Rebuilding my 2011 LM3886, question about grounding (or lack thereof...)

[lost eden]

Back in 2011 I successfully built myself a pair of LM3886 amplifiers using amp PCBs from Analog Metric & power supply boards made from perfboard/stripboard. I have been using this setup pretty much daily for 7+ years with zero issues. In fact not only do they sound great, but they quite possibly have the lowest amount of background hum/hiss/noise of any amplifier I have ever owned. The construction is very basic, as seen in this diagram which essentially shows every single wire, with nothing omitted for brevity.



I am about to embark upon a new project, where I will essentially rebuild this two-channel setup into a 3-channel 2.1 setup. Both of the current amp boards will be powered from one of the current transformer/power supply boards (for the L/R speakers), the now spare transformer/power supply board will be used to power a new 2x LM3886 (parallel) board (for the sub) & a new small transformer/power supply board will be added to power a new 2.1 crossover board.



I am aware that 76V is towards the high side for LM3886 (this was due to my inexperience, not realising that the transformers I bought were spec'd with 230V primaries while my AC usually runs 245-247V), but as the current two-channel setup has been running just fine like that since 2011 I don't intend to spend money on new transformers or regulators.

So my actual question is about grounding. Since completing the original two-channel setup, I have come across a vast number of very long Website articles, forum threads, etc. discussing different grounding techniques (star ground, bus ground, etc.). However my setup in its current two-channel state seems to ignore all of that. Taking into account the fact that it has been working flawlessly since 2011, what is wrong with the grounding of my current two-channel setup (both in terms of quality/performance & in terms of safety) that I should change for the new three-channel setup?

 

[aparatusonitus]

what is wrong with the grounding of my current two-channel setup (both in terms of quality/performance & in terms of safety) that I should change for the new three-channel setup?[/B]

Nothing...as long as you use separate power supply for each amplifier. The moment you connect two amplifiers to one power supply you will get ground loop problem(s). A quick and easy solution (without much digging on pcb) is to separate the signal ground from power ground on the pcb board of each left/right amplifier with 10 Ohm resistor. In any case, the best solution is to make a new power supply for the subwoofer channel (with proper VDC over LM3886 this time).

 

[lost eden]

So are the complex grounding techniques I see in so many LM3886 builds (like the attached pictures) only applicable for builds that run multiple separate amplifier boards from a single shared power supply?

If that is correct, I think I will wait for my new case to arrive & see if it is large enough to fit a third big transformer in the front for the sub amplifier... Because it seems like a much simpler, cleaner & more straight-forward approach to building? The total weight will be over 12kg but that doesn't concern me, as the current setup fills an entire 6U rack & this new build will be a single 2U case...

 

[scottjoplin]

It means you won't have any cross channel ground loops. There could be others, but they are simpler to remedy

 

[tomchr]

My take on the matter: LM3886 chip amp grounding.

Tom