John Sayers' Recording Studio Design Forum Archive

Hi,
I understand very well the concern of loop of mass but there is something I quite can't understand: in a rack the mount panel is almost all the time in some sort of steel. The devices being attached to it have their chassis in contact all the time, that is enough to create a mass loop, am I not right ?
What is the solution here ? What do they still construct rack that way ? Or does it not matter as the loop is small ?
Thanks
Alex

I've pondered that one as well; some of the "prosumer" gear, Emu in particular, has plastic cases so wouldn't matter. I've not had any serious hum problems using steel racks with all units bolted in place, but it's certainly possible.

One company even sells a set of "isolators" that are plastic, and wrap around the corners of each rackmount device to isolate them from the chassis rails - you also need small spacers and plastic washers to complete the isolation, and as near as I can tell you can't use these with standard rack rails ANYWAY, because there isn't room between units unless you leave every other rack space EMPTY

Another way to ensure things don't touch is to make your own rails, out of oak or another hardwood; there are brass threaded inserts available from online woodworking sites, etc, that can be used instead of screwing directly into the wood to hold the gear, and you can allow a small space between each unit for isolation by drilling your own holes.

http://www.yardleyproducts.com/tri_c.htm

The other "up side" to wood rails and small spaces between units is slightly better cooling without having to leave entire rack spaces empty between units... Steve

You have a good question, and I have a frustrating answer.

Well designied equipment has the electrical ground separate from the signal ground. Sometimes there is a jumper on such equipment to bond the 2 together. On poorly designed equipment they are the same. This also extends to the infamous "pin 1 problem."

Andre