"Metal Film" capacitor - is there an alternative name?

[Frank Jones]

Hi,

I'm trying to follow instructions on shielding an electric guitar which
calls for me to place a "0.33uf, 400v metal film capacitor" between the
signal ground and chassis ground to provide a measure of protection against
dc shocks. Anyway, I thought it would be straightforward to source a
capacitor of this spec here in the UK but I'm having no luck finding one.
I've tried all the obvious online places - Maplins, Farnell, RS - and many
non-obvious ones too and they don't have any caps that match same literal
description I'm looking for although there are plenty of "metallized film"
caps available. I'm wondering if I'm just searching for the wrong name,
e.g. is "metallized film" a synonym for "metal film", or maybe "metal film"
is some posh Sunday name and I need to be searching for some other term.
I'd really appreciate any help you can give me on this, is there a more
common term for "metal film" caps or are they genuinely hard to find at the
values I'm looking for?

Thanks in anticipation.

Regards, Frank

 

[Jim Backus]

On Fri, 5 Sep 2003 18:33:33, "Frank Jones" <frank.jones@lineone.net>
rolled up his sleeves and typed:

Hi,

I'm trying to follow instructions on shielding an electric guitar which
calls for me to place a "0.33uf, 400v metal film capacitor" between the
signal ground and chassis ground to provide a measure of protection against
dc shocks. Anyway, I thought it would be straightforward to source a
capacitor of this spec here in the UK but I'm having no luck finding one.
I've tried all the obvious online places - Maplins, Farnell, RS - and many
non-obvious ones too and they don't have any caps that match same literal
description I'm looking for although there are plenty of "metallized film"
caps available. I'm wondering if I'm just searching for the wrong name,
e.g. is "metallized film" a synonym for "metal film", or maybe "metal film"
is some posh Sunday name and I need to be searching for some other term.
I'd really appreciate any help you can give me on this, is there a more
common term for "metal film" caps or are they genuinely hard to find at the
values I'm looking for?

A capacitor won't help with DC shocks. It sounds as though the
original author was unclear about what they were doing. A capacitor
from a signal ground to a safety ground would halp to prevent ac
shocks by providing a lowish impedance between the two gounds.

If there is any likelihood that this capacitor my have 240 volts mains
across it it is important that it can handle the current safely. I
think metal film probably means the same as metalised film. I would
suggest a polypropylene capacitor as they are fairly robust.

However if you're not absolutely sure what you are doing, I strongly
recommend getting professional advice. The last thing you want is to
have something that should be earthed at mains voltage.

--
Jim Backus OS/2 user
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