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The Luddite


Microphone Pre-amplifier with LED Level meter

Project description

This microphone pre-amplifier was designed originally for portable recording (although it would be equally at home in a studio, or mixing desk). To this end (with the exception of the high pass filter) it is as neutral as possible, with no EQ, as it is expected any processing or EQ would be done in post production.

This comes on two parts, the microphone Pre-amplifier board, and the level meter board.

The Pre-amplifier itself is based on an SSM2017 or INA217 with Servo-null provided by IC2A, then followed by a third order Butterworth High pass filter. Input options include a 10dB pad, phantom power and Invert. IC2B is a precision half wave rectifier which feeds the VU meter PCB.

Shown above is the full 12 LED meter, note greyed out components are for other options, such as the rectifier, which is not needed in this case as there is one on the pre-amplifier board. Other options allow you to build the VU meter with either 4, 8 or all 12 LEDs.
I have also made up a spreadsheet (with Open Office) for calculating resistor values for the VU meter, available here as an OpenDocument spreadsheet.

Unfortunately the cost of Electronic components and shipping from Australia is not cheap, so I am selling these as short form kits (PCB, Instructions and any programmed parts) rather than complete kits.
At the moment I am selling these through Ebay which for this project includes:
PCB and
Assembly instructions (PDF)

Email for more details.
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