[andyr]

There was a thread a while ago about people building cases out of "anything but metal".

It seems AKSA fans are not the only mad buggers around ... here's a recent post from Tweaker's Asylum:
http://www.audioasylum.com/audio/tweaks/messages/113682.html

Wonder if perspex would be as good (it's easier to attach RCAs to than wooden cases!!)?

Regards,

Andy

[Al Garay]

Start cheap. Use MDF. It works.

[DSK]

.....interesting....I thought the argument had always been that the metal chassis acted as an RFI shield for the sensitive electronics inside.

Also, the analogy of the material used to build musical instruments versus hifi equipment is usually argued to be invalid as the materials, and their resonances, used in a musical instrument are critical to the sound of the instrument (hence brass, woodwinds etc etc) and the resonances are deliberately within the audible range. However, this is not the desired case with component chassis.

I would venture a guess that the "coldness" heard from the metal chassis was due to resonances of the metal case that could probably have been treated with something like cromolin, Dynamat etc etc.

Still, weird things happen in audio      

[Rom]

Hi Andyr,

Your right the perplex are easy to work with.

have a look at my work here

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=442

enjoy.

Cheers
rom

[andyr]

.....interesting....I thought the argument had always been that the metal chassis acted as an RFI shield for the sensitive electronics inside.

Also, the analogy of the material used to build musical instruments versus hifi equipment is usually ... invalid as the materials, and their resonances, used in a musical instrument are critical to the sound of the instrument ...

Hi, Darren,

I have always been on your side of the argument - firstly, surely EMI is going to impinge on the circuits if you don't have an earthed metal case and, secondly, we want the case which surrounds a piece of electronics to be neutral ... whereas a musical instrument, as you've said, implicitly depends on its materials for its sound.

And Hugh "Mr. AKSA" Dean specifies shielded ICs, to minimise the chance of RFI getting into the amplifiers!  Not much point, I would've thought, if the PCBs are exposed?

But, remember Kyrill has gone to all that trouble to make a wooden case but covered the inside with gold leaf for EMI reasons (the gold leaf is a) thin and b) non-magnetic).  And Naim use earthed aluminium cases (not steel) because they're non-magnetic.

So I'm starting to think there might be something beyond voodoo in all this!  At least the guy in the Tweaker's Asylum post actually compared one against the other.

There could be several influences at work here and, until someone builds the same device in multiple cases and compares them all, The Absolute Truth will not out!  

I suspect that "resonances of the metal case" might have something to do with the degradation of sound described in the Tweaker's Asylum post but perhaps more to the point are eddy currents induced in the steel case from the transformer and the AC input wires?  

So, a properly set up experiment would need five AKSA 55N+s or GK-1s in:
* a conventional steel, earthed case
* a fully stainless steel case (earthed)
* an MDF case with no internal earthed foil lining
* a solid-wood case with no internal earthed foil lining
* a perspex case with no ....

Any takers, anyone, for this important scientific experiment?  

Regards,

Andy

[andyr]

Hi Andyr,

You're right the perspex is easy to work with.

have a look at my work here

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=442

enjoy.

Cheers
rom

Beautiful, Rom!

Can you answer a few Qs for me:

1.  In DSC01818 (#1) and gk1topview (#4) what are the 2 silver "covers" used for ... as they don't seem to be a complete box for shielding reasons?

2.  The knob shown in woodknob (#5) - did you turn it yourself?  It's luscious.

3.  The speaker binding posts poking out the top of 55WN+ (#8) ... how are these connect to the PCBs so you can remove the lid easily?

Regards,

Andy

[Rom]

Hi andyr,

To answer your questions

1. the two metal on the GK1 are made of Anodized alum, they both have two purpose to shield and cosmetics, although the only earthed part is the one housing the transformer. I did not find any Hum or an stray noise to have the need to earth the one covering the the main GK1 board.

2. The knob, yes I just use my old trusty handrill and some sand paper to polish it. I use an old knob fixture and use a silicon sealant to hold it in place.

3. The connection is a bit tricky, but after the muck up I found the solution to it. Initially I want to use all plug and socket but having tha advantage of seeing the indside I solder the input part and the rest are sockets and spades.

I have an aluminum plate as well holding the the IEC socket on the N plus and looks better now.

cheers
rom

[Felipe]

Rom :

Wow, those are some seriously good looking cases you have there!!
I have never seen such bold and innovator look in a amp case.

I have a question regarding the sockets and spades you used to connect the pcb's. What kind are them ? The ones used in auto radio connections? I can get some of those but i think they are made of brass. Does it matter if they are brass/copper/gold-plated brass/steel/iron ?

Andy:

I am building new cases for my aksa100 (future to be aksa100N), plus a brand new gk-1. Currently the aksa is in a normal steel earthed case.
The new ones will be made of wood, but with stainless steel wrapping them from the outside. I'll keep in touch with the sonic results of these cases, hum issues and all...

See ya
Filipe

[andyr]

Andy:

I am building new cases for my aksa100 (future to be aksa100N), plus a brand new gk-1. Currently the aksa is in a normal steel earthed case.
The new ones will be made of wood, but with stainless steel wrapping them from the outside. I'll keep in touch with the sonic results of these cases, hum issues and all...

See ya
Filipe ...

Hi, Felipe,

I believe if you wrap the wood in metal - even stainless steel - you will be negating the "goodness" of the wood case.

However, as stainless is non-magnetic, I may be completely wrong!

Are you able to do this build in two stages - with the AKSA100 just in the wood case and listen ... then enclose the wood case in s/steel and listen ... to test out the two alternatives?  Otherwise you have nothing to compare it with ... unless there's another AKSA owner nearby with a conventional metal case!

Regards,

Andy

[Felipe]

Hi Andy,

Yes i can test the amp without some of the plates.

I still will have to leave the back plate where the terminals are inserted, plus an 2 extra :

1. An horizontal plate (made of normal steel) inserted inside the box covering all the inner area. Below it, is the mains wire that connects the toroids at the front of the amp to the back mains socket. I place this plate to isolate magnetic interference from the mains wire passing right next to the pcb's and power supply.

2. A vertical one separating the transformers from the other components.

Can you suggest to what plate (since they are all independent) should i connect mains earth? I was thinking of the vertical plate separating the toroids from the rest. I could connect a wire to the front plate too, in case there is a malfunction with the switch button.

Tx
Filipe

[andyr]

I still will have to leave the back plate where the terminals are inserted, plus an 2 extra :

1. An horizontal plate (made of normal steel) inserted inside the box covering all the inner area. Below it, is the mains wire that connects the toroids at the front of the amp to the back mains socket. I place this plate to isolate magnetic interference from the mains wire passing right next to the pcb's and power supply.

2. A vertical one separating the transformers from the other components.

Can you suggest to what plate (since they are all independent) should i connect mains earth? I was thinking of the vertical plate separating the toroids from the rest. I could connect a wire to the front plate too, in case there is a malfunction with the switch button.
 ...

Hi, Felipe,

Now you said you are planning on having steel for:
* the back plate, where the terminals are inserted (is this stainless)
* a horizontal plate covering the bottom of the case? ... to isolate the mains wiring
* a vertical one to isolate the toroids, and
* a front plate, to take the switch button.

From your description, it seems to me the PCBs are enclosed by metal:
* at the back
* at the bottom
* at one side, and
* at the front.

Metal on the top of the case and the other side would produce the equivalent of a complete metal case ... so where's the benefit (if the idea is to use wood for its non-negative sonic qualities) in putting wood over 3/4 of a metal case?

By the way, I would think it would be better to connect each metal plate to mains earth.

Regards,

Andy

[Felipe]

Andy,

You are getting the wrong picture. I initially said i was building a wooden case covered with stainless steel. This is for aesthetic reasons, not sound benefits. What i said later on reply to your post , was that i could test the amp before putting all the plates in it, besides a couple of them.

1. The back plate is stainless steel, where the terminators are inserted.

2. The vertical normal steel plate isolates the toroids from the transformers.

3. Forget the bottom one, i am not going to use it anymore, i'll just use a shielded mains cable below the wood.

4. The front plate is stainless steel but not needed to test the amp.

So to test the amp without metal, i'll have the back stainless steel plate, plus a steel plate in the midle isolating the toroids. Thats all. I think its pretty much a almost metal-less case. None at the bottom or top or sides.

After this i can put the metal in, and test it again to see if its better or worse.

Also....if the bottom, top  and sides do not have any type of contact with any type of component (just the wood box) do you still feel that they should be connected to earth?

Thanks for the comments,

Filipe

[Seano]

.........I think you're all forgeting the potentially confounding effects of the two cast aluminium heatsinks that your amps hang off.

[andyr]

Andy,

You are getting the wrong picture ...

1. The back plate is stainless steel, where the terminators are inserted.

2. The vertical normal steel plate isolates the toroids from the PCBs.

3. Forget the bottom one, i am not going to use it anymore, i'll just use a shielded mains cable below the wood.

4. The front plate is stainless steel but not needed to test the amp.

So to test the amp without metal, i'll have the back stainless steel plate, plus a steel plate in the middle isolating the toroids. Thats all. I think its pretty much a almost metal-less case. None at the bottom or top or sides. ...

Hi, Felipe,

OK, I get the picture now.  I would think that just putting plate #2 in place to isolate the toroids from the PCBs won't do much because the magnetic field will go all around that plate if it is just by itself and not enclosing the toroid.  Someone previously on the forum made a brilliant suggestion for isolating the toroids - put each one in a metal can (like a can used for babies milk powder).  Then the toroid IS completely surrounded by steel.  Brilliant idea!

... Also, if the bottom, top and sides do not have any type of contact with any type of component (just the wood box) do you still feel that they should be connected to earth? ...

No, I guess not.  For safety reasons, all you should do is earth the back plate (because of the IEC socket) and the front plate (because of the on/off switch).

Good luck,

Andy

[ginger]

I was waiting for someone to take this on - BUT I guess its up to me.

This is what I used to try to avoid stepping in when fetching the milking cows each morning from the paddock next to the house.

The key words are "Faraday Cage". The circuitry MUST be screened which means entirely surrounded by a earthed conductive case/metal mesh etc.

Intrusion of RF into the signal chain is a guaranteed way to make the sound harsh.

The interconnect shields MUST be an extension of the screen at least at Radio Frequencies - at audio frequencies its sufficient for it to be connected to signal ground. If the interconnect shields are'nt directly connected to the box then connect them to it at RF via a capacitor.

The sound improvements touted are amost certainly due simple to the rebuild having fixed dodgy connections, eliminatation of earth loops, the physical re-layout or similar. Either that or someone is hearing what they want to hear to justify the work they've just done, a trap that is easy to fall into. Given that most folks audio memory is good for about 5 minutes maximum, concurrent A vs B testing is essential.

By all means build your case out of perspex, MDF or what have you so long as you line the inside with something conductive and then earth it.

Given that - why not simply use a metal box in the first place.

Cheers,
Ginger

[andyr]

I was waiting for someone to take this on - BUT I guess its up to me.

... The sound improvements touted are amost certainly due simply to the rebuild having fixed dodgy connections, eliminatation of earth loops, the physical re-layout or similar. Either that or someone is hearing what they want to hear to justify the work they've just done, a trap that is easy to fall into. Given that most folks audio memory is good for about 5 minutes maximum, concurrent A vs B testing is essential.

By all means build your case out of perspex, MDF or what have you so long as you line the inside with something conductive and then earth it.

Given that - why not simply use a metal box in the first place.
 ...

Thanks, Ginger,

I agree, "cognitive dissonance" is a strong force (as you say above!) and, as my own aural memory is probably about 5 seconds, maximum, A-B testing is a must!  

However, there must be some voodoo in there somewhere because so many people are trying it - and remember, O Electrical Engineer ... EEs were telling us back in the early 80s that "a bit was a bit was a bit" - so don't bother isolating CD players from vibration like you had to with turntables!  And 20 years later, we now know different!

Can you from an EE's point of view, at least comment on whether it's magnetic steel which is the issue (or rather, the problem!) ... ie. would an earthed stainless steel, copper or aluminium case be better than a conventional steel one?  

And does a cage made of mesh do as good a job (as a Faraday cage) as a solid-sided case?

Regards,

Andy

[ginger]

Andy,
You do like to ask the obvious but sometimes bloody difficult questions.

The short answer is that any slot, hole etc in the case/shield will allow entry of RF and hence allow RF Interference. The trick is to quantify How big a hole can be before it causes problems.

A mesh cage DOES work as a shield against RF.

There is an engineers "rule of thumb" which we use when designing.  The maximum slot, hole etc dimension should be not more than:
wavelength divided by 12
up to about
wavelegth divided by 20

What the heck does that mean? - do I hear you ask?
Well if you want your enclosure to shield against RF signals up to say 400 MHz
1) Calculate wavelength = speed of light / frequency
so 400MHz => 0.75 metres
2) 0.75/ 12 = 62.5 mm and 0.75 / 20 = 37.5 mm
A mesh of not greater than 40 to 50 mm will give adequate shielding up to 400 MHz.

If you want to shield against signals up to say 2 Ghz then the mesh needs to be not larger than about 5 mm

These figures may surprise you - they show that holes can be resonably large before they give any problem except at the very highest frequencies.

It also tells you that that RCA socket  or fuse holder hole which you drilled in the wrong place by mistake is NOT, in general, going to cause you any grief.

Don't forget rules 1 and 2 - The mesh has to be conductive and it has to be grounded.

Now Magnetic Shielding - thats a whole new "Kettle of Fish".

More for your compendium of useless information

Cheers,
Ginger

[Gordy]

An excellent example of a mesh at work would be your see-through microwave oven door...

[Greg Erskine]

An excellent example of a mesh at work would be your see-through microwave oven door...

Arh.. a good source for mesh. Have you tried to get the mesh from the microwave oven door?

[andyr]

.. Now Magnetic Shielding - thats a whole new "Kettle of Fish".  ...

Thank you as ever, Ginger, for your explanation.

Yes ... "obviously difficult" ... I like that!  

However, I think you misinterpreted my Qu about magnetism.  

I asked: "... whether it's magnetic steel which is the issue (or rather, the problem!) - ie. would an earthed stainless steel, copper or aluminium case be better than a conventional steel one?"

I was not interested in what metal is good for shielding PCBs from magnet fields (I think I know that one ... Hugh said it must be normal steel (ie. not stainless steel)    )

What I was asking was ... if people are saying that taking electronics out of metal cases makes the "thing" sound better then what property of the metal is the problem?

Is it the fact that normal steel (given that most cases for hi-fi components are made from mild steel) has eddy currents generated in it from the mains wiring and the power transformer?

If so, would it be better to use stainless steel or aluminium or copper?  (I know Naim use aluminium, deliberately.)

Or are eddy currents generated by a power transformer in any metal?

Regards,

Andy