This high impedance step suggested by an English publication can operate up to 1 MHz with 1 V rms output. Input impedance is 1 M ohm.
The gated oscillator in the figure bellow tums on when a “0" Iogic Ievel is applied to its input....
In this project, from a Japanese magazine of 1973, only one channel of a stereo amplifier of 20 W...
We find this circuit in the manual of the used integrated circuits. The manual is from Linear...