03-07-2016, 06:42 AM
I'm working the same issue in the workshop thread V4 Hum Balance. These amps seem to develop ground issues over time.
The preamp (most of the amp except the echo board) is grounded via the input jacks. In many cases these jacks don't pass the ground to the front panel well but test fine with an ohm meter. The echo board is grounded by the footswitch jack (questionable design) which sometimes has the same jack issue. I replace all three jacks and the associated shielded cables/resistors.
If the star washers on the jacks are corroded, get new ones at you home improvement store. There will likely still be other hum issues but this is a good start. Follow my other thread. I will update it as time permits.
The preamp (most of the amp except the echo board) is grounded via the input jacks. In many cases these jacks don't pass the ground to the front panel well but test fine with an ohm meter. The echo board is grounded by the footswitch jack (questionable design) which sometimes has the same jack issue. I replace all three jacks and the associated shielded cables/resistors.
If the star washers on the jacks are corroded, get new ones at you home improvement store. There will likely still be other hum issues but this is a good start. Follow my other thread. I will update it as time permits.