another BeePre hum problem...

[Paul Birkeland]

Hmm, this is a pretty tough one.  Can you describe the nature of the hum from a cold start?  Is it there immediately, does it take a few minutes, an hour, etc?

[Mach2]

The hum starts immediately after I fire up the amp and is pretty consistent. I let the amp running for more than one hour today and it's not going anywhere.
I don't know how to describe it except that it's a generic low hum, and definitely not a ground loop.

[Mach2]

Looks like I have found out why my BeePre hums. I spent the last few days reheating random solder joints with no luck, but two days ago I stayed up very late and was surprised to find my BeePre quiet. I quickly measured all the voltages, and found out that the line voltage was at 230V at that time. The morning after the hums came back as usual, but again at yesterday night the line voltage jumped up to 230V again and makes the hum go away.

Note that when I say the hum "go away", it does not completely go away. However in order to hear it I have to stick my ear close to the speakers. The odd tube white noise is still there, but I supposed some burn in time may help.

I read a thread by another user here with the same hum problem with low 220v voltage, but he said 225V was his threshold so I thought at 227V that wouldn't be the case!

Now I only need to find a way to rise my line voltage up a few volts...