Re: loud humming in recordings

david wrote:

> is there something wrong with my mic-in socket?
> or something else in machine?

  It is possible but on THREE of the units?

Normally the sound you hear, Which is indeed called "HUM" indicates a 
bad ground.  I've had one MD that does it only on occasion and only when 
hooked to AC power (never on battery)

The bad ground may be on the jack to MD-Mother board or it may be in the 
mic cord

but you have tried different mics and different MD's which makes it 
likely it's a bad power supply