This circuit, to add the ambience effect, was suggested by National Semiconductor in documentation from the 90s. The amplifier needs an appropriate power source.
This is a simple 1-digit voltmeter circuit using voltage comparators. It was found in a 2004...
This circuit is from old documentation, but the regulator may be 78xx series equivalent and the...
This circuit appeared in the November 1995 issue of Electronics Now magazine. The circuit uses...