AV Buffs: Do I have a bad input wire?

Factual Questions
1

Helloo!

I have a nice vintage setup that I inherited from my parents (B&W Matrix 1 Speakers, ADCOM GTP-500 Pre-Amp, ADCOM GFA-545 Power Amp), and for lack of a better use, I’ve set it up next to my computer to be used as my speakers.

While doing so, however, I noticed that the amplifier only accepted the red/white (or in my case, red/black) RCA cables, while my computer outputs in one of two ways: The 1/8th inch sound cable ubiquitous to computers, and a S/PDIF output.

A quick google told me that if I wanted to get the S/PDIF output working with my speakers, I’d need to invest in a converter, so that was out.

I ebay’d a cheap speaker wire, and it works… for the most part.

I first noticed a problem when I heard a hum that wasn’t supposed to be there. I re-adjusted the cable (thinking it was a contact problem), and discovered that the humming got louder.

15 minutes of wire jiggling later, and the hum’s nearly gone (enough so that it’s acceptable for general use), although since I put my legs up on the computer case, one wrong move and the wire might move a little to the left or right and the humming starts up all over again. Argh!

It seems like the wire’s shorting itself, because if I bend the wire the wrong way, the humming also comes back. Upon closer inspection, it seems as though the RCA-headphone wire is not a twisted pair, if that makes any difference.

So my questions:

[ol]
[li]I’ve pretty much narrowed it down to the fact that I bought a cheap cable. $3 only gets you so far when you want high-quality audio. Would buying a new cable from a reputable store fix this problem, or is the problem not the cable, but something else?[/li][li]Is it still safe for me to use this cheapo cable until I can get a suitable replacement?[/li][li]Is there any difference between using an RCA-to-headphone wire as opposed to a $1 adapter?[/li][/ol]

For those musically inclined, the buzz is a B natural or C.

2

Could be anything, but my bet is “ground loop.”
Make sure both the computer and the amp are plugged into the same plug strip, and try running a ground wire from the chassis of the amp to the case of the computer. You might also try breaking the ground connection at your audio input.

3

It’s probably a ground loop hum, and probably has nothing to do with the quality of the cable. Most computers are not designed as high-end audio components, and they are often quite noisy electrically.

You might try using a ground lift, i.e., defeating the ground connection of one or both components, but that’s not as easy as it was back before all electrical plugs were polarized, and you could just pull them out, rotate them 180 degrees, and plug them back in. It often works, but it’s not a good idea, for a number of reasons.

The best solution is an isolation transformer. You can also get a similar item from Radio Shack. Check the connectors: the one from Amazon has males on the input side, so you could just plug the adapter cable you’ve got right into it.

Here’s more than you ever wanted to know about ground loops.

Good luck.

4

Thanks for the quick responses, both of you :slight_smile:

beowulff, the amps and my computer are not plugged into the same power strip, and I neglected to mentioned this before, but now that you brought it up - it is a very important point:

The amplifier are running on 240V with normal North American plugs, which plug into a power bar with these plugs. That power bar plugs into a massive (must be 20-25 lbs) transformer, which takes a normal 110V household current and outputs 240V to power the amps.

5

It’s possible that your mondo transformer is inducing hum in the input leads. Try moving everything as far away from it as you can.

6

I tried moving things far away, moving things closer, jiggling the wire even more, cursing, crying, etc.

Only difference was that the more I jiggled the wire, the more often the buzzing happened.

I brought a $6.99 RCA-to-Headphone wire. Problem solved. :wink: