10-11-2023, 08:53 PM
(This post was last modified: 10-11-2023, 09:00 PM by Mike Watterson.)
Some more work done.
I converted the holder position on the second mic and made two card tubes, covered on inside and outside with heavy black "duck" type tape as the N/LR1/Lady cells are skinnier than an AA.
Checking with a meter where the batteries are good (in the meter!), I get 684 Ω and 682 Ω for the resistor as load in the end caps. The voltages are -242mV and -159mV on the output connector, i.e. across the resistors. As the battery + goes to red of capsule via switch, battery - is output loaded by 680 Ω (nominal) and case is connected to black of capsule, this makes sense. Thus current of 230 μA or 350 μA. As the small cells are 800 mAH, that's about 2,300 hours running time on higher current!
Next to consider is the AC output impedance. The lower DC value of 159 mV suggests a maximum audio level of about 100 mV RMS is possible.
A quick search suggests about 500 uA is typical current on a FET in an electret. Typical load resistor is 2K2 ( 3V to 5V supplies).
If current was similar, then to have 1.5V instead of 0.24V, needs 6.25 x 680 Ω = 4.25 k
if 3.9 k Ω is used then @ 0.23 mA Vdc = -0.9V approx and @ 0.35mA Vdc = 1.4 approx
But can the paxolin inner cover of the end cap be opened?
Does it matter? How many mV is a loud sound? Maybe 9mV RMS is loud and 90mV RMS thus excruciating?
If the capsule is about 2K impedance, then 680 Ω in parallel gives about 500 Ω. Thus Rload can be increased even if 600 Ohms is wanted.
https://www.analog.com/en/analog-dialogu...ivity.html
I converted the holder position on the second mic and made two card tubes, covered on inside and outside with heavy black "duck" type tape as the N/LR1/Lady cells are skinnier than an AA.
Checking with a meter where the batteries are good (in the meter!), I get 684 Ω and 682 Ω for the resistor as load in the end caps. The voltages are -242mV and -159mV on the output connector, i.e. across the resistors. As the battery + goes to red of capsule via switch, battery - is output loaded by 680 Ω (nominal) and case is connected to black of capsule, this makes sense. Thus current of 230 μA or 350 μA. As the small cells are 800 mAH, that's about 2,300 hours running time on higher current!
Next to consider is the AC output impedance. The lower DC value of 159 mV suggests a maximum audio level of about 100 mV RMS is possible.
A quick search suggests about 500 uA is typical current on a FET in an electret. Typical load resistor is 2K2 ( 3V to 5V supplies).
If current was similar, then to have 1.5V instead of 0.24V, needs 6.25 x 680 Ω = 4.25 k
if 3.9 k Ω is used then @ 0.23 mA Vdc = -0.9V approx and @ 0.35mA Vdc = 1.4 approx
But can the paxolin inner cover of the end cap be opened?
Does it matter? How many mV is a loud sound? Maybe 9mV RMS is loud and 90mV RMS thus excruciating?
If the capsule is about 2K impedance, then 680 Ω in parallel gives about 500 Ω. Thus Rload can be increased even if 600 Ohms is wanted.
https://www.analog.com/en/analog-dialogu...ivity.html
