An observation.

[bikerhifinut]

Just to clarify Bob, when you removed the earth lift resistors, you didn't leave the HT and heaters "Floating" as that would not be safe. The negative rail of the HT still needs a path to ground for safety reasons as I am sure you know, but others may read this who don't.

A.

[Richard]

Originally Posted by bikerhifinut

Indeed.
Now here's a thing, If anyone wants to bond their PSU and Phono or Pre chassis earths together then there should be (if you built the kit to the destructions) a nice hefty earth post on each unit. So save yourself the effort and if it worries you that much get a length of wire and connect the earth posts together. it'll do exactly the same job.

A.

Not quite Andy. The PSU chassis earth post is connected solidly to mains earth. The Pre and Phono chassis earth posts are connected to 0V signal ground. Signal ground is "lifted" inside PSU by 100R. So if you bond the cases together you lose earth lift and may well get the hum Bob first described.

He then removed the 100R which would put 0V at the same potential as mains earth and in his case ite was quieter, presumably as he had changed the hum loop. That result may vary depending on other connections in the system.

I found on mine (with 5 pin umbilicals - all cases at mains earth) there was then a small further hum reduction from running a heavy earth wire between Pre earth post and power amp Chassis earth post as John also found. They were both nominally at the same potential (mains earth) but clearly connecting them directly was better than connecting them only via their mains plugs. Worth a try

[bob orbell]

You had me thinking yesterday after reading your post Andy, but Richard has confirmed that I have no problem and it works for me, the inspiration came from Richard and M Jones books, no ware in his books do his circuit diagrams show connections from mains earth to 0 secondary volts, I used pin 3 for the mains earth connection and in a perfect world this pin should be longer than all the others so as to make contact first when plugging in and last when removing. Bob

[John Caswell]

My Hi Fi/TV etc is all on a dedicated spur feed (6mm^2 TWE) from the dis board with a large (10mm^2 earth). I had eliminated all the clicks n pops from the kitchen (which is also on a separate ring) but was plagued by the garage fluorescent lights causing interference. Richard came up with the idea of a large earth cable between the pre and the main amplifiers, problem solved. The cable is 3 lengths of conduit type cable (6491X) into crimp connectors for those that wish to try it out. Of course because of different types of house/hi fi wiring it may not work. Perfect application of Sods Law.

John

[Chris]

I've read an article where a guy who designed recording studios always stipulated using 10mm earthing to the sockets.

Chris.

[John Caswell]

10mm is about the max you can get into a 13A wall socket, it is quite difficult to arrange as the cable is not very flexible.
When I was involved in studio installation the supply company usually installed 25mm copper plate on the incoming earth feed and thence to the studios with either copper busbars or if a difficult route at least a 25mm^2 earth cable.
This was mainly to avoid differential earth potentials between studios who may be on different phases of the supply.
Having been the recipient of different earth potentials it is not nice

John

[hawkinsec]

Originally Posted by John Caswell

Richard wrote
"I was told many years ago that one reason for going AC mains was that it caused you to let go of it whereas DC mains (around til the 50's) caused you to hang on to it...

John

I was always told the same, but remember one occasion when (lacking concentration due to a bad cold) I stuck my hand where I shouldn't have. That was a rail carrying mains and it certainly didn't throw me. I was quite aware of what was going on around me and finally managed a pathetic little squeak as I managed to let go.

[Little Mick]

Can never be said too many times keep one hand in your pocket however like John I did a far bit of TV repair in west London the telly was usually placed in the front room corner by the window often very near a Centeral heating radiator and on more than one occasion kneeling or sitting down behind the set, wet from the rain out side it was easy for some part usually my back to be touching a very well earthed one and have had shall we say the odd belt, I too was told that about DC and AC same time as the pocket first important thing I learnt.

[hawkinsec]

Unfortunately, you often need to have two hands inside the machine when working on some pieces of epuipment. Having said that, I should have unplugged the equipment rather than just turning it off, but as I said, I wasn't paying attention due to having a bad cold. Don't go to work when ill.