Dual-polarity DC Power Supplies from a Single-polarity Source
The circuit shown below can be constructed on perf-board, point-to-point connected and will work to
provide dual-polarity DC power supplies from a single-polarity DC source.
First, it helps to understand that a DC power source often has plus and minus markings for it, but when
there are only two terminals or wires from it, it is a single polarity supply. When one or the other is
connected as ground, or a circuit-common, or the 0v reference point, then the other is the polarity of the
DC voltage source. If the minus pole of the DC power source is connected to ground or measured with
the black or minus/common terminal of a tester and the plus pole measured the voltage reading is
positive, and vice versa. Note however, if the plus of the supply is connected to ground/circuitcommon/0vdc, then an analog voltage test would need to have its plus or red probe put to ground to
measure the resulting negative dc on the minus pole of the supply or else the needle would try to swing
the the left of zero or at-rest, leftmost setting (not good, unless the voltage scale of the tester is much
higher than the anticipated voltage and then any movement in wrong direction would only be slight if
at all. A DVM or digital readout of a voltage usually can be made with the black/minus/common probe
on the ground/circuit-common/0vdc node and if the other node is a negative amount, the reading will
be shown preceded with a minus symbol.
Two batteries can be connected as a dual-polarity dc supply by connecting them in series, the plus pole
of one to the minus pole of the other. This joined circuit node is then considered/used as
ground/circuit-common/0vdc and the free plus pole is a positive dc supply and the free minus pole is a
negative dc supply.
Many of the PAiA kits have a four-circuit dc power connection area with plus, G, SG, and minus
circuits. The plus goes to the positive dc supply, the minus to a negative dc supply and the G and SG to
the one ground/circuit-common/0vdc point of the power source. They are kept separate until they get
to the power source to keep the audio signal ground as 'clean' as possible.
The op-amp stage may be omitted and the ground/circuit-common may be tapped at the junction of the
two resistors, but the op-amp is preferred when there are more than a few active devices (ICs and
Transistors) of if there is much power involved in the circuit being powered. -- SL 03/18/2010