Poll - Ground Issues?

amplifiers, receivers and loudspeakers

How may hifi components have you bypassed the ground?

Poll ended at 04 Apr 2018 23:40

1. 1 component
1
100%
2. 2 components
0
No votes
3. 2 or more components
0
No votes
 
Total votes: 1

Analogcd
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Re: Poll - Ground Issues?

Post by Analogcd » 03 Dec 2019 16:28

I worked in Tech Support at Rane for over 20 years and took hundreds of calls relating to ground loops and hum. One of my tasks was editing and updating RaneNote 110: Sound System Interconnection. I can tell you firsthand that troubleshooting hum is time consuming and must be approached methodically. Typically, one should start with power amplifier connected to loudspeakers only, then plug in one additional audio component at a time, working toward the front-end (source). Realize that not only is there hum created by loops, but also noise-floor hum from poorly filtered power supplies (wall-warts, switchers and transformers). Also, legacy equipment was designed when AC power was much cleaner (no digital processors, no Bluetooth nor other wireless and far less electrical appliance complexities). Back in the 1970s some two-prong non-polarized AC cords used a resistor to reference chassis in home audio gear (my Sony equipment is prime example). This approach is dangerous and noisy by today's standards. Rewiring my Sony gear with three-prong AC cords was first step. I updated all my equipment for safety, then approached the hum symptom carefully. It merely required a couple additional chassis bond wires to get the system virtually silent, (total interconnected component count exceeds a dozen pieces). Always bear in mind that hum can be caused by currents which may be lethal. Pay attention to what you touch when changing connections of live equipment. Carelessness can cause shocks and sometimes far worse.

British Raj
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Re: Poll - Ground Issues?

Post by British Raj » 04 Dec 2019 19:10

I am suffering from hum off my NAD3020E integrated amplifier. Even with everything disconnected from each other i.e. the amplifier plugged into the mains and standing on its own, I can hear a hum when i put my ear to the chassis.

So I opened the 3 pin British plug that came on the end of the power cord on it (other end goes through a grommet into the chassis). There are only 2 wires - live and neutral. No earth.

Should I earth the amplifier? My safety head says yes.
How do I do this?
Will it possibly fix the hum issue if I do?

UsableThought
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Re: Poll - Ground Issues?

Post by UsableThought » 07 Dec 2019 07:18

British Raj wrote:
04 Dec 2019 19:10
I am suffering from hum off my NAD3020E integrated amplifier. Even with everything disconnected from each other i.e. the amplifier plugged into the mains and standing on its own, I can hear a hum when i put my ear to the chassis.
Given that you say you're putting your ear to the chassis, and not to a loudspeaker . . . Do you hear this hum with the volume all the way down, and/or the speakers disconnected? (It's safe to run a solid state amp without speakers being hooked up.)

If so, most likely the hum you are hearing when you put your ear to the amp is a physical vibration. Typically this would come from a transformer. This being a solid state amplifier, you're not going to have huge iron (transformers) in it the way you would with a tube amp that requires high DC voltages; the schematic for your 3020E shows DC rail voltages of +/- 48Vdc, +/- 28.4Vdc, and +/- 24.5Vdc - pretty typical for solid state & not requiring giant iron. Even so, transformers tend toward mechanical hum by their very nature - this phenomenon is known as magnetostriction & you can read about it here on Wikipedia.
British Raj wrote:
04 Dec 2019 19:10
So I opened the 3 pin British plug that came on the end of the power cord on it (other end goes through a grommet into the chassis). There are only 2 wires - live and neutral. No earth.
That would not have been how the amp was manufactured, I wouldn't think. Whoever added a faked ground plug on afterward was doing a disservice to everyone involved.
British Raj wrote:
04 Dec 2019 19:10
Should I earth the amplifier? My safety head says yes. How do I do this? Will it possibly fix the hum issue if I do?
Earthing an amplifier typically means earthing the internal metal chassis to earth ground for the AC distribution system for the building, via the ground prong on the power plug. This protects to some degree against a situation where the "hot" side of the AC wiring inside the amp accidentally touches the chassis & turns it live - i.e. it somewhat minimizes electrocution danger by making it more likely that such a condition would trip the breaker at the service panel before the user could get shocked by touching the hot chassis at the same time they touched an earth ground or neutrally wired bit of metal elsewhere (e.g. a mike stand, a properly earthed chassis for a different piece of equipment, etc.). Of course a GFCI outlet will protect the user even faster than a circuit breaker. Grounding the chassis on old audio gear seems generally recognized as good practice, but I will confess that I haven't always bothered. However with some old gear (as mentioned by Analogcd), the original power cord wiring was done in what is now considered a highly unsafe manner & really ought to be replaced by proper earthing.

As for how you would earth the chassis on your particular amp, I can only speak in general terms: If the existing power cord has only 2 wires (i.e. the 3-wire plug was faked all by itself), the cord would need to be replaced by a proper 3 wire cord. The ground wire for this cord would need to go from the earth prong on the plug to a proper point on the chassis. However there are standards for making such earth connections, both physically & electrically; plus it's critical to wire the plug correctly & not get hot & neutral reversed. Unless you already have the required skills & tools, you're better off hiring someone qualified to do the job for you.

As for whether a safety earth will somehow quiet the hum you are hearing:

1) If it's mechanical hum you're hearing when you put your ear to the amp, that has nothing to do with circuit hum & won't make any difference to any hum you might hear w/ this amp as part of your system at normal speaker listening levels.

2) Bear in mind also that safety ground (earthing) and circuit ground are two entirely different purposes. The use of "ground" for both purposes can result in confusion, as can the issue of circuit ground loops created via safety earthing to the AC mains (as mentioned by analogaudio). Any good primer can help clarify - see for example "Understanding, Finding, & Eliminating Ground Loops," by Bill Whitlock, formerly of Jensen Transformers, Inc. - link here.

3) If is mechanical hum you're hearing from a transformer in the amp, and it's loud enough to bother you, you might be interested in an article I came across (link here) on how DC noise (a.k.a. "DC offset") getting into the AC mains can aggravate such hum - I personally don't have experience w/ chasing down mechanical transformer noise & so can't speak to the accuracy of the article; but at a glance it seems credible. Be warned that the article explains DC offset in passing, on the way to reviewing a specific kind of power conditioner gadget. Whether such a gadget would fix your particular hum issue, I have no idea. You might first look for noisy appliances operating on the same line as your amp - the article explains how to do that.

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Re: Poll - Ground Issues?

Post by British Raj » 07 Dec 2019 18:55

Wow .. that is a comprehensive reply! :D
Last edited by British Raj on 07 Dec 2019 18:58, edited 1 time in total.

British Raj
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Re: Poll - Ground Issues?

Post by British Raj » 07 Dec 2019 18:57

Great bit of detailed information, UT, and thanks for taking the effort.

Yes, I disconnected everything from the NAD and it still hums when you put the ear to the chassis with the volume all the way down ... classic 50 Hz sound. I am not so sure it is a mechanical 'hum' There is no vibration at all .. however faint. It is definitely an electrical hum.

I am quite comfortable with changing the 2-wire power lead to a 3-wire and attaching the earth to the correct point as per your advice. I have done a fair bit of re-wiring, right from my school days (I am 54 next year :oops: )

aardvarkash10
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Re: Poll - Ground Issues?

Post by aardvarkash10 » 07 Dec 2019 19:49

ya'll need to read and understand this.

And stop bypassing the safety earth by disconnecting it. You put everyone in the house at risk, and, foreseeably, actually put your house at risk of burning to the ground (pun not intended)

Woodbrains
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Re: Poll - Ground Issues?

Post by Woodbrains » 07 Dec 2019 20:21

UsableThought wrote:
07 Dec 2019 07:18
British Raj wrote:
04 Dec 2019 19:10
I am suffering from hum off my NAD3020E integrated amplifier. Even with everything disconnected from each other i.e. the amplifier plugged into the mains and standing on its own, I can hear a hum when i put my ear to the chassis.
Given that you say you're putting your ear to the chassis, and not to a loudspeaker . . . Do you hear this hum with the volume all the way down, and/or the speakers disconnected? (It's safe to run a solid state amp without speakers being hooked up.)

If so, most likely the hum you are hearing when you put your ear to the amp is a physical vibration. Typically this would come from a transformer. This being a solid state amplifier, you're not going to have huge iron (transformers) in it the way you would with a tube amp that requires high DC voltages; the schematic for your 3020E shows DC rail voltages of +/- 48Vdc, +/- 28.4Vdc, and +/- 24.5Vdc - pretty typical for solid state & not requiring giant iron. Even so, transformers tend toward mechanical hum by their very nature - this phenomenon is known as magnetostriction & you can read about it here on Wikipedia.
British Raj wrote:
04 Dec 2019 19:10
So I opened the 3 pin British plug that came on the end of the power cord on it (other end goes through a grommet into the chassis). There are only 2 wires - live and neutral. No earth.
That would not have been how the amp was manufactured, I wouldn't think. Whoever added a faked ground plug on afterward was doing a disservice to everyone involved.
British Raj wrote:
04 Dec 2019 19:10
Should I earth the amplifier? My safety head says yes. How do I do this? Will it possibly fix the hum issue if I do?
Earthing an amplifier typically means earthing the internal metal chassis to earth ground for the AC distribution system for the building, via the ground prong on the power plug. This protects to some degree against a situation where the "hot" side of the AC wiring inside the amp accidentally touches the chassis & turns it live - i.e. it somewhat minimizes electrocution danger by making it more likely that such a condition would trip the breaker at the service panel before the user could get shocked by touching the hot chassis at the same time they touched an earth ground or neutrally wired bit of metal elsewhere (e.g. a mike stand, a properly earthed chassis for a different piece of equipment, etc.). Of course a GFCI outlet will protect the user even faster than a circuit breaker. Grounding the chassis on old audio gear seems generally recognized as good practice, but I will confess that I haven't always bothered. However with some old gear (as mentioned by Analogcd), the original power cord wiring was done in what is now considered a highly unsafe manner & really ought to be replaced by proper earthing.

As for how you would earth the chassis on your particular amp, I can only speak in general terms: If the existing power cord has only 2 wires (i.e. the 3-wire plug was faked all by itself), the cord would need to be replaced by a proper 3 wire cord. The ground wire for this cord would need to go from the earth prong on the plug to a proper point on the chassis. However there are standards for making such earth connections, both physically & electrically; plus it's critical to wire the plug correctly & not get hot & neutral reversed. Unless you already have the required skills & tools, you're better off hiring someone qualified to do the job for you.

As for whether a safety earth will somehow quiet the hum you are hearing:

1) If it's mechanical hum you're hearing when you put your ear to the amp, that has nothing to do with circuit hum & won't make any difference to any hum you might hear w/ this amp as part of your system at normal speaker listening levels.

2) Bear in mind also that safety ground (earthing) and circuit ground are two entirely different purposes. The use of "ground" for both purposes can result in confusion, as can the issue of circuit ground loops created via safety earthing to the AC mains (as mentioned by analogaudio). Any good primer can help clarify - see for example "Understanding, Finding, & Eliminating Ground Loops," by Bill Whitlock, formerly of Jensen Transformers, Inc. - link here.

3) If is mechanical hum you're hearing from a transformer in the amp, and it's loud enough to bother you, you might be interested in an article I came across (link here) on how DC noise (a.k.a. "DC offset") getting into the AC mains can aggravate such hum - I personally don't have experience w/ chasing down mechanical transformer noise & so can't speak to the accuracy of the article; but at a glance it seems credible. Be warned that the article explains DC offset in passing, on the way to reviewing a specific kind of power conditioner gadget. Whether such a gadget would fix your particular hum issue, I have no idea. You might first look for noisy appliances operating on the same line as your amp - the article explains how to do that.
Hello,

Just for your information, British mains plugs ALL have an earth pin as we call them here, (ground pin) whether they are connected to an earth wire or not. They have the double duty of opening a shutter in the socket, so the plug can be inserted. Without the earth pin, the other 2 pins cannot physically enter the socket, nor can any other 'foreign' object. It is a safety feature.

It is surprising how many amps do not have an earth wire. Of all the amps I've owned or used, I think I have only one with an earth wire. They were made without, specifically to reduce the chances of ground loops.

Mike.

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Re: Poll - Ground Issues?

Post by UsableThought » 07 Dec 2019 21:19

Woodbrains wrote:
07 Dec 2019 20:21
Just for your information, British mains plugs ALL have an earth pin as we call them here, (ground pin) whether they are connected to an earth wire or not.
Interesting, thanks.

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Re: Poll - Ground Issues?

Post by UsableThought » 07 Dec 2019 21:28

British Raj wrote:
07 Dec 2019 18:57
I am not so sure it is a mechanical 'hum' There is no vibration at all .. however faint. It is definitely an electrical hum.
You mean, it sounds electrical, yes? But that doesn’t mean what you’re hearing is related to the signal path in this amp.

There is no sound without vibration. Therefore something physical is vibrating for you to hear a hum. If loudspeakers or other similar devices for changing the audio signal into audible sound aren’t connected, then that vibration is probably unrelated to the audio signal path. It must be something else . . . and there just aren’t a lot of candidates inside your amp other than transformers. Resistors don’t audibly vibrate. Capacitors and transistors and ICs and op-amps don’t either.

When a power transformer vibrates mechanically in this manner, it does so at double the mains frequency. The result is likely to sound very “electrical” to most of us. Here’s a link to still another article on magnetostriction: http://hyperphysics.phy-astr.gsu.edu/hb ... trict.html

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Re: Poll - Ground Issues?

Post by UsableThought » 08 Dec 2019 07:31

The PDF you link to is a chapter that comes from Merlin Blencowe's wonderful book on designing tube guitar amps. I've read that chapter many times; as a hobbyist fooling with designing tube amps, it's been maybe the single most useful document I've found on circuit grounding.

However the article mentions safety earth only in passing, and doesn't mention hum issues with multi-component hi-fi systems at all. The focus is almost entirely on how to design quiet ground returns inside tube amplifier circuits.

As an alternative, if anyone wants info on grounding that is truly specific to hi-fi, esp. for DIY'ers, I'd suggest Dave Davenport's long technical article on "Audio Component Grounding and Interconnection". This article is new to me and I've only had a chance to browse it, but I like what I see. Davenport goes into detail about the danger of lifting ground on appliances that truly require it to be safe (i.e. have an exposed metal chassis and/or metal controls or other metal bits & can shock the user if things go wrong). He discusses balanced audio connections (as mentioned by @analogaudio) & also such knotty issues as the "pin 1 problem". And - of interest to anyone browsing this thread - he also describes safe methods of "ground isolation" that do what a lift does, but without the danger.
aardvarkash10 wrote:
07 Dec 2019 19:49
And stop bypassing the safety earth by disconnecting it. You put everyone in the house at risk, and, foreseeably, actually put your house at risk of burning to the ground (pun not intended)
I would qualify this statement slightly. It's worth bearing in mind that in today's home, GFCI outlets work much faster (and in this case, faster is definitely better) than circuit breakers to protect against electrocution. I say this because @Legrace, who posted first in this thread, mentioned that yes, he's bypassed ground on some of his gear . . . but he also mentions that this gear is plugged into a line protected with a GFCI. The thing to remember here is that GFCI breakers and outlets should be tested regularly.

Also, not all audio gear requires ground to be safe in the first place - meaning, you don't have to automatically replace a 2-wire cord on an old piece of gear if it doesn't need it. An example is my Dual CS 530 turntable - it has a plastic outer body & plastic controls, so it's fine with its ancient two-wire power cord. Same for modern electric drills & other small handheld appliances with double-insulated plastic bodies.

Personally, I prefer combining GFCI when possible with proper grounding practices for appliances that really do need it. So my analog oscilloscope & guitar amps will always stay grounded - no lifts for me. AND, the mains line in my shop has GFCI on it. GFCI is also a great idea in kitchens & bathrooms; here in the U.S. I think this may even be required for new buildings. I don't know what UK regs are for requiring GFCI, but would guess they'd be even stricter.

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Re: Poll - Ground Issues?

Post by UsableThought » 08 Dec 2019 10:48

Also I should mention that house fires due to electrical problems are most likely to occur when distribution wires inside the walls are overloaded (short or too much current draw on the line) or the wiring itself is old enough that the insulation is failing; or when wiring installation was done poorly in some other way and/or is deteriorating in some other way.

Prevention of electrical fires therefore has less to do with earth grounding & more to do with replacing deteriorating old lines (if need be) and making sure these lines are adequately protected at the service panel, e.g. that the breakers are in good condition and are rated properly, e.g. 15A @ ~125V for ordinary household lines in the U.S.

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Re: Poll - Ground Issues?

Post by British Raj » 08 Dec 2019 17:59

Ok ... Drama over, me thinks.

I took the NAD to a friend of a friend who understands amps and regularly re-caps, changes capacitors etc. He eliminated the transformer straight away .. there is no issue there. Then he went through the capacitors and found they were fine too. Finally, he hooked up the amp to his really nice passive speakers so that the amp was actually doing some work. Nothing - no hum! So with a smile, he sent me back home to check out the Bang & Olufsen Beolab 8000s.

They weigh 12 Kg (over 26 lbs) each. And I have them set out atop a foot high stone plinth because I like them at that height. I switched them off, took them down and had a look at the terminals. This is where the wires go in ...
https://i.imgur.com/CG8FIDG.jpg

As you can see, there is a switch that is a three way toggle between L , R , and LINE. One was set to R. The other to L. I went on the B&O forum and to my dismay, found that they should both be set to LINE. As soon as I did this, the hum was all but gone ... Once I set the speakers down in their spot and connected everything back up again, the whole thing seems so much more lively and dynamic ... I have been missing quality that I had for the last 6 months !

Now, where is that kicking myself emoji ??? #-o

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Re: Poll - Ground Issues?

Post by UsableThought » 08 Dec 2019 18:26

I’m glad you got it fixed. But the description you gave of the problem (hum with no speakers) doesn’t make sense with what you are now describing. If you really had no speakers attached AND it was still humming loud enough that you could hear . . . what was doing the vibrating?

From your latest description here, the hum that really mattered to you WAS with speakers attached. What got me on the wrong track was your saying you heard the hum with "nothing attached", meaning no speakers, and only heard it when you put your ear to the chassis. That perfectly fits transformer hum - which by the way is normal behavior; all transformers do it. Occasionally it's louder than usual, or someone is extra-sensitive to it.

It seems to me very possible that both things were true - you did hear a very slight hum with "nothing attached" (no speakers) and your ear right up next to the chassis - that would be normal for equipment with transformers, as I say - and also had a hum problem of greater concern with speakers attached. And because the two sounded so similar to you (given that all hum is going to be at mains frequency or double mains frequency, regardless of its nature), you got them confused.
Last edited by UsableThought on 08 Dec 2019 18:45, edited 2 times in total.

aardvarkash10
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Re: Poll - Ground Issues?

Post by aardvarkash10 » 08 Dec 2019 18:35

UsableThought wrote:
08 Dec 2019 07:31

The PDF you link to is a chapter that comes from Merlin Blencowe's wonderful book on designing tube guitar amps. I've read that chapter many times; as a hobbyist fooling with designing tube amps, it's been maybe the single most useful document I've found on circuit grounding....

Personally, I prefer combining GFCI when possible with proper grounding practices for appliances that really do need it. So my analog oscilloscope & guitar amps will always stay grounded - no lifts for me. AND, the mains line in my shop has GFCI on it. GFCI is also a great idea in kitchens & bathrooms; here in the U.S. I think this may even be required for new buildings. I don't know what UK regs are for requiring GFCI, but would guess they'd be even stricter.
Totally endorse all your comment. Merlin's article briefly covers ground loops on interconnected equipment, but the basics have to be understood first to really deal with the problem - hence all the background on power supplies and the modes of noise generation.

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Re: Poll - Ground Issues?

Post by British Raj » 08 Dec 2019 18:44

UsableThought wrote:
08 Dec 2019 18:26
I’m glad you got it fixed. But the description you gave of the problem (hum with no speakers) doesn’t make sense. If you really had no speakers attached AND it was still humming loud enough that you could hear . . . what was doing the vibrating?

From your latest description here, the hum WAS with speakers attached. What got me on the wrong track was your saying you heard the hum with no speakers when you put your ear to the chassis.

And just FYI, virtually all transformers do hum in the way I described. It doesn’t mean they have a problem - it’s normal behavior.

Sorry for throwing you off track. My knowledgeable friend convinced me that the hum I was concerned about from the chassis (with no speakers connected) was quite normal. He switched on some other amps he had and showed me that it was the same in all of them. Also, his point was proved perfectly when he wired my NAD to his speakers and though I could still hear the hum I was worried about from the chassis at that time, nothing was coming from the speakers.

So glad it is better now. Thanks for all the help anyway!