[AudioI] Input Impedance and coupling of Zero board line inputs?

[Tom Garwin]

Thanks, very helpful.

AC coupling helps me and all I really cared about was that the impedance
was greater than 2500 ohms (which is typically where opamp manufacturers
quote the max output compared to the rails)

All I am doing is to having an inexpensive stereo mic (designed for camera
mounting ) -- the  MOVO VXR280 --  feed the Zero soundcard and then have a
raspberry PI send the bitstream to another Pi Zero over IP -- this second
PI will decode the bits back to audio and feed a Sonos Connect box.   The
idea is to be able to listen to nature sounds from our river shed (which
has wifi) inside the house in Winter when the house is closed up.

I was assuming I will need to use an opamp to bring the microphone output
(even though it is labled line I don' t think it actually is) up to the
level needed for the sound card.

I have a limited amount of DC at the shed (12 v nominal for a camera) so I
was planning on using that with a buck to 5 volt to power the pi and was
looking for a rail to rail opamp with virtual ground for the amplifier -- I
was assuming I would drive the camera from the raspberry pi zero  3.3v
supply and the opamp from either the 5v buck or from a TLE2426 from the 12
volts if I can sort out all the grounds.

On Thu, Jan 21, 2021 at 2:07 PM Matt <matt at audioinjector.net> wrote:

> Hi Tom,
>
> The input line impedance varies with input gain. At 0 dB gain, the input
> impedance is listed as 30 kOhm. At 12 dB gain, the input impedance is
> listed as 15 kOhm.
>
> The line inputs are AC coupled. If you want to make them DC coupled, then
> you can short out the two 10 uF capacitors C11 and C12.
>
> What project are you planning on doing ?
>
> Matt
>
>
> On 22/1/21 3:53 am, Tom Garwin via People wrote:
>
> Sorry if this information is listed somewhere but I have two questions
> about the stereo line inputs to the Zero board:
>
> 1) What is the input impedance?
> 2) are the inputs AC or DC coupled?  In other words is there a
> blocking/coupling capacitor preventing DC to reaching any on-board
> amplifier or the A to D chip itself?
>
> Thanks
>
> --
> Tom Garwin
>
> --
> Checkout the community email list :https://lists.audioinjector.net/mailman/listinfo/people
>
>

-- 
Tom Garwin

(202) 669-4228 (cell)

PO Box 5359
Whitefish, MT 59937

tom.garwin at gmail.com
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