[sdiy] shielding question

[Andre Majorel]

On 2010-06-28 13:30 -0400, Harry Bissell wrote:

> Try Mumetal shielding. Best is to make a complete turn around
> the power transformer, if possible. DON'T get it too close or it
> will get VERY hot (if there is a lot of flux leakage)
> 
> Its possible that a flat sheet on top of the offensive unit
> might be effective, but you really want a complete path for the
> flux to run around in.
> 
> you might try to shield the receiving coils (inside the reverb)
> as well.
> 
> DON'T get too close to any magnetic pickup.

The Matrix-1000 has been out of the rack recently. I've discovered
how much 50 Hz hum it can induce into a jazz bass pick-up. At 15 cm,
it's about as loud as your playing. You need to move back about 1 m
before it fades into the background. And this is with the lid on !
(1 mm steel.)

It's an unusual design, a laminated core shaped like a rectangular
doughnut with one winding on each long side. Perhaps those leak
more.

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> Ask me about the time I made a mu-metal shield for an ARP Avitar
> hex pickup (to stop the 60Hz um). Describing WHY that was a
> really really BAD idea is left to the reader...   :^)

It got hot and burned your fingers ? ;-)

> http://www.goldmine-elec-products.com/prodinfo.asp?number=G16600A

Is ultraperm like mu-metal, in that it must not be bent ?

-- 
André Majorel http://www.teaser.fr/~amajorel/