• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Buzz through speakers when TV turned on, 12B4 preamp.

Good Morning,

I have a 12B4 preamp that works great, except when my TV is connected via RCA and turned on. I end up with something that sounds like a 120hz hum. Is this a grounding situation? I presume it has something to do with the switching PSU on the TV.

The hum remains no matter what source is selected.

I had considered running optical from the TV to a DAC to the preamp. It's not out of the question but I really don't want to lose analog volume control from the TV.

Thank you!

Yeah its grounding issue from cable line. You either need rca isolation transformers or go optical. Many tvs, including the last 3 ive had allow you to choose whether you want fixed or variable output on optical in setup

I actually don't have cable, or satellite for that matter.

Interesting that I can get a TV with variable optical out. That may actually be the right solution. I may have a ground loop isolator here somewhere I can test too

I generally have to run all my sources on two prong plugs or adapters. But if your tv is also interconnected to an av receiver with HDMI and your av receiver is on a 3 prong the ground loop will still be there. I don't consider my av receiver to be a source so it is on a 3 prong. I mever used my tv as an analog source. Av receivers and the tv combined make for a lot of ground loops.
Finally found the damn thing. I've been packing it around for over a decade unused. It fixed the problem. The TV and Stereo are on different circuits. When I rewire the livingroom I will be adding a circuit for the stereo, seems like I should tie off to behind the TV as well. Thanks for the help!