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Positive Feedback ISSUE 32
july/august 2007


Audio Ramblings - Part 2: More AC Gremlins and hum...
by Dave Clark


Okay, so here's Part 2. I decided to break these Ramblings into two parts as they deal with different issues relating to audio gremlins that require different fixes—the first you can buy the excellent PS Audio pieces or find the culprit, but this one deals with something that one has to solve on their own. As I ended Part 1 I mentioned a hum in the cables… ah yeah, this is a good one.

In moving up from the Clayton M100s to the much-improved M200s, Wilson decided to make some changes in the amplifier's design. One change did not relate to the gremlin issue, but bears a mention, in that the amplifiers, which run in class A, now only run in high bias—meaning that they do get hot. The M100s had the option to switch them from high bias to low bias where they ran much cooler and drew a lot less AC from the wall. Yes, you could switch them to high bias where things could not only heat-up, but warm-up tonally—that is, they sounded just that much sweeter in high bias. It was nice to have this option and it allowed me to keep them on and ready to play 24/7. The new M200s stay hot 24/7 meaning that they should be switched off if one wants to be seen as being green (they pull 450+ watts from the wall and the heat sinks feel about the same).

Two, while both models are fully-balanced designs, the M100s allowed for either RCAs or XLR connection via your choice of interconnect. With the M100s, I used either the Audio Magic Clairvoyant 4D or the Kubala-Sosna Emotions to very good effect. The AM cables are unshielded silver ribbons (lower capacitance and higher inductance/resistance), the KS are, well… not sure as Joe prefers to let the cables speak for themselves, but I do believe that they are based on larger gauge stranded copper conductors in a shield of sorts, all bundled in some geometrical arrangement (higher capacitance and lower inductance/resistance). Loved both cables as each made their own interpretation of music quite synergistically with the Cary SLP-05 (and before that the Blue Circle BC2000) preamp and the Clayton M100s. Always dead quiet and never a worry, whether I ran single-ended AM or KS, or balanced KS cables.

Along comes the fully balanced M200 with only an XLR input. Wilson decided that the added circuit and crap needed to convert from single-ended RCA to balanced was not worth the trouble, and while the Cary SLP-05 is also fully balanced, well got to go the balanced cable route now… no way am I going to muck things up with some adaptor. After all, since the preamp and amps are fully balanced, let's see them at their best. In goes the XLR versions of the Emotions and everything is hunky dory. The single-ended AMs I own, and converting them to balanced is not an option at the time, nor do I feel like begging Jerry to loan me a 3-meter balanced set—these are rather $$$ compared to the more affordable KS Emotions. Besides the Emotions are singing such a magical synergy, let's leave well enough alone for the time being. Audioland is a happy place. So I live with the KS cables between the SLP-05 and M200s (and remember I used them with the M100s as well) for a few months till Jerry and I are able to get the AMs converted to balanced XLR versions. What actually triggers that event is that Jerry had re-worked the Clairvoyants' design a bit and changed the metals used (now a blend of sorts) as well as a few other secrets up his sleeve. He was excited for me to hear this upgrade, so I sent him my single-ended cables to do what needs to be done to get them up to snuff and XLR balanced versions.

After a few weeks, I get the cables back, in they went and boy …what was that hum from the speakers?! Not an intolerable hum, but it was audible from across the room when no music was playing—so yeah, right …not really all that tolerable. What's really wild is that if I turn the preamp off and turn the amps on, the hum is that of a shorted ground connection—like when a cable's ground at the preamp is broken while the amps are still on …loud enough that it was audible from a few rooms down the hall! HUMMMMM! Scared the bejesus out of me! With the preamp on, the hum was way down in volume, but like I said earlier, still audible. What the heck is causing this? In goes the balanced KS cables and dead quiet—even with the preamp off. Back in go the AMs and the system is humming like there's no tomorrow…. Okay, so what is an audio bum to do? ARRRGGGHHHH!

Let's start the trouble shooting. First we check the XLRs of the Cary SLP-05 and M200s and both follow the industry standard as to pins (Pin 1: Ground, Pin 2: Positive signal input, and Pin 3: Negative reversed signal input). No problems there, they should play fine together. Output impedance of the Cary is 300 ohms, input of the Claytons is like 100k ohms (the amps use a separate amplifier measuring 47k ohms for each of the two balanced signals and Wilson says this makes them a more or less 100k ohms input impedance for a preamplifier.). No problems here either, they should play fine together.

Both manufacturers say that the designs are truly balanced, so what am I to believe? Doubt that either of these guys are out to mislead the world or haven't a clue as to what they are doing circuit wise. So that can't be an issue.

Check the continuity of the cables and everything is fine: Pin 1 to Pin 1, Pin 2 to Pin 2, Pin 3 to Pin 3 on all the cables. So that is not an issue… they all play music and pass a signal. No shorts, no faults.

Let's try some other cables. Borrow a 3-meter length of DH Labs balanced Revelations… they hum. Borrow balanced versions of a 3-meter length Townshend Audios …they hum too. Try some balanced Bybee cables …they hum! Okay so now this is weird …all the cables hum except the KS. All are balanced, and the AMs that hum did not hum when ran as single-ended versions between the same preamp and M100s—also a balanced amp.

Let's get crazy here… after by now we are grasping at thin air! We tried lifting grounds at the AC on any and all components in every conceivable combination, we disconnected everything hooked-up to the 05 preamp, we connected separate ground wires between the preamp and amps' chassis, moved stuff here and there, changed tubes, tried different power cords, did the hokey-pokey, etc. The cables still hum—no change. We tried this during different times of the day, the phases of the moon, sober, not so sober, etc. Nothing worked to eliminate or show a reason for the hum in any of the cables …or for that matter why there was not a hum in the KS cables. ARRRGGGHHHH!

Okay, let's try running a single-ended cable from the preamp out to any of the balanced cable(s) that hum with an RCA/XLR adaptor …uh, they still hum, though not as loud.

Okay, let's chain the balanced KS from the 05 preamp, individually into the three that hum …they still hum, though down in volume at about 50%. Okay that is weird… maybe it is an issue of cable design and/or measurements then? Uh, the KS and AM cable guys all suggest not.

Okay, let's connect the Clayton amps to my two balanced CD sources' outputs (the Cary 306 and EMM CDSA both feature balanced outs) while they are either off or on (no music playing naturally, duh…) …ah, none of the cables produce a hum through the amps—ALL are dead quiet. Huh, must be the SLP-05 preamp then!

Okay let's try two other balanced preamps (Cary SLP-03 and an E.A.R. 864) with all the same cables, AC wiring, amps, and …we get no hum at all—all of the cables are dead quiet with either of the preamps off or on and the amps on. These preamps are fine with all the cables when connected to the Clayton amps. The two preamps have the same output impedance as that of the SLP-05, so that appears not to be an issue. Are they of the same balanced design? Probably not. So then is it the preamp or not? It has to be, as these two preamps work just fine—they are dead quiet in any configuration. Yeah, but if it was the SLP-05 preamp, why no hum from the KS cables? ARRRGGGHHHH!

Alright, let's get some people on the phone… Wilson what do you think? Amps are fine. Dennis what do you think? Preamp is fine, as a matter of fact we have the same AM cables here and they are dead quiet with the SLP-05 and any of our amps. Jerry of AM, what do you think? Cables are fine. Joe at KS, what do you think? Cables are fine. Okay, let's go further away from the parties involved… someone more impartial. I called the who's who of audio and none could offer any idea as to what was going on to help me out—that is they all either came up with something different or nothing at all. What I got ranged from: it could be an issue of the Cary and Clayton not liking each ground-wise via the other cables… they like each other with the KS, but not the others due to some impedance/resistance issue; to it could be that one of the components is either not balanced or a poor execution of a balanced circuit, so you got problems; to you got me, that's a real head-scratcher. In other words, no one really knew exactly what was going on—though I suppose they all could be right! At least to some degree, but that would be a real kicker no wouldn't it? Yeah, maybe it it is a little of this and a little of that...

I would like to add that in talking to any and all involved (or not involved), that everyone was extremely helpful and at no time did anyone make any attempt to deflect the blame or cast doubt on other products and/or people either in general or specific terms.... everyone was great and all were as perplexed as I was as to what was going on!

Anyhow, let's send the preamp back. Maybe something is out of spec, perhaps a cold solder or something. After all there is no hum with the other balanced preamps, so something might be out of whack here. Off went the SLP-05 to Cary and after a couple of weeks I get word that …that …it's fine, nothing wrong. Measures fine, checked the soldier joints, etc… all okay here. They played it for a week 24/7 and it was dead quiet. Yeah, but then it must be the Claytons then! Well too difficult to send them back and since they work with other preamps… nah, they ain't the issue.

So the Cary arrives back here, and in it goes and would you believe me if I said the AM cables were dead quiet? I mean wouldn't that just be a slap on the fanny and coolest thing to ever happen? Well they weren't. Hummed like before! Okay, this is ridiculous, something is going on here. All I could figure is that the KS cables are higher capacitance and lower inductance/resistance and the ones that hum are just the opposite… ah, Jerry, let's change the ground to something bigger with less resistance. That has to be the issue. Something in the cables is not allowing them to establish a ground connection. Well, okay Dave but I really do not think that is the issue… ARRRGGGHHHH!

Okay, but before I send them back, let's try a Jensen isolation transformer… no affect whatsoever.

Now I am really nonplussed. So okay, there's one last thing to try here. Off the rack comes the Cary SLP-05 and on the floor it goes. Next to it I move one of the M200s, connect the two with a 1-meter length of the AMs (same design as the 3-meter that is humming) and …dead quiet. Nothing, silencio. Okay, in goes the 3-meter AM and… dead quiet too. Okay this is weird, you were just humming like crazy a minute ago, so now you are really pissing me off! What's so different? Well, the preamp and amps are on the floor in front of the rack… so back goes the amp to its normal place and still no hum. Okay, back goes the preamp and run the cables as usual and….the big hummer is back.

Okay so it hums on the rack with the cables routed as usual but not on the floor. Alright, let me move the right interconnect under the preamp and out the front of the rack and over this and around that, and… no hum! Ah he says…something on or near the rack is causing the hum. Yeah, but it is a wood rack. Okay, but let's try the other interconnect anyhow. The left one is more problematic in eliminating its hum, but we can get it almost down to nil. So, we decide to start at step one and take everything (component, cable, whatever sees AC or can produce a field of some sort) off the rack and then run the cables where we normally do to establish the hum as a foundation. We get the hum and start to route each interconnect just so (well, so we can live with it and it does not look too odd) and the hum is, for all intents and purposes, gone. In getting things just so we find that the right side of the rack is worse than the left… odd. Something is in the wall, as it appears that the farther away we move either interconnect the less hum, the closer to the wall they are, the louder the hum. And it is more powerful towards the right side than the left side...

Okay, with the preamp, amps, and AM cables sitting quiet and all, we add each component back one at a time. In doing so we find that this AC cord from that causes more hum here than there, that some accessories need to be moved way far away, and that if I run various cables just so and place Shakti Onlines and Stones at key points, the system is dead quiet—no hum at all with the AM cables and they sound quite magical. Of course the KS cables can go anywhere and sound quite magical in their own way as well! Nice to have an option!

Odd that I never had this issue before, never with any cable. Okay, so it must be an issue of these cables not being shielded, and the KS being shielded in some way, combined with what is going on inside the wall, and then something odd happening between the Cary preamp and Clayton amps (none of which is meant to be, nor should be construed as, an indictment against any of the products directly involved—or not directly involved! They are all top-notch!). It is odd though, that the AM's unshielded versions never hummed when ran as single-ended between the SLP-05 and M100s, but the balanced versions do so like a banshee with the M200s, even though the two amps measure the same. One would think that running balanced should address that issue... weird it is!

Well, as it stands, I do know that there is something in the wall that some cables do not like, and that in this configuration, the Cary and Clayton combo will cause these cables to hum, though not others. That is the combo allows some cables to be susceptible to whatever gremlin is in the wall. What is in the wall? I have no idea. Nothing there that I can figure would cause such an issue, but it is an old house so perhaps someone has placed something, somehow inside the wall to make my life not so happy in audioland. All I know is that I have figured out how to get things to work, I am able to use various cables without any problems, and well …the gremlins are once again under control …at least for a while.