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
If you have cable or satellite hooked to the television, you may need a ground lift or something similar to a Mondial Magic inline with the coax. I was told I didn't need that for satellite but turns out I did, and it worked. I would believe the cable/satellite/television is the culprit before doubting the Sim P5. Your local HT dealer should have some sort of an in-line ground lift in the $10-20 range - a good place to start. Good luck.
Thanks Mitch for your reply but will this happen if I have 2 dedicated lines and the preamp and amp are plugged in one line while my video and digital is in the other line as I have right now.
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.
Yes IME it can. Any connection between units having cable or satellite connections can cause hum. Consider if your DVD player or processor are hooked to the television (which is hooked to cable or satellite) and also to the preamp via an rca cable which has ground and positive, they then share a ground connection. I am not an expert, but a ground lift cured the same problem in my set up, when I was attached to cable, and then later again after switching to satellite.
but will this happen if I have 2 dedicated lines and the preamp and amp are plugged in one line while my video and digital is in the other line as I have right now.

Actually, you increase the chances of a gound loop (difference in gound potential) when components are plugged into different circuits.

It is also common for the ground point at the service entry for the cable or sat to be the offender.

As a matter of safety and electrical code, you should avoid using a ground lift unless you are absolutely sure that it does not break the safety ground. An isolation transformer is always a safer and better solution.

Do a web search on ground loops for more information.
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.
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.
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
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.

I believe Ron is correct. However, the bonding strap does oxidize and can loosen over time. Simply remove the strap, polish it up with a wire brush and reconnect it.

There is also the number of cable connections within the house to consider. Every connection is a possible point of high resistance (anything greater than zero) and can change the ground level. So even with the best grounding at the service entrance, you can still have a ground loop on the cable. As stated before, an isolation transformer is your best solution. Jensen makes good products for this.
Thanks for all the replies and suggestions. I tried to disconnect my coax to my satellite box and hum is stll there. I removed all my connectors one by one still there. Finally I switched the input from HT bypass to another input in my preamp and the hum is gone. Is the bypass input defective? Well maybe I will just do with this setup for awhile and just put the volume at 12:00 oclock as have been stated in other threads until I could have this fixed.
may be the ground connection is not soldered properly on that input?
Sounds like an issue with the bypass circuit. Try another source through the ht bypass that doesn't hum normally, and if the hum is still there, it sounds like the circuit. Good luck.

Sim Audio tend to have great customer service.

kw.....
Is on a different AC leg at the AC Box
To test if this is the case just plug in the whole system into One outlet strip out of just one dedicated outlet
and the hum should be gone.
Next have an electrician place the dedicated line on the same leg.
Let me know if this fixes
Cheers Johnnyr