HT Projector ground loop isolator

Once I got a projector (Epson EH-TW3200) connected to my surround amplifier I had a problem with hum in the speakers, and some nasty flickers because of bad HDMI signal quality. While connecting the HDMI between the surround amplifier and the projector I noticed a small spark when the metal on the HDMI cable connector came in contact with the metal on the receiver.

The setup with hum:

Projector (Epson EH-TW3200): Grounded
15M HDMI Cable
Surround amp: Not grounded (double isolated)
Media PC: Grounded
Sub: Grounded

I live in a pretty new house with 400V TN (terra neutral) grid. This is common in europe, but not so common in historically in norway.

I tried a small hack with tape on the safety ground on the wall power plug to the projector. Then the problems with flicker and hum went away. But I dont like having disconnected ground for safety reasons so i thought up this ground isolator:

It is pretty ugly, but it will connect the ground during a failure and trigger the earthfault circuit braker in my house. It is basically the same as a Zink Saver used for boats, but they have much more powerful diodes.



Disclaimer, this is most likely a bad idea and will probably kill you and your stereo, but if done correctly it should be better than to disconnect the safety ground completely.

What causes the groundloop in the first place?

The Surround amp/ Sub and PC is sharing the same wall outlet. 

The projetor have another wall outlet with another route to the house star ground point.

The chassi ground of the surround amp and the projector is connected together causing a triangle loop. When there is a potential difference of say 50mV between the ground in the two sockets there will flow current in the screen of the HDMI. I assume the resistance in the HDMI screen to be 0.1 Ohm. Then there will be 50mV/0.1Ohm = 500mA current flowing in the HDMI screen and into the surround receiver and adding noise to all analog logic referenced to this ground (like my Sub)

Adding the isolator the grounds must be more than 1-1.2V appart before there can be flowing any current in the HDMI cable. This will cover most noise and fields the groundloop can be subjected to.

Mounting a micro switch in the Eumig Mark 610D for synced telecine.

This is just a small followup of this post: http://oysteineliassen.blogspot.no/2012/09/diy-synced-telecine-with-eumig-mark.html

Someone on vimeo asked where I mounted the micro switch inside the 610D projector. 

Here are some pictures :-)

First off, i kept the big ALU part that locks the gear mechanism. It is held at fixed position (6 fps) with some pressure from the steel plate in the top of the first picture. I just rotate this plate to press inn the big alu gear part.

The mounting bracket for the switch is made of some black metal piece i did not need joned to strip of aluminium by a M3 screw and nut and then bent into position. Some double sided tape on the sidewall of the micro switch is securing it to the aluminium.

 The aluminium is bent into position so that the actuator of the micro switch is touching the metal flap that i noticed was "coming out" at each frame advance.

As for the reliability i managed to transfer 2 reels of 100 meters  and about 12 reels of 15 meters without breakdown of the micro switch.

Hope this is of some use to someone.