Frequently Asked Questions

All the possible configurations are listed on the site with the layout builder. We cannot change a push/pull to a blend or tone knob, swap the treble and bass stacked positions, change the amount of boost or cut, etc.

Please contact your pickup manufacturer for wiring diagrams and/or wire color code charts. These diagrams will include all the information about the hot, ground, and coil tap to help you hook up your pickups to the correct terminals on the Flexcore.

If you still need help, contact us, but please provide us with a diagram. If you don’t have the diagram, here are a few links to help you find one.

Nordstrand Audio
Fralin Pickups

The single EQ pots and tops of the stacked pots are 6mm and the bottom of the EQ stacked pots are 8mm.

No, unfortunately we do not supply knobs with the preamps. We recommend checking out the selection from our friends at or your favorite music retailer.

The Flex Core preamp itself is solderless. Usually, there is no need to solder grounding wire to the pots or the circuit boards. In some cases, if the shielding in the bass or the connection from the bridge ground is causing a grounding issue, then you might need to add additional grounding. Most of the time, the only soldering that might be required is the lengthening of the battery wires to fit inside a battery cavity.

The Flex Core preamp ships with a battery connector that is for 2 x 9 volt batteries (18 volts) but will function perfectly as a single 9 volt system. To convert your 18 volt battery connector to 9 volts, simply take a small flathead screwdriver and gently lift the wire retainers to pull the left 3 wires from the connector clip. They should release easily and have a small metal insert attached to the end of the wire. Set aside the extra 9 volt battery clip. Take the single black wire from the remaining battery connector clip and insert it into the far left retainer.

Please download the manual here. The battery clip information is on page 11.

If your instrument does not have room for a toggle switch for active/passive modes or if you just don’t want the passive mode, add a jumper to the outer set of pin connectors for always active mode.

Note: This takes the place of a switch for active/passive operation.

Height x Width

Balance: 29mm x 31mm
EQ (bass or stacked treble/bass): 28mm x 25.6mm
Treble: 15.9mm x 12.4mm
Single midrange: 26.7mm x 17.7mm
Stacked midrange: 28mm x 19.9mm
Single volume or push/pull volume: 29.7mm x 21.1mm
Stacked volume/tone: 29.1mm x 18.4mm
Passive tone: 18mm x 13.2mm

Height x Width

Active/passive, coil tap, midrange selector: 14.2mm x 19.4mm
Standby (Kill): 15.8mm x 20.2mm

Flexcore Switch Types

The switches that we use for the Flexcore are DPDT ON-ON types with PC pin terminals. We do not stock 3 position ON-ON-ON switches for series/parallel/single coil or other coil tapping wiring.

Flexcore frequency selection

Add a jumper or jumpers to the pin connectors to drop the frequency. The treble and bass frequencies are changed on the EQ board with a single jumper. The midrange frequencies are changed with a pair of jumpers on the pin connectors as shown.

Note: This does not apply if you have a switch or switches added for mid frequency selection.

Treble: 6kHz (jumper on) or 10kHz
Hi Mid: 1kHz (jumpers on) or 1.8kHz
Lo Mid: 330Hz (jumpers on) or 473Hz
Bass: 46Hz (jumper on) or 90Hz

The Flexcore can have up to two midrange frequency selector switches. This means that each switch selects between a pair of frequencies for each midrange band. For example, if you install a selector switch on the low mid (even with a stacked midrange board), then you will be able to choose between the two low mid frequencies, 330Hz or 473Hz. The high mid will not change. Of course, adding a switch to the high mid then gives you the option to switch those frequencies, 1kHz or 1.8kHz.

Hi Mid: 1kHz or 1.8kHz
Lo Mid: 330Hz or 473Hz

If you do not want or have room for the external switches, the frequencies can be changed with jumpers. Please see the FREQUENCY SELECTION tab for this information.

The coil tap function on the Flex Core essentially switches on/off the coil tap pickup inputs of the green connector on the balancer board. It turns both the neck and bridge on and off together. If you are looking to have individual coil tap switches for each pickup or series/parallel/single coil switching, you will have to wire them before going into the pickup input terminals. The wiring can be done from the pickups, to the switch, and the output of the switches into the pickup input terminals. You would not use the internal Flex Core coil tap feature and just use the pickup hot and ground connections.

The Flexcore jack assemblies have had a couple different color wires for the ring connection to the jack. This diagram shows those color differences and the connection locations on either a standard jack or barrel jack.

Flexcore Jack Wiring Information

This page will be updated periodically. Please download the manual for detailed a explanation of all the components and their functions.