I've just completed my first Ruby Amp on a perf board and it is working though it has a (very) audible hum. I built a first prototype on a breadboard and it was very clean so I know the circuit is a good one and it must be my first soldered up version that is the issue.

I presume that the hum is related to a poor ground somewhere, is that a reasonable assumption? Which is the more likely section to induce the hum, on the input side or the output side? Any suggestions on how best to debug the problem?

Other than the hum, the amp is working fine.

Hi,
I have just built my first Ruby and it works and sounds great! I am most definitely a newbie though and while I can follow directions and solder ok I really have no idea how to do any kind of circuit design.

I am looking for a mod to the power supply for the ruby. I would like to provide both a battery and a line power supply and have the battery automatically disconnected if the line supply is plugged in. So it would run off the battery supply normally until the line cord is plugged in which would switch the battery off and run off the line instead.

Does anyone have a simple circuit diagram that can accomplish this?