Hi All, recently purchased a used Krell Showcase amplifier to run my center and rear channels (plan on adding more later) However right now I have my C18 throwing a humming noise when the showcase is on. Its pretty noticeable and annoying as heck! The C18 doesn't throw any sound if i plug it into my receiver, and never acted like this with a previous PS audio m700 so I do not think its the C18. Right now it sounds like just the motion tweeter is what makes the noise. My other two speakers EM-ESLs do not have any noises or hum from the krell. I was wondering if anyone had suggestions? Right now I am running them all single-ended RCAs. The XLRs do not have any shorting pin as the unit did not come with any. I did order some and hoping they arrive soon but not sure if that really is the issue...Any help is appreciated!
Humming Sound C18
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Couple things.
Are you saying that you have RCA interconnects plugged into the Krell amp and the amp doesn't have shorting pins installed on the XLR inputs? I wasn't aware that this would work without issue, or maybe it's the cause of the issue.
Try unplugging the AC adapter for the C18, while the system is on and active, and see if the hum stops. If it does, then it's a ground loop hum and the adapter should be plugged into a different outlet that the amp likes.
Are you saying that you have RCA interconnects plugged into the Krell amp and the amp doesn't have shorting pins installed on the XLR inputs? I wasn't aware that this would work without issue, or maybe it's the cause of the issue.
Try unplugging the AC adapter for the C18, while the system is on and active, and see if the hum stops. If it does, then it's a ground loop hum and the adapter should be plugged into a different outlet that the amp likes.
So yes I have RCAs plugged in without the grounding pins.
However I found the culprit and wasn't expecting it. I found when I traced back to my avr, that when I unplugged the hdmi from the avr output to the TV that the hum went away. I played music without that HDMI attached all was good. However if I get the hdmi plugged back into the avr or even touch the back of the avr case with the HDMI cable the hum returns.
I replaced the cable and it helped a bit not as loud of a hum however not sure how to resolve this. My avr is kinda junky its an Onkyo rz920, it actually only has a 2 prong on the unit which I didn't realize and both the avr and TV are plugged to my panamax 5400. I'm not sure if it's the TV or crappy grounding in the avr....
Then it's a ground loop hum. You'll need to swap cords plugged into outlets to find a combo that works.
Map out what's plugged into which outlets on which circuits, mix and match, and see if some things, like the tv, can be plugged in closer to the AVR. You can also try lifting the ground on one component or another, like the tv for example.
Using a 3 to 2 prong adapter on the tv might resolve the hum. There's lots of info on this that talks about HT equipment being on the fewest grounds if possible. There are lots of ways to create ground loop hum, and the same amount of ways to avoid it. It just takes some experimentation to make it go away.
How about using something like a Furman power conditioner? Plug it all into one or two of those? Its what I use and Ive never had a problem. There are other brands too that probably work well, but the Furman is pretty affordable. Ive never experienced ground loop hum though, even when I was just using power strips.
Leporello
Well-known member
Just for grins and giggles, Is the 2 prong plug on the AVR reversible? Try reversing it.
Leporello
Well-known member
A power conditioner may or may not help. Unless it's capable of providing complete galvanic isolation between hot, neutral and ground of the input, and the output, it probably won't. It would require a large and expensive transformer to do that, which would not make it affordable.
Even if you understand the basic principle behind ground loops (for an ancient reference try Howard Tremaine's "Audio Cyclopedia"), abating them is often a matter of trial and error, since it's often difficult to determine where the loop is occurring. But throwing a power conditioner at it isn't the first thing I would try, unless you can borrow one.
Leporello
Well-known member
Other question: what happens if you leave the HDMI plugged into the TV, but have the power cord to the TV unplugged? And is there anything else plugged into the TV.
I have had a somewhat similar problem, which I will describe below.
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Have you consider a fiber optic HDMI cable? I have read that some people had luck with those and ground loops.
How about how thick or what material the insulation on the wire is made of?
Just to provide an update, found the hum was from the TV/AVR. The HDMI from the output to the TV was the source causing the hum. swapped the hdmi out and added grounding pins to the XLR of the new amp so far its been quiet since both changes
StimpyWan
Well-known member
A video ground loop can make for very loud, nasty hum. I'm glad to hear that you've resolved the issue.
There used to be a couple of different audiophile humbuster boxes available, but no longer. Pro audio has a few that could work for a stereo system, using adapters.
So what exactly was the cause in this case?
Leporello
Well-known member
Looking at the Krell Showcase amp, it looks like instead of having a switch on each input to select balanced or unbalanced inputs (like my Parasound and Cambridge Audio PA's), jumpers are used to connect the - input to ground on the XLR jack. The center pin of the RCA in goes to the + in of the XLR, and the shield goes either to either the - or ground. It's a perfectly good way of doing it. I was confused about the "grounding pins" of which codesx100 and ttocs spoke. But in any case, not using the jumpers with RCA inputs was probably the cause of your problem. Moving the HDMI may not have done anything (the problem in troubleshooting with doing two different things at once). Not surprising that it only affected the center channel, it depends on the grounding topologies of the associated equipment. Yes, the HDMI to TV was part of the loop. I'm curious whether any HDMI socket would have behaved the same.
I wouldn't have waited for jumpers to arrive, just strip some #16 or so solid wire (or bus wire, if you have it), bend it into a U and stick it in pins 1 & 3. Would have worked fine. Anyway, I'm glad you nailed it.
I wouldn't have waited for jumpers to arrive, just strip some #16 or so solid wire (or bus wire, if you have it), bend it into a U and stick it in pins 1 & 3. Would have worked fine. Anyway, I'm glad you nailed it.
Seems like the tv having a groundloop. however now that i added the xlr pins to the amp as well there is no hum
I think you mentioned changing out the hdmi wire helped some? I wonder, does the construction of the wire and it's ability to shield from magnetic fields make a big difference? This might be one obvious case where buying a nice quality cable makes a difference.
Yes I changed out a fiber HDMI to a copper one. I will say this seems like the fiber one was poorly made while the copper one was a bit nicer. Definitely do not cheap out on cables could be the difference of hum or not!
Leporello
Well-known member
I'm having a hard time wrapping my head around that one. An HDMI over fiber optic system isn't just a cable, you also need a transmitter and receiver. It should in principle provide total galvanic isolation end to end, making it unlikely to be a cause for ground loops. They are on the pricey side, though maybe not as much as some boutique "audiophile grade" copper cables. So even if poorly built, a fiber transmitter, cable and receiver system isn't going to be "cheaping out".
If the fiber optic modulator or demodulator had a power supply problem then that could cause hum, but not by just touching the shell to the chassis.
That's my thought too. Would a fiber cable even be susceptible to an electromagnetic field?
Years ago we had a lightning bolt take out our neighbor's tree. I think the surge entered our home through the cable line because it fried my pc's internet portion of the motherboard. I plugged in a network card and then it was fine. A few years later the cable company ran fiber in our neighborhood, and so now its all fiber here. I'm thinking, lightning probably can't travel through the fiber?
Fiber is non conductive, so not sensible to lightning in the vicinity. However if struck by lightning it will be destroyed, but not travel and affect connected gear.
