Two LM3886 in parallel w balanced/unbalanced preamp

[pbilous]

Hello everyone!

I decided to move this project discussion into a separate thread.

LM3886 is a great amplifier chip that I knew about for a long time. And since I have some extra time right now, I decided to get back to it and finally build an amplifier. I have had four of those chips laying around since 2016.

The project has two boards: one for the preamp, and the second one is for an amplifier. Boards are designed to be used together.

What I think is so cool about this project:

For power amplifier board:
- Output power is 100W into 4 ohm and 60W into 8 ohm
- Can be powered with +-35V with the amp connected to the 4 ohm load
- Two chips are used in inverted mode
- DC servos to correct for any DC offset on the outputs

For preamp board:
- Preamp has two input levels: +4 dBu (XLR and TRS combo connector) and -10 dBV (RCA phono connector)
- Input sources can be switched with a push switch
- Instrumentation amplifier for balanced inputs
- Low noise buffer amplifier for unbalanced inputs
- Can be switched to +-17V or +-15V power via 3-pin header placed on the board
- LM317/LM337 regulated power source - can be powered with a wide variety of voltages (~18V - 40V)

 

[pbilous]

Here are attached updated schematics and PCB design for the preamp.

Gerber file is included for those interested.

 

[pbilous]

In this post attached are schematics and PCB design for the two amplifiers modules.

Gerber file is included for those interested.