Hi guys.

I own Micromega Tempo 2 integrated amplifier.
Which basically works fine, except of one thing, it outputs a background noise to the speakers.
The level of the noise doesn't change when I increase or decrease volume.
Connecting or disconnecting sources does not help. The ground seems to be OK....
Does anybody know what could be wrong?

Can you please be more specific? What kind of background noise? A high freq tone or a low freq noise?

Well. It sounds like AC noise. I will try to be more specific:

The tweeter produces: ZZZZZZZZZZZZZZZZZZ noise
Mid woofer: mmmmmmmmmmmmmmm noise
Bass woofers: eeeeeeeeeeeeeeeeeeeeee



Sorry, if it looks crazy

Did you switch the speakers to another amp?
How far are the speakers from the amp, tv or radio? Could be RFI/EMI interferencies.

http://en.wikipedia.org/wiki/Radio_frequency_interference

I tried this amp with different speakers (same result), also current speakers with another amp(no problem).
But when I plug in headphones no noise...
I don't have any equipment nearby.
Could it be the problem with main capacitors?

The speakers are 3-4 feet apart

The level of the noise doesn't change when I increase or decrease volume.

The main power supply capacitors would also afect the headphones output. Could be many things: a leak capacitor, a resistor, an op-amp, a bad output transistor, etc
Do you have any diy skills?

Headphones output goes via preamplifier...

Yes I have some DIY skills

.....which is fed by the power supply and the big filtering caps.

One more thing. Do you have a few more appliances or other electric equipment plugged in the same electric circuit? If so, unpugged everything else except the amp and see what happen.
Dimmers are inherently "noisy". The noise is not so much radiated into the room AFAIK but is sent along the wires to anything else plugged into the same circuit. So the simplest/cheapest solution is to plug your gear into a different circuit -- if you can find one in your room.

Also, do speaker cables lie along or near any mains cables?

Just for the info:
I unplugged the amp from the AC outlet, disconnected RCA connectors, connected
them back, plugged to AC again and the noise become slightly noticeable, almost disappears ... Then I tried to do this procedure again and the noise has come back...

One more thing... When I press on any button on the amp, the noise slightly changes..

maybe a bad interconnect?

Just a thought, unplug the unit again and rotate the plug. Newer electronics have one large spade so possible polarity issues are automatically addressed.

Definitly a ground loop issue.

There's something about it here in ST, look for Ground References, here:

http://www.sound-thinking.org/index.php?showtopic=583&st=30

I just opened the unit up....

For the info:
It looks like the control amp is fed through another chain of filtration, and has nothing to do with the big filtering caps...

I disconnected internal ground wire in the amp and all related equipment (CD transport and DAC)

(The amp was connected only to the speakers and AC outlet with no ground) The noise is still here. It means that the noise (perhaps ground loop noise) is somehow produced internally...

Correct me if I am wrong, you suggest to switch the neutral wire with the phase one for the test?

About my system:

Interconnects: "Opal" by Audioquest
Speaker cables: "Midnight II" by Audioquest
Speakes: Quinta and CALLAS by Opera
CD transport and DAC by Micromega...

I checked the AC connection to the toroidal transformer in the amp:
AC Neutral to transformer's Yellow --- what is yellow ?
AC Hot Line to transformer's Grey --- what is grey?

AC Ground to the amplifier's case (currently disconnected)