Very low noise microphone preamplifier with 2.0 V bias outpu

[lilltroll]

Version: 1
Status: Under development
License: BSD

This project aims to connect a low-price, small size solution, very-low noise mic pre-amp to the USB 2.0 Audio card that can use the same power-supply as the Audio-Card.

The electrical power transfered from an electret microphone is very small. To achieve a good microphone SNR - the amount of noise in the analog cuircuit must be extremly small.
This evaluation is based on the TS472 chip.

http://www.st.com/stonline/products/fam ... /ts472.htm
Images:

[lilltroll]

The CODEC input tolerates 3.6 V PtP at a railvoltage of 4.3 V, if the input voltage divider is bypassed.

[shawn]

I like this project for a number of reasons.
It's Audio!
It complements another all ready cool project.
Project can be justified in the robot group ++
It can be exploited in music experment's
It could make a nice product.
I love Pro Audio.

[lilltroll]

The output of the TS472 chip can deliver between 1.9 to 2.1 V PtP singel ended, but it has a differential output that can deliver ~ 4 V PtP before clipping. The CS4270 has singel ended inputs.

[lilltroll]

I have tested that it works fine with reference board, but I have also made some PCB-cards, to try out the SNR.
The design is made in Eagle - feel free to copy and paste into your design - but maybe after errorvalidation of the design.

[lilltroll]

I have som problem with induced 50*n Hz components. Working with a common groundpoint and a star formed ground layout. Líttle tricky to make that with several preamp cards.