OPA1612 as microphone pramplifier

[RuudNL]

In the updated schematic, the gain of the first OpAmp stage can be extremely high, with a feedback resistor of 1 M.ohm. (Depending on the drain impedance of the FET.)
The termination of the microphone capsule is low, with a resistor of 1 M.ohm.
I would think about a value of for example 100 M.ohm.

 

[abbey road d enfer]

@abbey road d enfer
I thought I could use DC-DC converter to isolate PC's supply noise and buzz.

I believe cleaning a power rail can be done without resorting to a DC/DC converter.

To everyone: I had to leave C1=50pF, when I increase it into 1n I got more input noise:

OPA1612 is a bipolar opamp, it is not optimized for such high resistance. Ideally R1 should be about 5-20 kohms.

+1 for increasing R0 to much larger. Typically 1Gohm is found here.

 

[Devicet]

Thank you for reminding about R1.

Am I right, that I could leave second stage like this?



Nothing wrong gonna happen when P1 = 0 ohm.
I would connect C2 straight into 3.5mm jack and short R and L chanel. I did it before and had no issues. After searching web I'm taking into consideration to use two 10k resistors. Important info - Rinput is just model of my sound card input impedance.

 

[abbey road d enfer]

Am I right, that I could leave second stage like this?

More or less.

View attachment 138996

Nothing wrong gonna happen when P1 = 0 ohm.

Except that the output of the opamp is loaded by 440 ohms, which may impair headroom and increase distortion.

I would connect C2 straight into 3.5mm jack and short R and L chanel. I did it before and had no issues.

It would work.

After searching web I'm taking into consideration to use two 10k resistors.

It would also work, with little less headroom.

 

[Devicet]

Thanks for all help. I would leave it like that: