This three-transistor circuit was found in Radio Electronics magazine from May 1969. The circuit is for hearing aids and has earphone listening.
This circuit is from a 1980 publication. In it we have a half-wave power control in which the SCR...
We found this circuit in the 1994 Linear Applications Handbook from National Semiconductor. The...
This sound intensity meter was found in a 90s Elektor. The circuit uses an integrated device from...