We found this circuit in a Poptronics from 1998. The circuit can be extended to more competitors with another 4011. The power can be made with voltages from 6 to 12 V.
This circuit with two 555s was found in the Encyclopedia of Electronic Circuits volume 5 of 1995....
This circuit was found in a 1976 technical publication. It is possible to obtain an 11 dB gain in...
Using transistors at the time, this circuit was found in a 1967 Ferranti documentation. The...