NEVER, NEVER REMOVE THE GROUND PIN FROM ANY POWER CORD PLUG OR AUDIO GEAR.

Now, let’s have some rules and regulations about this issue first:

When two or more devices are connected to a common ground through different circuits, a ground loop can occur. Thus, a system grounded at two different points, with a potential difference between the two grounds can cause unwanted noise voltage in the circuit paths. Currents flow through these multiple paths and develop voltages which can cause damage, noise or hum in our audio system.
In simple terms the ground loop can be eliminated by converting the system to a single point ground eliminating the others ground paths.
Hence my last post.

Now, to accurately determine the correct solution of this problem you first have to find and isolate it. For example, if you simply start flailing away, swapping gear and cables and everything all at once, you may never know what actually caused the problem.

Start simple.

Ground loop problems involves taking things in order and checking a few basic things, common elements to see if the problem is simple, or complex. For example, if adjusting the volume on your amp does not alter the hum level – which I think is the case here - then the problem must be occurring after that point. It if occurred prior, then the amp would typically raise the overall level of noise. Make sense?

So the problem must be after the amplification stage of the amp. This amplifier seems to be very sensitive to DC output because it is DC-coupled.
Here’s some interesting specs – use your multimeter, but be careful electricity kills – from the Micromega Tempo2:

The huge toroidal transformer from your amp delivers 2x33V for the power stage and most of the auxiliary power supplies. It is followed by a recovery and filtering altogether rather crude (2x10000uF) with a voltage of + /-43V. Stage drivers BF869/870 receive a power supply voltage on the + /-60V . The op-amps are LM324 and the power transistors are TO3. Check for data sheets.
Carefully measure this values and in the meantime you can also visualize if some electronic components seems fine, caps ( look out for tantalum caps... ), resistors, transistors,diodes.

Hope this helps. Hum issues sometimes are hard to find and fix.

Thanks. I really appreciate your concern!
About the ground pin: I've looked for the ground loop everywhere in the system and found that the DAC delivers the ground through the line output to the amp. Another thing is that when the AC ground is unplugged the hum is less noticeable...

Believe me, I've tried a lot of ways to find the problem (of course step by step investigations). The most effective one has been the way to disconnect the amp from the power source and unplug RCA connectors. I really don't know why it helps (until next power off), may be some affected capacitor is discharging during this operation... who knows?

I had a chance to visualize components on both PCB's when I was looking for another problem. It was the sound disappearance on left channel. It took me about 3 months to figure out the problem and finally I've found the solution: the contacts of the output relays (Micromega uses atmospheric relays for speakers' protection) were corroded. A little cleaning of contacts fixed the problem...

Micromega Tempo is very (VERY) sophisticated unit! Probably too sophisticated for DIY projects. It requires special skills, equipment and a lot of luck

Also it's a good amp too.... with very pleasant sound (except for the noise )



I will try to measure some of the components....



Thanks again

Your welcome, amigo. Sometimes these hum problems can be frustrating….
One more thing, did you checked the shield on the Cable TV wire and the TV/Cable box (if you have cable, of course)? Try disconnect cable/coax and everything TV related.