Ground versus -vs

[SprinkleSpraycan]

I'm trying to use this schematic as a jumping off point for an overdrive project. But can someone explain to me the difference between ground and -vs? Is it not the same? Dont I tie both together on my breadboard?

[GGBB]

That's a dual supply circuit, so there are two voltage supplies - positive and negative - which are supplied to the opamp V+ and V- respectively, and ground is used for the opamp bias and signal ground.

A single supply circuit on the other hand uses a positive voltage supply only plus ground as V+ and V-, and establishes (usually via a voltage divider) a bias reference voltage between the two e.g. V+/2.

[GibsonGM]

At its most simple, one could use 2 9 volt batteries to get the dual supply. This pic illustrates how this works, note ground 'in the middle' between the 2 potentials:

[antonis]

Redrawn for more visual convenience..



An a single supply modified version..

[SprinkleSpraycan]

Thanks so much for drawing this out. I'll give it a go.

[bluebunny]

If you really build this with a TL072 (or any other dual opamp) make sure that you do something with the other opamp on the chip: connect the output to the inverting (-) input, and connect the non-inverting (+) input to V_bias.

[antonis]

What Marc said above..!! 

Or use the other amp as Vs/2 buffer..
(you'll not need any additional item..)

P.S.
R1/C1 values are recalculated for higher input impedance while maintaining the same HPF corner frequency..

[Lino22]

Antonis, what is the buffer on the DC/2 for? Does it help to keep the voltage steady with an extensive current drain?

[antonis]

More or less, yes..
Op-amp output acts as voltage follower (current amplifier) so it can provide enough current while maintaining constant voltage..
(it makes Vs/2 immune to current demand..)

"Extensive" current drain shouldn't happen here 'cause TL072 input bias current lies in pA range but buffering Vs/2 shouldn't do any harm..
(after all, "unused" amp should be wired somehow, as Marc said above..)
https://www.ti.com/lit/an/sboa204a/sboa204a.pdf?ts=1665489039271

Wε simply transfer bias resistor connection from Vs/2 node to pin 7, et voila..!!

[SprinkleSpraycan]

At its most simple, one could use 2 9 volt batteries to get the dual supply. This pic illustrates how this works, note ground 'in the middle' between the 2 potentials:

What is the advantage of duel supply? My experience has been 18v equals more headroom. Does that apply here?

[GibsonGM]

The pic is just the basic, easiest way to get a dual supply.  They can be built better with regulators on-board, or by other means...the 2 batteries are fine for experimenting tho.   You'd probably want reservoir caps/R on each line (more later if you are interested in pursuing dual supplies, it will work fine as-is for now).

Basically, if you run the dual batteries, your signal rides around zero volts, and can amplify nearly to plus AND minus 9 volts at its output....that's a lot of headroom - the signal won't clip as long as the output is below approx. plus/minus 9V.   This depends on the gain of the opamp and the magnitude of the input signal.

With the bias network, you are 'jacking up' the input by half the supply voltage (4.5V is being added to the input signal), so that the signal rides around that DC level....on 9V, that means you only have nearly 4.5V 'each way' before it clips (up to 9v, down to zero).   Most opamps can only come close to the supply as they amplify, too..so it's less than 4.5V +/-, FYI.  So about half the clean output is possible, compared to the dual supply.

AC signals have no problem 'having DC added to them', and then removed by the cap on the output (C2).  So the output will still be an AC signal, after that cap.
But it won't be able to be amplified as much as if it was done using a dual supply (all things being equal....a higher supply voltage that doesn't exceed the chip's max rating could do the same).  Adding a DC bias is a little 'trick' done to simplify the power supply.

[antonis]

Well said, Sir..!!

@SprinkleSpraycan: Just make sure both batteries have equal voltage or else you'll have asymmetrical headromm for signal positive and negative waveform..

[amptramp]

One thing to watch for is the 4µ7 C2 in the case using two supplies has to be a non-polar capacitor whereas the single supply version can get away with a polarized electrolytic with the + side connected to the op amp output.  I know you can get film capacitors in this size (I have some 10 µF film caps) but the single-supply version does not have a problem with polar caps.