K5881 Mains Earthing

[Mr Spook]

Greetings, I have been looking at a WAD K5881 (unsure of which flavour - Mk1 or Mk2) for a customer. It would appear that the chassis is connected to the IEC socket earth via a 10 Ohm 5W resistor in parallel with a tubular polyester capacitor.

I do not have the original construction information so I asking is as specified? There is a shield wire from the mains transformer which is directly connected to the IEC socket earth, however I have not tested it's continuity to the chassis. On the face of it the situation appears to be very dangerous and certainly illegal here in Australia. I have attached an image....

Can anyone advise if this is stipulated in the construction details please?

Regards

Mr Spook

[Richard]

Hello and welcome,

It looks to me as though someone has just cut the solid mains earth connection and attempted to "lift" the connection with that resistor. These were kits and whenever I've had a secondhand one (several) the first thing I check out is the earthing as if a previous owner has had hum they may have tried modifying the earthing.

I've just checked the 3 variants of the K5881;

Both p-p versions I and II had no signal ground lift, signal ground was solidly bonded to chassis and mains earth at the input rca.

The PSE version shown below (and possibly because single ended can be more prone to hum) had its signal ground lifted from mains earth by 10R with a parallel cap providing a hf ac path. This is a popular way or lowering hum;

1) bond the chassis solidly to mains earth at an earth post
2) isolate signal ground from the chassis (this may include needing to fit isolated rca sockets if not already used) and check with a meter that it is completely floated inside the chassis
3) then connect signal ground at it's earthiest point (big psu cap negatives usually) to the chassis earth point via 10R // 0.1uF

You should find the mains TX shield wire is isolated (check with a meter) and, if so, can go to either signal ground or chassis mains earth, I would go with the latter. In all cases imho the chassis should end up solidly bonded to mains earth (not via a resistor) which I think is your concern.

[A Stuart]

This does not reflect badly on the original builder (nothing to do with me ) This is how the original instructions with the K5881PSE specified.
Exactly as Richard describes, John Caswell did advise me (met him at one of the Bristol shows) to alter mine. ie replace the supplied phono inputs with insulated ones, and attach the mains earth end of the lift network to the chassis.
Alastair

[Mr Spook]

Hello Gentlemen, Thanks for the information :-)

I will sort the earthing out as per your replies ....

Best Regards

Mr Spook