| falcott |
Once more into the breech --
It's been a while since I was here. After spending a couple of years on house renovation, I'm turning my attention once again to my partly built VBIGC.
I previously gave a lot of thought to building monoblocks, but with only a few simple hand tools I decided that making the cases was too daunting. Therefore I celebrated when I found an old 1960s or 70s hi fi tuner on the roadside. Now gutted (it was AM only - not much point in restoring it), with a change of faceplate and a solid 12mm aluminium plate for the backplate/heatsink, it is going to look nicely retro -- aluminium, wood and vinyl (yes vinyl, really!)
Ok, so to fit into this case I've got 2 amp boards and 3 torroidal transformers (amongst all the other bits) -- 2 of the transformers are for the valve/tube buffer and they're not very large.
Within the limitations of the case dimensions, I have to make a choice for layout:
a) the 2 amp boards at each end of the case with the 3 transformers sitting between them, or
b) the 2 amp boards close together in the centre of the case between the transformers (2 at one end, 1 at the other).
Which option is better? Is it preferable to have the 2 amps close together? And with either option, should I shield the transformers in an aluminium box? |
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| AndrewT |
Hi,
shielding in aluminium will achieve very little.
A good electrostatic screen can be made from any conductive material but I believe copper is best.
Electromagnetic fields (from transformer) can only be shielded by magnetic materials. Some use Mu metal but it is very expensive and has handling issues. The cheap solution is iron or steel sheet. (I have seen a steel ring around a toroid in both a power amp and in a pre-amp, both Sugden). |
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| falcott |
Thanks for your response, Andrew.
One of the things that prompted me to ask the questions was that the grounding might be more efficient if the amp boards are mounted close together -- i.e. a short, thick wire linking the 2 boards and then a single connection from the centre of the link, via a resister/cap, to the chassis.
My shaky memory was stirred by your observation about steel shielding. I thought that I read somewhere that putting an amp inside a steel casing is Not A Good Thing. My new (old) casing has steel top and bottom...
Your thoughts? |
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| AndrewT |
Hi,
some say amps play better if there is NO IRON nearby.
This means either no metal or using aluminium but that then allows magnetism in. I have heard of copper foil shielding and some oriental manufacturers have used copper plating.
However, toroids are very good for low leakage and what little gets out can be attenuated by rotating the transformer around it's fixing bolt (if long flexible leads are used). |
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