How to Stop Subwoofer Hum That is Caused by a TV Set Top Box


Whenever a customer calls and says, “Hey, listen I’m experiencing hum,” our first question is, are you experiencing it on all inputs and on all sources, or is it really just one?

About 80% of the time they think about it or they go back and do some testing and say, “well, really it’s just my television set top box.”


It doesn’t matter if it’s Sky TV over in the UK, AT and T over here or DirecTV there’s usually a reason. Well, those set top boxes are marvels of actually very high-tech engineering. The fact that we can pull up an image from a satellite or beam things around over thousands of miles through underground cable networks is incredible, but they’re very noisy environments for ground.

Whether you know it or not, you’re linked with 2000 or 3000 of your nearest neighbors and all of their ground potentials and noisy refrigerators and all that. So, what you want to do, if you find out that it really is just your set top box, is you want to isolate it.


The way to do that is to buy one of these pieces. Now, there may be other people who produce these, but this is the best one we know of. It’s made by the Dean Jensen transformer company who are legendary. They made all the great microphone transformers used in the sixties and seventies in recording studios, and they produce a piece called the ISO max. Couldn’t tell you the price. I believe it’s around a hundred dollars US over here.


What it does, is you put this right at the input where the cable comes in from whatever mechanism. Whether its RG 59 being fed by an actual cable network, or if it is coming from your direct TV, your satellite feed, you put the F connector into here before you get into the set top box and screw it in. Then, plug it in from here using another short length of cable into, presumably the set top box input and from that point on everything downstream of that in your system is isolated and it gets rid of the hum on everything. It just simply can’t creep in.


So, again, this is called an ISO max. It’s a one-to-one transformer. It’s only function in life is to isolate the input for the set top box from all the noise that’s outside in the environment. And it works beautifully.

January 21, 2020 - Posted in: Q & A With John Hunter, Videos