The circuit below is suggested by National Semiconductor in technical documentation on the LM3909. The circuit is powered by a single battery and has a very low consumption.
We found this configuration in a 70s American documentation. The circuit makes use of operational...
Other amplifiers of the series like the MC3301, MC3401 and LM2900 can be used in this circuit. We found...
We found this commercial circuit sold as PT-40 in Japan in the 1960s in a documentation of the...