Originally Posted by markg
I have tried what Nutflush suggested and played around with cables etc. No luck. From doing this though it has become apparent that 4 things all need to simultaneously occur for there to be intereference through my speakers:

1. The power amp must be turned on (obvious I suppose, as I would otherwise hear nothing from my speakers hence no noise); and
2. The Oppo is turned on (includes standby mode); and
3. Cables are connected from the Oppo to another piece of kit (any one item, incl TV); and
4. That piece of kit, somehow, has a cabling system that can be traced thru to the power amp. It doesnt matter if that piece of kit is turned on/off or even plugged into a power source.

Point 4. is the important one to note. An example may help to clarify - its a little complicated.

I unplugged all other AV kit from a power source other than the power amp and headphone amp (both in the power board) and the Oppo (direct to wall). All 3 were turned on.

The only audio/video cabling from the Oppo that was plugged into anything else was the analogue outputs, which went into the headphone amp. 2 scenarios then followed.

Scenario 1: The headphone amp also had plugged into another one of its input, the analogue outputs from my Digital TV set top box (e.g. like a Sky HD / cable box).

Scenario 2: Only the Oppo was connected to the headphone amp.

Outcomes: Scenrio 1 = Noise; Scenario 2 = No noise.

I figured that the signal under scenario 1 was making its way back to the power amp via the various cabling. My set top box is also connected to the 568.2mm (via coax digital out), which in turn feeds the power amplifier. So, I figure that the "noise" was going from Oppo, to headphone amp, to Set Top Box, to Meridian, to power amp and finally speakers.

Under Scenario 2, the "noise" had nowhere else to go as nothing else was connected to the headphone amplifier other than my headphones.

Mark,

a few follow up questions:
- did you have an active sub (or any other active speaker = power plug!) connected to your amp? If so: what happens if you disconnect it?
- what was the effect when BOTH amp & Oppo were connected to the SAME power board (including twisting one of the 2 power plugs as a second scenario)?
- do you have a power cord WITHOUT ground (meaning only 2 pins but no other metal parts that connect to any part of the socket)? If so: what is the effect if you try it on the Oppo (or amp)?

Just a little explanation: the "noise" that you hear is a current that is running from one GROUND (i.e. socket 1) to another GROUND (i.e. different wall plug or antenna etc.) passing your amp inbetween (amp is amplifying this current to an audible level and sending it to your speakers for you to enjoy...). That's the reason why simply turning a device off doesn't help (The connection to GROUND is still there. Only the 2 wires from the pins are interrupted, but not the wire to the ground contact.). Only pulling the plug will make a difference.

Although you might think that "GROUND is GROUND = NO CURRENT" there may actually be a voltage difference. So this "noise" is not produced by the Oppo, but rather the result of making a connection between 2 voltage differentials (like the plus & minus sides of a battery). This connection is made by attaching a cable (like the analogue out cables) to the devices (only metal cables count here since an optical connection for example doesn't allow an electrical current to flow). If you connect the 2 devices with a cable that has LESS resistance (i.e. thick cable) the current will take this route and if you are lucky it will NOT pass anything that amplifies it. That's why a (thick) cable connection between the 2 chassis may solve this problem as Gary proposed.

Please let us know how you're going,
Thomas

P.S. More info here: http://www.gbaudio.co.uk/data/ground.htm

Last edited by NutFlush; 2009-10-21 16:48.