Power Transformer Humming

[Matt Yarling]

How much humming noise from the BeePre power transformer is normal?  I have a pretty noisy 60-cycle hum emanating from the power transformer (sound from the unit itself, loud enough to be heard throughout the room) as well a similar hum within the sound output, loud enough to be heard over very soft passages in the music. 

Is it normal for there to be zero resistance between the chassis plate and the four bolts that hold the power transformer in place?  I'm not sure I understand the purpose of the shoulder washers where those bolts pass through the chassis plate; but if the object is to have the bolts that secure the power transformer insulated from the chassis plate, then maybe that's where the problem is.     

 

[Paul Birkeland]

Yes, the screws should show continuity to the chassis, but it's very important that the nylon shoulder washers and black shoulder washers are installed and keeping the screws from touching the chassis plate.  Without those, you could end up with a power transformer that hums. 

If that's not the issue, I would tighten down the transformer screws, as loose screws will also allow the PT to hum.