[ltp] Thinkpad R40 mic input and phantom power

[Ben Pearre]

Thanks!  In case anyone else is interested: it turns out that there's
4.77 volts across the pins (at least, on my R40; YMMV etc).  That
counts as a "bias voltage", not as "phantom power" which is usually
somewhere in the 9V--56V range.

The mic in question (Audio Technica AT822) is a condenser, but is
self-powered with an AA battery and doesn't want phantom power.

On 2005-12-20  4:42, Richard Neill wrote:
> 
> 
> Christopher Sawtell wrote:
> > On Tue, 20 Dec 2005 15:44, Ben Pearre wrote:
> > 
> >>I know, I should call IBM or Intel, but I like you guys better :)
> >>
> >>Any idea whether the R40's soundcard supplies "phantom power" to the
> >>microphone jack?
> > 
> 
> It's certainly true for the A22p, since I use an electret microphone
> with it. But if you are worried, put a capacitor of perhaps 0.1uf in
> series with your Mic: this will block the phantom power. That said,
> iirc, the only mics that don't use phantom power are
> 
> i)crystal piezo mics (very cheap/indestructable)
> 
> ii)moving coil mics - which shouldn't care if you pass a small current
> through them.
> 
> 
> Richard
> -- 
> The linux-thinkpad mailing list home page is at:
> http://mailman.linux-thinkpad.org/mailman/listinfo/linux-thinkpad


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