Line Level to Microphone Level Input

Thread Starter


Joined Mar 25, 2012
Hi all,

Need a help with audio related stuff. I'm using mono microphone on GoPro and wanted to feed the another unused Right channel with intercom speaker out. So to reduce the voltage to feed it into the GoPro on unused channel I used the below schematic. However, there is a little bit sound getting into the microphone channel even though no wire is attached to it except the common GND. If I push the volume up it will defeat my purpose.

So I need help to fix this I don't know how. I want to keep this separate.

GoPro can also accept the line in level signal and there is so such issue if feed the speaker out directly. However then I need to amplify the mic using battery to use on its channel. To try that I also bought MAX4466 but can't get it to work, searched the whole lot internet.

Any help is greatly appreciated.



Joined Jul 10, 2017
Can you give us a sketch of the way you have everything connected please. It will make it much easier for us to understand exactly what you are doing. Then we may be able to offer some suggestions on how to get it working.

Audioguru again

Joined Oct 21, 2019
Your 330 ohms to 1.5k ohms resistors barely attenuate the line level signal. Their total is 1830 ohms and the output resistor is 1500 ohms so the attenuation is 1500/1830= 0.82 times. Line level to mic level needs an attenuation to about 0.05 times.

We do not know the type of mic or its impedance. We also do not know the input impedance of the GoPro input.

A battery is not a mic amplifier.
A MAX4466 mic preamp is tiny and is designed for an electret type of mic that maybe you do not have.


Joined Oct 7, 2019
The chances of a youtube circuit working is low. The circuit only drops the signal by 2db. A wire is 0db. Also the capacitor causes a 80hz low blocking filter. I assume you want base.
I assume you have these parts so I used them for the circuit on the right. -23db and flat frequency.