[Mondial]

Regarding the hum, you might check the chassis grounding for possible ground loop currents. You mentioned previously that you added an additional ground wire from the circuit board ground to the chassis. Try disconnecting the additional ground and see if it makes any difference in the hum.

If you have multiple connections from the circuit board ground to the chassis, there may be induced AC currents flowing through the ground wiring caused by the magnetic field generated by the power transformer. Ideally there should only be a single connection between chassis ground and circuit ground. Also make sure that the audio input jack grounds are isolated from chassis and only connected to the circuit board ground at the input circuit.