Sound hole installation, no need drill hole, easy to install. The preamplifier is suitable for mounting on guitars with sound hole diameter during 95-110mm. Cork pad clamp design, no damage to paint of instrument. It is a pickup that can be operated on your mobile phone (download the free APP: Double+). It has various effects, including compress, reverberation, chorus and delay. It supports active recording, wireless output, BT audio, really a magical preamp. With wireless transmission mode, thus you can connect the amplifier through the wireless receiver. Comes with a wireless receiver for wireless output, you can connect guitar to amplifier without cable. Receiver with 1/4inch audio plug, it can be connected to AMP or audio controller. Support 2 different sets of BT transmissions at the same time. for DOUBLE G0 PRO LE for connect for APP, and it you want to input some or accompaniment via BT device, connect it to the for DOUBLE G0 PRO. With record and preserve music function, just connect your device with a suitable cable to the 3.5mm active recording output jack(4 channels). Both of preamp and receiver are powered by built-in polymer lithium battery. Battery is rechargeable, large capacity, and has stable performance. Equipped with a high quality pad, which is washable and reusable, convenient to use anywhere. APP: Double+ Battery: 2000mAh Colour:Black Material:ABS+PCB Package Contents: 1 x Guitar Preamplifier Kit(Due to different product batches, the appearance , which does not affect the use) Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.