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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">You probably want to use something a little more complicated for the best performance. Douglas Self covers this well in Chapter 26 of his book.<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Synth-diy [mailto:synth-diy-bounces@synth-diy.org]
<b>On Behalf Of </b>Tom Wiltshire<br>
<b>Sent:</b> 05 May 2021 10:17<br>
<b>To:</b> synth-diy francesco mulassano via<br>
<b>Subject:</b> [sdiy] Differential amps and noise cancellation in dsPIC 33FJ128GP802 uP's DAC<o:p></o:p></span></p>
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<p class="MsoNormal">Hi all,<o:p></o:p></p>
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<p class="MsoNormal">The dsPIC 33FJ128GP802 uP (and others in the family) includes a 16-bit DAC on the chip. The outputs from the DAC are provided as a differential output to help cancel any noise generated by the uP internally. NOt a bad idea, seeing as that
is probably inevitable. Despite this precaution, the DAC is reasonably noisy and not suitable for all applications.<o:p></o:p></p>
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<p class="MsoNormal">The example circuit for combining the differential outputs is shown attached - a simple diff amp with 10K resistors everywhere.<o:p></o:p></p>
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<p class="MsoNormal">Now, my question is this:<o:p></o:p></p>
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<p class="MsoNormal">If I change the gain of the differential amp by increasing R6/R8 (to 47K, say) does this affect the noise cancellation properties of the diff amp?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">It seems to me that it might, because the positive input now has a different proportion of signal going to it than the negative input.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks,<o:p></o:p></p>
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<p class="MsoNormal">Tom<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">==================<br>
Electric Druid<br>
Synth & Stompbox DIY<br>
==================<o:p></o:p></p>
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<p class="MsoNormal"><img width="318" height="307" id="E4F38BDC-A6F1-4372-A2AD-1C4D7D375348" src="cid:image002.png@01D7419C.66312780"><o:p></o:p></p>
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