Further noise reduction

TomMasz
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5 years 1 month ago #1695 by TomMasz

Further noise reduction was created by TomMasz

I've tried a number of the suggested changes to reduce output section noise. I have increased C6 to 33nF, use a battery pack for power, disabled Bluetooth and WiFi to only minimal improvement. Looking at the schematic and the Sallen-Key filter doc from TI, it would appear C6 and C7 are related. Should C7 also be changed when C6 is changed? Any other tips for noise reduction? Thanks.

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Ray
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5 years 1 month ago #1698 by Ray

Replied by Ray on topic Further noise reduction

Hi,

Have you tried just the sinewave generator to see if the output stage is clean?
If you want to go further more, you can lower all the Low pass filters on the circuit:
www.electrosmash.com/media/kunena/attach...dal-pi-schematic.png

R2&C2 have a fc= 4.9Khz, if you double C2 (just placing a 6.8n Cap in parallel with C2) the new fc= 2.6KHz
With the S&K filter is the same, placing 6.8nF caps in parallel with C6, c7 and C8 will half the fc.

I am talking about placing caps in parallel because you can just add them to your board (under the PCB) without being destructive.
You can calculate simple filters and sallen key filters with:
sim.okawa-denshi.jp/en/CRtool.php
sim.okawa-denshi.jp/en/OPstool.php

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