dual-Voltage Headroom

What separates this preamp from simpler two-band onboard circuits is the third band and the way the midrange is wired. A black mini-toggle switch on the control plate lets you select between 400 Hz and 800 Hz as the midrange center frequency, so a player can dial in either a warmer vintage voicing or an aggressive, honky slap tone without re-soldering anything. The unit also runs from a single 9V battery or two 9V batteries wired for 18V operation, with the higher voltage giving noticeably more clean output when you push the attack hard at stage volume.

EQ Bands Tuned for the Way a Bass Sits in a Mix

The three center frequencies are chosen specifically for the way an electric bass behaves in a full band mix. The bass shelf at 40 Hz handles the foundation and sub-bass weight, the switchable 400 Hz / 800 Hz mid sits right in the growl and presence region of an electric bass, and the treble shelf around 6.5 kHz shapes pick attack and string detail without harshness.

• Bass Boost/Cut: 18 dB at 40 Hz
• Mid Boost/Cut: 16 dB at 400 Hz or 800 Hz selectable through the mini-toggle switch
• Players notice that the treble boost/cut at 6.5 kHz allows clear string attack shaping without unwanted harshness.

Separate Treble, Mid, and Bass Pots With Mini-Toggle Switch

The "TK" suffix refers to the kit configuration: three separate pots for Treble, Mid, and Bass, rather than a stacked pot layout, paired with a black mini-toggle switch for selecting the midrange center frequency. This control layout puts one knob per band on the bass face, which is faster to grab mid-song and easier to label on a control plate. Installation reviewers report Aguilar provides wiring diagrams for many different layouts, including combinations with master volume, blend pots, and passive tone switches.

• Kit Configuration: Separate Treble, Mid, and Bass pots
• Pot Value: 50 k_x001A__x001A__x001A__x001A__x001A__x001A_ confirmed by installation feedback
• Mid Frequency Switch: Two-position mini-toggle selects between 400 Hz and 800 Hz

9V or 18V Battery Operation With Higher Headroom at the Higher Voltage

The preamp is designed to run from a single 9V battery for a standard install, or from two 9V batteries wired in series for 18V operation. The higher supply voltage raises the internal headroom, so slap pops, aggressive fingerstyle transients, and pick attacks come through without running into distortion before the signal ever reaches your amp's input stage. Both Sweetwater's and Aguilar's official copy confirm the dual-voltage capability, and Thomann lists the dual-battery option for users who want the full headroom headroom.

• Operating Voltage: 9V (single battery) or 18V (two batteries)
• Circuit Design Goal: High headroom and low distortion across the full dynamic range of the instrument
• The preamp includes Aguilar-branded wiring diagrams which support a variety of control layouts.

Bassists Customizing Their Sound Directly Onboard

This model is aimed squarely at bassists who want full EQ control permanently installed in their instrument. Suitable for players upgrading the electronics in a Fender Jazz, Precision, or aftermarket body, luthiers building customs from the ground up, and gigging bassists who find themselves reaching for the EQ on their amp during every song. Endorsers using Aguilar onboard preamps include John Patitucci (Chick Corea), Adam Clayton (U2), and Paul Turner (Jamiroquai). Installation reviews describe the wiring as about a two-hour project for a careful novice, supported by Aguilar's own diagrams and the included toggle and pots.

Aguilar Amplification A Bass-Player-First Brand Since the OBP-3 Era

Aguilar Amplification was founded on a single premise: build pickups, preamps, amplifiers, and cabinets for bass players, by bass players. The OBP-3 platform has been on the market since the late 2000s, with Thomann listing availability back to August 2009, and it remains the company's most flexible onboard preamp design. Across all OBP-3 variants the TK, TK/PP, SK, and SK/PP the preamp circuit itself stays consistent; Aguilar stands behind every unit with a three-year limited warranty covering the original owner against defects in materials and workmanship.