This symmetrical four voltage source was found in a 1968 Motorola documentation. The circuit is of a type that was commonly used in that time amplifiers.
This 80's circuit uses an audio amplifier to obtain a symmetrical source from a single source. The...
I found this circuit in a 1986 English magazine. It can still be easily assembled, exchanging Q1...
Found in a 1970s documentation, this circuit has a flat response from 15 Hz to 130 kHz. Modern...