power tranny noise

alo
today when i switched on my g9,i noticed a noise coming from inside the box,and it comes from the power trannys(2).
ps:i also have this problem (noise) with my fetboy.
what is this?
the noise goes like this:rrrrrrrrrrrrr(don`t laugh at me).
best regards
pedro

There was a post about power supplies over in the Drawing Board forum. Gus and Brian Roth posted some interesting info about this very subject.
Often a mechanical noise is caused by the presence of DC on the primary. Let me see if I can remember why--if power supply filtration stage impedance is too low, you'll see a back-DC component on that primary. Gus mentioned his solution was to add a small value resistor (1 ohm or so) in series between the diodes and the first filtration cap.

Here's a link to that thread in case you want to read it:
http://www.groupdiy.com/index.php?topic=10552&highlight=roundtable

There can be DC on the mains supply also. In this case a mains filter can fix it - a big electrolytic with anti-parallel diodes is sometimes used (4700µF 10V and 1N5408s in the filters I have).

Best regards,

Mikkel C. Simonsen

You can get acoustical noise from a transformer without any d.c. as well---most all magnetic materials are magnetostrictive. It can't be wholly eliminated but reducing peak currents helps, as well as damping the vibrations of the laminations etc. with various sorts of impregnated goop.

I had this same problem with a small hammond power transformer in my mic pre. A friend suggested that I "pot" it in clear varathane. So I dopped the whole thing in a can of varathane, pulled it out and let it drip dry.........Worked great! Really reduced the hum.
Cheers,
Freddy :sam: