For guitarists venturing into the world of guitar synthesizers, the 13-pin GK interface can sometimes feel like a barrier. Many players wish to experiment with their existing guitars and effects through a GK-compatible device like the Roland GR-55 without the need for a permanently installed GK pickup. This article explores how to bridge this gap by creating a custom 1/4″ to 13-pin adapter cable, allowing you to connect your standard guitar directly to your GK synth.
Understanding the 13-Pin Connection and the Need for an Adapter
The 13-pin DIN connector is the standard interface for Roland’s GK guitar synths and compatible systems. It carries not only the individual string signals from a divided pickup but also control voltages for volume and other parameters. Pin #7 within this connector is specifically designated for the normal guitar signal input. While seemingly straightforward to connect a standard 1/4″ guitar output to this pin, there are crucial considerations that “tone purists” and all guitarists should understand.
The typical GK setup, using a GK-3 pickup, includes an internal op-amp buffer (IC4A in the schematic). This buffer conditions the normal guitar signal before it reaches Pin #7 of the 13-pin output jack. This buffering is important because the GR-55 and similar units expect a low impedance input signal on Pin #7.
Without this buffer, connecting a passive guitar directly can lead to signal loss and impedance mismatch. This is where understanding the nuances of creating a 1/4″ to 13-pin adapter becomes essential.
Crafting Your 1/4″ to 13-Pin Adapter Cable: The Basics
The fundamental concept of this adapter is to route the signal from a standard 1/4″ guitar cable to the appropriate pin on a 13-pin DIN connector. For the GR-55, Pin #7 is the target, as it corresponds to the “Normal Guitar signal input.”
To build a basic cable, you will need:
- A 1/4″ male plug (to connect to your guitar).
- A 13-pin DIN male plug (for the GK synth).
- Wire.
The wiring is relatively simple:
- Connect the Tip of the 1/4″ plug to Pin #7 of the 13-pin DIN plug.
- Connect the Sleeve (ground) of the 1/4″ plug to the Shell (ground) of the 13-pin DIN plug.
This basic connection will get your guitar signal into the GR-55. Locking 13-pin DIN male plugs are recommended for a secure connection.
Addressing Potential Issues: Impedance and Volume
While the basic cable provides a connection, several issues can arise, particularly for guitars with passive pickups like standard Stratocasters or Les Pauls.
Impedance Mismatch and the Need for a Buffer
The GR-55’s Pin #7 input is designed for a low impedance signal, expecting the presence of a buffer, typically found in the GK-3 pickup system. Guitars with active electronics or EMG pickups generally output a low impedance signal and may work adequately without additional buffering. However, passive pickups usually require a buffer to prevent signal degradation.
The solution is straightforward: use a buffer pedal in your signal chain before the adapter cable. Even a Boss effects pedal in bypass mode incorporates a buffer. This ensures your guitar signal maintains its strength and clarity when entering the GR-55.
Volume Level Discrepancies
Another common problem is volume inconsistencies. GK systems often rely on the “GK-VOL” control (or equivalent on other GK-compatible preamps) to manage input levels. Without this control signal, many GR-55 patches might produce little to no sound when using the 1/4″ to 13-pin adapter. Furthermore, a significant portion of GR-55 patches do not inherently utilize the normal guitar signal input. You’ll need to manually enable the normal guitar input on each patch you intend to use with your adapter.
The Workaround: Simulating the GK-VOL Control
To address the missing GK-VOL control, a clever workaround involves adding a voltage divider circuit directly within the 13-pin plug of your adapter cable. This circuit simulates a GK-3 GK-VOL control set to maximum (“10”), ensuring a usable input level for the GR-55.
This circuit uses:
- One 240 ohm resistor (243 1%)
- One 120 ohm resistor (121 1%)
These resistors are wired as a voltage divider to feed approximately +5VDC to Pin #8 (Synth Volume / GK Volume) of the 13-pin connector. This “tricks” the GR-55 into thinking a GK-VOL control is present and set to maximum volume.
Implementing this modification requires basic soldering skills and careful wiring within the 13-pin plug.
Alternatives and Considerations
While building a custom adapter is a viable solution, there are alternatives. Using a complete GK-3 system, even without mounting the pickup, offers a plug-and-play solution. You can connect your regular guitar to the 1/4″ input of the GK-3 control box and then use the GK output to connect to your GR-55. This approach retains the intended buffering and GK-VOL control functionality.
For bass guitars, a similar approach can be used. While a dedicated GK-3B bass pickup utilizes only the inner four poles for a 4-string bass, the principle of adapting a standard 1/4″ jack to a GK connection remains the same. A simplified schematic, as shown below, can be adapted for bass, potentially including a GK Volume control.
Conclusion
Creating a 1/4″ to 13-pin adapter cable opens up possibilities for guitarists to explore GK-compatible synthesizers with their existing instruments. While a basic cable is simple to construct, understanding and addressing impedance and volume issues is crucial for optimal performance. By incorporating a buffer in your signal chain and considering the GK-VOL simulation circuit, you can effectively use your standard guitar with a Roland GR-55 or similar GK synth, unlocking a world of sonic possibilities.
