We found this circuit in a 1977 documentation. The National Semiconductor's LM380 is no longer easily found, but if used on this amplifier it provides excellent reproduction quality.
To obtain variable frequency signals, the circuit in the figure is recommended. In this circuit, the...
This circuit was found in old English documentation. It can be improved by using resistors of...
This circuit was published in a 1979 magazine, but it can still be easily assembled as the...