Quote Originally Posted by ImpMan71 View Post
Hi,

Thanks for all the replies - I believe this all comes down to earthing and I need to study it more closely. From memory I have taken the earth from the iec socket to the chasis (but I'm sure this is at it was before?) I will have a look on the Dada forum as well, thanks Dave.

I tried dropping the earth from the plug top anti surge and this resolves another earthing issue that occasionally happened, which is the left channel hisses and distorts, but goes away when the volume is turned up.

When I swapped the boards over it stays on the left, so has to either be a PSU or earth issue.

The boards are Chinese built with all new components, mainly from Farnell, or the obscure inductors from Dada.

I think it is an exact copy of the Dada V2 board (photo attached) which are considerably different from both Quad 405 MKI and MKII original boards.

I'm going to have to put the 103 back in the main system and get inside the Quad again.

I have used it with a Meridian 101 before rebuilding it and not had any issues.

It is unlikely I will be able to take a look until the weekend now. I am going to remove the caps across the transformer and see if this helps; I cannot remember now where I saw this recommendation (will have to search through my browsing history) but these have been on since I first did the rebuild, so hopefully may be the cause.........
You may have bigger fish to fry here.... what you describe with the left channel could well be due to ultrasonic oscillation. I hesitate to recommend any cure as this is something where one really needs to be there... and with test gear etc....