[andyr]

The AKSA's are worth the best approach

SO I use the transformators and their "difficult" magnetic fields in a seperate EMI and RFI shielded box. The distance now between the box and the AKSA pcb's is appr. 1 mtr (2 yrds)

Kyrill,

Just wondering why U chose to separate the "power supply" box from the "AKSA pcb" box by 1m of cable, if they are enclosed in an RFI-shielded box?  (I would've thought 300-400mm was plenty!)

Do you have the power supply PCB in the "power supply" box with the transformers or in the "AKSA pcb" box?

Regards,

Andy

[kyrill]

Hi Andyr

The pws pcb is in the shielded wooden box of the AKSA amps. In the other (very far away box ) are only the three transformators per channel (active 3 amping).The cable between pws box and amp box is interwoven in a way that "common mode rejection" surpresses EMI and RFI pick up.

I have choosen also because of Hugh's comment for EI structured trafo's. They have the "old-fashioned" form., like the very small ones Hugh supplies for the GK-1, although  toroïds for those pre amp values also exist
The magnetic fields of EI trafo's is more complex and vast than of the toroïds

And I exaggerated a little bit. It is not one mtr but 75 cm (1,5 yrd)

[andyr]

Hi Andyr

The pws pcb is in the shielded wooden box of the AKSA amps. In the other (very far away box ) are only the three transformators per channel (active 3 amping).The cable between pws box and amp box is interwoven in a way that "common mode rejection" surpresses EMI and RFI pick up.

I have choosen also because of Hugh's comment for EI structured trafo's. They have the "old-fashioned" form., like the very small ones Hugh supplies for the GK-1, although  toroïds for those pre amp values also exist
 ...

Aah, thanks, Kyrill,

I agree with you about using EI transformers but can U tell me why U decided to put the PS pcb in with the AKSA pcbs and not in the transformer box?

NB: 75cm is 2'6" ... ie. less than 1 yard.

Regards,

Andy

[kyrill]

Andyr

The pcb of the pws is actually already part of the amp, as I see it, being part of the "direct current" family

So outside the negative influence of the trafo's means, to keep it away from the trafo's and certainly not in the same box close to them.

[andyr]

Andyr

The pcb of the pws is actually already part of the amp, as I see it, being part of the "direct current" family

So outside the negative influence of the trafo's means, to keep it away from the trafo's and certainly not in the same box close to them.

Yes, Kyrill,

But your way, you have 39v AC entering the "amplifier" case.  If you put the PS pcb in the transformer case, you would only have DC entering the AKSA case ... perhaps this would be better.

Regards,

Andy

[kyrill]

[...
But your way, you have 39v AC entering the "amplifier" case.  If you put the PS pcb in the transformer case, you would only have DC entering the AKSA case ... perhaps this would be better.

Regards,

Andy

Andy
I have no idea what would be better in that respect.  I suppose it does not matter alternate or direct current coming in as soon as it is "clean"

I see an amplifier as an active special modifier of wall current only.  It modulates the current from the wall socket in such a way that the speakers can handle voltage and current and it "fluctuates" in a musical manner.

The cleaner the "unmodified" wall current is, the cleaner the output

[andyr]

Andy
I have no idea what would be better in that respect.  I suppose it does not matter fluctuating or direct current coming in as soon as it is "clean"

I see an amplifier as an active special modifier of wall current only.  It modulates the current from the wall socket in such a way that the speakers can handle voltage and current and it "fluctuates" in a musical manner.

The cleaner the "unmodified" wall current is, the cleaner the output

Kyrill, yes I agree with you in terms of your last sentence.

My own view is that you don't want AC mixing with the signal - even at 30v (out of the transformers).  Therefore if you are going to the effort of making a special case for the transformers, you should also put the power supply PCBs in with them, so all you get inside the "signal" case is DC ... hopefully, clean, if you've put AC mains conditioning measures in place.

Just my opinion - I guess we need someone to build three AKSA N+s - identical save:
* the first is all-in-the-one-box
* the second puts the tranformers in a separate metal shielded case, and
* the third puts the PS PCBs in this separate case too,

before we will get the definitive answer as to which is best!!

Regards,

Andy

[jules]

Some more thoughts and research on EMI .....

The perfect shape for a mu metal screen is a ball [or an infinitely long tube!]. If there is a hole in the shield there should be a distance of 5X diam the hole to the magnetic source. Overall I reckon shielding for EMI is counterintuitive in that the whole thing is very different to shielding for RF, sound and other frequencies we are more familiar with. Check this website:-

 http://www.amuneal.com/pages/magshield-intro.php

If Naim are using Aluminium [and others are using stainless steel] it seems they aren't too worried about eddy currents. Ginger has pointed out that eddy currents are generated in anything that can conduct electricity and that presumably means the better the conductor the stronger the eddy currents. Aluminium would be high on that list with copper, silver and gold above it.

If Naim and others aren't using steel I'd be guessing that it's the ability of steel to transfer magnetic fileds that is the problem. Placing a toroid tight in the corner of a steel case or placing a [flat] screen so that it almost touches a toroid  at one point, looks like a great way to send magnetic flux lines wandering off to who knows where. Placing a circular ferrous screen of some sort outside a transformer is akin to creating an external "core". It appears that it's hard enough to make an effective EMI screen using mu metal in a perfect shape but almost impossible to make an EMI screen using steel.

I've been thinking about copper as a shield and I've dug up the following ... Copper and brass shielding is used to enclose high frequency RF circuits. What happens is that the magnetic fields set up by the coils of the RF circuits induce a current in the shield which in turn sets up it's own magnetic field which will apparently oppose the original field [according to Lenz's law ?!] and prevent it from spreading.

These shields can be of copper, brass or Aluminium. They need to completely enclose the coil and there should be a reasonable amount of space around them because the process of setting up currents in the shield diminishes the power in the coil.

I don't know how this applies to toroids [edit: or more particularly the  EIs in GK pre-amps]  at ~50 Hz but maybe someone else can offer an opinion here.

jules