J-Core-4B is a 4 band active preamp with SIDE mounted jack
J-Core
The J-Core preamp takes our widely acclaimed Flexcore Onboard Bass Preamp to the next level—now in a hassle-free Jazz Bass plate drop-in design. No modifications, no soldering, just pure performance.
Powered by the incredibly flexible and supremely musical Mike Pope-designed preamp with either a 2-band or 4-band EQ, the J-Core puts tonal control at your fingertips. With internally selectable EQ points for each band and refined signal path enhancements, it’s designed to bring out the best in every note you play.
All this, plus a 9-volt battery, fits neatly into your existing Jazz Bass control cavity. Effortless design meets exceptional sound.
We’ve swapped out traditional jumper-style selectors inside the J-Core for intuitive rocker-style mini switches. These make it easier than ever to fine-tune the frequency centers of each of the 4 EQ bands, allowing you to customize the EQ to match your bass’s unique voice and your personal tonal preferences.
With selectable frequencies for bass – 46Hz or 90Hz, treble – 6kHz or 10kHz, low mid – 330Hz or 473Hz (4 band only), and high mid – 600Hz or 900kHz (4 band only), the J-Core offers precise control to shape your sound exactly how you like it. Additional switches allow for 0, +3, +6, or +8 dB of output gain.
A hallmark of a truly versatile Jazz Bass is its passive tone control. Some players prefer a subtle tone roll-off that preserves midrange presence, while others lean toward a darker, more classic passive tone. The J-Core comes stock with a .022 Cap and can be easily customized with an additional through-hole parallel capacitor.
For years, the Flexcore has set the benchmark for players seeking unparalleled fidelity, clarity, and warmth from their active instruments. Until now, however, it wasn’t available as a drop-in replacement for Jazz Basses.
With the J-Core, you can finally bring the renowned flexibility and performance of the Flexcore into the Fender universe— elevating your sound without changing what you love about your instrument.
FREQUENCY SPECIFICATIONS
Treble: +/- 15dB at 6kHz or 10kHz
Hi Mid: +/- 15dB at 600Hz or 900Hz
Lo Mid: +/- 12dB at 330Hz or 473Hz
Bass: +/- 12dB at 46Hz or 90Hz
All J-Core preamp kits include: Prewired output jack, battery connector clip, preinstalled on a jazz bass control plate. *Matte black knobs are optional
* The matte black knobs provided are manufactured in the USA by Kilo International, known for their exceptional quality and finish.
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"It's so crystal clear and punchy. It's the best sounding amplifier I've ever played through and that's no BS. It reminds me of being in a control room and hearing your bass through the Neve and some ATC300's. I'm stoked! It's great to have an amp that sounds like yourself, only a lot louder!"
Tim Landers
"I've been looking for a versatile amplifier that compliments the quality of my instruments and playing style. I love playing through my Trickfish rig! And as an added benefit, it's light‐weight and fits in the trunk of my car!"
Hussain Jiffry
"It’s everything I was looking for - warmth, balance, punch and power. The sensitivity or speed of the amp is amazing and the dynamic range is so musical… It was such a relief to just let go and play music without thinking about the amp. I love it!"
