This conventional filter circuit is from American documentation from the 1990s. The operational amplifier admits an equivalent and the power supply must be symmetrical.
This circuit was found in the October 1987 Radio Electronics magazine. The triac must be matched to...
Found in a 1980s American documentation, this circuit can use a SCR and a general-purpose transistor....
The circuit shown is from National Semiconductor's Linear Applications Handbook. The LM3900 is a...