Diy helph

Headache.

Nice one fuzztone, 
assuming that your connection is with rca's then most propably a ground is touching signal. Have you checked both cables or just one? What happens if you rock the rca's at pre's output or power's input while both cables are connected? Unscrew top covers-units off mains- and check that rca's at both units have a tight fit.
You can use a voltmeter to check any kind of shorting if you wish.
G

At first I thought that the title of the thread was in a different language.

Have you tried interchanging the cables? I had a situation where one of my cables potentially had damaged shielding and would catch radio interference when connected to my turntable.

have you try a ferrite ring on power cord of preamp and or amp close to the unit

Nice one roxy54
All you can do is try every combo and it still might not go away. Move the pieces and IC around. I have a bag of iso transformers I try..
Start with in between.
Lotso luck.

Thanks for the info , I'm trying to eliminate an earth loop at the moment , rerouting the input leads inside amp to one side.
The title of this thread was a typo but I couldn't edit it for some reason.
Cheers
Mike

Hey!

Always try the DIYaudio forums.

Ive just put together an amp / preamp combo.

Those are DIY amp and preamp?

Agreed with @erik_squires that diyaudio is likely to be of more help with this issue.

Perhaps this thread is somewhere to start: https://www.diyaudio.com/forums/diyaudio-com-articles/163575-audio-component-grounding-interconnecti...

When dealing with ground loops it can be useful to just unplug everything and try to eliminate possible sources. Do you have to same issue if the pre is taken out of the loop? Do you have equipment plugged into multiple outlets? 

Good luck, ground loops can be a bitch...

Have eliminated about 80% of the hum so far .
Have a look at this PDF file
http://hifisonix.com/wordpress/wp-co...ound-Loops.pdf
Cheers
Mike

@milo66 congrats and thanks for posting. Looks super useful...