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Hum in preamp when using HT bypass

I have a Sim Audio P5 preamp that has an HT bypass input. AT first I was using RCA interconnects from CD to preamp, preamp to amp and the HT bypass and had no problems. When I switched to balanced from CD to preamp and preamp to amp leaving the RCA connection for the HT bypass I am getting the hum. There is no balanced input for the HT bypass. When I choose my CD input I do not get the hum, only when I switch to the HT bypass input. Any suggestions?
kayoboy
audphile1's avatar
audphile1
5,314 posts
 
I was going to suggest trying rca to xlr adapters, but you don't have XLR input for HT bypass.
so, most likely it's a ground loop from your catv. try disconnecting your coax cable from your cable box and then turn the system on to see if there is still hum. If the hum is gone, then get the Mondial magic box or something similar.
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hals_den
77 posts
 
Chris Hoff of BPT thankfully hipped me to the video isolation transformer from Parts Express (part #180-075) and it eliminated the ground loop from my HT/stereo system. It was $10. You may need one for each of coaxial cables, ie. antenna, satellite, and cable.
mitch2
4,058 posts
 
Just to be clear, my recommendation for a "ground lift" was for the coax line from your cable or satellite source, and not an AC ground lift. I probably misused the terminology, since it is correctly described as "video isolation" by Hals_den. I agree with Bob_reynolds regarding grounding and safety.
rontube
44 posts
 
It is rule of the National Electric Code that a cable system or satellite installation MUST be bonded (grounded) to the fuse box and ground rod of your house. If this is done you will not have hum or need ground lifters on the cable line. If your cable company resists call your local city building inspector and report the code violation. They will respond.

Thanks,
Ron-C
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