If you use opamps like the TL082/84 you’ll be in need of a “split” power supply. That is a power supply that has a positive voltage, ground, and the equivalent negative voltage (eg +5v, 0v, -5v). Since most audio signals are AC you need the opamp to operate in this range to be able to process them.
One way to get a split supply is to build a full-on rectified AC to DC power supply using a transformer…
But sometimes we only have +5v to work with (like when powering from a USB port). So what can you do…?
A simple way to generate a negative voltage is use a charge-pump circuit – like this one based on a 555 timer.
The timer is in astable mode, so it’s oscillating and producing a square wave. Through careful placement of diodes it’s possible to direct one transition of the square wave to one side of a capacitor. Since the capacitor only sees one side of the waveform it is “pulled” into a negative configuration. This negative charge can be tapped on the opposite plate of the capacitor. The only current available will the charge stored in the capacitor – so in other words not a great deal. But it should be enough to run a TL084 for basic signal processing – just as long as you are not trying to power a speaker or anything.
The 555 timer runs relatively quickly, so charge is replenished rapidly as well. I have run the above circuit with an Arduino and been able to process simple audio signals +5v input gives -5v output.
It’s worth pointing out that there are custom negative voltage generator chips available too (The MAX232 is one of them) – but this circuit is so simple and the parts are really easy to find.
The following is an etch mask to make your own – 600 DPI TIFF file.
600dpi Etch Mask
Another option is to split the 5v itself to give -2.5v. 0v and +2.5v – but you need to be sure to bias everything correctly.