bipolar power from one battery

[Ashurbanipal]

Does the bipolar power with one battery trick that's in the 6 band EQ on GGG work well if you use a +9v power supply instead of a battery and if that power supply is also powering several non-bipolar effects? I ask because I've trouble with bipolar effects and non-bipolar effects before. I had wired them wrong, but I want to verify this will work well before I spend time on it. I don't want to use the charge pump solution because I don't have any of those ICs lying around.

[Ashurbanipal]

Oops, here's the schematic I'm talking about:
http://www.generalguitargadgets.com/pdf/ggg_eq6b_sc.pdf

[Mark Hammer]

How tall are you?  This is a simple enough question, but one whose answer depends on several important things being assured.

First, I cannot measure your height if you are floating on water.  I cannot measure your height if you are moving.  I cannot measure your height if you are hunched over and unable to stand straight.  I cannot measure your height unless ALL of your body's length is available for measure.  So, I make you stand still on terra firma, as upright as you can, and measure your height from the ground up.

So it is with electronic signals.  When gain is applied to a signal, that assumed gain is based on multiplying its known amplitude, relative to a pre-identified reference point.  When a circuit has a pre-identified reference point in the form of "true" ground, then measurement is easy as is calculation of circuit parameters.

But what if there were no "true" ground?  What if I wanted to measure your height, but your were barefoot and the ground was so uneven and painful to stand on that I had to provide a platform for you to stand on?  Should your height be assumed as the distance from the rocky surface to the top of your head...should it be the distance from the platform to the top of your head?  The answer is obvious to us.  We measure from the arbitrary point of reference.

So it is with circuits.  We provide an artificial arbitrary reference point; the "floating ground", or reference voltage (Vref).  What should that Vref be?  Well, following our principle of allowing you to stand up straight so that your true height can be measured, we set the Vref to be at a point that permits the negative and positive voltage swings from ground to be "their full height".  Setting Vref as half the supply voltage provides that opportunity for both halves of the signal to "stand up straight".  This is why Vref is generally (though not always) derived by having two equal-value resistors divide the V+ in half.  Whatever supply voltage is used, the Vref will be half that voltage by means of this voltage divider.

The "trick" that appears to be used by the EQ circuit you link to, is no trick.  It simply provides a way to use either 1 or 2 batteries.  If there is but a single 9v battery then a 4.5v Vref is obtained.  If there are two 9v batteries used, then the pair of capacitors provides smoother supply voltages from both sides of the supply.  Normally, when you see a Vref circuit, you will see two equal-value resistors and a single electrolytic cap to ground.  In those instances, smoothing of the overall supply voltage istaken care of elsewhere, and all we are concerned with is that the 4.5v derived ground/reference be smooth.  So, only the one cap is needed because a single battery is assumed.

[Ashurbanipal]

So if use a +9v or +12v power supply instead of a battery and have other eefects power from that same supply, will it work?

[Mark Hammer]

Yes, it should.