Different toroid trans mounting produce different sonic?

[cent88]

Naim and some other amps toroids are filled with black thingy(epoxy?) in the center core. is it better than the standard mounting(cover on top).

I felt there is some sonic difference between cover top mounting and without mounting(lye on table). without mounting sound more airy.

 

[AndrewT]

Must be the Helmholtz resonator affecting the airy sound !

 

[cent88]

or may be I need thicker silicon/rubber pad to isolate it?
I can feel the vibration when touching both left/right side of top cover.

 

[bobodioulasso]

Looks like you have a noisy transformer, or Dc is present at your mains.
Search for DC blocker.

 

[cent88]

@bobo
I'm using nuvotem talema toroid(non-isolated).
Theres a lot of noises in my mains, electrical/electronic stuff's trans will buzz especially the water heater is on.
I wonder that my neighbour grounded her neutral(illegal) will affected my mains or not.

 

[bobodioulasso]

I have many transformers but no Nuvotem, so i can't say.
Some are more or less noisy and some are silent.
If Dc is present on your mains it can make a transformer hum.
Look at:
http://www.diyaudio.com/forums/power-supplies/104626-dc-blocking-filter-mains-2.html
Also search into DIYAudio using "DC blocking" between brackets.

 

[cent88]

wow.. there are a lots of DC filter but which one is safe to use and effective?

can I simplify it by using X2 caps in series with both live and neutral?

 

[AndrewT]

can I simplify it by using X2 caps in series with both live and neutral?

No.
The 50Hz AC impedance of the caps must be very low in comparison to the effective impedance of the transformer.
This usually requires 5mF to 60mF of capacitance in the power line.
AND some form of diode protection to stop you blowing up the caps during high pulse start ups and/or system failure and/or shorting out the speaker terminals.