Supra Mains Block MD06-EU/SP MK3

After some problems with HDMI dropouts between my Projector and Receiver i decided to try a "proper" mains filter and surge arrest and a new HDMI cable from supra. Seeing that the HDMI cable alone solved my issues i was curious to see what was in the power strip.

Supra MD06-EU/SP MK3 power strip.

For some reason the manufacturer web page is not showing like it used to so here is the cached one:
http://webcache.googleusercontent.com/search?q=cache:7api80Fi4hsJ:www.jenving.se/products/view/mains-block-md06-eu-sp-mk3-3024000030+&cd=7&hl=no&ct=clnk&gl=no

According to the manufacturer it have

• a non intrusive filter (NIF) that does not slow down dynamics :-)
• 3 way protection (Live Neutral and Earth)
• Dampen noise from from cell phones, dimmers etc

Curious as to what was inside i opened it up :-)

End cap and IEC socket removed. 

Surge protection circuit board

The EMI filter consist of a single turn common mode choke around live and neutral between each outlet.

Ferrite cores in heat shrink tubing between each outlet

As commented in Supra the socket closest to the IEC inlet terminal does not have a filter. When removing the heat shrink on the MOV a thermal fuse reveled itself. 

After what i can see the schematic is like this....i might be wrong.

Comments on the circuit design

• There is a 10A ceramic fuse in the inlet IEC receptacle on Live, none on Neutral. With schuko there is no lock or indication of what is live and neutral. So the fuse might be on the Neutral line.
• The filter consist of a single turn common mode choke between the outlet sockets. There is no other filtering element in the design, Not a single capacitor. Differential noise cannot be filtered by this design. Maybe that's why its marketed as a NIF (Non Intrusive Filter).
• The surge protection is a clamping design built using MOV (metal oxide varistors) in parallel with the main current flow. The clamping deceives are protected against overload using 5A 115C thermal fuses in the same heat shrink as the MOV its protecting. 
• The Gas filled spark gap conducts if PE deviates more than 470V from the lines during lightning stirkes.
• A bit surprised to see the LEDs directly in series with resistors across 230V mains. I doubt that normal LEDs have a reverse voltage of that much but the ones used might have a proper avalance spec. A normal diode in antiparalell would not hurt. I really doubt that this design will survive a 2.5kV test voltage after the surge protection fuse is over heated.
• How can a gaping hole of 43x5cm in the faraday cage block any EMC? Its more like a tin foil hat than a faraday cage.
• I really like the looks workmanship and the mechanical quality so i will definitely keep it in my system :-)

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.