Ferrous vs Non-Ferrous amp casing/chassis.

[chebby]

Why would a completely non-ferrous (aluminium and plastic) amplifier case (and chassis) be "desirable at any price*"?

* From a reviewer.

 

[Al ears]

Why would a completely non-ferrous (aluminium and plastic) amplifier case (and chassis) be "desirable at any price*"?

* From a reviewer.

Not sure, who was the reviewer?

Having said that all of mine are with exception of the power amp.

It's certainly debatable that acrylic is cheaper to produce but some aluminium cases are extremely expensive.

 

[Vladimir]

As far as I know metal is preferable since it will act as a Faraday cage. *unknw*

 

[chebby]

As far as I know metal is preferable since it will act as a Faraday cage. *unknw*

Yes I agree (that's why I opted for the metal case option on my amp rather than the wooden case) but why would the reviewer be so insistent on the desirability of non-ferrous metals?

Magnetism? I don't know.

The reviewer was Jason Kennedy ...

http://www.hifichoice.co.uk/news/article/rega-brio-r--pound;398/8857/

"... the only real concession to cost being the ABS front and rear panels. The main chassis is aluminium, so the whole thing is devoid of ferrous metals and that’s a desirable quality at any price."

Are there sound technical reasons for his dislike of steel in amplifier chassis and cases?

 

[plastic penguin]

Why would a completely non-ferrous (aluminium and plastic) amplifier case (and chassis) be "desirable at any price*"?

* From a reviewer.

I'll give you one good reason: In socks there's no static (never covered the Arcams in M&S specials). With the Arcams it was awful when touching the case/knobs, not so with the Leema.

 

[plastic penguin]

As far as I know metal is preferable since it will act as a Faraday cage. *unknw*

That's all good if you sit the amp under the apple tree but indoors?

 

[Vladimir]

Probably something about parasitic magnetism.

 

[Covenanter]

IIRC a Faraday Cage can be made out of any conductor so aluminium should be as good as a ferrous metal.

Chris

 

[chebby]

IIRC a Faraday Cage can be made out of any conductor so aluminium should be as good as a ferrous metal.

Chris

So we've establihed that the reviewer's objection to ferrous materials - at in amplifier chassis and cases - is nothing to do with Faraday cages.

I am going to email the reviewer (if it's possible) to see if he can clarify.

 

[Al ears]

I think rather than a Faraday cage keeping stuff (magnetic interference?) in you'd want to let it out.

Would be interested to see what Mr. Kennedy's thoughts are, I am sure he's quite approachable.

Tom Evans uses acrylic boxes for all pre and phono amps, and I am sure the reason isn't to cut costs.

 

[james_LR90]

There is plenty of talk about this subject on the HiFi subjectivist forum as it is run by the man behind NVA. All NVA products use acrylic cases including their speakers.

 

[chebby]

Jason Kennedy has replied ...

"Hi chebby,

Ferrous metals harbour eddy currents and tend to be avoided in better quality components for that reason. Denis Morecroft is particularly knowledgeable about this which is why he used acrylic casework in his DNM components."

http://www.dnm.co.uk/materials.html

So why aren't all amplifiers (even upmarket ones) made of acrylic? (According to that DNM link even non-ferrous alloys harbour eddy currents.)

Is this something we can safely put down to the beliefs of one-or-two niche manufacturers and a reviewer?

 

[Covenanter]

Jason Kennedy has replied ...

"Hi chebby,

Ferrous metals harbour eddy currents and tend to be avoided in better quality components for that reason. Denis Morecroft is particularly knowledgeable about this which is why he used acrylic casework in his DNM components."

http://www.dnm.co.uk/materials.html

So why aren't all amplifiers (even upmarket ones) made of acrylic? (According to that DNM link even non-ferrous alloys harbour eddy currents.)

Is this something we can safely put down to the beliefs of one-or-two niche manufacturers and a reviewer?

1) Eddy current brakes are often made out of aluminium! I remember experimenting with one at Uni a lifetime ago. Google it if you don't believe me.

2) You need a fluctuating magnetic field to get an eddy current in anything, ferrous or non-ferrous. If there is such a thing in your kit if will be inducing eddy currents in everything conductive including all the circuitry. Perhaps we should make those out of plastic too!

3) Ferrous metals don't "harbour" eddy currents. An eddy current will dissipate if not sustained by a changing magnetic field.

4) Even if there are eddy currents in the casing, which I doubt, they would be very small unless you have huge magnetic fields around. What evidence is there that, if present, they have any effect.

Just a case of the usual psuedo-scientific BS you see in the hifi world. They just find some physical phenomenon and see if they can attach it in some way to some aspect of their kit and pretend it's important.

Chris

 

[chebby]

Jason Kennedy has replied ...

"Hi chebby,

Ferrous metals harbour eddy currents and tend to be avoided in better quality components for that reason. Denis Morecroft is particularly knowledgeable about this which is why he used acrylic casework in his DNM components."

http://www.dnm.co.uk/materials.html

So why aren't all amplifiers (even upmarket ones) made of acrylic? (According to that DNM link even non-ferrous alloys harbour eddy currents.)

Is this something we can safely put down to the beliefs of one-or-two niche manufacturers and a reviewer?

1) Eddy current brakes are often made out of aluminium! I remember experimenting with one at Uni a lifetime ago. Google it if you don't believe me.

2) You need a fluctuating magnetic field to get an eddy current in anything, ferrous or non-ferrous. If there is such a thing in your kit if will be inducing eddy currents in everything conductive including all the circuitry. Perhaps we should make those out of plastic too!

3) Ferrous metals don't "harbour" eddy currents. An eddy current will dissipate if not sustained by a changing magnetic field.

4) Even if there are eddy currents in the casing, which I doubt, they would be very small unless you have huge magnetic fields around. What evidence is there that, if present, they have any effect.

Just a case of the usual psuedo-scientific BS you see in the hifi world. They just find some physical phenomenon and see if they can attach it in some way to some aspect of their kit and pretend it's important.

Chris

Don't shoot the messenger! Just passing on the reply I got from the reviewer and a link to a manufacturer's website. This in no way betokens any expression of 'belief'.

I had my doubts which is why I asked here and emailed the author of the Brio-R review that prompted the question.

 

[drummerman]

Not sure but I love the magnesium/alloy casings of cyrus. Solid.

I am not to clued up on technicalities of faraday cages but know that the size of any spacings, mesh, openings, cooling vents etc is crucial depending on frequencies which need to be kept out.

Also, unless wifi modules etc which are now increasingly included in amplifiers etc are properly shielded themselves, an external 'faraday cage' is probably of no great use. A test bench investigation of a Micromega amplifier which included such an unshielded (switched on) module clearly showed the implications.

Others will no doubt know more (read; do google investigations) 🙂

 

[Vladimir]

No Faraday cage case and unshielded transformer. What genius improvements.

 

[Al ears]

No Faraday cage case and unshielded transformer. What genius improvements.

Does it come in black? 🙂

I guess this goes to show reviewers are not exactly Professors of Physics and tend to believe BS if they get fed it often enough. However, they do get paid to listen to a lot more equipment than I could ever hope to and they formulate their opinions around their own reference systems so they should indeed be listened to.

In the end they are just guideposts and you have to go listen for youselves.

It's my opinion that many, but not all, who make these acrylic boxes do so purely to save on cost.

 

[Covenanter]

I've just looked at their website. It's very, very funny. If he wasn't long gone I'd email it to my old Electronics professor. He liked a laugh.

Chris

 

[Vladimir]

Few vids: 1 / 2 / 3