audio-talk

little mick wrote:Well shield the O/P transformers from the mains transformer i.e. with an insulation plate (metal)

yes that was the plan (my previous post i asked if alloy is ok and it is )
tha next step is to put a fused iec socket in the rear so i can do away with the fuse halfway down the pcb, tidy the wiring and put in a proper bolted chassis earth . from this i was going to try a 100r earth lift resistor to the pcb . the heaters are centre tapped is that to chassis earth or litted earth

dave

With regard to a lift resistor (I can't remember the wiring) but you could end up with a potential on the ground plane this is connected directly to the output transformer and you headphones, I would say a definite no to that, what would be the purpose of it.

little mick wrote:With regard to a lift resistor (I can't remember the wiring) but you could end up with a potential on the ground plane this is connected directly to the output transformer and you headphones, I would say a definite no to that, what would be the purpose of it.

poss in this circuit not suitable. but in other power supplies (these are in valve power amps)i have 100r after the chassis earth with a small cap across it, to reduce noise this earth is then called earth bus ?

dave

Yes the chassis where your mains goes in should be connected to mains earth sure, otherwise your amplifier 0V can be connected to that point with a 100R earth lift.

[quote="Mike H"]Yes the chassis where your mains goes in should be connected to mains earth sure, otherwise your amplifier 0V can be connected to that point with a 100R earth lift.

thanks mike, so is heater center tap chassis or lifted earth

Lifted earth! You wanna null it relative to your circuit



 

thank you all for your help

dave