hum loop solution

[sumday]

my fairly basic system consists of roksan kandy cd player and pioneer a400 amp feeding q 2050i loudspeakers.
the amp is 3 cored mains as is the cd player. the previous amp was a two cored mains Marantz and I had no earth hum problem.
the pioneer however now has a low main hum which is only present when the cd player is present in the system...I have lifted the earth on the player....hazardous I know but just to check the effect and the hum vanished.

is it safe to earth the cd player through the amps ground terminal...as above I tried this and of course the hum went away.....just wondered if this can be a permanent solution.

I have also looked at buying a hum loop filter but was worried these would rob the system of some lowlevel detail.


any thoughts??........nige.

[StanleyB]

I am surprised that the CD player has an earth lead in the mainsplug. Only the amp should be earthed. So you did the right thing to lift the earth wire in the CD plug.

[Reffc]

my fairly basic system consists of roksan kandy cd player and pioneer a400 amp feeding q 2050i loudspeakers.
the amp is 3 cored mains as is the cd player. the previous amp was a two cored mains Marantz and I had no earth hum problem.
the pioneer however now has a low main hum which is only present when the cd player is present in the system...I have lifted the earth on the player....hazardous I know but just to check the effect and the hum vanished.

is it safe to earth the cd player through the amps ground terminal...as above I tried this and of course the hum went away.....just wondered if this can be a permanent solution.

I have also looked at buying a hum loop filter but was worried these would rob the system of some lowlevel detail.


any thoughts??........nige.

First off, whilst lifting an earth to check for earth loop hum is one thing, it is never safe to leave an earth lifted. You risk your life, or the life of anyone else using the machine if a fault condition occurs.

One solution is to have an earth lift fitted to the amplifier. The cause of the earth loop is simply that you have small currents circulating between voltage potentials in the grounds between bits of connected kit. That can couple to the signal creating the hum so a way I've successfully used previously is to de-couple the amplifier chassis ground from the signal ground by introducing a larger signal earth ground impedance for the signal earth ground which prevents chassis earth currents contaminating the signal. To do this, you lift, or float the star earth for the signal grounds within the amplifier and take a new common earth through a bridge rectifier to the chassis ground with a capacitor/resistor network between chassis and earth ground paths. 9 times out of 10, that cures earth loop hum without the need for costly 1:1 earth loop transformers or other such solutions. You can implement this with some basic DIY skills and knowledge or have someone competent do it for you. The cost of components is about £7.

[The Barbarian]

I am surprised that the CD player has an earth lead in the mainsplug. Only the amp should be earthed. So you did the right thing to lift the earth wire in the CD plug.

I probably got around 9 CD players in total, every single one is 2 Core mains..

[Oldpinkman]

I probably got around 9 CD players in total, every single one is 2 Core mains..

That should be because they are double insulated. If a cd player has an earth then it is likely it is not double .insulated. I'm not saying it complies with regulation but providing the cd player is securely earthed from its chassis to the earthed chassis of the amplifier it is as safe as if it had a direct earth through its own mains cable. Be sure that chassis earth is good though.

[Reffc]

I am surprised that the CD player has an earth lead in the mainsplug. Only the amp should be earthed. So you did the right thing to lift the earth wire in the CD plug.

Not so and no disrespect intended but potentially very dangerous advice. If the CDP was designed to be earthed, then earthed it should be. People are free to do what they want though, but unless the CDP is double insulated and certified as such, it is not a very bright idea to lift the mains earth from any appliance. Period.

Also (in response to Richard's post above) Unless the person doing the work understands mains current and fault voltage potential for a particular piece of kit, then they may not have a clue on the appropriate rating for separate earth cable and in particular its insulation rating to an amp so again I would strongly recommend that no one messes with earthed appliances. If it catches fire and you're lucky enough not to have been electrocuted, then any subsequent insurance claim would likely fail if the insurance loss adjuster finds out that the appliance has been messed with. I gave a safe solution. It's cheap, it's intrinsically safe and it doesn't involve doing anything dangerous. Advice is freely given. There's loads of reading on earth loops and there may be a cure without the need to fiddle with anything so perhaps going through the connections, where each power supply is taken from etc could be tried before anything else needs to be considered?

[StanleyB]

I am not going to enter in a discussion with anyone about what I wrote and what they offer as a counter evidence. One can instead read up on it. Four links that I can provide are:
http://www.rane.com/note110.html
http://www.rane.com/note151.html
http://www.engineeringharmonics.com/sites/default/files/grounding%20systems%20and%20implementation.pdf?q=p apers/ground_systems.pdf
http://audiosystemsgroup.com/SurgeXPowerGround.pdf

[sumday]

well thanks for the prompt replies fellas.....just to clarify, my solution uses a heavy piece of speaker cable soldered to the earth from the cd player at the plug end then routed back with a soldered 'hook' which is securely clamped to the amp earth post.
just for the record, the pioneer a400 is a leap up from the budget Marantz I was using. I understand it is not loved by some but for the princely sum of 100 quid its doing me proud and got a firm grip on my Qs......cheers, NIGE.

[337alant]

In a hifi system the signal ground should be connected to the chassis mains earth in one place only in the individual boxes, this is normally in the pre amp or int Amp.
if the signal ground is connected to the mains or chassis earth in 2 individual components that will create a mains loop and resulting hum
So I would look for a link in your CD player's signal ground to earth and disconnect that.
As others have said if an item comes with a 3 core mains lead then it is not double insulated and it is risky to disconnect the chassis earth, your fix does at least give a path to earth in a fault status but you are not fixing the real problem

Alan

[Reffc]

In a hifi system the signal ground should be connected to the chassis mains earth in one place only in the individual boxes, this is normally in the pre amp or int Amp.
if the signal ground is connected to the mains or chassis earth in 2 individual components that will create a mains loop and resulting hum
So I would look for a link in your CD player's signal ground to earth and disconnect that.
As others have said if an item comes with a 3 core mains lead then it is not double insulated and it is risky to disconnect the chassis earth, your fix does at least give a path to earth in a fault status but you are not fixing the real problem

Alan

Exactly.

The signal earth loop can be broken at the amp. I've done this before when I've had earth loop problems and it works. The principle is that by floating the earth you take away to direct path to earth shared by the chassis, but you maintain a low signal to earth potential via the bridge rectifier and create a high signal to earth path (or mains earth to signal earth pathway via the chassis) with the introduction of the resistor bypassing + capacitor (rfi filter) bypassing the rectifier. The rectifier has two safe paths to earth should one burn out (unlikely as it should be rated to 600v or similar) and if that blows, the fallback is the resistor. The chassis maintains a low impedance path to earth as previously. It's safe, it tackles the root cause (the earth loop) and it works.

[Oldpinkman]

Paul

You are quite right. I did note that the earthing arrangements I suggested wouldn't pass regs, but I picked up some bad habits from the engineers at Pink, and when trouble-shooting and trying to isolate the problem have in my sinful youth lifted the earth to an appliance and replaced it with an earth to another chassis. Usually, earthing the chassis WITHOUT lifting the earth in the signal unit does the job. I have some naughty guitarist friends who are "lifters" too, often at gigs with completely unknown electrics. At least at my gaff the mains comes via hair-trigger RCD's :)

[Oldpinkman]

I am not going to enter in a discussion with anyone about what I wrote and what they offer as a counter evidence. One can instead read up on it. Four links that I can provide are:
http://www.rane.com/note110.html
http://www.rane.com/note151.html
http://www.engineeringharmonics.com/sites/default/files/grounding%20systems%20and%20implementation.pdf?q=p apers/ground_systems.pdf
http://audiosystemsgroup.com/SurgeXPowerGround.pdf

They're very long for most of us to read. Safety is important even to accountants and others who are not electrical engineers. Correct me if I'm wrong. In the EU an item which is Class 2 must bear an appropriate symbol , must be double insulated, and MUST NOT have a mains lead earth connection to the chassis. I am assuming that applies to the 9 CD players Andr'e referred to. It applies to my DVD player. We're assuming it doesn't apply to Nigels cd player, since it has a chassis earth via the mains lead, and that would be a breach of class 2 regs.

Class 1 devices are NOT double insulated and MUST have a chassis connection to earth via the mains lead. We are assuming this applies to Nigels cd player. It applies to my CD player and DAC. Theoretical discussions about how ground loops arise, and boozed-up guitarist gig fixes fail to comply with safety regs, and as Paul has pointed out would probably invalidate insurance cover.

Wiring such as I suggested should be viewed as "lab test" rather than "permanent domestic"

[sumday]

bottled it...!!!
after much reading and digesting the info posted I realise the subject I have bought up is way over my head and as such I'm going to err on the side of safety.
with regret I have pulled the roksan and put my old Cambridge cd4 back in my system.....this player is of course two core mains.
the presence of earths in power leads is something I will pay close attention to in regard to future upgrades etc.

thanks again fellas....nige.

[Reffc]

Paul

You are quite right. I did note that the earthing arrangements I suggested wouldn't pass regs, but I picked up some bad habits from the engineers at Pink, and when trouble-shooting and trying to isolate the problem have in my sinful youth lifted the earth to an appliance and replaced it with an earth to another chassis. Usually, earthing the chassis WITHOUT lifting the earth in the signal unit does the job. I have some naughty guitarist friends who are "lifters" too, often at gigs with completely unknown electrics. At least at my gaff the mains comes via hair-trigger RCD's :)

It can be a can of worms Richard. I know of one person who lifted an earth on a (valve) power amp claiming that the RCD was protection enough. A fault later developed and the power supply insulation melted, with the amp catching fire and the chassis also remaining live long enough to fry whoever would have touched it. The RCD on that occasion didn't trip for whatever reason and the mains fuse protection didn't pop until enough current had been drawn to set fire to the thing. Not worth shortcuts, especially when other family members might be using the hifi. It never ceases to amaze me just how many in the gene pool are willing to put their lives and those of their families at risk for the sake of a problem which can be otherwise safely addressed. Natural selection eventually comes to bear :mental:

[Reffc]

bottled it...!!!
after much reading and digesting the info posted I realise the subject I have bought up is way over my head and as such I'm going to err on the side of safety.
with regret I have pulled the roksan and put my old Cambridge cd4 back in my system.....this player is of course two core mains.
the presence of earths in power leads is something I will pay close attention to in regard to future upgrades etc.

thanks again fellas....nige.

It might be worth searching out someone local Nige who can sort the issue for you as it does seem a shame to limit yourself, especially if you liked the CDP in question, but as far as your own efforts are concerned, you've done the responsible thing.

[Audioman]

I had similar problems with a Pioneer 400x but the player attached was a class 2. Got all the kit to wire in a shunt rectifier then remembered I had a Rotel amplifier that turned out to have 2 core cable. Prefered the sound so left that in the system. I now have a passive pre between the same universal player and power amps which are earthed and no problems. Strange thing never a problem with a Teac Cd also no earth lead. It appears the Pioneer is designed in a way that it just does not like some earthing arrangements on likely newer equipment whether class 1 or 2.

BTW Paul have you read my post on using a Lehmann buffer stage with Albarrys ?

Paul.

[Reffc]

I had similar problems with a Pioneer 400x but the player attached was a class 2. Got all the kit to wire in a shunt rectifier then remembered I had a Rotel amplifier that turned out to have 2 core cable. Prefered the sound so left that in the system. I now have a passive pre between the same universal player and power amps which are earthed and no problems. Strange thing never a problem with a Teac Cd also no earth lead. It appears the Pioneer is designed in a way that it just does not like some earthing arrangements on likely newer equipment whether class 1 or 2.

BTW Paul have you read my post on using a Lehmann buffer stage with Albarrys ?

Paul.

Hi Paul

nope, but I'll have a look. I'm guessing it's a match? I built one a while back and used it between the Croft/Albarrys and it worked quite well but ultimately preferred the Alby preamp (which just happened to come up at the right price at the right time....more chance of winning the lottery I know!)

[The Black Adder]

Has anyone tried a pair of top quality 1:1 transformers (eg. Sowter) in the link to break the chain of an earth loop?... eg. pre to power....? If so, is there any deterioration in the sound?

Just interested...

[Reffc]

It's a very expensive solution Joe as the transformers need to be very high quality, multi-leaved high bandwidth and low distortion. Sowters would be a good choice though. Cheaper ones such as you see advertised for a tenner ruin the sound and are a waste of money. An earth lift circuit is a fraction of the price.

[lurcher]

It can be a can of worms Richard. I know of one person who lifted an earth on a (valve) power amp claiming that the RCD was protection enough. A fault later developed and the power supply insulation melted, with the amp catching fire and the chassis also remaining live long enough to fry whoever would have touched it. The RCD on that occasion didn't trip for whatever reason and the mains fuse protection didn't pop until enough current had been drawn to set fire to the thing. Not worth shortcuts, especially when other family members might be using the hifi. It never ceases to amaze me just how many in the gene pool are willing to put their lives and those of their families at risk for the sake of a problem which can be otherwise safely addressed. Natural selection eventually comes to bear :mental:

A RCD would never catch that. RCD works by comparing the live and neutral current, and if there is any difference its assumed its going to earth, so trips. If the amp chassis was live, then the RCD would trip if someone had touched it (maybe not in time) as the somebody would provide a path to earth. But even then, if the secondary of the valve amp transformer was shorted to ground through a bus full of school children, the RCD would never see it as the live and neutral into the primary would remain equal, so it would see no fault.

Ironically, the RCD would have provided some protection if the earth was connected, but by lifting the earth the RCD was rendered less than useless.

[Reffc]

I think that was the problem Nick; By lifting the earth, the RCD was rendered useless. I wasn't there when it happened but I was shown the aftermath. A mass of burnt plastic inside the amp where wiring had obviously burnt off the insulation and a fried mains transformer.

[Naughty Nigel]

It can be a can of worms Richard. I know of one person who lifted an earth on a (valve) power amp claiming that the RCD was protection enough. A fault later developed and the power supply insulation melted, with the amp catching fire and the chassis also remaining live long enough to fry whoever would have touched it. The RCD on that occasion didn't trip for whatever reason and the mains fuse protection didn't pop until enough current had been drawn to set fire to the thing. Not worth shortcuts, especially when other family members might be using the hifi. It never ceases to amaze me just how many in the gene pool are willing to put their lives and those of their families at risk for the sake of a problem which can be otherwise safely addressed. Natural selection eventually comes to bear :mental:


This is a fascinating thread which raises a number of important issues.

Firstly I would like to explain that RCD devices (earth leakage circuit breakers) will only trip if the device detects a leak to earth of about 10 milliamps or more. (Most are rated at 30 mA, but will usually trip at a lower value). RCD devices work by comparing current in to a circuit with current out, and tripping the supply if there is an imbalance (suggesting a leak to earth). RCD devices do NOT protect against fire or overload unless the fault current happens to flow to earth. The test button on RCD devices allows a small current to flow to earth via a resistor to check its operation.

RCD devices protect against electrocution as long as fault current through the body flows to earth. They do not prevent electrocution caused by touching live and neutral conductors at the same time! (Believe me, I have tested this myself more than once! :steam:)

Fuses and overcurrent circuit breakers will only protect against excessive currents. They do not protect against electrocution, and do not necessarily protect against fire in fault conditions. As an example, a one amp fuse can provide 240 watts of power at mains voltage. If a fault situation arises where 240 watts is dissipated across a half watt resistor or other small component the outcome will be obvious!

None of these devices is infallible under all fault conditions. Cleary then, audio circuits must be designed so that dangerous fault conditions are very unlikely to occur. Anyone modifying a circuit or changing its components must understand these parameters if safety is to be preserved.

So much for the safety lecture. Hum loops are created when magnetic fields generate alternating currents in earth circuits between audio equipment. Usual practice is to avoid hum loops by only having one device earthed (usually the amplifier), although as discussed this can be problematic if two or more devices are fitted with three core cables. (This includes computers of course.)

In my view it is dangerous to 'lift' the earth connection on an earthed appliance under any circumstances, as the circuit is no longer fail-safe. (An isolation transformer may be acceptable, but this usually is an expensive and impracticable solution.) Fitting external earth cables is NOT an acceptable substitute as earth continuity is not guaranteed.

(There are numerous design features intended to maintain the safety and integrity of earth connections, such as the longer and larger earth pin on 13A plugs, and the longer earth cable inside the plug, so that the earth connection should always be the last to be broken. These things are all there for a good reason.)

So how can hum loops be dealt with? Prevention is always better than cure, and the first step is to minimise the size of any loop, thereby minimising the effects of magnetic fields. Wherever possible, mains leads to different earthed HiFi separates should run together from the same source, such as an extension socket, rather than forming a loop. Plugging separates into different 13A sockets is asking for trouble! Interconnects should be as short as possible and run close to one another, and close to (but not alongside) mains cables (again minimising the physical size of any loops).

I should mention that separates fitted with two-pin 'figure of 8' chassis connectors can also be problematic owing to capacitive coupling of internal mains-voltage circuitry to the metal chassis, especially when switched off. Unplugging these connectors and reversing the connections often reduces mains hum significantly. (Likewise two pin European style mains plugs.)

If hum loops remain, and earth connections really do need to be 'lifted', the safest solution is to fit a pair of blocking diodes into the earth circuit of the offending appliance. These are simply a pair of heavy duty rectifier diodes connected in reverse parallel formation. The diodes allow a fault current to flow safely to earth, but the forward voltage (Vf) of the diodes (typically 0.6 volts) prevents unwanted current flow that might cause hum.

The voltages involved in hum loops are very low (usually just a few millivolts), whilst induced currents are similarly low (milliamps or micro amps), so the 0.6 volt Vf of the blocking diodes will be like a brick wall!

As a matter of interest, such diodes are commonly fitted into the earth circuits of yachts where shore lines are used. This is not to prevent mains hum, but to prevent electrolytic corrosion of metal fittings caused by earth leakage faults in marinas, and sometimes in other boats nearby.

But that is an entirely different subject for another day. :)

Nigel.

[Reffc]

Very good post Nigel. What you describe is exactly what I would (and have) done between pre/power amps in the past where neither had an earth lift and hum occurred (in that case, I fitted the diodes to the preamp section). It cures it completely and is intrinsically safe. The interesting part, and one which people often fail to grasp is that just because a circuit is fitted with an RCD, that in itself is not enough to guarantee protection against electrocution. The other thing worth mentioning is that at mains voltages, it only takes as little as 20mA or more for a severe (potentially lethal) shock partially because it's the threshold for sustained muscular contraction. It's a worthwhile thread (sorry for the slight thread drift to the op) because people need to be aware that messing around with mains unless they know what they're doing is plain dangerous and as you say, lifting a mains earth on a component designed to have one is dangerous. Finally, valve amplifiers hold some pretty lethal voltages so unless fully qualified to do so, no-one should go poking about in the inside of one especially as the power smoothing caps etc can hold some serious charge even after unplugging. As you say, lecture over but all important and worthwhile stuff to highlight.

[Naughty Nigel]

Very good post Nigel. What you describe is exactly what I would (and have) done between pre/power amps in the past where neither had an earth lift and hum occurred (in that case, I fitted the diodes to the preamp section). It cures it completely and is intrinsically safe. The interesting part, and one which people often fail to grasp is that just because a circuit is fitted with an RCD, that in itself is not enough to guarantee protection against electrocution. The other thing worth mentioning is that at mains voltages, it only takes as little as 20mA or more for a severe (potentially lethal) shock partially because it's the threshold for sustained muscular contraction. It's a worthwhile thread (sorry for the slight thread drift to the op) because people need to be aware that messing around with mains unless they know what they're doing is plain dangerous and as you say, lifting a mains earth on a component designed to have one is dangerous. Finally, valve amplifiers hold some pretty lethal voltages so unless fully qualified to do so, no-one should go poking about in the inside of one especially as the power smoothing caps etc can hold some serious charge even after unplugging. As you say, lecture over but all important and worthwhile stuff to highlight.

Thank you Reffc.

What I failed to mention is that earth bonding between separates components can also help to reduce hum; although any bonding cables should be as a short as possible (for the reasons already stated, and to minimise resistance), and with cable of at least square millimetre cross section. Offcuts of loudspeaker cable are ideal.

On your point about HT voltages, the voltage across terminals of a valve rectifier can easily exceed 700 volts, so I agree this is not something for anyone to play with unless they know exactly what they are doing. Even then, mistakes can happen.

If you do ever poke around inside a valve amplifier make sure you are insulated from the ground, (rubber soled shoes, etc.), and keep one hand behind your back so that current doesn't flow through your body.

Nigel.

[Barry]

Good post Nigel.

An alternative to the back-to-back diode arrangement (incidently, the current rating of the diodes ought to be as high as possible) is to 'lift' the ground with a 10 Ohm (5W) resistor. This will provide a current path sufficient to blow the fuse under a fault condition.

[Reffc]

Good post Nigel.

An alternative to the back-to-back diode arrangement (incidently, the current rating of the diodes ought to be as high as possible) is to 'lift' the ground with a 10 Ohm (5W) resistor. This will provide a current path sufficient to blow the fuse under a fault condition.

...or do both ;-)

Here's an over-kill earth lift circuit I installed into my last croft preamp to cure hum:

http://i1140.photobucket.com/albums/n577/24pacman/Hifi/_MG_6359_zps6bdc118b.jpg

The white wire to the right is the link from the diodes to the chassis earth and the one coming in from the left is from the signal star-earth point which was floated. Bridge rectifier provides safe path to ground.

[Barry]

...or do both ;)

Here's an over-kill earth lift circuit I installed into my last croft preamp to cure hum:

http://i1140.photobucket.com/albums/n577/24pacman/Hifi/_MG_6359_zps6bdc118b.jpg

The white wire to the right is the link from the diodes to the chassis earth and the one coming in from the left is from the signal star-earth point which was floated. Bridge rectifier provides safe path to ground.

Yes, a 10A or 25A bridge rectifier would be ideal. I assume the capacitor in parallel is there to provide a low impedance path to RFI. What value did you choose? 100nF 400V?

[Reffc]

Yes, a 10A or 25A bridge rectifier would be ideal. I assume the capacitor in parallel is there to provide a low impedance path to RFI. What value did you choose? 100nF 400V? That's right Barry. I think it was a 100nF ( probably still have a box of the things somewhere) so may check and put the circuit up for anyone interested in adopting something similar.