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Positive Feedback ISSUE 32
july/august 2007


Audio Ramblings - Part 1: AC Gremlins and PS Audio's UPC-200HB
by Dave Clark


Audio gremlins… don't we all just love them? You know what I am talking about: the hum that comes and goes… how everything is just perfect and out of the blue, things just don't work as they had prior to some inconsequential change. Except one realizes eventually that this change was not so inconsequential after all. So you change this and that, and after while nothing is working as it should! Nothing makes sense and getting the system to play happy and nice as a whole becomes an exercise in frustration. Irritation and nerves become raged, tempers flare, and you just toss in the chips.

In the past few months of making music with the new Clayton M200 amplifiers, I have had a few gremlins make the world of happy audioland become an unhappy place—one where the populace, laying in trembling fetal positions as they pull their hair, sing the mantra of "What the heck, this makes no sense…" over and over.

First off there was the audible hum from the amplifier's transformers that would come and go. Hear it now? Yeah, the transformers are humming. I can hear it from across the room! Odd, it didn't do that earlier. What's going on? Got to be DC in the AC. Okay, but what is causing it as it wasn't there earlier… or later… or just now it stopped…. No wait it is back!

Let's try a different outlet. No fix. Float the grounds. No fix. Let's unplug this and that and see what may be causing the problem, after all the M100s never hummed and nothing else has changed. Well, not true. The M200s use a different transformer, so perhaps the new trannies are more susceptible to DC that the older ones? Okay, that is reasonable—though one would think that time would allow for better designs so that they are less likely to be set a humming from this AC/DC gremlin. Plug this in, un-plug that—after an exhausting day of trying every combo and nada… still comes and goes during the course of a day.

In for the rescue the PS Audio's UPC-200HB designed to address hum caused by DC, along with an XStream Statement AC cord ($499) to get the most from the wall without any hindrance of restraint. In they go and heck… plug the M200s into the two outlets and…. no hum. Dead quiet the amps are… all during the day and night. Never an audible hum from even a few inches away. Heck, the PS Audio works… though what else does it do to the amplifiers? Anything on the downside?

Letting the unit cook with the amps for a few days, and after some critical listening, I found the PS Audio unit to impart little if anything of its own character into the music. I have always found that the Clayton amplifiers (either the M100s or the M200s) sound their best fed straight with no chaser—that is direct into the wall (their own 20-amp circuit with 10-gauge Romex wire, a pair of Jena Labs' cryo'd Hubble outlets, and each with their own JPS Aluminata AC cord).

The UPC-200HB uses PS Audio's Ultimate Power Cell Technology, has one UPC module, one Humbuster module, and provides for unrestricted high current via its two Power Ports. With all that inside the unit allows for: 100% surge and spike protection, creates a one way gate for noise, blocks DC from the power line, lowers or eliminates transformer hum, stops internal mechanical hum, and therefore, eliminates core saturation in a transformer. You get a very smart and elegant box that packs all Paul has garnered over the years to address various AC gremlins for just for $499. A good deal for sure.

With all that I expected some sonic signature to reveal itself—another gremlin to deal with? Not really, though I found there to be a slight residual coloring to the sound—nothing that would draw attention to itself, unless one went back and forth between using the pair and not using them, and who in the real world would do that?! This coloration was perhaps best described as an ever so slight shift in the frequency balance—a bit less hue and color to the mids. This is less of what one hears without the pair; a slight thinning of sorts. Nothing serious and not something to waste any more time on, as this was not the least detrimental to the music—or to the fact that the hum was gone. One could even prefer this slight thinning as cleaning up the middle and after all don't many of us here need to clean up our middles a bit anyhow? Even so, this was an artifact that robbed the music of a warmth or presence that could be, for some perhaps, more musically beguiling. Of course, if your system and music needs this sort of shift, then be happy—this is the way go.

The PS Audio combo did allow for the bass to get a little lower and deeper, though perhaps a bit fatter as well. More bloom to the bass than without, not a bad thing, but certainly a different thing. This would be a benefit for those who need to add a bit of bloom and fullness to their music, but as my system sits, this is not where I need to go. We are quite happy with the performance at that frequency range, so this addition was not a plus. So we were not as happy

Would I recommend the pair? Without a doubt they drove the gremlins away and did so with little to criticize. The slight audible changes could be construed as either being a godsend or a mucking with what you got, though like I said, this was not a deal killer. So sure, the combo is highly recommended when the AC gremlins are causing things to go south.

Of course it would be nice to figure out what was causing the DC and then a device like the UPC-200HB would be superfluous, unless what else it did was necessary for one's happiness in audioland.

The amplifiers are not humming in the AM, but really hum in the PM—what's the difference? So we get up early and after a good coffee or two, turn on the system and no hum. Okay, what else is on or off in the house? Well, in searching around we realize that nothing else is on, except for the Malibu light transformers, the refrigerator, and the coffee maker—but these do not appear to be causing the hum as there ain't none. Even so, let's unplug them one by one and see what happens. Nada, no change… no hum, no change in any sense of a hum. Okay, so now the fun begins as we turn on one light, appliance, whatever that is plugged into a wall outlet throughout the house, one by one.

Anything now? No, dead quite. What about now? No, nothing, still that same. Okay how about… stop they are humming. What did you do? I turned on the halogen light above the stove. Try it again. Okay, how about now? No, they aren't humming anymore. What about now? Yeah, now they are.

Okay, so if the light is on low the amplifiers hum but on high there is no problem. Cool, found the problem, but to be sure let's continue throughout the house. Well after a good hour or so of turning this and that off and on, we found that the dimmer for the lights in either the living room or the dinning room causes DC and hum in the transformers, depending on where the dimmer is set. Ditto the light above the range. So the fix is to make sure these are off when listening, and then we get no hum. Gremlin found and removed. Happiness in audioland returns, and so I guess I don't need the pair from PS Audio— heck I just saved me a grand!

Ah, but what is that hum coming from the system now? And, yeah, the lights are off… and this hum is sort of oscillating as it comes and goes… so in goes the pair from PS Audio and fixed again. Except it ain't anything in my house causing it as there ain't anything on that could cause it… got to be the neighbors then, and well… been trying to fix them since they moved in. What to do? Well, I can either live with it or concede to the powers of PS Audio, except this hum is new and after a few days seems to have left audioland, as the system is dead quiet again. So I decide that since the amps like it best straight into the wall, let's keep it au naturel. I can use the money, and besides, simpler is usually the better.

So as fine as the PS Audio's UPC-200HB and XStream Statement AC cord are, let's keep it simple. Still recommended for those who just can't find them gremlins… like the ones causing the hum in the cables…. Yeah, that's in Part 2!