This circuit was obtained in an old Popular Electronics. It makes use of quite common components. The speed of the effect is set to R7. The circuit drives 20 LEDs.
This circuit, obtained from the component manual used, has an ultra narrow 1 kHz range given by...
Mouser Electronics is providing the MGA-622P8 low noise amplifier for frequencies from 1.5 to 2.7...
This circuit of the 1970s uses Germanium transistors. Changes can be made to use silicon...