09-11-2023, 10:33 PM
(This post was last modified: 09-11-2023, 10:52 PM by Mike Watterson.)
So how serious is it to have a battery without decoupling in series with the microphone signal?
I don't know. I'll make some measurements
But a download pdf from NIST https://tf.nist.gov/general/pdf/1133.pdf
Some other stuff I'll study
https://www.sciencedirect.com/science/ar...8622015006
Two LR1s in series may have more noise because they are higher resistance cells, but electrochemical noise is likely higher than themal resistance noise. That will be affected by current. So I'll measure the current and wire up without the microphone to a load drawing the same as microphone and compare battery noise with and without decoupling. Then compare with microphone. The electret and FET in the capsule both generate noise too.
Seems a battery is much quieter than a PSU and EC noise is roughly current proportional and low.
Extract
The NiCd are lower resistance than NiMH, which are much lower than Alkaline.
It seems alkaline AA is about 0.15 to 0.30 Ohms. I'd expect an alkaline N/Lady cell/LR1 to be about 2700/800 higher as that's ratio of capacity in mAH, about 3.4x more, so 0.5 to 1 Ohm. That's still pretty low compared to FET source and 690 Ohms load resistor in series. The probably 680 Ohm resistor might advantageously be a higher value. I can put sound and see what AC load halves the signal to find out source impedance.
I don't know. I'll make some measurements
But a download pdf from NIST https://tf.nist.gov/general/pdf/1133.pdf
Some other stuff I'll study
https://www.sciencedirect.com/science/ar...8622015006
Two LR1s in series may have more noise because they are higher resistance cells, but electrochemical noise is likely higher than themal resistance noise. That will be affected by current. So I'll measure the current and wire up without the microphone to a load drawing the same as microphone and compare battery noise with and without decoupling. Then compare with microphone. The electret and FET in the capsule both generate noise too.
Seems a battery is much quieter than a PSU and EC noise is roughly current proportional and low.
Extract
The NiCd are lower resistance than NiMH, which are much lower than Alkaline.
It seems alkaline AA is about 0.15 to 0.30 Ohms. I'd expect an alkaline N/Lady cell/LR1 to be about 2700/800 higher as that's ratio of capacity in mAH, about 3.4x more, so 0.5 to 1 Ohm. That's still pretty low compared to FET source and 690 Ohms load resistor in series. The probably 680 Ohm resistor might advantageously be a higher value. I can put sound and see what AC load halves the signal to find out source impedance.
