Using circuits from Analog Devices, this circuit does not need a symmetrical power supply. It is also offset adjustable and is based on the LT1498 and LT1167 op amps.
This circuit with only one transistor was obtained in an old English documentation and can be...
This circuit for old lines was found in the March 1986 Radio Electronics magazine. The circuit is...
Suggested by an old Popular Electronics, this circuit is based on an uncommon integrated today,...