This circuit was found in Texas Instruments documentation from 1968. The transistors are from that time, admitting modern equivalents. The response ranges is from 20 to 20 000 Hz.
This indicator was found in a 1974 publication, but it can be fitted with the BC548 transistor or...
This circuit has a traditional configuration explored in several other points of this site. The...
This version of a mixer with a transistor appears elsewhere in this section and on this website. The...