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PreFix with local TRs

P

Paul3

pfm Member
I've just fitted local TRs to my Prefix.
I have built a separate ps (not a HiCap) and attached the separate earth wire to the case of this, which is earthed to mains. There is mains hum generally, which gets much worse when I turn on the TV.

I have no earth on my preamp, a B4 yet. The case is not earthed.

The B4 ps case is earthed to the mains supply. Should I earth to this?

Is there anything in the PreFix that needs changing because I've fitted the TRs?

Paul
 
Does your prefix have the earth mod, extra caps on the input/output of the earth wires inside the case?
 
The Earth wire seems to come straight from the arm, with the other wires, but does not go into the electronics. So I guess the answer is no
 
in a tt system with a naim mc stage you must connect signal ground to mains ground in at least one place. If you don't then the stage will amplify mains hum.
 
The earth wire comes from the arm, so is it signal ground? I don't think so.
Signal ground and power ground is the 3rd pin on the 5 pin hicap plug
 
The earth wire just earths the metal bits of the arm /tt it doesn't touch the signal/return path at all

The naim PS system is completely floating, no pin on the hicap dins is connected to mains ground.

many CDP's or DACs will make the link between signal and mains ground, but if yours doesn't then you need to do it somehow.

sticking a bent paper clip into one of the Hicap 4 pin sig ground pins and touching the other end to one of the screws that fixes the socket to the chassis will instantly tell you if lack of ground tie is your probem. The hum will vanish if it is.
 
Paul, later prefix came wiht extra caps to decouple the tonearm earth wire fro the rest of the signal earth, they are notorious for humming, especially if you prefix is one with lower capacitive loading. (I have 5.6nf on mine and it's fine).

Check you prefix for proximity to sources of hum before you assume it is earthing rather than radiation.
 
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