This filter has the components calculated for the frequency of 1 kHz but can be changed. The input resistor can be 100k and the source symmetrical. Any operational amplifier can be used.
This is a voltmeter with high input resistance. The transistor is germanium. We found it in an...
The sophisticated signal tracker/follower with a JFET and integrated circuit 741 was found in a...
I got this4 circuit from Hands-On Electronics, 1988. The American magazine no longer exists, but...