Earth loop problem?

Posted by: Graham Russell on 14 May 2005

I'me still running in my new CDX2, 202, 200 and I thought I'd reconnect my home cinema kit:
Pioneer 656A DVD player
Yamaha E800 processor

I think I've got an earth loop causing severe mains hum when I select the AV input on the 202.

I'll try and describe what I've done to narrow down the problem.

E800 connected to 202 AV input via phono. (Waiting for 3m phono <-> din cable to arrive)

202 powered by 200. 200 connected to home-made hydra.
Hydra has 3 wires - 2 have IEC sockets for 200 and CDX2. 3rd connected to 4 way block.
E800 and DVD plugged into this 4 way block.

Because 4 way block and 200 are connected to same hydra I assume they have a common earth.

If I use a coax digital connection between DVD and E800 I get mains hum.
Using a digital connection doesn't produce hum.

DVD player has no earth - 2 pin mains cable. I assume this means it's got a floating earth that may be causing my problems. Is this assumption right?

I'd also like to connect the 6 output channels of the DVD to the 6 inputs of the E800 so I can play SACDs and DVD Audio disks.

Obviously using the optical interconnect from DVD to processor means DVD isn't earthing through processor and/or 200/202. But I really want to use the coax interconnect and connect the 6 analogue channels too.

I hope this description makes sense.

Any ideas what I can do to improve this situation? Is there some way of earthing the 656A DVD properly.

Thanks for any ideas.

Graham.

Posted on: 15 May 2005 by Graham Russell

I guess one way around this is to desolder the shield from one end of the cable between the Yamaha processor and the 202 pre-amp.

Posted on: 15 May 2005 by Tam

It's worth making absolutely certain which bit of kit is causing the loop (you can do this by unplugging things until it stops).

I has a similar problem (though it my case it was caused by my sky box). I stuck a ground loop isolator between my dsp-e492 (precursor of your 800) and my nac 32.5:

http://www.beststuff.co.uk/xitel_ground_loop_isolator.htm

Bascially, it does just what you suggested doing yourself and cuts the ground signal between the two units.

But you have my sympathy, earth loops are an absolute ****** to track down and cure.

regards,

Tam

Posted on: 15 May 2005 by Graham Russell

I took the whole lot apart yesterday to narrow the problem down. I suspect the TV and the sky box will cause similar probs too. However, using an isolator like you suggest, or desoldering the shield in the connecting wire will fix it for all sources.

Better get the soldering iron warmed up....

Posted on: 15 May 2005 by Tam

Agreed - as long as you put it (or des-older)
between the processor and the pre-amp the issue should be fixed.

Sky boxes and vcrs (etc.) are particularly culpable since the ground from the aerial or dish can often be at a different level to the main ground (that certainly is what does it for me). It also caused a similar problem with my tuner.

I hate ground loops. Hopefully you'll get yours sorted out without too much bother.

regards,

Tam

Posted on: 15 May 2005 by Manu

I vote for the Sky box. Ground the shield of the aerial cable close to the Box or use a ground isolator.