I’m getting a loud hum from both speakers when using a single ended connection between the Directstream and amp. The volume is not affected by varying the volume on the DS.
This does not happen when using a balanced connection. No hum at all. Very quiet background.
Also using the same RCA cables with a Rotel power amp produces no hum.
Any suggestions would be appreciated.
Use a balanced connection 
As an experiment, if you haven’t already tried (and if they aren’t already) plug the DS and BHK into the same outlet, power strip or power conditioner. If they happen to be on the opposite phase of your house wiring that can sometimes cause a hum, and sometimes there’s too much voltage difference between the grounds of two outlets even if they are on the same phase.
Thanks Ted. I tried that. The hum still remains.
“Use a balanced connection” 
I need the single ended connection to work to go via my tube preamp (balanced to the preamp, single ended to the BHK).
With this setup I still get the same hum.
The two other “standard” things to try are running a separate wire from the DS case to the BHK case (like you would for a turn table…) and as an experiment try a cheater plug on the DS.
The hum might be coming from an input to the DS - if your running a computer to the DS try plugging it into the same outlet… Or if TOSLink is a possibility that’s the ultimate isolation.
I’ll certainly try those things. Meanwhile, does the fact that I get no hum using the Rotel power amp suggest that the DS or inputs to the DS may not be the problem or is that an over-simplification?
Do you have a ‘ground lift’ switch on your Rotel amp you can try?
Your next step might be to insert this one in the RCA IC loop: Iso trafo
alcarp said I'll certainly try those things. Meanwhile, does the fact that I get no hum using the Rotel power amp suggest that the DS or inputs to the DS may not be the problem or is that an over-simplification?Groundloops suck. Much of the time no particular device is at fault - they just happen and are difficult to eradicate with our more and more connected world/audio systems.
You could unconnect everything then start at the amp with nothing connected to it, if there’s no sign of hum then connect one input, but have that device have no inputs, see if there’s a problem yet, … When you add something that causes the loop you’ll know a little more than you do now. But that loop could be to anything that’s already in the system…
Frode’s idea is a good one if you can’t fix it in a simpler way, say by plugging into different outlets or turning non polarized plugs over…
The Jensen Transformers web site has a lot on diagnosing hum and fixing it.
The samw thing happened at Fremer’s house and we used a simply cheater plug on BHK’s AC plug and it stopped.
I had the same issue with my Spectral amps (using RCA - no problem in balanced). The only thing that ended up solving the problem was lifting ground using cheater plugs.
Ted … I followed your suggestions first having nothing connected to the BHK - no hum.
I then connected the DS with no inputs to the BHK- the hum occurred; doesn’t happen with balanced; doesn’t happen with unbalanced to the Rotel.
You mentioned running a wire from the DAC to the BHK. What will I attach the wire to at either end?
Re: cheater plugs I think their use is illegal in Australia.
Well that’s about the minimum interaction I only suggested using a cheater plug as an experiment. I agree that it’s not a proper long term solution. And are the DS and BHK on the same outlet, at least as an experiment? If not that might be the simplest answer (as long as having them together on the same outlet doesn’t cause other audible oddities.) The hope is that a wire from chassis to chassis would conduct most of the ground loop current keeping it away from the interconnects. A place on the DS is under one of the bridge screws (or the screws on the plate if you don’t have a bridge.) I don’t know if the BHK has a ground screw terminal or not, so I’m not much help on that end.
Hope Paul or BHK can help with the BHK end.
Tried the BHK and the DS on the same outlet. Hum persists.