The circuit is from the 1990 Motorola Linear Databook. The circuit can be implemented with other operational amplifiers. The power supply must be symmetrical.
This General Electric circuit is from the 80's. The PUTs used in this meter are not common...
This wired control circuit serves both volume and balance between channels. We found it in Radio...
This circuit was found in a publication from the 50's. The circuit uses germanium transistors of...