[sdiy] shielding question

[Harry Bissell]

I'd say that a bent piece of Mumetal is still better than a sheet
of steel, even a really thick sheet of steel. I still try and get a complete
wrap to create a flux path.

The Matrix 1000 is awful. Most small transformers run at high flux to start with,
even worse if its overloaded.  A saturated core does not contain ~any~ flux... 

H^) harry



----- Original Message -----
From: Andre Majorel <aym-htnys at teaser.fr>
To: synth-diy at dropmix.xs4all.nl
Sent: Tue, 29 Jun 2010 04:21:13 -0400 (EDT)
Subject: Re: [sdiy] shielding question

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/
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-- 
Harry Bissell & Nora Abdullah 4eva