[LAU] 3.5mm microphone into audio interface?

David Kastrup dak at gnu.org
Sun Apr 11 16:47:36 CEST 2021

Edgar Aichinger <edogawa at aon.at> writes:

> Am Sonntag, 11. April 2021, 15:00:49 CEST schrieb David Kastrup:
>> Alf Haakon Pietruszka Lund <alf at mellomrommet.no> writes:
>> > I see I missed a small but important point; these are condensator
>> > mikes. Yikes...
>> Yes and no: electret condenser.  They don't need phantom power for
>> polarising the capacitor capsule as it comes prepolarised.  But they do
>> need some power (typically 3V–6V) as plugin-power to power the built-in
>> FET preamplifier without which the weak capsule signal would not make it
>> through the microphone cable.
>> The infamous Neewer BM800 can convert phantom power to plugin power and
>> thus can be run on either depending on the cable type (while providing
>> S/N ratios that are not impressive for either application).
>> But a lot more typically, devices only work with one kind of power.  The
>> kind of soundcard/computer providing 3.5mm TRS (or TS) microphone inputs
>> tend to carry plugin power (sometimes switchable by software), XLR
>> inputs tend to have an option for phantom power (almost always +48V
>> these days), sometimes switchable in groups.
> While I'm all for using better equipment, I wonder if this mic really
> needs phantom or plugin power (I don't even know that term)

Cheap compact microphones invariably are electret condenser and
invariably need a power source: plugin power, 1.5V battery or something

> If it's designed for a laptop headset jack, that wouldn't supply that
> either?

Laptop headset jacks invariably provide plugin power.

> It can probably get that power from USB.

USB soundcards can also power actual phantom power since the actual
current requirements are low, so a stepup converter will make for +48V
if you manage to design it in a manner not contributing converter whine
into the sound experience.

> Anyway, the Amazon product page talks about batteries, and I know that
> cheap and not so cheap (I had one by Sony) electret external stereo
> mics with mini-jack plug for home video cameras etc. existed long ago
> already.

Invariably using plugin power unless they require their own batteries.

David Kastrup

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