Disk noise when connecting H120+3.5" disk to amplifier

[bonapardo]

I have just successfully completed a 3.5" 250GB 'upgrade' to an iRiver H120 using a homemade 50pin to 40pin IDE adapter (by simply linking the IDE pins). It is set on the front of a dual harddrive enclosure (the purpose of which is to provide a bit of additional space and an additional molex power connector should I need it (assuming the power supply in the unit is set up to run more than one disk at once). Rockbox runs well and there is no problem with data transfer.

However, when the Line-out is connected to my amplifier, the amp picks up disk noise even when set to another audio channel. The noise is very loud, not background, the spin-up being particularly painful to listen to. The noise happens whether the power is connected or not. I did try to hook the 5V line to the DC-in of the iRiver (even though I knew it was making still the noise without power connected) and as expected, the problem still occurred. Incidentally, the molex is not compatible with the iRiver - it supplies power to the device but the disk loses power occasionally - that's another story. I have not made any special arrangements for grounding the device - I have no idea about grounding.

There are effectively five parts in my chain. The H120, the cable, the HDD, the enclosure and the amplifier. The iRiver is clamped onto the oustside of the enclosure (which is plastic), linked by the ide cable to the disk. An obvious place to start is the possibility that the bare pins on my adapter could be touching the metal which the HDD is screwed to inside. I'm reluctant to move it around too much for the sake of it (that cable took ages to solder and test) so haven't insulated it yet. I can do though if anyone recommends it. It is also possible that a screw from one of the clamps could be touching something inside but a quick check did not reveal anything obvious. The disk is mounted within the enclosure in the above metal 'cage', power supplied via a 12V DC adapter bundled with the enclosure.

I am in the UK (using three-pronged plugs).

To re-iterate, the amplifier picks up the disk noise regardless of the channel and amp volume (even 0). When the line-out is disconnected, no disk noise. The headphone out only exhibits the same disk noise on the correct amp channel at the set volume level (i.e. 0 is silent). There is no disk noise when listening through headphones so is this a problem with my amp? None of the above occurred before the unit was opened. I could plug it into the amp with no problem.

I have a workaround - using optical out which is beautifully digitally silent. Before I splash out on a lovely external DAC though (and before I fry the new addition to my audio setup), does anyone have any advice on what could be going wrong?

Thanks in advance and apologies for the long description but I thought it best to provide as much info as possible.

[saratoga]

Probably a ground loop somewhere.  Not sure how to fix it without seeing a more detailed wiring diagram though. 

[bonapardo]

Thanks for the reply.  When you talk of a wiring diagram would you need shematics of the component equipment or just a simple diagram of how the bits are connected inside?