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/...nd_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.