Description: 1. Using 6J1 tube 2. The main filter is from 470UF/25V, and the coupling is 1UF. 3. The uses a % metal and a high-precision chip to ensure a good signal-noise ratio. 4. The adopts 1.6mm thick double-sided sheet, 2.0 copper thickness, and the whole process of tin-spraying ensures the good passing performance of large and small currents. 5. The input and output plated , which is very durable. 6. Bluetooth adopts QCC3003 Bluetooth 5.0 Tips: First, this machine is a pre, not a power , it must be used with a post- or active speaker. It is not allowed to directly connect passive speakers, speakers, headphones as a power ; can not be used. Second, the use of general audio cable or filtering may cause bottom noise current, it is recommended to use a good audio cable or . Third, please make sure that there is no problem with your own sound source. The pre itself has a pre function. If the sound source itself has noise, then the only amplify its noise. Please use a good sound source for testing. Fourth, check whether the tube is plugged in with the base. Please insert the tube and the base sure to insert the tube in case of power failure. Specification: Power: DC12V 2A (DC) Net weight: 0.55KG Size: Deep 157mm x Width 126mm x Height 44mm (without tube height) Package Includes: 1 preamp 2 x 6J1 tubes （not include ）