DIY 12AU7 Tube Preamplifier Project DIY 12AU7 Tube Preamplifier. This is a high gain preamplifier that is suitable for use where a lot of gain is required - to drive a power amplifier that needs plenty of gain or perhaps for use with instruments, like a guitar or microphone. If you need less gain, take a look at the RCA 12AU7 / ECC82 Cathode Follower Tube Preamp Schematic which has a gain of about 8.Ecc82 · DIY Audio Projects 12AU7 (ECC82) Cathode Follower Tube Preamplifier Schematic 12AU7 (ECC82) Cathode Follower Tube Preamplifier Schematic. This schematic below is a simple two stage line-level preamplifier using a single 12AU7 (ECC82) tube per channel. The overall voltage gain of the circuit is about 8. The output stage of the circuit is a Cathode Follower and is suitable to drive a low impedance amplifier.