These basic bass controls were obtained from an article in Electronics Now magazine in February 1995. They are basic passive circuits in (a) basic tone, (b) boost, (c) cut, and (d) flat response.
This circuit is from a documentation from the 60s. The circuit can be built with transistors like...
Found in a 1966 General Electric documentation, this dimmer should only be used with incandescent...
To control relays safely with double insulation, we suggest the circuit in the figure. The optical...