[sdiy] Toggle switch for mic

[ColinMuirDorward]

Thanks, Steve, that's good info.

I ended up asking Dave, at Advanced Audio, since it's his capsule I'm
putting in the 990. What he does is use a horizontal PCBmount switch on a
PCB that is cut to follow the profile of the mic interior. Then I think
there are some small angle brackets to mount the PCB to the mic body.

Colin


On Tue, Sep 22, 2020 at 12:28 PM Steve Lenham <steve at bendentech.co.uk>
wrote:

> On 22/09/2020 17:57, ColinMuirDorward wrote:
> > Thanks for this tip.
> >
> >     except it really really needs to have gold-plated contacts if you
> want
> >     it to be reliable in this sort of application.
> >
> >     Using the same general-purpose silver-contact toggle that you'd
> choose
> >     to switch 12V for a motor is something you would almost certainly
> >     regret!
> >
> > Is this because the current is very low in this application? Curious
> > about why.
>
> Yes, basically. Silver is a great conductor when it is clean, but tends
> to build up an insulating tarnish as time goes by, especially if the
> atmosphere isn't perfect. This doesn't matter if you are switching a bit
> of power, because the slight arcing as the switch makes and breaks burns
> through the tarnish and the process has to start again from scratch. But
> with small signals, there are not enough amps/volts for this to happen,
> so the contact resistance builds and builds until the switch no longer
> makes properly.
>
> Gold doesn't tarnish in this way, so is great for small signals. BUT -
> it's no good for switching power as the same process that burns off the
> tarnish from the silver will also burn off the gold! It's horses for
> courses. Gold-contact toggle switches usually have low ratings like "30V
> 0.4VA maximum", while silver-contact ones will be rated at 125/250V and
> 1A or more.
>
> Just for the sake of completeness, I learnt recently that there is a
> halfway house in the form of switches with gold-over-silver contacts.
> These can be used for small signals or power, but if you use them for
> power then the thin gold layer burns off and leaves you with just the
> silver. You then can't go back and use the same switch for small
> signals. This might sound daft but it lets you stock just a single
> switch for both purposes and also to use a double-pole switch to
> reliably switch one power signal and one low-level one. I specced this
> type of switch for a mic preamp I recently designed, so that a single
> part could switch both low-level audio and 48V phantom power.
>
> Cheers,
>
> Steve L.
> Benden Sound Technology
>
>

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