This is an active bass electronics based on the old electronics known from the Wal Pro Bass II (five knobs), built in a modern modular form, but maintaining the classic sound. Preamp is analog design.
eBay
Bass Booster Clean Boost Preamp Bass Effect Pedal Clean Preamplifier High Quality Demonfx
Aliexpress UK
Fantastic condition Darkglass Tone Capsule, the highly regarded onboard preamp voiced with a unique mid-forward character — perfect for modern and aggressive bass tones. Included in the sale: • All original paperwork • Darkglass sticker and plectrum • Original packaging One of the best ways to upgrade your bass tone from the inside out.
eBay
MOSKY GAMMA PREAMP Electric Bass Guitar Preamp/Direct Box Highly Flexible Tone With a Headphone Out And Aux-In Based On Aguitar
Aliexpress UK
Preamp is analog design . Handmade, high quality, each preamp tested. Low noise op-amp on board. Low noise. High input impedance, suitable for electromagnetic transducers.
eBay
Demonfx SIM-AMP High Quality Simplifier Bass Station | Preamp Simulator, Power Amp SIM, Stereo Cab SIM & DI Out for Electric Bas
Aliexpress UK
Bass - +-12dB @70Hz. You'll need 3 50K Linear pots with centre detents to complete the install. Hi Mid - +-12dB @2.8kHz. Mid - +-12dB @500Hz.
eBay
mosky Beta Ultra Bass Preamplifier Preamp/ Distortion/6 Band EQ Effect Pedal for Electric Bass
Aliexpress UK
Preamp is analog design . Handmade, high quality, each preamp tested. Low noise op-amp on board. Low noise. Easy installation on guitar. High input impedance, suitable for electromagnetic transducers.
eBay
1set Bass Guitar Tone Control Wiring Harness Set for 4 Strings Electric Bass Pickup Active Preamp Circuit Installation
Aliexpress UK
Preamp is analog design on discrete components. Easy installation on guitar. Included: manual, battery connector, 6.3mm stereo jack (socket) . Small size. Low noise. Very high input impedance: 3.3Mohm (on request 10Mohm for piezo transducers).
eBay
SONICAKE B Factory Analog Bass Preamp, comp and Overdrive Guitar Bass Pedal QDS-05
Aliexpress UK
Fishman Presys 101, Fishman 101 Preamp, Fishman acoustic preamp no mic, piezo pickup acoustic guitar, Fishman EQ tuner preamp, onboard guitar preamp, acoustic guitar electronics, Fishman guitar pickup, under saddle piezo pickup, Presys EQ system, acoustic guitar tuner preamp, Fishman preamp tuner, Presys 101 pickup system, Fishman no mic preamp.
eBay
Mosky Gamma Classic Bass Preamp Effect Pedal 4-band EQ with treble, bass, low midrange, and high midrange controls
Aliexpress UK
Upgrade your acoustic guitar's sound with theFishman 101 Presys Piezo Pickup EQ Tuner Onboard Preamp. No Mic Design: Designed with apiezo-only pickup system, the Fishman 101 Presys is great for players who want to focus purely on the natural acoustic sound of their guitar without the need for a microphone.
eBay
SONICAKE B Factory QDS-05 Analog Bass Preamp Comp And Overdrive Guitar Pedal - Vintage Sound for Bassists
Aliexpress UK