Micro Booster MK4 Onboard Guitar Preamp with Push-Push Switch-Pot

89,00 99,00 

Build to order, 2-4 workdays

SKU: uBST4 Category:

You can order this product in the USA from Gear Hero HQ.

The Micro Booster MK4 Onboard Guitar Preamp is designed to amplify the magnetic pickup signal and provide a selectable boost that can be quickly engaged for solo performances. The built-in two-band equalizer facilitates subtle tonal adjustments and offers a range of boost modes including Clean Flat Boost, Mid Boost, Treble Boost, Boosted V-Cut, among others, that can be tailored to suit specific preferences or practical requirements.


 Wiring Examples & FAQ
 Manual
 Demo Video | More
 9V battery not included.

The Boost Knob

From buffer level up to +16dB of clean boost with gentle Baxandall EQ and Push-Push True Bypass.

The BECOS Micro Booster MK4 Onboard Guitar Preamp can be easily installed in any guitar or bass to amplify the signal from passive magnetic pickups. It can be powered using a single 9V standard alkaline battery or two batteries connected in series for 18V increased headroom. The booster is activated when the instrument cable TS mono plug is inserted into the instrument output, and it has very low power consumption, allowing it to run for months. It is recommended to remove the instrument cable when not in use to conserve energy.

The Micro Booster MK4 utilizes high-performance monolithic amplifiers that deliver pristine audio quality with an exceptional frequency response and extremely low noise and distortion.

A tone correction stack adds flexibility for independent tonal adjustment of Lows and Highs, offering mild adjustability of +/-6dB at 70Hz and 3.5KHz and zero to +16dB variable general Gain. This allows for configurations such as Clean Flat Boost, Mid Boost, Treble Boost, Lows Boost, Boosted V-Cut, and more, without going to extremes. The boost is completely flat when the tone knobs are centered, and it acts as a silent high-quality buffer when the gain is set to zero.

The Micro Booster MK4 can be configured with a linear B500K switch-pot (used with humbuckers) or with a linear B250K switch-pot (used with single coils), which will be pre-soldered directly on the circuit board. The potentiometer side of the switch-pot only replaces a potentiometer in your instrument (volume or tone), while adding the convenience of a signal routing switch on top of it. The mechanical PUSH-PUSH switch side of the switch-pot routes the signal through the booster (switch UP) or sends it True Bypassed straight to the output (switch DOWN).

A board-only version is also available if you wish to add the Micro Booster MK4 alone, without replacing a potentiometer in your instrument. In such installations, a separate DPDT switch (not included) needs to be wired for signal routing.

An iron-made shielding covers the entire active circuitry to protect it against radiant electromagnetic interference.

Several shortcut points are added on the circuit board to eliminate the usage of some wires when reconnecting the replaced potentiometer. Insertion points are also available for a neat transfer of the guitar Tone Capacitor directly on the booster’s board if the booster is to be placed on top of a tone potentiometer.

The basic interconnecting wires, battery holder, battery clip, and a new TRS output connector are supplied along with the uBST4 board and the desired Push-Push switch-pot.

The Micro Booster MK4 is pin-compatible with MK3.

More info


 Wiring Examples & FAQ
 Manual
 Demo Video | More
 9V battery not included.

⚠️ Note! It is recommended that the installation be carried out by a qualified technician who has a good understanding of guitar electronics, wiring diagrams, and signal flow. The technician should also be capable of performing any necessary or desired modifications. Please note that we are unable to create custom wiring diagrams. We can only offer the most commonly used wiring examples from which you can derive a specific configuration. We strongly advise that you document and store the original wiring of your instrument for future reference. To guide your custom installation, we suggest creating a plan on paper. The installation process will require manual work and soldering, and may also involve woodworking. Adequate mechanical, electrical, and testing tools will be necessary.
Box Weight 0,2 kg
Box Dimensions 11 × 6,5 × 5,5 cm
Technical Specifications

Input impedance: >1MΩ
Output Impedance: ~100Ω
Power Voltage: 9V-18VDC
Recommended Battery: 9V Alkaline (not included)
Power-On Switch: The circuit is powered when the instrument cable's plug is inserted (take it off the instrument to preserve battery life)
Current Consumption: 1.7mAh @ 9VDC; 2mAh @ 18VDC
Frequency Response: 10Hz – 30KHz (flat)
Tone Stack: Center frequency 720Hz, Lows +/-6dB @ 70Hz, Highs +/-6dB @ 3.5KHz
THD: 0.02% 1.0 kHz, 0Bu in / +15dBu out, 600Ω Load, 18VDC power
Max Input Level: +15dBu
Max Output Level: +15dBu
PCB Circuit & Switch-Pot body, without trimmer knobs: 49.3mm (length), 31.6mm (depth), 27.7mm (height);
Push-Push Switch/Pot (the potentiometer is not part of booster's circuit)
Parts Supplied: 1 x Micro Booster MK4 board, 1 x 8-Wire Set 20 cm long, 1 x 10-Pin Header (unsoldered), 1 x Battery Holder, 1 x Battery Clip, 1 x TRS Output Connector, 1 x Push-Push Switch-Pot (optional; B500K linear pot for humbuckers or B250K linear pot for single coils)
Product Weight (without battery): 54 gr.
Packed Weight: 160 gr.

Build Option

500K Switch-Pot (push-push), 250K Switch-Pot (push-push), No Switch-Pot (board only)

Note! The product name, design, circuit, components, description, pictures, technical specifications, functionality, etc. may change anytime and without prior notice (Terms and Conditions). We advise you to check the manual (only available as a downloadable PDF above in this page) for details on the product's current features and functionality. If you spot errors, inconsistencies, or if you need more information or assistance, please contact us.

Frequently Asked Questions

The booster comes latest in the signal path, after the pickup's switch, so, yes, it works for all pickups in the instrument. The booster comes with its own output connector, and the whole ensemble simply replaces the existent output connector in your instrument. The potentiometer side of the switch-pot is not part of the booster circuit. It just replaces a pot in your guitar (volume or tone). As a result, that pot/knob also becomes a push-push switch. The booster board is just neatly attached neatly to the new switch-pot. The switch side of the switch-pot permanently routes the signal through the booster (switch UP) or is bypassed directly to the output of the instrument (switch DOWN). Please download and read the manual for relevant information and consult the wiring diagram examples available.

The potentiometer side of the switch-pot is NOT part of booster's circuit, and is meant to replace volume or tone potentiometer in your instrument for the convenience of having a switch and a potentiometer into one single physical device. So the potentiometer has to be rewired just as it used to be - passive. If it is the tone control that is put in place of, the tone capacitor has to be moved to the new pot as well. If it is the volume control that is to be replaced, you just have to rewire the new pot as it used to be. Booster's PCB is just attached to the switch-pot to pack everything in place. The switch side of the component routes signal through booster or true by-pass.

Here's what can help to contain the noise:

  • A proper shielding of the electronics cavity.
  • Connect all ground wires in a single point that makes contact with the shielding.
  • Reduce the length of every wire in the electronic cavity before the booster, because every wire is an antenna.
  • Stay away from the guitar amplifier and other electromagnetic sources such fluorescent lights or tv or power lines - they all radiate noise which is picked up by the pickups and the wires in the guitar, which amplified, will start to be heard. Also change the position of the guitar in relation to these sources, to hear the influence on noise. More noise will be heard when you don't touch the strings.
  • Single coils are notorious for being a bit noisier than humbuckers.

The booster is powered only when the instrument cable is inserted. Power consumption is very low, and a good alkaline battery can last for months. Most likely, the battery will have enough power for at least 300 hours of continuous usage, maybe more. The optimum battery voltage is above 7V. The booster can be powered with up to 18VDC by using two 9V batteries connected in series. When the battery voltage drops low enough the booster is likely to distort.

Yes. Installing it in a Gibson original or a Gibson-like guitar is the easiest installation because there is plenty of room in the electronic compartment. The Push-Push switch pot's shaft precise dimensions (9.8mm) allow for the easiest installation in place of bridge pickup controls (tone or volume), because they are placed on the edge side of the guitar, where the top wood is thinner. We did install it in place of neck pickup tone control though, where the body wood is a bit thicker (around 8 mm) and we had to remove some wood. Of course, every guitar is a bit different and the wood may be thicker or thinner from one instrument to another. We have a video installation of the Micro Booster MK3 in an original Gibson Standard Traditional guitar on our You Tube channel which you can check-up.

Probably not, if the switch-pot is soldered on the board, or with difficulties due to the MK4's bigger size. The Telecaster electronics compartment is very narrow and the bottom between the potentiometer and the pickup switch may have to be routed so that the 9V battery can also be fitted inside. Some wood trimming might be needed as well just near the tone or volume control to make room for the booster's circuit. If needed, the booster knobs can be taken out through the metal plate of the controls, but because they are off-axis with the switch-pot, the holes will not be in line with the other holes in the plate. However, the booster can be added as board only and a separate DPDT mini switch could be wired to the board for by-pass function. Obviously, it can also be installed as an always on preamp.

Most likely, yes. There is usually enough room underneath the pickguard for the battery and booster's circuit. If needed, the booster knobs can be taken out through the plastic pickguard. Some wood trimming may be needed in some bodies if the booster is to be installed on the bridge/center tone pot. Please watch a video of the Micro Booster MK3 installation in a Fender guitar on our You Tube channel.

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