To Float or not to Float...

I believe the "float" switch is there for some equipment which have circuits that depend on a "floating ground".  It is always best to disable "float" and set it to "ground" position unless there is a reason not to.

I've never had any hum or buzz problems, but I follow this:
 
Ideally the system should only have one ground point via the mains plug, be it amp, preamp or source. This way there is no "earth loop" via the grounds and your house earthing. As all earths are carried to the all three components via the interconnects to the ones that aren't.
Myself I like the one earth to be at the poweramps end because it's the least sensitive component and any rf gets dumped to it. Others like it to be the preamp because it's in the middle and represents "star earthing".

Cheers George  

georgehifi

... This way there is no "earth loop" via the grounds and your house earthing. As all earths are carried to the all three components via the interconnects to the ones that aren't ...

This is extremely dangerous - interconnects are not intended to carry safety grounds. Following this practice means that a component's chassis could be energized with lethal voltage. Safety grounds should be "earthed" only through a properly grounded power cord, or a chassis that is itself directly connected to a safety ground.

I have a DeHavilland preamp which has a switch allowing one to "float" the ground. I’ve always used it in the "float" position, however recently, perhaps due to some connectivity issues with my interconnects, there is a small buzz emanating from my speakers with the switch in this position.

Like Erik said above, which ever way sounds the best.

perhaps due to some connectivity issues with my interconnects, there is a small buzz emanating from my speakers with the switch in this position.

You might try cleaning the male and female connectors with some isopropyl alcohol.

cleeds is correct about substituting the small gauge signal ground wire of ICs in place of the safety equipment grounding conductor of the power cord.

As for the ground lift switch on your preamp.... Do you know for sure what ground it actually lifts?
Does it lift the preamp circuit/ground from the chassis? (User safe)
OR
Does it lift the safety equipment grounding conductor of the AC power cord from the chassis of the preamp? (Dangerous, not user safe. I have read where some manufactures do this.)


https://positive-feedback.com/Issue12/dehavilland.htm

Right off the back, I had to deal with a minor hum problem that occurred upon powering up the UV. This happens from time to time with a component. Normally, I have to pull out my floater plugs, isolate the problem, and float the ground on that side. Fortunately, deHavilland placed a feature on the UV that I don’t see often enough on fine preamps: a switch on the back panel to float the ground. One flip of that switch fixed the hum problem immediately.

I noticed in the picture showing the switch it is right next to the IEC power inlet connector. Does the switch lift the AC mains safety equipment ground from the chassis? IF the switch does lift the safety equipment ground from the chassis then that is the same as using a ground cheater adapter to lift the ground at the wall receptacle outlet.
You can easily find out 100% for sure with a multimeter.

Jim

Thanks for all of your responses.  Cleeds triggered the solution when he (or she) wrote "a properly grounded power cord", which reminded me that I was having intermittent problems with the connecting plug of the preamp's power cord.  Swapped out the power cord and problem solved.  I also have a pair of DeHavilland mono block amps with the same ground/float switches, and in the manual it states that leaving the switch in the "float" position may result in a "cleaner sound".  At any rate, a fully functioning grounded power cord has done the trick...