RCA Interconnect Line Noise Problem

[douglasbjordan]

I have two receivers in two separate rooms connected to each other via two 20 ft optical cables and two 20 ft analog rca interconnects. The in/out on either receiver goes to the out/in on the other, that way I can mirror sound in both rooms from all my digital and analog devices. Anyway, here's the (analog) signal path I'm trying to get to work: Cassette Deck -> Receiver 1 -> Receiver 2 -> Computer. (I'm working on trying to get computer to record my cassettes.)

Now for digital devices, the setup works great. I can play a DVD in my living room and have a very clean signal in my study (I attribute this to the optical cable). For analog devices, it's not quite so good. In Cassette Deck -> Computer signal path above, I have a constant line buzz noise on the speakers connected to Receiver 2. I tried disconnecting the output rca cable from receiver 1 and the buzz disappeared, so apparently it only exists when a signal is getting sent that rca cable (i.e., the cable is not picking up the buzz sound on its own from outside influences). Even when I'm not playing a tape, I can still hear the buzz from the Receiver 2 speakers -- simply having the two receivers connected over such a long run causes it.

The rca cable is a 20 ft radio shack red/white interconnect, and I think this may be the problem. My theory is that the signals in the rca cable are suffering inductive interference -- it's in a fairly hostile environment, since it runs right alongside three speaker cables and a coax line for about 15 feet of its 20 foot length.

Any suggestions on how to fix this? My next step to validate my theory would be to disconnect receiver #2 and put it within 3 ft of receiver #1 and see if it gets that same buzz (in which case I blame the receiver, not the cable), but this is a pain because I hafta disconnect all the connections to move it to the other room for a quick test. Do you think I should do this, or is it more likely to be the cable's fault?

If it is the cable's fault, any suggestions on a set of decent-quality shielded 20 ft RCA interconnect cables that I might purchase? Thanks in advance for any help!

[markw]

Actually, this sounds more like a grounding issue than a cable quality problem. It's possible that one of the cable ends COULD be bad, but a difference in potential between the units seems more likely.

Try "borrowing" another cable from the shak to try it. It's not likely you would get two bad cables.

[douglasbjordan]

Actually, this sounds more like a grounding issue than a cable quality problem. It's possible that one of the cable ends COULD be bad, but a difference in potential between the units seems more likely.

Try "borrowing" another cable from the shak to try it. It's not likely you would get two bad cables.

Tried another cable, but it yielded the same results. How do I solve a grounding issue?

[Norm Strong]

What you have is a ground loop. My advice? When it comes time to make a copy of your cassettes on the computer, bring the cassette deck into the same room with the computer and connect it directly. Do not connect either receiver.

[Beckman]

Tried another cable, but it yielded the same results. How do I solve a grounding issue?

See:
http://www.epanorama.net/documents/g...oop/index.html

[douglasbjordan]

Hmmm I tried running an extension cord from the receiver in the computer room to the same outlet that the living room receiver is on (the article on Beckman's link suggested it), but nothing changed. Is this ground loop stuff specific to analog? Would it possibly help to convert the analog output signal on receiver #1 to a digital PCM signal and connect it to one of the optical inputs on receiver #2? This device http://www.audioreview.com/Cables/CA...3_1584crx.aspx might do the job, but would it help any?

[Beckman]

Hmmm I tried running an extension cord from the receiver in the computer room to the same outlet that the living room receiver is on (the article on Beckman's link suggested it), but nothing changed. Is this ground loop stuff specific to analog? Would it possibly help to convert the analog output signal on receiver #1 to a digital PCM signal and connect it to one of the optical inputs on receiver #2? This device http://www.audioreview.com/Cables/CA...3_1584crx.aspx might do the job, but would it help any?

You could also try:
http://www.radioshack.com/product.as...t%5Fid=270-054

Keep in mind that coxaial cables for cable television are paths to ground.

[JoeW2]

I suspect your problem has more to do with shielding issues than a ground loop. EMI/RFI interjects niose into the signal path. The longer the cable, the greater (or worser) the problem. Think of it as an antenna.

If it was a ground loop, you would hear a consistant hum. Cable length would have little, if any effect.

Cable runs of that length are problamatic. After you avoid running them near household electrical lines, there are 'environmental' factors - TV towers, cell phone relays, etc that are sources of radio pollution. Shielding is crucial to a clean signal path.

[eisforelectronic]

Is it possible he is double amplifying pre-existing noise inherent to one or both receivers?

[douglasbjordan]

Is it possible he is double amplifying pre-existing noise inherent to one or both receivers?

Hmmm... wouldn't this only happen if I had connected receiver #2 to the pre-amp outputs of recevier #1? I've connected it to the line-level outputs.

In any case, I've also tried connecting it directly to the cassette deck (which is in the same room as receiver #1, 20 feet of cable length) outputs and still got the constant hum. I don't think that would change anything in the diagnosis.

If it was a ground loop, you would hear a consistant hum.

My initial post called my symptom a "line buzz" but after reading more about ground loop problems, I think a better description would be a "low frequency hum." Incidentally, what would be the symptoms of a unshielded line noise problem? Background hissing/static/popping? I'm not getting these (well, I might be... if I am, the hum is drowning them out and I guess if I get the hum fixed then the unshielded cables might be the next problem to tackle :-).

Thanks everyone for your help so far. At this point in my experimentation, my cassette deck is still connected directly (20 ft away =) to receiver #2. Just for kicks, I'm going to try running extension power cables from the cassette deck to the ac outlets that are built into receiver #2 and see if that changes anything. I'll probably "borrow" the ground loop filter thingy from Radio Shack and try it, as well. Thanks again!

[jneutron]

Does the hum go away when you disconnect the computer...I assume you are running into the sound card input.

Try disconnecting both rca's at receiver 2..hum goes away. Then, connect one rca shield to the receiver 2 shield..any hum? Does it hum if you touch both shields to both outers of the r#2 inputs (no signal connection, just grounds.)

When connected and humming, does pulling receiver 2 plug stop it instantly? Or, pulling comp plug. (yah, I know, lousy way to turn off computer..)

Cheers, John

[douglasbjordan]

I just got the ground loop isolator from Radio Shack and it completely eliminated the hum. Thanks everyone for your help! It's been quite educational. =)