This filter for frequencies from 300 Hz to 3.4 kHz was found in the February 1995 Radio Electronics magazine. Other operational amplifiers can be experimented, and the source must be dual.
This circuit uses two sensors that are placed at the intersection of a miniature railway, causing...
This circuit with RIAA equalization is from 1985 US documentation. The circuit has a flat response...
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....