XXHighEnd

Anyone following the Gainclone Heaven thread may have noticed that I had some hum "issues" after completing the build of the bi amped bridged gainclone amp - well maybe not that bad (I thought) but still there was some hum with ear right next to LF drive units and I mean right on the cone of the drive unit (92db sensitivity). OK not that bad because the sound quality was good and the bridged bi amped GC sounded great. And then I had all sorts of problems at home and then a project to build three pairs of speakers (uurrgh). So the hum problem got sidetracked and forgotten - BUT actually not quite forgotten.

Those that read this thread http://www.phasure.com/index.php?topic=1575.msg26747#msg26747  will know what I am talking about.

So always in the back of my mind was the thought that hum MUST be eliminated - (from experience of my first GainClone build when Peter badgered me to get noise to the absolute minimum and when I succeeded wow what a difference).

If you check out the thread above the thinking was that the hum was possibly due to much bigger transformers in the new bridged GC amp and maybe linked to some EM interference. BUT to modify my amp by moving the transformers well away from the amp (to reduce EM problems) is a very very big job. So today it seemed like a good idea to make sure that all possible earth loop problems were looked at before taking the VERY big step of ripping the amp apart. So I tried every possible combination of earthing and I found a combination that really made a difference as follows:

Amp - electronic ground NOT connected to PE
NOS1 - as above but that is the way NOS1 is built anyway :)
Amp & NOS1 electronic grounds connected together (but not to PE) via the balanced i/c pin 1 connection.

But this is where it gets weird. Previously the PE of the amp and NOS were connected to the PE of the balanced power transformer which in turn was connected to an earth rod in the garden. So the metal boxes only of the amp and NOS1 were earthed via the supply to the main earth in the garden. Nothing wrong with that Eh?

Well today I changed the earthing by connecting the PE of the amp and NOS1 with separate wires to the earth rod in the garden. So I ran separate earth wires from the boxes of NOS1 and the amp to the earth rod. A proper star earth arrangement. My PC remains connected to the earth of the balanced transformer which in turn is connected to the earth rod. So now I have three earth wires connected to the earth rod in the garden instead of one. Now this could not possibly make any difference could it? (because amp and NOS1 PE's are only connected to the boxes and not the electronic grounds). Wow what a difference!!!. With this earth arrangement detail has increased to a new level, imaging is much better, depth of sound stage is much better strings sound much sweeter.

The above is not something I would have ever thought possible until reading Peter's musings about grounding. This seems to move away from simple ground loops to RF earthing problems - how else can connecting the boxes only of amp and NOS1 separately to the earth rod make that difference?

BUT I can still hear a very very low level of hum (MUCH reduced from before). OK there has to be total quiet in the house and ear right on the cone of the LF unit to hear it but it is there JUST. But I now know that even that HAS TO GO. So I am going to have to find some way of looking at the noise on the earth rail.

Maybe Nick will be kind enough to help me with his super duper scope when he comes next? - who knows but now I am absolutely determined to reduced noise to the ABSOLUTE minimum.

So probably a rebuild of the amp will go ahead anyway - but for other reasons as well as hum and that is I need bigger heat sinking.

Of course my amp has no volume control as I do not have a pre amp so it is on full blast all the time. So for those that have pre amps and no control over grounding arrangements how much noise do you hear when the volume is turned right up to maximum? it would be interesting to know because if you do have some noise (any at all) then there is the potential to improve your system by getting rid of it.

By the way why is it that all the Sage's of the hi fi world say that balanced connection gets rid of earthing problems - I found it much easier to get noise levels down with single ended RCA connected i/c's than balanced connected. But there again my experience could be a one off.

All the best

Paul

Hi Paul,

I use a preamp in my system and yes, I can hear some hum when I open the volume up (or should I say "reduce the attenuation").

I am thinking about a power conditioner to help me in this, but for the moment I am trying to identify the source of this noise...

Alain

Paul hi,

Absolutely top stuff ! This sounds really interesting for my system too given the similarities  :) I'd like to sit down and draw out what you are describing to see if its possible to work out why the noise level is improved.

Don't forget the NOS1 internal signal ground IS connected to PE. The connection is via a 4.7nf cap and 110k ohm (EDIT just checked the resistor is 104k ohm) resistor (R and C parallel with one another) on the NOS1 USB board which connect the NOS signal ground via the USB lead's shield (I must also check the USB signal earth as well) back to PE in the PC.

You really have me thinking haha.

Nick.

Ps what gauge of wire did you use for the additional chassis earths to the NOS1 and the amp, how are they connected to the chassis and have you lifted the main plug earth now that you have the star earth arrangement ?

Hi Nick - I hope you had a brilliant holiday and welcome back to hifi "work".

A couple of things actually my USB plug internal to NOS1 that plugs in the back of the case USB socket (the plug that is connected by wire to the USB board) has PTFE tape round it to isolate its earth from the chassis temporarily. Well it has just now as I wanted to know if it made a difference (after implementing all the changes above) it did not that I could hear anyway. I am going to remove the PTFE tape again today for another listen.

Actually NOS1 signal ground is connected to PE via the incoming USB plug from the PC (I checked it using my meter). So for sure the signal grounds are connected to PE but at only one point.

Interestingly though I just pulled the incoming USB plug out of the DAC (and so disconnecting the NOS1 signal ground from PE altogether warning: be very careful to switch your amp off before doing this and check DC offsets before switching back on) and it makes no difference from what I can hear. Does this mean that a fibre optic USB link to provide galvanic isolation may not make any difference to earth noise?

Anyway for my system installing dedicated earth wires back to the earth rod from the cases of the amp and NOS1 was fairly simple. Behind my equipment rack there are two mains cooker sockets one each dedicated to the amp and NOS1. I taped back the incoming earth wires. With the cooker socket removed revealing the metal box inside the wall I then drilled through one of the "punch out holes" in the back of each metal box straight through the wall to the outside. I then installed 16mm earth wires through the wall (one for each cooker socket - then connected one end to the earth rod and the other end to the earth "pin" in the cooker sockets. Hey presto "proper job" star earthing.

Oh by the way it was the dedicated earth wire from the amplifier case to the earth rod that made the biggest difference I am not sure if the NOS1 dedicated earth made much difference. Maybe that indicates that there is substantial "EM Hash" on the case of the amp (from the big transformers) and that a dedicated earth gets much of that hash away from the rest of the system more effectively. Maybe that is what is happening because I cannot see that electrically I have removed any loops with this new earth arrangement. Just a thought anyway.

If the above is correct then it is likely a similar arrangement could benefit other users. It would also explain why I did not really have this problem before with my SE GC amp with its much smaller transformers.

Another project will be to separate the transformer box well away from the amp box (with separate dedicated earths of course) to see if I can reduce noise even further. A job for a rainy day!!

Anyway more important just now is that I have to fix my bike and get out for a ride!!

By the way with changes in the last few days I think you will notice quite a difference for your next visit!!

Best Regards

Paul

Nick,

A thought occurs to me maybe you have already done a similar thing to me when you connected the PE of your amp to the PE of you new balanced transformer (for bass units) thereby diverting "hash" away from the rest of the system - just a thought!!

Anyway given the really satisfying imp

Paul

Alain,

Just thinking about your remarks. The hum comes when you decrease attennuation, so that will be hum on the signal side. If you want to know how silent your amp is, just short circuit the INPUTS (signal direct to ground). It probably is very silent.

The DAC is probably also very silent if you would have the means to establish that. So I think a line filter will solve a non existent problem.

I recognise this hum phenomenon, and it boils down to proper earthing, good shielded cabling and positioning of the components (no transformers or powercables next to signal cables etc).

Regards, Coen

Hi Coen,

I will try to do some tests with these suggestions in mind. If I was to answer know, I would probably "flood" Paul's thread with "newbies" questions, so I prefer to postpone my answer.

I already have a thread about my concerns (http://www.phasure.com/index.php?topic=2690.0), even if I did that much too early (and in a clumsy fashion).

Your suggestions are noted though and I will certainly appreciate your input when my working area will be better organized. And I sure hope this will happen soon :)

Thanks and regards,

Alain