Flummoxed by a Hum issue (1 Viewer)

[SteveJohnny]

I'm a newbie here, and this is a long shot hoping that more experienced hands might have some insight.

A couple of years ago I built a PC to integrate with my not particularly impressive HT setup. It has hardly been used. But I've got a burning desire to dub some old LPs to CD, and this is my only realistic option. So I fired it up, but have been thwarted by an insidous hum problem. I've spent hours trying to diagnose it, and my conclusion is that I'm SOL.

Everything is hooked up thru a fairly modern Denon AVR-4800 receiver. The PC is hooked up to VCR2. When I play a CD on the PC the signal is weak and there is what I think is 60hz hum. It is not the sound card, I just replaced a Guillemot Fortissimo with a Turtle Beach Santa Cruz.

What totally befuddles me is that the hum is present only when:

1. The CATV jack is plugged in to the cable box or directly into my VCR (VCR1).

2. VCR Out from the receiver is plugged into the input jack on the sound card.

3. The AC plug is put into the PC, whether is is turned off or on.

i.e. the hum occurs only when the CATV and the PC are hooked into the system at the same time. If either one is disconnected the hum disappears (although the actual sound coming from the PC is still weak when the cable is unplugged, but it is clean)

Two things baffle me. (a) why does the presence of a CATV cable connected to a different input on the receiver cause a hum when a different input is hooked to the PC sound card, and (b) continues to do so even when the PC is turned off, but plugged in?

Any keen insights or possible solutions will be appreciated. O/w it appears that this PC will have to be parted out.

 

[SteveJohnny]

One thing I forgot to include fwiw. If the CATV is connected, as I insert a 1/8" plug into the sound card into the PC I hear what I think is NPR or PBS; once the plug is fully inserted, thats gone but there is the hum. I've used several cables, shielded, unshielded doesn't make a difference.

 

[Philip Hamm]

It's very common to get 60 cycle from cable. There's a device you can get to isolate your cable, do some searches here, I think the information is here somewhere.

 

[SteveJohnny]

Thanks. I had a bit of a time finding it, but I think the product to which you refer is the Xantech Ground Breaker. They are available online from a couple of sources. Here in Columbus OH they sell them at Progressive Audio for $11.99. It sounds like exactly what I need.

 

[John S]

before you buy, at least just try to pull the ground on one or both of them.

I know I know, seems backwrds, but I have solved a fair amount of hum issues, by actually pulling grounds.

 

[Bob McElfresh]

Let me ask you a question: What is an antenna?

Answer: A long piece of metal strung through the air in the hopes of picking up electro-magnetic signals.

What is a CATV coax?

Answer: A long piece of metal cable strung through the air in parallel with 60 hz power wires.

While it does not intend to be an antenna - CATV coax strung between houses acts like an antenna and picks up 60 hz humm. This is ignored by the CATV equipment, but it contaminates your electronics with a signal in the audio range.

Does that help explain things?

 

[PerryD]

I had the same problem, I had installed Dish Network approximately 7 years ago just to pick up HBO & Showtime in high definition, and wanted to keep my regular Cable TV for everything else since it was split to many TV throughout the house. Just like you, I had a ground issue between the two sources, if I removed the satellite, the hum went away, if I removed cable, the hum went away. I solved it by forgoing cable tv just the from the affected HDTV, hardly the desired solution I wanted!