Using two 741 operational amplifiers, this low-pass circuit has a cutoff frequency of 10 kHz. We found it in an article in the magazine Electronics Now from August 1993.
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....