WHY ALUMINIUM CHASSIS?

[cornel moldovan]

HI , EVERYONE.. I WONDER IF MR. ALEX HOWARD DUMBLE CAN TELL US , WHY HE CHOOSED TO BUILD HIS AMPS ON ALUMINIUM CHASSIS AND NOT ON USUAL IRON CHASSIS AS FENDERS AND MARSHALLS DID.. HOW MUCH CAN AFFECT THE MAGNETIC FIELD THE SIGNAL PATH, IF WE DO NOT CREATE SHIELDING LOOPS , THE TRANSFORMERS ARE MAGNETIC INSULATED, AND CORRECT PLACED ON DIFFERENT AXES.

[M Fowler]

But as discussed recently HAD did not place his transformers properly as most do. He put them side by side very close and not oriented opposed.

Aluminum is easier to work with and some say better for circuit stability? I have no clue, myself.

Mark

[Structo]

BECAUSE IT IS LIGHTER!

[M Fowler]

Nice one Structo

I like them because its easier to drill and file on. I don't like the painted chassis because sanding ground points is hard even with my dremel. Otherwise they would be good. Turretboards.com make sure their ground points are bare on all their painted chassis nice touch. Also, they use studs for ground points which I really liked as well.

Mark

[glasman]

Outside of the better (as in none) magnetic properties of aluminum and being easier to machine, it is also a better conductor of electricity, only surpassed by Silver, Copper and Gold.

[Structo]

Oh yeah, grinding powder coat off of a chassis is a real buzz kill.

The smart guys put stickers over the holes that will be used for ground points.
After powder coating you peel the sticker off, nice bare metal.

[Max]

But as discussed recently HAD did not place his transformers properly as most do.

Yes, Mr. Dumble obviously had no idea at all how to build a 'boutique amp':

Wrong transformer placement, off the shelf replacement transformers, high capacitance (up to 80pF/feet) shielded cables, PVC wire, transistors in the signal path (FET), plastic tube sockets, Shack-parts everywhere, no gold contacts, mini-switches without gold contacts, carbon comp resistors (70ies amps), No birch-plywood cabinets, 6550A tubes (harsh and and of no use in a guitar amp!!!), AC on the heaters, Class A/B power amps, non parallel effects-loop, and so on and on....

Cheers

Max

[M Fowler]

Max,

Exactly what was HAD thinking about!

Mark

[cornel moldovan]

Clever discussion boys..i just finished my second built on a diminished iron chassis..DOESNT LOOK SO GOOD BUT THE SOUND IS TOTALLY OUTSTANDING... COMPLETELY SILENT.. WHEN I FIRED IT , AT FIRST I THAUGHT IT DOESN-T WORK AT ALL. NO HUM NOISE, ONLY WHEN I INTERFERE WITH THE STRAT PICKUPS NEAR THE PT.I WORKED A LOT , I MEAN MECHANICAL WORK ON THE IRON CHASSIS .. I HAD TO DRILL AT EVERY HALF INCH TO BEND IT.I BUILT IT FOR ONE OF MY GOOD FRIENDS FOR THE ACOUSTIC GUITAR. I-LL PUT SOME MP3 DEMOS SOON JUST ONE PROBLEM .. THE MIDDLE AND THE PRESENCE KNOB, ARE SLIGHT EFFECTIVE..I'LL TRY TOMMOROW WITH MY 2X EVM 12 L to hear the middle response...IF YOU TRY TO REDUCE AT MAXIMUM THE CHASSIS FOR 2X 6L6 HERE ARE THE OVERALL DIMENSIONS :17 1/4X 7 3/8X 2 1/2 .NO HUM NOISE.no risk of magnetic problems. Little Dumble is born.NOT TOO HEAVY, NOT TOO BIG. I ONLY MADE SOME ECONOMY OF SPACE IN THIS TIMES OF CRISIS.

[heisthl]

IF YOU TRY TO REDUCE AT MAXIMUM THE CHASSIS FOR 2X 6L6 HERE ARE THE OVERALL DIMENSIONS :17 1/4X 7 3/8X 2 1/2 .NO HUM NOISE.no risk of magnetic problems. Little Dumble is born.NOT TOO HEAVY, NOT TOO BIG. I ONLY MADE SOME ECONOMY OF SPACE IN THIS TIMES OF CRISIS.

Nice project, I like using steel chassis (is that the same as diminished iron?).
Not true on minimum size though - I do a 50 watt amp with 2 more preamp tubes(7 tubes total) in a 15.25" x 7" x 1.5" chassis.

[Structo]

By the way, using all caps is considered yelling in web speak.

['67_Plexi]

I always use steel.

If anyone can give me a reasonable argument as to why aluminium is that much better that it makes an audible difference in tone and noise floor, I'd love to hear it.

However, I'm likely to come back and say that 3mm of lead dress on one wire or one preamp tube could negate any benefits 10x over.

Steel has one great benefit that overshadows any perceived tonal benefits of Alu, that is it's so much stronger, which in a 100W that gets thrown around a lot moving from city to city every day might be a plus factor. How many early JTM100s still have a straight chassis ?

The honest truth why a lot of builders chose Alu is simply that it's way easier to work with, drill and machine. Steel needs to be protected with paint to stop it rusting.

[talbany]

If anyone can give me a reasonable argument as to why aluminium is that much better that it makes an audible difference in tone and noise floor, I'd love to hear it.

I agree..I don't see the Aluminum being any quieter either...I use the steel for the strength...If you use powder coating silk screen the Aluminum looks nicer to me..


Tony VVT

[Max]

I always use steel.

If anyone can give me a reasonable argument as to why aluminium is that much better that it makes an audible difference in tone and noise floor, I'd love to hear it.

Steel has one great benefit that overshadows any perceived tonal benefits of Alu, that is it's so much stronger, which in a 100W that gets thrown around a lot moving from city to city every day might be a plus factor. How many early JTM100s still have a straight chassis ?

Hi 67 Plexi,

as far as I know this is the reason Alexander used aluminium:

As you all know, he was eager to deliver stuff, that would not break down in any unhappy accident.

That's why he did a lot of testing in regard of a sturdy construction by throwing his amps from stages, from cars (pick ups his favorites!), from buildings (one of the reasons he went from Santa Cruz to LA: higher buildings!) and so on.

He documented all those test and calculated the flight curves he had observed. What he found is, that by some unknown (to me) reasons the flight curves of alu amps led to a certain result: when they hit the ground, they did so in a specific angle with the outcome that they did never break or warp.

After those first promising results of his throwing tests he decided to use alu and still does.

Those throwing tests Alexander repeated many times (reportedly sometimes with the assistance of Cris Cross) and they continued at least till '85:

In the Guitar Player interview David Lindley reports one of those test, when an ODS was thrown out of the fifth floor of a building and after changing tubes was still working fine.

So you see: If you're a Dumble owner and your drummer or bass player is too hefty for the thousandth time, you have at hand something to throw at him. But beware: If your bass player uses a Dumbleland and can carry it by himself he could perhaps think of throwing something back. So if he turns in the direction of the Dumbleland: better run!

Cheers

Max

[tubeswell]

Steel is a good shielding material, and is stronger, but heavier and harder to bend. Mr Dumble probably found Aluminum easier to fabricate in his garage.

One of the earlier posters mentioned the Aluminium has a higher conductivity. This is concurrent with lower resistivity. Therefore Aluminium makes a really good grounding conductor, reducing the likelihood of localised micro rises in ground potential, therefore reducing the likelihood of unwanted AC getting into the signal path through the chassis/ground-return connection points (where there are multiple grounding points).

Also Aluminium is non-magnetic, which makes it easier to use your magnetised screwdriver to pick up nuts and washers etc when they fall into the chassis (:-)