Ground loop w DS?


#1

I recently added my tube pre back in which is very picky and seems very sensitive to ground loops.

When nothing is hooked to the pre but my amp - everything is quiet. When I connect the DS - I get a low level hum - which seems to go up w volume increases on the pre.

So I added a cheater plug to the DS. This ‘fixed’ the hum. Any guidance as to whether this is problematic for the DS ? Any suggestions on a better fix?

Do we agree this is probably a ground loop?

Thanks all. Tim


#2

Are they all connected SE or Balanced or mixed?


#3

Oh… Yes. It is all SE interconnects - audioquest king cobras


#4
timm said

So I added a cheater plug to the DS. This ‘fixed’ the hum. Any guidance as to whether this is problematic for the DS ? Any suggestions on a better fix?


If something were to go wrong (in the 120V parts of the DS) then the interconnects (either digital or analog) will be your “safety” ground and could have 120V on them. This isn’t likely, but if you ever have the top off it can happen much more easily.

You may be able to break the ground loop other places - have you tried things without any inputs connected to the DS but the output connected to your preamp? If there’s no hum without a cheater plug and without inputs connected then perhaps you can consider doing an isolated digital connection (or TOSLink if that’s adequate for your purposes.) If your preamp doesn’t have balanced inputs and you can use a balanced digital input, doing so may help.


#5

Hi Ted thanks for the response. I have USB only connected to the DS but did not try your suggestion of removing it and leaving the DS connected to the pre. I’ll give that a shot. Yah it is a completely analog SE pre. I am basically setup w USB hub w 4 external HD connected to a laptop w USB out to the DS (going thru a wyred 4 sound recovery). I did remove the recovery unit just to check that.


#6

You may get lucky and the ground loop “source” might be whatever powers your USB hub or your laptop. You might also try reversing the AC power connector for your laptop (if it’s one of the unpolarized C7/C8 types (two conductor / figure 8))


#7

Does it hum when the laptop is running on its battery?


#8

Good question. I will check this out in regards to battery.

One thing … I had everything hooked up - was playing for 6 hours or so - and then I had hum over the speakers. So it isn’t a constant - or if it was there initially - I can’t hear it and it gets louder.

I do have a bit of static in the room - being winter here in Michigan. I have tried to get all cables lifted off the ground.

Right now w cheater - no hum thru speakers. This pre has never been plugged into this room as it is a new room.

I think I’m going to have to start over. Remove the cheater - and remove all sources - then just start adding one back at a time.

On a positive note - it sounds fantastic.