Aluminium vs steel chassis

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
As mentioned in an earlier post I am building my first power amplifier from scratch. I have decided upon the Dynaco St70 (availability of parts, relitive simplicty of construction + wanted to build a stero unit) but I am setting up my own layout and design. So far I have built a cardboard mock-up and I am about to take it to a sheet metal worker.
Here's the question - according to Morgan Jones, 'steel is not suitable for valve amplifiers'. Is this an absolute rule or is steel OK provided that the transformers are mounted with something between them and the chassis.
I use steel. I like the magnetic shielding it provides from the transformers and chokes above. You could have eddy currents in said chassis, but the field is still shielded from the signals below.

I would think it important to electrically isolate the transformers mounted on it. I use rubber washers (with the additional vibration control) with teflon shoulder washers. Each device then gets bonded to chassis in one point. This avoids circulating currents.

I'm not sure why Jones said this, though there may be some context to it that we're missing. If it has to do with induction, there are usually procedures and installation methods that avoid or minimize it.

Ease of installation has nothing to do with the choice, in my book. My punches and drills go through both Al and steel.
Steel vs Aliminum

Steel is stronger and cheaper.

Consider your final product...are you planning on painting or some other method of finishing? Aluminum can be left unfinished and look great, steel needs some sort of protection to keep from rusting. Also consider HOW your chassis is going to be assembled, nuts,bolts,rivets,welded,screws - this might influence the material you use - and the gauge. You may want to discuss these points (and cost) with whomever you hire to build the chassis...
Disabled Account
Joined 2006
The notion of circulating currents in a steel plate is valid. I am not sure about how strong a field would be required to induce such a field, or how easy it would be for that field to couple on to other components.

Steel would provide superior shielding, whereas aluminium would provide no opportunity for inductively derived circulating currents, and be physically easier to work.

Humm, an interesting choice...
Joined 2004
Paid Member
I have wrecked more than a couple of punches on steel chassis obviating any savings in cost between the two.

Aluminum is a much better thermal conductor that steel, and this helps when using the chassis as a heatsink for regulators and power resistors.

Steel is a better magnetic shield, but is no more effective against electrostatic fields.

Steel is stiffer and stronger when heavy weights are an issue.

Steel rusts, aluminum doesn't.

Steel is a little easier to paint, that said I have aluminum chassis painted a decade ago with no issues.

Hammond sells aluminum chassis that are pre-primed and easy to paint.

Some people allege that a given circuit sounds better in a non magnetic chassis as opposed to steel - perhaps this due to magnetic fields in conductors interacting with the chassis. (aka increased parasitic inductance.)

HH Scott used AL chassis for both thermal and sonic reasons based on the comments made by former employees. (And some of their literature as well.)

With careful design either material ought to be fine, AL is generally easier for the typical diyer to handle with simple hand tools.

I like copper even better, but it's too expensive, really hard to work because of it's softness, (Clogs drill bits, end mills, punches, etc), greater thickness is required for a given load on the top plate, needs to be well protected from oxidization, and is prone to bending and scratching. However nothing looks better than clear coated copper IMHO.. :D
I have always been parshall to silver plated copper then clear coated It looks good. But stainless would do a good job as long as you dont bend it or work it to much as 300 seires becomes magnetic from cold working. It could feasably polished to a mirror finish for a top plate for a amp.

I send my punched steel plate in to a local shop for nickel plating. Mirror finish, easy to clean, and good resistance to rust.

Expensive at $125 a plate. I have considered buying an electrolytic plating kit for a few hundred, but that would be for some larger project, like monoblocks with separate power supplies.

I have easy (and free) access to as much copper as I want, busbar, foil, etc. I agree with Kevin, it's just too darn difficult to work with: galling, softness, clogging tools. Also quite heavy for a given strength in comparision to Al or steel. Looks beautiful, tho. I love Gary Dahl's Aurora- I think that's copper.
Last edited by a moderator:
Why would steel be a problem due to magnetism?
Magnetism cause currents, but a good builder would endure one (1) grounding point anyway. This leaves the currents with little effect, I would think.

Personally, I use both iron (soft metal, not steel), and Aluminum.
AL for brackets and items with much machining, iron for sheets and items that need a higher strength/thickness ratio.

Yes, theoretically, this mix causes corrosion. In my indoor climate, this hasn't shown to be an issue yet with my 9 year old design.

Just to let you know dissimilar metals causes galvanic corrosion it doesn't matter if it's inside or not. But just for clarification aluminium is just slightly more active then mild steel so galvanic corrosion realy wouldn't be a problem.

For it to be a problem you would have to put a highly active metal lets say iron in contect with a very noble metal say silver and you would see a horrific lose of material in a matter of just a few days.

The only thing is aluminium in open air will actually corrode quite quickly but you really dont see it all you see is this white powder that appears there and you dontt know where it came from. This white powder is aluminium oxide.

The reason I say magnetized steel is bad for one reason when you are machining it it's really hard to get the filings off of it after your done" you can just bang it on something" and the magnetic feild will effect chokes if the feilds are parallel.

Flux leak

Yes , MJ indicates that flux leak under the transformers is the problem. He goes on to state that this can be largely dealt with by placing washers (or similar) between the transformer and the chassis but I presume that there has to be at least on point of electrical contact between the transformer chassis and the amp chassis in order to earth the transformer chassis?
I appreciate the response so far - It seems to me so far are that the advantages of steel are strength and signal isolation (between transformers and inside) but the disadvantages are induced currents, possible magnetism, and it is difficult to work with compared with aluminium.
Overall my problems with construction are minimal as I am geting a workshop to do it. Also I am looking at nickel plating so I am leaning towards steel. It is reassuring to hear that both materials have been used here with success.
Thanks for the response.
Depending on what type of titanium it is you could have a heck of a time machining it. How thick is it most people dont realize titanium is flimsy so if it's to thin is will sag under weight of you transformers. You should invest in some good titanium boronitride coated drill bots if you wante to put wholes in it.

Good luck

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.