Updating link to recording.
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@ -311,7 +311,7 @@ This simple design is included in the Standard for all to use with no obligation
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* C1: 1uF ceramic or other non-polarized capacitor. At least 6.3v rating.
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* The low-end frequency response of the microphone can be adjusted by changing the value of C1. Frequency = 1/(2 * Pi * R * C). R is roughly 27k and 75k in parallel, or about 20k ohm. C is the value chosen for C1.
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* The low-end frequency response of the microphone can be adjusted by changing the value of C1. Frequency = 1/(2\*Pi\*R\*C). R is roughly 27k and 75k in parallel, or about 20k ohm. C is the value chosen for C1.
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* 1uF into the ~20k ohm impedance of the amplifier rolls off at about 8Hz. Using a .1uF would roll off at 80Hz instead, eliminating some rumble and wind/handling noise.
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* R1: 75k ohm resistor, at least 1/16W.
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* R2: 27k ohm resistor, at least 1/16W.
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@ -319,7 +319,7 @@ This simple design is included in the Standard for all to use with no obligation
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* Q1: S9013, or similar NPN BJT transistor.
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* Tests were performed (by Mark Smith in 2022-08) using an S9013 transistor, but nearly any small signal NPN BJT should work. For example, a 2N3904 (through hole) or MMBT3904 (surface mount) should work equally well.
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An example recording of audio through this microphone preamp design is [here (full path)](KiCAD/MicPreampTest/Recordings/2022-08-18%20First%20Test%20Of%205%20Component%20Preamp.mp3) or [here (relative path)](2022-08-18%20First%20Test%20Of%205%20Component%20Preamp.mp3).
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An example recording of audio through this microphone preamp design is [here](https://halibut-electronics.github.io/Open-Headset-Interconnect-Standard/2022-08-18%20First%20Test%20Of%205%20Component%20Preamp.mp3).
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This circuit is only a slight modification of a conventional common emitter transistor amplifier, similar to what's analyzed [here](http://www.guitarscience.net/calcs/ce.htm). The difference being that we are using the 2.2k ohm resistor in the Radio side (upper right corner above) as the collector resistor. This means the top-side base resistor (R1 above) connects to the output, not to Vcc.
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