Earthing centre tap

[pre65]

Hi-on my PT15 i need to earth the mains transformer centre tap (toroid) and just asking if this goes to the "star" earth of the amp or to the mains (chassis) earth ?

Also if i take the amp circuit earths to one point do i need to connect that point to chassis earth via an earth lift resistor ?

If so what value ?

I dont want hum problems.

[Nick]

There are many different answers, notmally you would take it to the star earth, but there is somethihng to be said for taking the smmothing caps directly back to the center tap, then creating a star earth from the -ve of the last cap in your supply. Then the circulating current from the earlier part of the supply is kept away from your signal ground.

As I have said before, star isn;t always the best, you need to learn to think about where current is flowing in the amp, and work it out. There isn't a one size fits all answer in these things.

Your metal parts should be directly to mains earth, then the signal ground can be lifted (if needed) with the resistor. But again, there is no one answer here.

I have never needed to use a earth lift, untill I built the monoblocks, then I needed one.

I must get some "prototyping is a good thing" t-shirts printed