If the current is 800mA then the 5V linear regulator needs a heatsink to get rid of 5.6W heat.

Can you make a test by using the 9V battery for the mic + opamp circuit in case the noise is coming through 12 V supply?

 

If the current is 800mA then the 5V linear regulator needs a heatsink to get rid of 5.6W heat.

Can you make a test by using the 9V battery for the mic + opamp circuit in case the noise is coming through 12 V supply?

Yes, I can do that.... I will let you know what I get. Thanks.

 

jjw,
I connected 9v to my step down to feed 5v to the DVR. I connected a pos & neg lead to the batt & supplied the circuit with 9v. I am getting the same noise as when I use 12v. As soon as I disconnected the DVR, the noise went away. I did not have the aud-in or aud-out connected. Only the 5v pos/neg leads from the DVR. It is the DVR that is creating the noise when powered by the same supply as the circuit, 9v or 12v....
All sounds great when listening through the ear buds and no DVR connected.

BTW, the step down pcb was still connected after I disconnected the DVR leads and the noise went away. However, I suppose the step down pcb could be creating the noise.....

 

I meant to supply the mic+ amp with separate 9V battery
and the buck converter from 12 V
Probably it won't help, but if it works, you can supply the mic+opamp from 12V to linear ( about 9V )regulator.
No heatsink is then needed because the mic and opamp need very small current.

 

I meant to supply the mic+ amp with separate 9V battery
and the buck converter from 12 V
Probably it won't help, but if it works, you can supply the mic+opamp from 12V to linear ( about 9V )regulator.
No heatsink is then needed because the mic and opamp need very small current.

I misunderstood. I can try that and see what I get..