Aluminum or Steel Chassis?

[tubeswell]

'Old post but
What he means is that using a chassis to connect grounds is not good practice. Grounds carry audio and there is no way to predict the interaction between them when using a chassis to connect grounds, there is no way to steer the ground. I agree that Audio ground should go to one place at the chassis and chassis ground to the wall should be at another preferable at least a few inches away or much more. The chassis should not be used to connect any other grounds in the audio path.

Depends on whether you do a split-ground or not. I have done several split-grounds on my amps and they have been dead quiet. This might not work for all amps and steel is probably noisier than Aluminium.

[lowell]

I use ~16 Gauge (1.2mm) Aluminium sheetmetal that I buy from the factory in town - it comes with a white durable peel-off plastic lamination on one side, so you can bend it, tap it, punch it, drill it, engrave etc without leaving scratch or dent marks, then when you peel off the film, its shiny and unblemished. It is about the maximum thickness I can bend by hand. I bend everything up on my benchtop with very primitive tools and pop-rivet end caps on. If you bend so that you only have to hammer the back side, you get quite a tidy job (where it will be exposed to the light of day). It makes for a very rigid and strong chassis that takes really heavy trannies no problem. I use 4 mounting bolts in the top to secure it - doesn't need any other mounting bolts.

Nice work! May you suggest what riveting tools you use as well as how you engraved the text on the front panel? I really like this, great job.

[tubeswell]

Nice work! May you suggest what riveting tools you use as well as how you engraved the text on the front panel? I really like this, great job.

Thanks lowell

Mr Minit down at the local Mall does the engraving for me with his little hand engraver. He does the top and bottom all up for about $30. If I had a hand engraver I'd probably have a go myself. He is cagey about being watched at his craft.

For riveting I use 1/8" aluminium pop rivets and a pop rivet gun

[lowell]

cool thanks!

[husky]

Depends on whether you do a split-ground or not. I have done several split-grounds on my amps and they have been dead quiet. This might not work for all amps and steel is probably noisier than Aluminium.

I have done split grounds as well, also used the chassis as a ground. Of course you can make anything work but I am used to doing very high gain work that shows off any issue. I like a ground buss and individual star ground going to the buss. It just eliminates any voodoo coming from the chassis and also gives you the option of doing a lift if there is a ground issue.

[mooreamps]

I'm not sure it makes any difference "tonally" between al or steel. I did choose a steel chassis for my bass amp to support the weight of the components ; and yes it is a little tougher to punch holes in steel. But I also think for any lightweight project, like a combo amp, al would be perfectly fine. However , for any build or project, one should always use the star grounding method.



-g

[Chuck H]

Star ground...Yes.

I actually use three star ground points on the chassis for most of my AB1 builds. One near the input for the preamp. One at center chassis for the preamp filters, the PI, any presence type controls, preamp master volume controls and power tube grid grounds. And one very close to chassis ground for PT CTR, main filter, OT, 6.3V wind, speaker jacks and power tube cathodes. Every grounded circuit has it's own lead (no daisy chains) and I NEVER ground pot cases. This actually makes the earlier posted unpredictability of chassis grounds very predictable as long as your layout is following the signal foreward and the PSU backward as it should. Distance equals resistance so as long as your layout doesn't double back on itself, resistance is resistance. My amps are very quiet. So quiet it's unnerving when I fire up a new build and I don't hear anything. Even with the high gainers I have to turn them up loud to get a little hiss so I know they're working before I plug in. In almost twenty years I have never had to hunt down a ground scheme related problem.

I like aluminum because it conducts so fast and well. It cut's easier for my DIY skills and tools. And it won't conduct any electromagnetism from my transformers into my signal chain.

Steel is heavy, slow and harder to cut. The extra cost of aluminum is pedantic weighed against the advantages.

Chuck

[Chuck H]

As a funny aside, my fondness for aluminum just bit me in the a$$. I'm working on an attenuator that I want to place inside the head cabinet with the amp chassis. But the aluminum chassis can't block the EMF of the inductors in the attenuator, which is of course in an lauminum chassis to act as it's own heatsink, and I'm getting some resonant noises...Ahhh.

So there's one strike against aluminum.

Chuck

[black_labb]

i like aluminium as you can buy aluminium extrusions whoch work great for chassis's. you can get up to 200mmx50mm up to 6.5M long. its more economical than chassis bought, and less work than making your own. they are 3mm thick so they are plenty strong. you just have to cut the bottom out (and do the holes for the components obviously). means you have plenty of size and strength for big amps with big trannies.

[Chuck H]

Where do you get aluminum extrusions? I'm interested in trying that. Does your source do custom shapes?

Chuck

[black_labb]

i just get the rectangular extrusions, which are mass produced in huge quantities. i've seen a tiny combo with a speaker and the circuitry fitting around the speaker by cutting the extrusion where the speaker got in the way. made for a very small combo (about the size needed for the speaker itself).

heres one source. i've seen others with 200mm wide extrusions. i got mine from an aluminium manufacturing business that sells aluminium as well. i'd go out on a limb and say that it would be easier to source in america as things can be hard to find things used in manufacturing in australia.

[Steve Conner]

You could try Metal Supermarkets. Last time I was in there, they had lots of aluminium extrusions. I mostly use the L shaped stuff, but they seemed to have I-beam, channel and box section as well. Channel is like a box with one side missing, so you don't have to cut the bottom out.

I also prefer to use an aluminium chassis, with a separate ground bus for the audio circuitry that only connects to the chassis at one point (ideally the input jack)

[tubeswell]

Yep I get mine from an Aluminium supply and manufacturing place.

Aluminium Extrusions and Rollformed Aluminium from Ullrich Aluminium

There's got to be gazillions of them in the US

[black_labb]

You could try Metal Supermarkets. Last time I was in there, they had lots of aluminium extrusions. I mostly use the L shaped stuff, but they seemed to have I-beam, channel and box section as well. Channel is like a box with one side missing, so you don't have to cut the bottom out.

I also prefer to use an aluminium chassis, with a separate ground bus for the audio circuitry that only connects to the chassis at one point (ideally the input jack)

the channel is a good idea, but you would have to ensure that you have a suitable connection to the cabinet/head case. not hard, just not as easy as the other systems.

[tedmich]

Morgan Jones builds neat enclosures with Al angles, like this from here:
IndustrialAmp


Morgans are fancier including "trapeze" preamp tube suspension platforms, check out his books!