Ok...gearing up for my next build. I'm going a step further in DIY by bending my own chassis and was wondering about materials to use? I have heard somewhere that aluminum was superior to steel because it's lack of magnetic properties. True or false? My four options metal wise are steel, stainless, aluminum, or copper. What, if any, effect does gauging have on chassis...aside from maybe workability ? Each build I do, I intend to go a step further...maybe someday I'll wind a tranny, who knows.
Thanks for all of your collective coddling. I have learned quite a bit in the short time I have been on this site.
Thanks for all of your collective coddling. I have learned quite a bit in the short time I have been on this site.
Aluminum is indeed nonmagnetic and a heck of a lot easier to machine than stainless steel (also nonmagnetic).
One neat trick is to use perf aluminum as a top plate- plenty of ventilation that way.
One other trick is to put the conventional chassis out of your mind, then wander around a kitchen/restaurant supply store for inspiration and materials.
One neat trick is to use perf aluminum as a top plate- plenty of ventilation that way.
One other trick is to put the conventional chassis out of your mind, then wander around a kitchen/restaurant supply store for inspiration and materials.
As a practical matter, I haven't seen any hard data showing the superiority of a good build on different material chasses (if there is such data, I'd love to see it)
A magnetic steel chassis will have theoretical challenges from the potential increase in inductance of nearby leads, inductive coupling of hum fields from transformers and high current feeds (especially AC heaters). These can be worked around in the mechanical design, but unquestionably, aluminum is more forgiving.
A magnetic steel chassis will have theoretical challenges from the potential increase in inductance of nearby leads, inductive coupling of hum fields from transformers and high current feeds (especially AC heaters). These can be worked around in the mechanical design, but unquestionably, aluminum is more forgiving.
There is a whole thread here on aluminium vs steel -
http://www.diyaudio.com/forums/showthread.php?s=&threadid=103815&highlight=
Rob
http://www.diyaudio.com/forums/showthread.php?s=&threadid=103815&highlight=
Rob
Steve Eddy said:
Yeah but, no but... (for fans of Vicky on Little Britain)
I don't know if it's the case now, but the folks who make mu-shield pleaded with folks to cut up an aluminum beverage can before using square feet of their stuff.
For my money, there is nothing which is superior to a piece of PCB material and mounting your components dead-bug style. It's probably superior to the FR4 PCB stuff we use as air is a superior dielectric. Ugly, but superior functionality.
Wavebourn said:
If the steel is used as the laminations for the transformer, then no. But then that's apples and oranges.
If the transformer is encased in the steel, then it will shield from external fields.
Why do you think CineMag, Jensen, Lundahl, Sowter et al. encase their transformers in MuMetal shields?
se
jackinnj said:
An aluminum beverage can would work ok for electrostatic shielding. However it wouldn't work too well for magnetic shielding given that the permeability of aluminum is nearly the same as air.
For electrostatic shielding, sure. Copper is very good at that. Steel isn't quite so good because of its lower conductivity. But steel is good for magnetic shielding, provided the fields aren't strong enough to saturate it.
se
Steve Eddy said:
2 wires going in parallel to each other have inductances. If we put a magnetic material near them their inductances will be higher, and they will be better coupled. It is exactly how the transformer works. (Wife: "my husband's profession is transformer. He gets paid $240, gives me $120, and hums on the rest")
Yes, if each turn is complete, i.e. magnet fields cancel each other.Steve Eddy said:
Similarly, if twisted balanced symmetrical pairs go near the steel chassis, their magnet field cancel each other. But how many balanced pairs do you have in your amp?
My Pyramid-V amp was designed with a steel chassis, but it did not hurt him: I knew properties of the material I used.
bereanbill said:
I dunnow. For my projects, I got 16 Ga sheet steel ("black iron", not galvanized). Punches make nice holes in it, unlike aluminum, it's not sticky and doesn't chew up Dremmel cutting wheels, it doesn't take the edge off drill bits like aluminum. Big power xfmrs and OPTs don't cause it to sag under the weight. It's a good deal easier to paint. For that, I give it a real good scrubbing with plenty of soap and hot water. Dry off, and wash down with acetone and let dry. After that, don't touch it. Then give it a couple of coats with Rustoleum primer, dry 24 hours, and paint. Looks quite good, and keeps looking good without the paint bubbling.
Aluminum is a real biotch to paint. Requires anodizing, and that requires some nasty chemicals you don't just pick up at the local hardware store. If you don't do that, it won't stay painted for long.
As for the actual wiring, I do this with copper clad circuit board, and modified "Dead Bug" style for each subsystem.
Once that's done, finish off by mounting on a wood cabinet.
Indeed, one can leverage the properties of steel by isolating the transformer from the chassis- a big air gap is a good idea. With transformers tightly bolted without a gap, the chassis can do a nice job of coupling the stray field. Remember, it's not a closed box surrounding the transformers, and all the wiring is on one side...
Some venerable designers will rather use nonmetallic enclosures, because of interaction between signal wires and a chassis.
http://www.dnm.co.uk/about.html
I can't offer anything quantitative to substantiate this, other than to invite anyone interested to play around with the internal wiring of a high-gain guitar amp. you can hear the hum increase as sensitive wires near the chassis, and heater wires couple to the metal. OK, some of these designers actually run power-stage currents THROUGH the chassis (Marshall), but I suspect there is something to watch out for.
My personal preference is for wood. Dry it out properly (and preferably seal it) and it presents a very reasonable dielectric.
I use pieces of copper-clad FR4 to build each individual stage, then wire them together on the wood platform. The whole lot stands above the power supply on a chunk of 2x4 (50x75mm roof timber).
You don't need to screen any stage (even MC cartridge inputs) if you keep all the wiring loops VERY small - and the wiring between stages twisted.
The picture shows my B.300B-SE.
you can see the power supply at the distant right, covered in copper foil to limit emissions from the 6CJ3/UF4007 hybrid rectifier.
The output transformer is remote from the amp, mounted on the loudspeaker support - even a 300B output valve picks up the emissions from these (unless you have a toroidal) - and better still, I don't need any speaker cables, or need to get into any endless argument about which kind work best!!
http://www.dnm.co.uk/about.html
I can't offer anything quantitative to substantiate this, other than to invite anyone interested to play around with the internal wiring of a high-gain guitar amp. you can hear the hum increase as sensitive wires near the chassis, and heater wires couple to the metal. OK, some of these designers actually run power-stage currents THROUGH the chassis (Marshall), but I suspect there is something to watch out for.
My personal preference is for wood. Dry it out properly (and preferably seal it) and it presents a very reasonable dielectric.
I use pieces of copper-clad FR4 to build each individual stage, then wire them together on the wood platform. The whole lot stands above the power supply on a chunk of 2x4 (50x75mm roof timber).
You don't need to screen any stage (even MC cartridge inputs) if you keep all the wiring loops VERY small - and the wiring between stages twisted.
The picture shows my B.300B-SE.
you can see the power supply at the distant right, covered in copper foil to limit emissions from the 6CJ3/UF4007 hybrid rectifier.
The output transformer is remote from the amp, mounted on the loudspeaker support - even a 300B output valve picks up the emissions from these (unless you have a toroidal) - and better still, I don't need any speaker cables, or need to get into any endless argument about which kind work best!!
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