Boredbrain Music's Injectr module is a game-changer for electric guitar and bass players who want to integrate their instruments into a modular synthesizer setup. It features a high-impedance input for electric instruments, an overdrive-capable preamp drive circuit with germanium diodes, an amp simulator with analog tone shaping controls, and a dedicated eurorack-level FX loop.
The INST IN input feeds into a variable gain circuit, which can produce tonal responses ranging from clean to heavily overdriven. The DRIVE parameter's smooth character is a result of a soft-clipping topology using a classic 4558 op-amp and four diodes, two silicon and two germanium. The LEVEL control trims the output of the preamp stage. A Red LED indicates that the signal is reaching the typical eurorack audio level of 10 Vpp, and it is recommended to adjust the LEVEL control so that the LED is illuminated with moderate to heavy playing.
The module also has an envelope follower circuit that produces a control voltage signal at the ENV output jack based upon the input's volume dynamics. The ENVELOPE parameter adjusts the sensitivity of the circuit, depending on how the instrument is being played. The response time can be set using the SLOW MED FAST switch and affects both the rise (attack) and fall (release). The GATE output jack provides a 0-5 V gate control signal derived from the envelope signal, which can be adjusted using the GATE parameter. The Amp Simulator circuit uses analog filters to provide a wide range of amplifier-like tones. The CHARACTER parameter can dramatically alter the sound, giving the user control over the middle “dip” frequency and bandwidth. The PRESENCE parameter adjusts the low-end response, and the BRIGHT switch enhances high frequencies, combining to provide a wide range of tones.
The module is equipped with a eurorack-level effects loop, which serves as an access point to process the signal after the Preamp/Drive circuit but before the Amp Simulator. The OUT jack provides a post-simulator eurorack-level audio signal, while the LINE OUT jack provides the same signal at line-level, suitable for sending the signal out to external gear, interfaces, and amplifiers.
Overall, the Injectr module is an excellent addition for guitarists who want to add their instrument's unique tonal characteristics to their eurorack rig. Its high-impedance input, overdrive-capable preamp, versatile amp simulator, and control voltage extractors provide a wide range of tones to explore and play with.
Example Usage
If you're new to using the Injectr module by Boredbrain Music, start by plugging in your electric guitar or bass to the high-impedance instrument input, INST IN. Use the DRIVE parameter to adjust the amount of overdrive, and adjust the LEVEL control to match the output level to the typical eurorack audio level of 10 Vpp. You can adjust the tonal response further with the Amp Simulator circuit, using the CHARACTER, PRESENCE and BRIGHT parameters. Experiment with the envelope follower and gate voltage extractors, adjusting the ENVELOPE, SLOW MED FAST, and GATE parameters, to add more expressiveness to your playing and generate control voltage signals to modulate your synthesizer modules.
An example of how to use the Boredbrain Music Injectr module to inject the sound of an electric guitar into a Eurorack system is to patch the INST IN to the output jack of the guitar, adjust the DRIVE and LEVEL parameters to achieve the desired preamp overdrive effect, and adjust the ENVELOPE and GATE parameters to extract CV signals based on the input volume dynamics. The Amp Simulator circuit can then be engaged to add an amplifier-like quality to the signal, while the FX Loop can be used to process the signal with external Eurorack modules. Finally, the audio signal can be output from the OUT jack for further processing or sent to external gear through the LINE OUT jack.
Further Thoughts
One way to use Boredbrain Music's Injectr module is to combine it with an eurorack sequencer to create dynamic guitar-inspired synth sequences. Start by patching the guitar into the INST IN jack and adjusting the DRIVE and LEVEL controls to get the desired amount of signal saturation and volume. Use the Amp Simulator circuit to shape the guitar's tone and the CV extractors to trigger other modules in the system, such as filters and envelopes, in sync with the guitar's dynamics. Then, use a sequencer to modulate different parameters of the Injectr module, such as the Drive and Amp Simulator parameters, to create evolving and harmonically rich synth sequences that respond to the guitar's input in real-time. With the Injectr module, eurorack users can explore the potential of combining electric guitar sounds and synthesis in a way that is both creative and intuitive.