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OK - re-read the whole thread.
1) Are you still using any mods (like the zener) or is it all stock?
2) What is the exact problem? Does it start to motorboat after 30 seconds? Does this only occur in chassis?
3) You have the PCB grounded to the chassis. Have you tried connecting your safety ground also to the chassis?
4) Are your RCA input jacks always isolated from the chassis?

Shannon

separks wrote:OK - re-read the whole thread.
1) Are you still using any mods (like the zener) or is it all stock?

All Stock

separks wrote:2) What is the exact problem? Does it start to motorboat after 30 seconds?

Yes

separks wrote:Does this only occur in chassis?

Yes (the metal part of the chassis is the top plate, the rest is all wood)

separks wrote:3) You have the PCB grounded to the chassis.

Not anymore, something was touching the chassis so I've applied an electrical tape on the top plate surface where the PCB is sitting.

separks wrote:Have you tried connecting your safety ground also to the chassis?

No (the chassis is currently not connected to anything, e.g: earth)

separks wrote:4) Are your RCA input jacks always isolated from the chassis?

Yes mounted on the wooden frame

Three steps:

1) Connect safety ground to chassis. Power up in the current state and make sure everything is A-OK. Power down, unplug and give the caps 5 minutes to drain.
2) Connect one wire from J1-5 or J1-6 to chassis (board otherwise still isolated from chassis). Power up in the current state and make sure everything is A-OK. Power down, unplug and give the caps 5 minutes to drain.
3) Put board back in chassis. Make sure RCA jacks are isolated. Power up and make sure everything is A-OK.

If one of the steps fail (or gives results other than motor-boating in 30 secs) go ahead and stop and post. Thanks!

Shannon

Thanks a lot Shannon!! The motor-boating is gone!
Could you please explain the reason why? :)

Otherwise I'm getting a bit of static/cracles when I crank the volume up. Need to test a little bit more.

The biases are perfectly set to 350mV.

Cool!

cedricb wrote:Thanks a lot Shannon!! The motor-boating is gone!
Could you please explain the reason why? :)

The chassis plate was "floating around" at 50Hz. When your audio ground was connected to it, it caused issues with your power supply. I presume the toroid transformer might make this phenomenon more pronounced than a standard EI transformer.

Shannon

Thanks for the details.
Do you think I should use a cl60 between the PCB ground and the earth/chassis to act as a ground loop-breaker? (this was mention in one of Nelson Pass amp schematic)

cedricb wrote:Thanks for the details.
Do you think I should use a cl60 between the PCB ground and the earth/chassis to act as a ground loop-breaker? (this was mention in one of Nelson Pass amp schematic)

Not if you aren't having any issues.

Shannon