Ferrous materials

[RochaCullen]

Hi All,

I've got a question related to the use of steel in an amplifier enclosure. I've recently updated the gainclone thread with what I have begun to assemble. Part of my setup is a steel enclosure to isolate the transformer from the power supply and amplifier boards:

http://i830.photobucket.com/albums/zz230/rochaCullen/GaincloneBuild/isolation2.jpg

The enclosure in position:

http://i830.photobucket.com/albums/zz230/rochaCullen/GaincloneBuild/layout1.jpg

So my question is, will the steel enclosure cause more trouble than it solves?

Nathan

[RochaCullen]

Fellow DIYers have no opinions on this topic??? Amazing!

Nathan

[Reid Malenfant]

I doubt it will have much if any effect in all honesty ;) Toroidal transformers already have a very low magnetic leakage due to the inherent design..

I'm not sure exactly what you mean by trouble, please explain why you think a steel enclosure will cause problems?

[Welder]

Hmm, I know aluminum can do strange things to certain types of capacitors and chokes near field. I’ll see if I can dig up the info.
Yer man AnthonyT has the right idea with his copper and stainless steel chassis imo. I had my crossovers in an ally enclosure until I read up a bit on the effect.
For some reason I think steel may be better than alloys but I’m not sure.

If my memory serves me this guy measured the effect of metals near field to chokes but i cant find the relevant article. Its in here somewhere.
http://www.troelsgravesen.dk/Diy_Loudspeaker_Projects.htm

There is also an engineering article on the effects of ferrous metals on various electronic componants on my other laptop I think. I'll see if i can find it when i get it back.

[Marco]

Hi Nathan,

Personally, I wouldn't use steel in any hi-fi application which involves housing electronic circuitry, although if it's just a mains transformer and some caps, you *should* be ok.

Steel will have the most detrimental effect, sonically, on more 'delicate' preamp circuitry, than with a PSU. It's to do with magnetic fields generated by ferrous metals and their effect (and also those of eddy currents) on electronic components.

There's a reason why almost no reputable commercial manufacturer these days uses casings made from ferrous metals to house their designs.

I suggest you do some research on 'eddy currents', 'magnetic interaction', 'ferrous metals', and read, for example, why companies like DNM use acrylic cases, not metal, for their designs :)

Marco.

[Welder]

Yep, something like what Marco said. There’s a bit more to it than meets the eye but I’m f****d if I can recall enough info to be useful or find the right articles :doh:

I should add the steel enclosure was for the crossover in above. ;)

[Reid Malenfant]

Steel will have the most detrimental effect, sonically, on more 'delicate' preamp circuitry, than with a PSU. It's to do with magnetic fields generated by ferrous metals and their effect (and also those of eddy currents) on electronic components.
:scratch: Erm, do you use SUTs on the front end of a valve phono pre amp or am i imagining things here? Transformers are lumps of ferrous metal, if it wasn't ferrous there would be no transformer action ;) I thought MCs were the lowest output type of cartridge so obviously the most "delicate" :)

[Marco]

Hi Mark,

The idea is that you minimise the effect as far as possible. Obviously you can't do much about the 'ferrous effect' of a transformer (other than move it to a separate box), but you can help matters significantly by not housing circuitry inside a steel case in the first place ;)

After all, one of the benefits of having external PSUs on equipment (CDPs or preamps) is getting rid of that big lump of metal (called a transformer) from sharing the same case as the more 'delicate' circuitry (read as being more susceptible to interference).

Moving the stock PSU from underneath the platter of the Techie into a separate box is also done for similar reasons :)

Basically, in almost any serious hi-fi application steel = bad!

Marco.

[Welder]

Anthony would be good guy to talk to about it.
He must tackle the problem of building a Farady cage without using steel in his amps.

[Reid Malenfant]

Ok, agreed :) However it appears that our friend here is attempting to screen the transformer so as to reduce the effects of any stray magnetic field even further. This is pretty common practise on a lot of "high end" HiFi kit.

Notice the screening cans on the ends of your transformers on you copper amp, also the dirty great big steel pot that the Krell transformer in my KSA250 has. It's also standard on virtually any transformer used on medical equipment as it's required, not optional.

If you can't remove the transformer from the local vicinity of the circuitry then by all means screen the thing imo :) In this case non ferrous metal would be a total waste of time, if screening is the intention..

[Marco]

Hi Mark,

Yes, agreed, but I'd still avoid using a steel case of any description in the first place when something sonically better could be used instead :)

So in answer to Nathan's question, I'd bin the steel case and use an aluminium one, or perhaps one of non-magnetic stainless steel, such as that used in my Mana equipment supports.....

I'll never forget the *huge* (and I mean HUGE) sonic improvement I got getting rid of my old ferrous angle-iron Mana stands and replacing them with the non-magnetic SS versions I have now - it was almost like having a new hi-fi system!! :eek: :eek:

Marco.

[Reid Malenfant]

Hi Mark,

Yes, agreed, but I'd still avoid using a steel case of any description in the first place when something sonically better could be used instead :)

So in answer to Nathan's question, I'd bin the steel case and use an aluminium one, or perhaps non-magnetic stainless steel, such as that used in my Mana equipment supports.....
If he's attempting to reduce stray magnetic fields from the transformer further than what they are already then using a non ferrous metal is bloody stupid as it'll have zero effect. Why do you think a lot of MC SUTs are screened with mu metal? To prevent outside interference with that miniscule 0.25mV ;)

Mu metal (http://en.wikipedia.org/wiki/Mu-metal)

If you want to screen against RFI then you'll be 100% fine with a non ferrous metal. If you want to screen against both RFI & magnetic interference then only a ferrous metal will do..

[Rare Bird]

Post Number:23 that seemed to be ignored or maybe not hence this discussion :)

http://theartofsound.net/forum/showthread.php?t=3458&page=3

[Marco]

Hi Mark,

I haven't read the Gainclone thread (I simply read the title of this thread 'Ferrous Materials' and Nathan's first post here on the subject, so perhaps I've misunderstood his intentions? :)

However, if I'm reading things correctly, and this steel case is to go inside the main amplifier casing to, as Nathan says "isolate the transformer from the power supply and amplifier boards", then in my experience you don't want a big lump of steel beside said power supply and amplifier boards, for reasons already given.

I understand what you're getting at though, but what the best compromise is to facilitate what Nathan needs, I'm not sure.

Could the whole PSU (including the transformer) not be put into a separate box, thereby negating the need to isolate the transformer, using the steel case proposed, in the first place?

Marco.

[Reid Malenfant]

Could the whole PSU (including the transformer) not be put into a separate box, thereby negating the need to isolate the transformer, using the steel case proposed, in the first place?
That would indeed be a better idea :)

[Marco]

Well, as they say, if you're gonna do a job, then do it _ _ _ _ _ [fill in the blanks] ;)

Marco.

[RochaCullen]

Thanks for all the advice guys, and given the fact that the steel ones are already made, I may ask my old man to knock up some aluminium versions also. That way we can experiement. Nothing wrong with trying it both ways. I'll keep you posted on what the outcome is.

Andre, I decided to start this new thread to discuss the topic as I assumed, as was true in the case of Marco, that a few people with knowledge of this specific topic would not be paying attention to the Gainclone thread.

Any thoughts I have on the merits of the steel enclosure over the aluminium or vice-versa, I will be adding to the Gainclone thread.

I should be getting the rest of the compenents I need today or tomorrow, so hopefully I will have a few extra posts on my progress very soon.

Nathan

[Marco]

Hi Nathan,


Andre, I decided to start this new thread to discuss the topic as I assumed, as was true in the case of Marco, that a few people with knowledge of this specific topic would not be paying attention to the Gainclone thread.


You were quite correct to have done that, as I wouldn't have noticed your query otherwise.

The detrimental sonic effect on hi-fi equipment of ferrous metals, I know something about, building equipment circuits, I don't! ;)

Marco.

[Rare Bird]

At the end of the day only poorly wound transformers give of stray magnetic field to worry about, all metal cans do is reflect the magnetic field back into the core causing performance problems.High quality transformer with just a non ferrous partition between the transformer & the electronics should do fine. high quality toroidal transformers are generally nothing to worry about alone in most applications other than the really highly sensitive imho.