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Gear / Technical Help => Battery Boxes, Preamps, Mixers, ADCs, and Processors => Topic started by: udovdh on January 03, 2006, 10:57:23 AM
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Hello,
In my simple battery box the resistor controls the gain that the FET on the mic capsule generates.
More resistance is more gain.
If I lower the resistance, I get less gain.
Currently the resistor is at factory recommended value.
I need less gain, as I wrote elsewhere, for loud situations. (-6 dB would be nice)
I can lower the resistor a little without problems.
The manufacturer, though, cannot say if the lowering of the resistance versus gain is a linear process.
Does anyone here have some kowledge about what type of behaviour, curve I can expect?
I am getting closer to the minimum resistor value, but have been at 22 times the minimum value.
What form has the gain/resistance graph?
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Hello,
In my simple battery box the resistor controls the gain that the FET on the mic capsule generates.
More resistance is more gain.
If I lower the resistance, I get less gain.
Currently the resistor is at factory recommended value.
I need less gain, as I wrote elsewhere, for loud situations. (-6 dB would be nice)
I can lower the resistor a little without problems.
The manufacturer, though, cannot say if the lowering of the resistance versus gain is a linear process.
Does anyone here have some kowledge about what type of behaviour, curve I can expect?
I am getting closer to the minimum resistor value, but have been at 22 times the minimum value.
What form has the gain/resistance graph?
doh...
Please, could you post some schemas?
I can't easily understand what you're trying to say without taking a look to the schema you're using in yout BB design...
Thnks
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A simple battery box.
9V battery via resistor to mic capsule.
Where the resistor reaches the mic capsule, a capacitor is attached as well to filter the DC component and get only the audio component for the recorder.
Ground of the battery is ground for the mic and line out.
+--[ R ]------- +9V
|
| C
+--||----- audio
|
|
|O
|
+----------------- ground
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The effect will depend on the input impedance of the pre-amp you are connecting to. Ignoring bass rolloff and other frequency dependent effects:
if Rb is the battery box resistance and Ri is the pre-amp input impedance, the voltage gain is proportional to
Rb*Ri / (Rb + Ri)
If you need to work in dB, remember that -6dB is half the voltage gain and -20dB is 1/10 the voltage gain.
To reduce the level by 6dB, the new battery box resistance should be (where Rb is the original battery box resistance):
Rb_new = Rb*Ri / (Rb + 2*Ri)