This filter configuration used in telecommunications uses 4 Jaumnann crystals that are interesting for low and medium frequencies. The circuit is from an 80's documentation.
This circuit, which can be used as a shield or in other applications, can be found elsewhere on...
This isolation circuit for audio signals was found in the August 1992 issue of Radio Electronics...
This circuit with the operational amplifier CA3130 was found in a documentation from 1977. The...