[owain_thomas]

I'm trying to cure a ground loop problem thats cropped up since I got a BFD but not having much luck.

my setup is as follows:

source: HTPC (earthed)
pre: yamaha DSP 800 (double insulated)
Power for fronts: aaron (double insulated)
Sub: SVS PB10-ISD (double insulated)
BFD (earthed)

There are no issues at all until I connect the BFD to the mains and the pre/pro. when I do this I get a very noticeable hum from my front speakers. The BFD doesn't even have to be on, it could just be plugged in and I get this problem.

I've tried (as mentioned elsewhere on here) connecting the chassis to earth using some mains flex and a 3 pin plug (only the earth wire connected, live and neutral insulated and not in the plug body just to make sure). This had no effect. What I find puzzling is that when I checked it out using my multimeter there seemed to be no continuity between the case and the earth pin of the plug I was using - there should be shouldn't there?

does anyone have any ideas how I can get rid of this annoying problem?

cheers
owain

[bob1]

Have you tried removing the earth on the bfd yet to see if that helps.

[eviljohn2]

Before removing the earth check that the BFD has the double box symbol on the back (one white box inside the other usually near the socket). If it doesn't then it may not be wise to remove the earth lead.

Maybe someone else with a BFD can clarify?

[bob1]

I wouldn't recomend removing the earth permently (even though they do on the snapbug site) its just to see if the hum goes away.If something is earthed its done for a reason and with the bfd having a metal case i would not remove it without putting in some other protection in line.

[bob1]

Originally Posted by owain_thomas

I've tried (as mentioned elsewhere on here) connecting the chassis to earth using some mains flex and a 3 pin plug (only the earth wire connected, live and neutral insulated and not in the plug body just to make sure). This had no effect. What I find puzzling is that when I checked it out using my multimeter there seemed to be no continuity between the case and the earth pin of the plug I was using - there should be shouldn't there?



cheers
owain

This does not make any sense, its earthed anyway why would putting another earth on do anything.Anyway i checked my earthing from lead to case with the meter and all was fine conductive wise so the case of the bfd is definately earthed.

[owain_thomas]

Right, I'm really confused now, are you saying that your BFD's case has continuity with the earth pin of its normal plug?

[bob1]

Originally Posted by owain_thomas

Right, I'm really confused now, are you saying that your BFD's case has continuity with the earth pin of its normal plug?

Yes it does.
Without opening it up i would guess the the earth wire connects directly to the case.

[owain_thomas]

Ok, I've checked mine again, there IS continuity between the case and the earth pin but it's very dependant on how I touch the probe onto the case. This seems a bit odd to me.

I tried removing the earth from the power cord temporarily and the hum stopped, so I presume it is a problem with a ground loop.

How can I go about fixing this?

thanks
owain

[bob1]

Have you treid the bfd in a different socket to the htpc ,if that doesn't help you will have to remove the earth from either one to cure the hum.A rcd might help with the safety.

[owain_thomas]

cheers bob,

the bfd has been tried in different sockets with no change

How can I safely remove an earth from one of them? are RCDs fitted to the consumer unit or can you get them for specific items?

cheers
owain

[bob1]

I was thinking about the plug in type rcd i don't know if it will work but I found this ,

Sound Equipment

Earth connections
Lack of maintenance of earth connections causes the commonest electrical safety problem with sound equipment. Any item of equipment which is mains powered should either be double insulated or correctly fitted with a protective earth.

If you are in any doubt about the connections of equipment, consult a competent electrician. Remember that an audio expert might not be an expert in electrical safety.

Single items of equipment, if poorly maintained, usually present very little problem. If a number of items are connected together, however, it is possible that cables screens, together with protective earths, form loops resulting in mains hum on the system.

Do NOT remove protective earth connections. This has been one of the common causes of entertainers receiving electric shocks, some of which have been fatal.

Good quality sound equipment should not cause hum although in some cases you may need to disconnect the screen at one end (only) of interconnecting audio cables. In other cases rearranging the equipment so that the wires do not crisscross the stage can solve the problem. When obtaining new equipment, discuss your needs with the supplier. Some equipment has a facility for disconnecting the 'signal' earth from the safety earth without affecting safety.

[owain_thomas]

Right then, I've done a bit of searching and found RCDs from maplin that can replace a normal mains plug, am I right in thinking I could use one of these and safely remove the earth from the BFD?

Is this 100 %safe or is there a better way of getting rid of this annoying hum?

[bob1]

Have you sorted this yet ,after being on another thread i have done a bit of digging .
I have now found out you can get earth loop isolators ,you can do this with mains transformers or low level with something like this.

[eviljohn2]

As this thread has been resurrected I'd like to make a point with regard to removing the earth from a BFD.

DO NOT DO IT UNDER ANY CIRCUMSTANCES!!!!!

Snapbug are very wrong to do this.

I got my BFD through today and it is not of a design which is safe to remove the earth from (unlike most other AV equipment). Unfortunately this also means that it's not possible to power the BFD from the output sockets on the back of my amp but electrical safety must be paramount.

[bob1]

Originally Posted by eviljohn2

As this thread has been resurrected I'd like to make a point with regard to removing the earth from a BFD.

DO NOT DO IT UNDER ANY CIRCUMSTANCES!!!!!

Snapbug are very wrong to do this.

I got my BFD through today and it is not of a design which is safe to remove the earth from (unlike most other AV equipment). Unfortunately this also means that it's not possible to power the BFD from the output sockets on the back of my amp but electrical safety must be paramount.

I aggree with you on this but it is possible to to use the out put socket on the amp you just need to connect a separate earth to the bfd(via the lead).
I got a 2m lead (earthed up ),stripped back to 1m connected a 2pin eruo plug then connected the 1m length of earth wire to the mains block i use to power it all up.( i fully tested this)
Mains voltages can kill don't mess unless you know what your doing.

[eviljohn2]

That is correct bob1 although for my setup makes the amp socket a bit redundant since I'd still need a plug into my mains block.

Those that are capable of doing such a mod hopefully wouldn't need the warning though.

[bob1]

Originally Posted by eviljohn2

Those that are capable of doing such a mod hopefully wouldn't need the warning though.

Some people struggle to wire a plug.

[eviljohn2]

Originally Posted by bob1

Some people struggle to wire a plug.

I know
Hopefully those people would just plug it in and let it be rather than trying to make it all more "elegant" and use as many available sockets as possible.

A little off-topic now but essentially the message is: no matter how bad the hum is, do not remove the earth pin of a BFD power supply blindly. The unit must be earthed.

1st off, seasons greetings.


Have you earthed your receivers chassis to the bfd and the sub?

Euqual potential earthing should solve your hum issues.

Run a length of cable from the receiver gnd terminal or chassis screw to the bfd (or a plug next to it on a gang strip) and make sure the sub is also on the same socket or the same potential.

HTH's

+ If anything, it makes your system safer.

[JIT]

Finally got round to setting up my BFD and i also have a hum problem, any other ideas about how to remove it?

It is quite bad and i think i'd prefer not to use a BFD if there isn't a solution.

[bilba]

The humm occurs because you get a current circulating between pieces of equipment that are earthed and are connected together by shielded cable where the shield is connected to both pieces of equipment.

You can use an isolating transformer to break the direct connection between equipment, but there is an easier way.

Disconnect one end of the earth sheath for cables that are going between two pieces of equipment that are both earthed.

Where one of the pieces is double insulated, leave the shield intact at both ends.

This method leaves the earth intact for equipment that is intended to have an earth, thereby safety is not compromised.

[JIT]

Which cable do i need to this on exactly?

Cable from receiver to BFD or cable from BFD to sub?

[bilba]

Receiver to BFD.

I have attached a small graphic showing your equipment wired with open circuit shield depicted as the red cable. The earth side of the signal just goes "the long way" via the earth connections on the HTPC and the BFD.

Note: the graphic only shows the shield connections. The signal conductor (not shown) is not interrupted

You could alternatively have made the interruption between the pre-amp and the source. Only one cut per earth loop though!

If you put it between the BFD and the sub, not only would it not break the loop, but it would cut the signal to the sub!

Let me know if you want more detail and I'll add a page to my website.

[JIT]

Any more help would be nice as i don't want to disconnect the wrong wire.

[bilba]

As promised, I have written this up as an article on my website. Here's the link:
http://www.users.bigpond.com/bcolliso/earth-loop.htm

If you want even more info, the article has additional links to info for solving problems where you are using balanced cables.

Hope this solves your problem.

[owain_thomas]

bilba,

that is an excellent article. thanks very much for clearing this problem up. I'll try what you suggest when I get home today. My BFD is currently lying dormant due to this problem (and the fact that I've not got round to trying to solve it since I got back from my snowboarding season!).

Very useful, I'll post an update on how I get on.

owain

[bilba]

Thanks for your comments Owain,

I'll be away for a week, so I look forward to hearing your results when I get back. BTW, I've added a little more content to that page.

bilba

[JIT]

owain thomas

Did you manage to solve the hum problem by altering your sub cable?

[docb]

I have had this problem but by trial and error managed to solve it (for my system anyway).

I managed to track the hum as being caused by a connection between the amp and a lumagen.
The only reason for the link was to enable the use of the onscreen menu's etc. I now only connect the two when i am in tinkering mode, to allow me to see the OSD. At all other times it is disconnected and no hum.

Hopefully this will help someone who has this annoying problem, as i didnt really realise how bad it was until it wasnt there.

Doc

[owain_thomas]

hi,

just an update, unfortunately this method doesn't seem to have worked for me. I have a set of custom cables from mark grant and he has left the ground disconnected at one end of the cable that joins my amp to my sub (as described in the website). unfortunately the hum is still there.

I'm pretty puzzled by this as the explanation seemed to make perfect sense.

the situation I'm in is the following:

Amp -> BFD -> sub = hum

Amp -> Sub = no hum

bfd -> Sub = no hum (i.e. bfd attached to sub but not connected to amp)

any other ideas?

owain