3e Audio amps very loud popping noises

[ozlegend]

Many thanks for all the info.
I have taken a lead to the -ve output of the SMPS from the earth ground that forms a star ground for the system. I hope you can see this in the attached photo. The SMPS has mains L-N-E inputs on the far left (that come from a fused switched mains socket at the bottom right) followed to the right by 3 -ve DC outputs connected in parallel and then 3 +ve 47V DC outputs. The star point I used is at the upper middle left connected by a tab underneath to the SMPS chassis that is itself connected to the main amp chassis. Apologies to anyone who is offended by the look of the amp and its connections but is difficult to pack 6-channels even into a 19" 3U case - and I am more interested in sonic beauty than visual beauty in this case! And of course safety.
It has now completely removed any hum, even when the output from the DEQX preamp/processor is at full volume - with no music playing! Note the the DEQX outputs I use are balanced (though it also has unbalanced ones) connected to the amp through good quality XLR cables - 6 of them for the 3-way active speakers.
I have therefore not connected the inputs ground (I suspect the DEQX connects its output ground to earth).
I think this now gives me confidence to reorder the stereo amp module from 3e Audio that they insisted I return under warranty.
Thanks again,
Rod

 

[ozlegend]

PS Forgot to mention that there are now no loud "bangs" when turning the PS on or off nor when changing music tracks - so it all seems due to an earthing/ground misunderstanding!

 

[charlielaub]

That's looking better, but I see a couple of possible improvements in terms of safety and WRT the star ground. The way I understand it (and code requires that) the mains earth connection should immediately be attached to the metal chassis right next to the mains inlet. The physical connection should be done using a machine screw and a toothed washer must be placed next to the chassis metal. Crimp wires that attach here to a ring terimal. The first wire next to the toothed washer is the mains earth, then the wire that leads off to the star ground point. Sorry if I was not clear about this before. The star ground point MUST NOT be attached to the metal case but should be insulated from it. All system grounds should connect to the star ground point (amp board grounds and PS ground).

Connecting the mains ground immediately to the chassis with a toothed washer to bite into the metal insures a low-impedance path to ground in case there is a short to the chassis metal and is typically recommended by your electrical code. The short length of wire between the chassis connection and the star ground (this wire can be thin) adds a slight bit of impedance between the star ground and the earth ground. Although it's not typically necessary, you can insert a "loop breaker" into this connection such as the one shown in this pic:

All of the connections between the star ground and internal circuitry should be low impedance to make sure they all connect to the ground potential located at the star point. You can twist all the wires together at the star ground point, solder them to make sure there is a good electrical connection, and then mount them to a plastic standoff or other insulator from the chassis metal.

One other comment: the wires connecting to your SMPS are a problem waiting to happen... you might consider terminating each wire with a forked crimp terminal and then screwing those down instead of the bare wires. One stray strand of wire can ruin your day by making an unintended connection between adjacent terminals.