Preamp Deal of the Century

If it was me having a hum issue, I will find out first if it is electrical or mechanical. Electrical, well, try simple process of elimination. Mechanical, make sure the bolt that hold the toroid in the PSU is tight (can easily seen from the top of hte PSU).

Pardon me but I have a question to ask to those who understand the subject matter well than I can. Bear with me and I dont intend to insult anyone. How can the umbilical cord produce a hum? I thought it carries DC voltages only. Hum if electrical, is AC isn't it? Its an oscillation ain't it? On this regard, another question if you guys do not mind. Why would an umbilical cord make a difference with regards to shielding if it only carries DC? Not to mention that the first stage that the power after rectification (PSU unit) will encouner is the regulator (there is an specific tolerance range where the regulator if working properly will regulate the voltage +/- a certain criterion)on the main preamp box itself so that the length of the cord, if not excessively long, will not degrade/decrease the DC voltages to a significant amount for the application as it encounters environmental interferrence when travelling from the PSU to the main preamp box.

Using a decent power cord from wall to the PSU, I understand that there can be improvements because I am experiencing it. Vibration points, I understand as well and agree that it makes a difference. But a shielded umbilical cord that carries DC improves the preamp performance? In what way and how?

Please, forgive me, but I am not looking for an argument but an explanation only. I want to learn what I am not familiar with (no sarcasm whatsoever!).

Halogen lights[or their transformers?] in my house can cause hums.
Fortunately I only have them in an adjoining room and can turn them off.

Any number of experts wil tell you this should not happen but it does.

I once had a louder then normal hum coming from the power supply of my Chenin.I was letting things warm up ,came back into the room. The hum was loud enough that it caught my attention from across the room.First thing I checked was the power and umbilical cords,they were fine.I went about listening to music. I marked it up to fluxuating a.c., a dip in current coming into my house.We have moved since then and I have not experienced this loud hum again.

Another point I want to bring up regarding a.c. coming into your home.Residential and commercial construction through out North America in the past few years has been incredible. This has put a strain on the grid in some areas resulting in poor supply, inconsistent supply of a.c. to your home. Where we use to live tens of thousands of new homes have been built along with many commercial factorys and business.Moving to another area, far less population, I have noticed consistent performance with my system . Like your vehcile,if its getting proper air density /fuel mixture it will perform at its peak....

Here is a link with some more info on transformer hum induced by DC on your AC line.
http://www.diyaudio.com/forums/showthread/t-83784.html