Op-Amp amplified audio in?

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1

Beagleboad users!

I’ve had terrible static issues with an un-amplified microphone plugged into the audio in port on my BeagleBoard-xM. I’ve read that the BeagleBoard needs an amplified input audio signal.

Would it be possible to make an amplifier with an Op-Amp?

2

Quoting Garrett Weaver <wagarrettweaver@gmail.com>:

Beagleboad users!

I've had terrible static issues with an un-amplified microphone plugged
into the audio in port on my BeagleBoard-xM. I've read that the BeagleBoard
needs an amplified input audio signal.

Would it be possible to make an amplifier with an Op-Amp?

Yes. The gain you'd need would probably be in the region of 10 to 30.

Don't forget to provide bias at the input to work the electret microphone.

Dave

3

Thanks Dave, what should the voltage rails be?

4

Quoting Garrett Weaver <wagarrettweaver@gmail.com>:

> Quoting Garrett Weaver <wagarrettweaver@gmail.com>:
>
> > Beagleboad users!
> >
> > I've had terrible static issues with an un-amplified microphone plugged
> > into the audio in port on my BeagleBoard-xM. I've read that the
> BeagleBoard
> > needs an amplified input audio signal.
> >
> > Would it be possible to make an amplifier with an Op-Amp?
>
> Yes. The gain you'd need would probably be in the region of 10 to 30.
>
> Don't forget to provide bias at the input to work the electret microphone.

Thanks Dave, what should the voltage rails be?

Whatever you can get comfortably. You don't need much range at the
output of the op amp, so a single rail of 5V or even 3V3 would be
enough, assuming you use an op amp designed for such low supply
rails. A single supply rail means more work biassing the thing
midway; the alternative is to use dual rails (i.e. positive and
negative), but there isn't a negative rail associated with the BB,
so you'd have more work instead to create one. You choose your
preferred compromise :slight_smile:

As for the bias for the electret: I'm not familiar with typical
values, simply that it is necessary for most common microphones
to work at all.

Dave

5

search on google, there are many you can build, even single transistor ones or one like this using a 741.
http://www.rason.org/Projects/hbmic/hbmic.pdf
Regards
Sid.

6

I built the amplifier today from http://www.rason.org/Projects/hbmic/hbmic.pdf

It worked. The signal is a bit noisy, but it is far better that what I got before, I can hear a distinct output.

I used a 5v source, same as is used on the beagleboard. The one modification I made to the circuit was that I used a 100k potentiometer in place of R5 to adjust the amplification.

7

Hi Garrett,

if you have used the 741 mentioned in the schematic: a NE 5534 or a TL 071 might reduce noise . Both are inexpensive and popular. They are a bit prone to oscillation, however.

Peter