This circuit was obtained from a 90s Radio Electronics. The value of R1 determines the scale according to the table next to the diagram. The power suppley must be symmetrical.
This circuit was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...
If you have an old cassette player or bought one from a junk shop, you can set up a small table...
This circuit was found in a 70s American documentation. The converter can be of any type and the...