Hey Gilbert! No worries i’ll lend a hand, but unfortunately I can’t provide full support for everyone who just builds from the free schematics. Ok so first problem, you don’t say how loud the 60hz hum is? Is it loud at zero volume or do you need to come up to 1/2 volume to hear it.
Ground topology is critical to a low noise pre or amp. Here are the basics.
Mains safety ground (green wire) from IEC – bolt directly to metal chassis ground point – nothing else.
Power supply ground returns to a star ground point separate from safety ground but close by. I like to take this return from the largest filter capacitor point. Important only one return from each power supply circuit – one.
All RCA, Preamp, Potentiometer ground returns to a star ground point as far away from power supply as practical. Important you must use isolated RCA jacks.
If you watch the build series, you’ll see all of this in practice on the Kit Build.
Now other common sources of hum can be the system grounds interacting – so all audio equipment should be plugged into ONE quality power bar – this will keep all system grounds at the same potential.
I’m presuming you don’t have a scope or I would give some general test procedures to help you isolate the problem.
Never give up, ground loops and related noise are very common in all beginner builds – which is one good reason to start with a Kit – it helps you get oriented to good layout topology, build methods and of course they work perfectly on start up – most of the time!
Good luck!
Cheers,
Jim
