Index: simulation/raw/18_opamp_ac.html
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--- simulation/raw/18_opamp_ac.html	(revision 7872)
+++ simulation/raw/18_opamp_ac.html	(revision 7873)
@@ -14,6 +14,7 @@
 <a href="18_opamp_ac.rs"><img src="18_opamp_ac.svg" width=600px></a>
 <br>Click the image to get the sch-rnd sheet</center>
 <p>
+More info on the circuit: <a href="https://www.electronics-tutorials.ws/filter/band-stop-filter.html"> www.electronics-tutorials.ws </a>
 
 <h2> Preparing for simulation </h2>
 <p>