I've been setting up a new system (to me; most gear is used) and had a hum in the speakers. I started disconnecting equipement, and finally determined that I could reproduce the hum when only the pre-amp (NuForce AVP-16) was connected to the amp (Parasound HCA-1000). I could remove all other equipment and still get the hum (no video was in this system at all). So far, so good.

Interestingly enough, the hum was present whether or not the pre-amp was on. As long as the amp was on, and connected to the pre-amp, the hum was there. Turning on the pre-amp changed the hum a bit, but not much.

Disconnecting either of the interconnects would make the hum go away.

Now, this is where it get weird, for me. The interconnects I was using between the pre-amp and the amp were Kimber Cable Heros that I bought about 9 years ago. On a hunch, I pulled them out and replaced them with some newer Blue Jeans interconnects I have, that use the LC-1 cable. Hum is now banished from the system.

Anyone want to take a shot why the Heros hummed (there's a joke there somewhere) and the Blue Jeans did not? Looking at the specs, all I can see is that the capacitance of the BJ cables is lower (36 pF for a 3 foot cable, as opposed to the Heros @ 76.5 pF) but I'm not sure what to make of that. And I don't know if the specs on the Heros have changed over the years.

I suppose it's possible the Heros are damaged, but if I removed either one, the hum went away so I'm thinking that means they would both have to be damaged in the same way. I also have no recollection of any event that would have caused damage. In fact the sat for a few years unused.

Anyway, just wondering why this happened.

It may have been because your previous interconnects were not a balanced 75ohm.

Interesting, thanks. Is it more crucial to have balanced 75ohm connectors between a pre-amp and an amp than say, between a CD player and a pre-amp?

75 ohm has NOTHING to do with analog audio. My guess is that there is some electrical interference in your system and the Heros were improperly shielded and the BJ cables are properly shielded.

Typically a hum like you experienced is due to the pre-amp and amp being plugged into different outlets, although there can be numerous sources for this problem.

You can be pretty sure you had ground-loop issues, not an interference/shielding problem. Were you replacing balanced interconnects with un-balanced? I believe your pre-amp is capable of either.

No, both are un-balanced. Pre-amp has balanced connections, but amp does not.

Both are plugged into a garden-variety surge suppressor. Other than changing the interconnects, I made no change that would have affected the presence (or lack thereof) of a ground-loop.

Even when I plug everything back in (again, no video/cable) and turn the amp on: dead silence. Although when I turn the pre-amp on, I get a barely-perceptable hiss out of the tweeter, which I can only hear when I put my ear right next to it. Does not get louder with volume.

Kimber Cable construction from the SoundStage! web-page:
In "Kimber Speak," the Heroes are assembled using Varistrand® conductor geometry, GyroQuadratic field geometry, and Teflon®-based dielectics. Translated to plain English, the Heroes consist of four Teflon® coated copper wires of varying gauge braided in a particular geometric configuration. According to Kimber, the construction of this cable is designed to reduce signal and return/earth interaction as well as offering heightened immunity from RF and other types of EMI. Those hungry for additional technical details or interested in seeing phrases such as "field relational format possibilities," "interleaved polarity," "summed flux density," and "periodic ratios," used in actual sentences can click over to the Q & A portion of the Kimber Homepage [http://www.kimber.com/] for further exploration of cable design theory.
That sounds like it has a large number of ways to get it wrong!

I didn't mind when my patch cords would go bad and hum but now that they're "interconnects" I expect better.

LOL, so true. Particularly when you pay so much.

I'm sure glad I found Blue Jeans.

You may likely never get a good answer. I have a very hum-proof system (audio only, no video allowed) but got several pair of Van Den Hul cables that hummed like crazy in my system. No other cable or equipment has ever hummed in that system. Several friends have tried them and had no trouble at all. I have three pairs, purchased new so I'm pretty confident they are good.

That said, I've heard quite a bit of "buzz" about the NuForce stuff being prone to hum, more so the older your version.

I just put one of the Heros back on, with the other still being BJ. Same result, even if I carefully route the cable away from all power cables.

I guess we'll just chalk this up to a case of "anit-synergy." NuForce: No Kimber Cable for you!

The ground (shield) connection in the cable must be missing, broken or reversed. Do you have an ohmmeter?

Somewhere, yes. What do I test - the outer barrel of the connector?

Somewhere, yes. What do I test - the outer barrel of the connector?


Just throw them in the trash George, they've gone bad. With 35 years in this hobby I've had many patch cords go dead or start humming. In the trash they go and I'm off to Radio Shack or digging through boxes of parts looking for some other ones.

Yeah, I wasn't looking to fix them. Just an inquiring mind that wants to know "why."

Just throw them in the trash George, they've gone bad. With 35 years in this hobby I've had many patch cords go dead or start humming. In the trash they go and I'm off to Radio Shack or digging through boxes of parts looking for some other ones.

I wonder if you see the correlation between Rat Shaq and busted cables?

I wonder if you see the correlation between Rat Shaq and busted cables?


Actually it's mostly the "gimme" patch cords that come with the gear that have gone bad, Radio Shack cords are pretty well made. Cheapies from Parts Express hold up well too.

In any event they're cheap enough that replacing them would be no hardship. But if you want to buy something else on the odd chance you might save yourself a trip to Radio Shack have a field day.

Somewhere, yes. What do I test - the outer barrel of the connector?

Yes I'm just curious myself, not to salvage them. See if the shield connection, which is the outer concentric part of the RCA connector measures near 0 Ohms to the same place on the other end of the cable. Ditto with the male center pin.

Just throw them in the trash George, they've gone bad. With 35 years in this hobby I've had many patch cords go dead or start humming. In the trash they go and I'm off to Radio Shack or digging through boxes of parts looking for some other ones.

Wow, all that experience and that is your answer? Hmmmm....

While they could indeed be damaged, before throwing them away, why don't you first try them in another system and see if they don't work fine.

About 22 years in this hobby have taught me that anomalies happen sometimes that are difficult to explain.

Wow, all that experience and that is your answer? Hmmmm....

While they could indeed be damaged, before throwing them away, why don't you first try them in another system and see if they don't work fine.



Not worth the bother, not to me. Trying them in another system would involve moving furniture and other hassles that are more trouble than getting another set of cords.

I'm not sure about those Kimbers but they may be directional. Is there an arrow or anything on them? You said it only happened with both cables connected. Were both arrows (if any) pointing the same way?

Before I get flamed for talking about directional cables, if they are like some of the boutique cables, they aren't a normal coax. They use a twisted pair arrangement for the signal and ground which are connected at both ends. They do that to reduce capacitance. The shield around the whole works is only connected at one end to prevent ground loops. Normally, you'd want the grounded end of the shield hooked to the source component but it can work either way as long as they are all hooked up the same.

Of course, they may have just gone bad. ;)

Before I get flamed for talking about directional cables, if they are like some of the boutique cables, they aren't a normal coax. They use a twisted pair arrangement for the signal and ground which are connected at both ends. They do that to reduce capacitance.

What you are refering to is shielded twisted pair (STP). STP cable would not have RCA connectors.

In real STP cables however the reason for twisting is not to reduce capacitance but to reduce the loop area and induced differential mode noise. It only works with equipment having balanced interfaces.

STP cable would not have RCA connectors. You wouldn't think so but some boutique brands are made that way. I'm not sure about the Kimbers in question but I'm guessing they are since you can buy the same cable with either RCA or XLR connectors. Not that I endorse the practice or anything. Plain old coax is good enough for me. ;) Just trying to come up with an explanation for why either cable alone worked fine for the OP but he had problems with both of them connected and I was thinking the directional thing might be something to look into.

OK, I checked the Kimbers, and there is no indication of directionality.

On my DMM, the resistance for both paths within the Heros came in the high 1-ohm range, although I don't think that's an accurate measurement - I had a hard time getting a consistent reading, and I think most of the resistance measured was due to the small point of contact between the probes and the cable.

FWIW, the BJ cables came in at the same range - high 1's.

Thanks for all the replies. Always good to get a continuing education, even if the answer is "dunno."

Contact Kimber. They'll probably replace them at little or no charge if they think they're defective.

BTW, not sure about the Heros, but some Kimber Kables have no shielding per se.