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Old 20th June 2007, 02:43 PM   #21
nhuwar is offline nhuwar  United States
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Silicon rubber works great for isoloating them.

Nick
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Old 20th June 2007, 11:25 PM   #22
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Rob11966,

In several decades of building both transistor and tube amps, I always had trouble with some hum with the about 5 x steel chasses I tried - had to scrap some. I am at present trying to help someone with a EL84 15W amplifier with all Partridge transformers on a steel chassis, and minimal hum could only be obtained with the power transformer held at a crazy angle in space. I have also tried with several other transformers, all to no avail - that my experience.

In contrast I never had real trouble on an alu chassis (dozens of projects, some 100 watters). I am a little reckless in earthing anywhere on the chassis (close to whatever component, except for inputs), still OK. I avoid using drop-through power transformers. I cannot say that I ever particularly tried to do electrical insulation, but it is practical if some members had bad experience by not doing it.

As far as aesthetics go I use powder coating, screening earth points with stickers. Anodization could look more classy, but is quite expensive (over here, at least).

YET! Many commercial amplifiers are built quite successfully on steel chasses! But for my preference .......

Regards.
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Old 21st June 2007, 05:18 AM   #23
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Default Aluminium it is!

Hi Johan,
Your personal experiences with this have been very instructive. I really need to make this as fool proof as possible and the potential 'hum' with the steel does concern me. My main reason for choosing steel was the ability to gety a nice electroplated finish but after speaking with the electroplaters today they tell me that aluminium is easier for them anyway. So aluminium it is!
Cheers,
Rob
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Old 21st June 2007, 05:47 AM   #24
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Default Alu

Hi, I agree with Johan. Less hum with alu I found in the few I've built. Star grounding helps with ground loops but is messy wiring wise. As far as magnetically induced noise goes, toroidial transformers are better at keeping their fields to themselves. (Hope thats helpful)
Cheers,
CB
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Old 21st June 2007, 05:55 AM   #25
jnb is offline jnb  Australia
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Quote:
Originally posted by Dynsdale
toroidial transformers are better at keeping their fields to themselves.
Yes, when used wisely.
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Old 21st June 2007, 05:56 AM   #26
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Default Steel not a steal

Some high-end manufactures of audio gear will not use aluminium. They claim they do not like the sound of aluminium. I go for thick die-cast aluminium. It's heavy (2mm thick) and moderately dead.

Thin aluminium on cases should be avoided due to resonance problems.
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Old 21st June 2007, 06:47 AM   #27
jnb is offline jnb  Australia
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Default Re: Steel not a steal

Quote:
Originally posted by mhouston
Thin aluminium on cases should be avoided due to resonance problems.
What, in your opinion, is a good thickness to use?
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Old 21st June 2007, 11:09 AM   #28
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Default How thick

After saying avoid alu I should clarify to say avoid flimsy cases. If you were making your amps in 2mm thick pure alu I would say that’s alright. Still some high-end audio gear manufacturers will not use alu. If you build a steel case even a thin one it is going to be stronger than an alu one. What I try and do is use 2mm die-case cases. Because I use a lot of off the shelf Jaycar stuff this often means remote supply for amps. So one case for the amp and one for the PS. They have done me a favour.

Yes they are alu but they are solid as!. Also the cases I use are cheap. This actually works to my advantage because there is all sorts of other metals in there making a heavy dense 2mm thick material. Dampen your case too. I caused a riot on another thread talking about resonance so unless you really want to know I will say no more about it here. I said resonance NOT vibration – so many try to say they are the same.
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Old 21st June 2007, 11:28 AM   #29
jnb is offline jnb  Australia
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Great. I am currently getting a chassis made up of 2.0mm Al. I am having it laser cut from a CAD drawing and paying well for it so I'm glad to get your feedback.

Quote:
Originally posted by mhouston
I caused a riot on another thread talking about resonance so unless you really want to know I will say no more about it here.
Fair enough.
Quote:
I said resonance NOT vibration – so many try to say they are the same.
OK. I am planning to instal a bulkhead for strength and for electrostatic shielding between the noisy half and the clean half of the underside of the chassis. In response to your comments on resonance I am thinking of also tacking some bitumen roofing strips beneath the chassis in the free areas, as this seems the logical thing to do. Come to think of it I may have seen this done before in commercial designs.
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Old 21st June 2007, 11:55 AM   #30
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Default you got it

You are very much on the right track – in fact we think a like when it comes to that dirty word “resonance”. Jaycar (I see you’re from Australia) sell a plastic/rubber mate which is used to line speakers. It has barium in it which make sit heavy. Glue it every where in the case which does not get hot. Glue it under the case. There is no need to disfigure you case to do this. The amp should not only sound beautiful but look beautiful too. If you are married you will know about WAF.

If trannies don’t get hot grommet mount them. I grommet mount my cct. brds in my valve preamps and then use self adhesive computer mounting feet. Jaycar sell heavy brass isolation feet ($30). I don’t use the double sided sticky rubber pads they provide bolt them direct into the case. Use isolation plates under your amp. I have too favourites. ˝” glass plate on thick silicon feet and the other ˝” Italian marble on silicon feet. Both 300 X 400mm. I also use silver wire in the audio path. This is pure silver .7mmm thick and I cover it with spaghetti or cotton insulation. It is cheap and generally you don’t use much.

I could go on for hours but I will bore you. Let me know if I can make some more suggestions or just disagree with me as so many other have done.
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