This circuit in its original version was found in an 1975 English publication. It is a preamplifier with a feedback network that reinforces the bass. In the current version we can recommend changes in component values which have been changed to the current standardization. The potentiometer output can be 22k which is the current commercial value for this type of component. In the original it was recommended a pot of 25k, for example. The source need not be symmetrical, but must have excellent filtration. It can also be used battery, since consumption is low. Likewise it may be used the equivalent operational amplifier.
