Barking up the wrong tree

August 18, 2022
 by Paul McGowan

When we're chasing down audio gremlins like hum or jitter it's always helpful to know what's actually happening.

Take hum for example. We might suspect a nasty buzz is caused by something (seemingly) obvious, like the AC powerline, but later find out it was from a cable TV ground.

Or jitter. If we hear an improvement in sound quality after upgrading our ethernet cables we might think we're lowering jitter. Of course, there is no timing in ethernet (so no jitter either), though it's entirely possible we lowered noise and that affected something else that's prone to jitter down the line.

If we know what "tree" our problem is sitting in it's a heck of a lot more effective than simply barking up every tree until something shakes loose.

Take a moment to understand the potential sources of the problem first.

You're much more likely to catch what's hiding up in that problem tree.

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27 comments on “Barking up the wrong tree”

  1. Anyone who is missing 'Soundmind', aka Mark Fischer, go here
    & read his post in the comments section under 'Mark Fischer' 😀

    https://www.youtube.com/watch?v=gzYDmP51_ig

    Also, it is now claimed, by at least one YT home-audio reviewer, 'Jay Lee',
    that a sonic difference in audio cables can now be scientifically measured 😮

    "Scientist Finds Measurable Difference In HiFi Audiophile Cables ! PROOF"

    https://www.youtube.com/watch?v=a4R6I_TtKQQ

    Enjoy!...or not.

  2. Am I the only person who doesn't bark up the hum and jitter tree? Even when I had rubbish electrics I had good grounding, and now I have brand new, superb electrics and great grounding. Very low impedance as well. Fibre cable to the audio system (did that years ago). These are all basics. The only hum I've had related to placing a power supply too close to a phono amp, easily resolved by separating them and using shielding (Devialet Expert with a 4mm copper base plate and full metal jacket acts as a great shield), and when a ground cable fell off. Get the basics right and stop worrying about cables.

  3. I love the sound of conrad-johnson amplifiers. I know it is corny but their slogan "It just sounds right" says it all. I also hate to say that sometimes their amps hum. I have pair of P12's that I used as my power amps. I noticed that when I turn on my system I could hear a low level hum, that did not sound like a ground loop hum. Sometimes the hum was there, sometimes it was not.

    So, when I heard the hum I did not bark, I listened. The hum was coming from the right channel. So, I switched the amp leads and the hum stayed in the right channel. So, I listened to the right channel with no music playing and discovered that the hum was NOT coming from my right speaker, This perplexed me. What is humming? What was humming was the right power amp. How can this be? The amp is humming. But the sound goes through the cables to the speakers, right? No, wrong.

    After touching various part of the amp while it was on I discovered than when I touched the power supply transformer the hum stopped. The transformer was physically vibrating inside causing a low level hum sound. To make maters even stranger when it warmed up ( after about 30 minutes of power on ) it would stop humming. And it the summer it hummed less and in the winter it hummed more. The transformer had a metal shield around its sides, but was open at the top. I found that when I touched that shield the hum stopped. This went on for a year or so.

    Then, one day, I had an ah-ha moment. I took a library index card ( remember those ), folder it in half and slipped into the small space between the shield and the transformer. The hum stopped!

    Don't bark, listen and think.

    1. Regarding amplifier transformer hum another possible source is DC on your AC mains. You can buy or build a DC blocker that can fix this as well.

      My earlier amps had this issue and the DC blockers removed the hum.

      Another effective method similar to your library card is to fully encapsulate the transformer in epoxy and prevent the vibration.
      My latest amps employ this method so no need for DC blockers.

      I assume the PS Audio regenerators remove DC from the AC mains as well.

      1. You are right about DC and transformer hum. I was pretty sure it was not caused by DC because the P12 is a mono amp and its twin did not hum at all and was plugged into the same power source.

  4. What todays post seems to be about is classic troubleshooting. Cause and effects. Fixing the symptom only masks the cause. Understanding why a cause created the symptom in the first place leads to better overall understanding. Orderly isolation is the key. Don’t pick the most esoteric cause but the most probable and easiest to address. Move up and on from there. Knowing when you’re going in over your head and when to call in ‘the troops’ is equally a requirement.

    1. Also, based on many years of experience troubleshooting there have been many times when the thing "it can't possibly be" and you eliminate early ends up being exactly the cause of the issue.

      1. That’s why starting at the beginning and working forward or starting at the end and working backwards is best. Even with experience starting in the middle makes an assumption. Looking at the few replies, we all know that assume makes an ass of u and me 😀

    2. That’s so true about going for the easiest option first. Apart from the fact that it is the ‘easiest’ it’s also the more likely cause. Many times in telecoms colleagues would suggest the most convoluted reasons why something had gone faulty when it wasn’t that uncommon for the cleaner to have turned the power off.

  5. Living in an old farmhouse wired in the early 60s, balanced cables are my saviour. Prior to going XLR, it was ground loop isolator central ‘round here. I’m certain the house has tinnitus and anything you plug in becomes a carrier…

    Several years ago, feared concern forced me to hire an electrician to come & check the old green cloth looking wrapped house wiring. “Oh my…” was his reaction when he saw it. “That bad eh?” I reaffirmed my dread. “Nope,” he said still gazing at the basement ceiling joists, “Don’t TOUCH it! There’s more pure copper in this wiring than ten new houses.
    So ONE good thing for my old dilapidated crooked sinking Dr Seuss house!
    Plus it is easier to make an omelette when the pan/stove/floor are at a 13 and a half degree slope… 😉
    Sometimes when I leave my home & stand outside I get “house legs”…

  6. “ Take hum for example. We might suspect a nasty buzz is caused by something (seemingly) obvious, like the AC powerline, but later find out it was from a cable TV ground.”

    I know him, 60 or 120 Hz.
    But when I added a new power amp pre-out, the buzz was awful.

    I barked up all the trees I could find until I discovered the cable box issue. A $15 part fixed it.

    Doh!

    1. Yup, I remembered some trouble shooting in my PSaudio manual…but inpatient as i am i thinned out some HDMI and just have optical except for CD player..but if i want to watch a DVD i will see what happens when i reconnect that HDMI. And eventually my little record player

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