LM3886 in parallel - balanced inputs - instrumentation amp idea

[pbilous]

Schematics was created by myself utilizing following resources:

1. article "The G Word" by Bruno Putzeys - link,
2. website - https://neurochrome.com/pages/output-power
3. forum post - https://www.diy-hifi-forum.eu/forum/showthread.php?10114-Balanced-Endstufen-mit-Chipamp
4. forum post - https://www.diyaudio.com/community/...ed-input-lm3886-design-and-pcb-layout.371161/
5. continuation of this thread - https://www.diyaudio.com/community/...llel-with-servo-circuit-build-attempt.383676/

Attached are schematics and gerbers for two boards:

1. Pre-amp
2. Main amp board

Pre-amp board has mounting space for Neutrik NCJ9FI-H combo XLR and TRS connectors. It also has power regulators that can be fed +/- 35V. The voltage is reduced to +/- 15V required for LM4562 chips. Two LM4562 act as buffers to impedance match input differential signal that is fed into the "+" and "-" inputs of the LM3886. Differential signal is protected from ground's dirty currents. Meaning there is no need to try and avoid creating ground loops. The PCB board was designed with signal and power ground plains separated just for the clarity. For those who want to connect both, there is a place for a header that will allow to connect two ground plains. Each chip has a space for its own two bypass ceramic capacitors. In addition there is a space for two bypass OS-CON Aluminum-Polymer Solid Capacitors.

Amp board has two LM3886 connected in parallel. Those chips act as a summing amplifier for two differential signals and as a result double the voltage fed into them. For example, if both input differential signals are 2 Vpk each, signal received by LM3886 will be 4 Vpk total. Using two LM3886 in parallel allows to share the current that is fed to the load, and so we can power both safely with 35V and load with 4 ohms speakers.

Circuit was developed and simulated using LTSpice simulator.

Any comments are welcome

 

[pbilous]

Following YouTube videos helped to understand the theory behind instrumentation amplifier:

• youtube video from TI -
• youtube video from TI -
• youtube video from TI -
• youtube video from TI -

 

[ByronInPortland]

Did you ever get these built? I'm curious about the results.

 

[pbilous]

Did you ever get these built? I'm curious about the results.

I ended up building something similar but different - https://www.diyaudio.com/community/...uit-build-attempt.383676/page-11#post-7218527

Here is more on the discussion of the above design-
https://www.diyaudio.com/community/...m3886-will-be-in-the-schematics-below.393125/