amplifier hum

I am rather new to Audiogon. I am using a Sonographe SA 120 power amp and that I can hear it hum slightly. I was told that it is normal for amplifiers with large transformers to hum a bit. My concern is that if I listen closely to my speaker's woofer, I can also hear the hum coming out of its woofer and my tweeter makes a slight buzz too. The hum/buzz is reduced if I disconnect my pre-amp which is a McCormak micro line drive (used as a passive pre-amp.) My interconnect cables are quite short at less than 1 meter and I keep them away from power cords.

My amp uses a 2 prong power cord so I am thinking that it is not a ground problem. The amp requires 220 VAC so it is plugged in to a power conditioner which is in turn plugged to a 1000 watt step up transformer.

Is this hum/buzz coming through my speakers caused by RFI or is there something wrong with my amp?

To what extent will the step up transformer affect the sound quality? I don't listen to music that loud, up to 12 o'clock at the most in my volume pot so I'm thnking that my amp won't be needing that much current. I listen primarily to cd's and use a Rotel cd player connected to a basic MSB link Dac III.

I will highly appreciate your comments or suggestions.
I would wager its the transformer. Have you taken wire and grounded everthing to each other? And now I read your post again, why do you have a two prong post on a 220 amp? Did not come from Sonographe that way I am pretty sure. Run a ground wire from your amp to your 3 prong pre amp, thats gong to help some, but I still go back to the step up trasnsformer.
perhaps you should try isolating the problem systematically, beginning with the power amp. if you have another power amp handy, trying plugging it into your system and see. i had similar problems with my ARC gear...turned out to be an op-amp problem
good luck!
Thanks for your suggestions Jvia and Anne audiophile. My amplifier is an Asian version. I brought it with me when I came to Canada. That is why it requires 220 vac and has 2 prong power cord. My step up transformer, however, was purchased in Canada so it has a 3 prong power cord. I'll try adding a ground wire attached to the chasis and to a 3 prong power plug. My pre-amp uses a wall wart power supply and also has only 2 prong but I'll still try to experiment. It is only the link dac 3 that has a 3 prong plug.

I'll try to borrow an amplifier and see what happens. I'm also thinking of replacing the power cord with shielded ones like the Belden wires but I still have to look for them.

Do you have cable tv ? If so it might be your source. This problem can be easily remedied by using two adapters back to back (at the wall) the first 75ohm to 300 ohm and the other 300 ohm to 75.

You can purchase them at Radio Shack or a local home Depot for about $3 a piece.