Soulreaper
Sensei
Supreme Ruler of Emptiness
Posts: 155
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Post by Soulreaper on Jun 18, 2014 1:24:36 GMT -5
LAst week I received my Jolida jd5t tube preamp and since I've hooked it up I've been hearing transformer hum whenever it's plugged in and my xpa5 is running. I'm using the Niles axp1 as my rca switch between my jolida and my yamaha receiver. Even if my switch is set to my receiver input I hear the hum. Ive tried unplugging one component at a time, switching power cords, testing my ac receptacle grounds, and using different outlets in my Panamax PC. None of these have worked. I tried a cheater plug and it eliminated most of the hum but using a cheater plug a the time is a fire hazard. It has a ground plug for a reason. Any ideas for a solution?
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Post by aud on Jun 18, 2014 9:09:57 GMT -5
Just to make sure, are you hearing the hum from the transformer directly or from the speakers? I agree, never use a cheater plug, there is no need to if the hum is from the transformer itself. If you have a multi meter, check the voltage at the receptacles.
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Post by Priapulus on Jun 18, 2014 9:30:30 GMT -5
This is a reoccurring theme and problem. It would be wonderful if someone like Keith Levkoff could give us an essay about ground-loops and ac-hum causes and cures, and sticky it.
Sincerely
/b
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Post by aud on Jun 18, 2014 9:58:32 GMT -5
This is a reoccurring theme and problem. It would be wonderful if someone like Keith Levkoff could give us an essay about ground-loops and ac-hum causes and cures, and sticky it. Sincerely /b Ok I'll leave it to Keith. |
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Post by jedinite24 on Jun 18, 2014 10:03:10 GMT -5
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Post by Priapulus on Jun 18, 2014 10:10:18 GMT -5
This is a reoccurring theme and problem. It would be wonderful if someone like Keith Levkoff could give us an essay about ground-loops and ac-hum causes and cures, and sticky it. Sincerely /b Ok I'll leave it to Keith. No, please join in; who knows what Keith will do... /b
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Post by Boomzilla on Jun 18, 2014 11:08:22 GMT -5
A cheap solution is the Absolute PNF-200 ground loop isolator, available from Amazon.
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Soulreaper
Sensei
Supreme Ruler of Emptiness
Posts: 155
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Post by Soulreaper on Jun 18, 2014 12:33:27 GMT -5
Yes the hum comes through my speakers whenever the jolida is plugged in and my xpa5 is powered on. I used my multimeter to test my ac receptacles and they are working fine.
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Post by Gary Cook on Jun 18, 2014 16:25:34 GMT -5
LAst week I received my Jolida jd5t tube preamp and since I've hooked it up I've been hearing transformer hum whenever it's plugged in and my xpa5 is running. I'm using the Niles axp1 as my rca switch between my jolida and my yamaha receiver. Even if my switch is set to my receiver input I hear the hum. Ive tried unplugging one component at a time, switching power cords, testing my ac receptacle grounds, and using different outlets in my Panamax PC. None of these have worked. I tried a cheater plug and it eliminated most of the hum but using a cheater plug a the time is a fire hazard. It has a ground plug for a reason. Any ideas for a solution? In Australia a "cheater" plug is simply one with no earth pin/connection, they have an active and neutral but no earth. I don't see how that is a fire hazard. We have earth leakage circuit breakers that compares the active and the neutral, if there is a current difference Ie; leakage direct to earth, then the breaker trips. The are plenty of electronic devices that don't have an earth, Apple iDevice rechargers are a common example. So if your "cheater" plug, because of its lack of an earth connection, is a fire hazard then so are millions of Apple chargers.  Cheers Gary |
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Post by lionear on Jun 18, 2014 23:17:09 GMT -5
There are a few possibilities. Firstly, does the Jolida need to be checked? If the Jolida is fine, then....
I guess the XPA-5 has a 3-prong plug, and the Jolida has a 3-prong plug. And all the other components have 2-prong plugs, right?
If so, you are probably getting the ground loop because of the Earth connection on the XPA-5 and the Jolida preamp. The interconnects between preamp and power amp close the loop.
If you "float" (use the cheater plug) the XPA-5 OR the Jolida, then you should be fine. They will Earth each other via the interconnects and then ONE of them will connect all your components to your house Earth connection. As long as you always switch them on when they're connected via interconnects, there are no electrical issues. If you need to switch them on when they're not connected to anything (probably not recommended for the Jolida, anyway) then you'd want to make sure that they're not floated (remove the cheater plug).
I'd Earth the preamp and float the power amp, especially if you listen to LP's.
Manufacturers will say NEVER FLOAT THEIR GEAR. However, I think this is because of liability issues, and the potential for people to not know that they need to preserve the Earth connection on ONE component.
Alternatively, you might get the power amp powered by a wall socket that comes off a different circuit breaker than the one that your preamp is connected to. You may want to test this out by finding the wall socket, and using a extension cord.
Or you can float everything, then run a wire that's connected at one end to the chassis of your preamp, and the other end is connected to a copper rod that is driven into the ground - so that becomes your exclusive Earth connection for your sound system. The rod should be long enough to reach the water table. I've been told that one old way - to connect your custom Earth to your water pipe because the pipes eventually run underground - is frowned on.
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Post by Gary Cook on Jun 18, 2014 23:35:45 GMT -5
I've been told that one old way - to connect your custom Earth to your water pipe because the pipes eventually run underground - is frowned on. Yep, electrified taps are a bit scary  Cheers Gary |
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KeithL
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Post by KeithL on Jun 19, 2014 11:42:52 GMT -5
There are two reasons I can think of why that would be true: 1) Depending on the specific conditions in your area, the Earth may or may not be a very good ground. If the dirt is too dry, then it won't conduct well, and so won't be "a good ground". Also, depending on how the power grid in your area is grounded, there could be enough AC ground current flowing in the ground (from your local power transformer or substation) that there may actually be noise on the "real Earth ground". (You CAN "force" AC signals, or even audio, "into" the ground itself. Usually only a few millivolts, but that could be enough if what's there is hum, and that's what you're trying to get away from. A "clean audio ground" needs to be a lot cleaner than a good safety ground.) 2) I suspect the major reason is that nowadays a lot of pipes are being made out of plastic rather than metal. Just because the pipes you can see are metal, it's no longer safe to assume that you have a metal path all the way to ground. Most modern homes are no longer piped with copper, and homes with metal pipes may have, at some time, been repaired with PVC in some spots.... and it wouldn't surprise me if even some newer water mains may be plastic or fiberglas/cement composite of some sort. I've been told that one old way - to connect your custom Earth to your water pipe because the pipes eventually run underground - is frowned on. Yep, electrified taps are a bit scary Cheers Gary |
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KeithL
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Post by KeithL on Jun 19, 2014 14:19:24 GMT -5
I hear my name  I'll put something about ground loops on my to-do list... In the mean time... The Jensen paper looks quite good - and quite thorough - although I do detect a tiny bit of "hammer and nail syndrome" ("when you sell hammers, everything looks like a job for a nail"). Specifically, not all hum is caused by ground loops. There's also the fact that transformers tend to introduce distortion and assorted variations in frequency response. (In all fairness, I've heard that Jensen makes excellent quality transformers, but even the best transformer is going to add some distortion, and have a less flat frequency response, than, for example, most of our equipment. If you even imagine that different interconnects, or different speaker cables, sound different, then you should expect a signal transformer to be FAR more audible that either of those. if the problem is a ground loop, then adding a signal isolation transformer will probably fix it - but it will also probably audibly affect the sound at least slightly.) I'm not quite sure what's in the other little gadget. It most certainly is NOT a power isolation transformer; a 700 VA power isolation transformer would be much bigger, heavier, and more expensive. (There were some really "far out" guesses and explanations amongst the Amazon comments.) I looked around, and a lot of people seem quite convinced that it lifts the ground connection with a "soft lift" made up of a pair of diodes. (This would allow it to appear as if the ground was lifted for signal purposes, but still allow the ground to "be there" for safety purposes.) If that's what it is, then it would give you (more or less) the same hum benefits as using a cheater that disconnects the ground, but still provide the protection of being grounded. Depending on what's causing the hum, it MIGHT help - or it might not. As for the immediate problem.... First off, if the hum is mechanical hum from the transformer itself, then odds are nothing much is going to help. (That's easy to recognize; is the hum coming through the air from the preamp - even when the power amp is Off?) If there's DC offset on your power lines, it could cause a power transformer to hum excessively (in which case a CMX-2 might help); if not, then you simply have a transformer that hums. If the hum is coming from the actual output of the preamp, then it might or might not be related to a ground loop. Tube equipment in general operates at very high impedances compared to solid state equipment, which makes it very sensitive to picking up hum from the environment in all sorts of ways. Here are a few things I would try first: 1) Move the preamp around a bit, and rotate it at least 90 degrees - and see if the hum goes away (or gets worse). if the hum changes based on position or orientation, then the preamp is just sensitive and you're going to have to find a location and position that it likes. 2) Try grounding the chassis of the preamp to other equipment (try running a wire from the chassis of the preamp to the chassis of the power amp - just put a stripped wire under a chassis screw at each end). You could also try grounding it to the chassis of your source equipment, or grounding all the chassis together. Likewise, you could try grounding it to a real ground - like a water pipe. Note that there are all sorts of grounding schemes - especially with tube equipment. The chassis could be independent of any of the power cord grounds, and so grounding the chassis itself to a real ground, or the chassis of other equipment, could well eliminate the problem even if nothing you do with the power cable does so. This is one of the first things you should try with a piece of tube equipment that hums. 3) See if the problem happens when you have no input interconnects connected to the preamp. (If possible, short the inputs on the preamp when you do this; open inputs on high impedance equipment can pick up hum.) I'm also not getting a sense of how much hum we're talking about here. Perhaps the preamp just isn't as quiet as other equipment you're used to; if so then the hum could just be normal for it. (Depending on the power supply design, tube equipment tends to be noisier than good quality solid state equipment - although I certainly haven't heard specific comments about Jolida in that regard.) |
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KeithL
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Post by KeithL on Jun 19, 2014 15:57:54 GMT -5
The issue is not so much that it is a fire hazard as that it is a SAFETY hazard. Here in the 'States, we call those circuit breakers Ground Fault Interruptors (GFI) - and you can even get individual outlets that have that feature. In most locations, they are required by code in areas where water is present (kitchen counter outlets, bathrooms, outdoor outlets), but are NOT required in most other indoor applications - and many older houses don't even have them in the bathroom. (Many very old houses only use two-wire outlet wiring with no separate ground connection at all.) The whole point of the third ground wire is that, IF a short occurs, and the equipment chassis "goes hot", the ground connection will short the voltage to ground - causing a circuit breaker or fuse to blow - and so preventing the voltage from trying to find a path to ground through someone who touches the "hot chassis" of the faulty equipment. In locations where GFI outlets are not installed, there is a serious potential for damage (or electrocution) if a piece of equipment fails such that the "hot lead" shorts to ground. If there is no ground pin connection, and such a fault occurs, if you touch the equipment ground and Earth ground you could well get a serious shock. Long ago, nobody much thought about it. Currently, most power tools and equipment intended to be used without a ground is "double insulated" (it has several layers of insulation to ensure that such a fault cannot occur). However, in this country, it is assumed that equipment which includes a third safety ground connection is intended to be used with it connected to ground, and that using a "cheater" to disconnect it increases the chance of serious damage or injury. (You would also have serious problems with your insurance if your house burned down and they discovered that you had "deliberately circumvented the safety ground" on the equipment that caused a fire or injury.) As a simple matter of troubleshooting, do you get the hum if you connect the Jolida to the power amp - and disconnect the receiver and everything else? Try JUST connecting the premap to the power amp, both directly plugged into the wall, and see if the hum remains... You say "you've tried unplugging each component one at a time" and "it hasn't worked".... are you saying that the hum remains no matter what you disconnect? If so, then it sounds like it could just be the normal noise level for the Jolida (or it could be faulty). LAst week I received my Jolida jd5t tube preamp and since I've hooked it up I've been hearing transformer hum whenever it's plugged in and my xpa5 is running. I'm using the Niles axp1 as my rca switch between my jolida and my yamaha receiver. Even if my switch is set to my receiver input I hear the hum. Ive tried unplugging one component at a time, switching power cords, testing my ac receptacle grounds, and using different outlets in my Panamax PC. None of these have worked. I tried a cheater plug and it eliminated most of the hum but using a cheater plug a the time is a fire hazard. It has a ground plug for a reason. Any ideas for a solution? In Australia a "cheater" plug is simply one with no earth pin/connection, they have an active and neutral but no earth. I don't see how that is a fire hazard. We have earth leakage circuit breakers that compares the active and the neutral, if there is a current difference Ie; leakage direct to earth, then the breaker trips. The are plenty of electronic devices that don't have an earth, Apple iDevice rechargers are a common example. So if your "cheater" plug, because of its lack of an earth connection, is a fire hazard then so are millions of Apple chargers. Cheers Gary |
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Soulreaper
Sensei
Supreme Ruler of Emptiness
Posts: 155
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Post by Soulreaper on Jun 19, 2014 23:21:29 GMT -5
Wow thatnk's! This was actually very I normative and much more helpful than the searches I did on other forums. I was also thinking about making my own dedicated ground with rod and a wire running to my amp.
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Post by Priapulus on Jun 20, 2014 9:00:13 GMT -5
Wow thatnk's! This was actually very I normative and much more helpful than the searches I did on other forums. I was also thinking about making my own dedicated ground with rod and a wire running to my amp. That doesn't help. And could make things worse.
Lightning is a big explosion of electrons that are trying to get to the earth. A heavy ground rod and cable to conduct those electrons to the earth, instead of burning down your house, is good. But that is for power lines, and has nothing to do with signal grounds, Your Zappa music isn't trying to get to earth.
The important thing about signal grounds is that you should only have one of them. For example, lets say you have a powered sub on the other side of the room, connected to your pre/pro with an RCA cable, containing your signal and its signal ground or return. But wait, the sub is plugged into the wall, so you have a second ground thru the ground pins on the power cords of your sub and pre/pro.
The difficulty is that you plugged the powercords into different outlets on opposite sides of the room, perhaps even on different breakers. Your refrigerator is also on the same Sub power circuit; the fridge has leaky motor capacitor so there is a few millivolts of noise on the sub ground powercord (compared to the pre/pro powercord ground on the other side of the room). That few millivolts will take a shortcut and loop into the sub, along the RCA signal ground to the pre/pro and out it's powercord to wall socket; injecting its noise into your signal.
The fix is simple; have only one grounding point, so there is no looping. Plug all power cords into the same powerbar.
A common noise source is the CATV coax, whose shield is grounded elseware, probably badly, and always carrying noise. Just bond the shield to your "one ground point".
Hey, airplanes have complex avionics, no connection to earth, and work just fine. But they do have an excellent common point ground system.
Sincerely /b
p.s. I'm presuming your house power is properly grounded at the meter, as required by code. If you have an old house, or amateur wired, you should make sure it is properly grounded at the meter and all the way to the outlets, for safety reasons..
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