Powering unipolar devices from a bipolar power supply

[Yazoo]

I have just built a bipolar powered circuit and I would like to combine it with an Equinox digital reverb pedal I built a while ago. This is powered by 9 volts DC. I once tried something similar but found everything shorted out when I tried to connect the ground of the 9 volts DC device to the ground of the bipolar powered device.

I have been experimenting on a breadboard with 2 test circuits, a bipolar powered LFO and a unipolar blinking led running off a 555 timer. What I found is that connecting the unipolar ground to the bipolar ground does not work. However, if I connect the unipolar ground to the bipolar negative, the circuit does work correctly.

I then get very confused when it comes to the audio ground. Isn't this common regardless of the type of power supply?

[PRR]

Please draw pictures.

What you say in words "can" work if done correctly; or maybe I am just too experienced to see what you are doing different.

[R.G.]

As Paul said, please draw pictures.

As you said, you do not understand grounding. That's not a bad thing, just a pointer to where you need to go study next.

As a type in here and in other forums from time to time, "ground" is not a single thing. We use the word for many different situations. "Ground" can  be at least:
- a voltage reference point, literally a "standard" voltage reference of 0.00000... volts
- a signal current return path, like the shield braid on a guitar cord
- an interference shield, like the metal box around a circuit
- a safety shield, like the metal box around an AC-powered appliance that connects to the AC mains safety ground
- a return path for "used electricity" from a circuit's operation, the return from the power supply to the circuit back to the "ground" terminal of the power supply

In many circuits, the "ground" will combine two or more of these functions. Sometimes this works OK, especially if there is not much current involved or only small signals and low impedances. But sometimes it goes hugely wrong, as you have found out.

When you say "everything shorts out" about connecting your bipolar ground to the 9V ground, you're finding that the unipolar 9V supply uses the minus side of the power supply as both a return path "sewer ground" and as an audio signal ground. Your bipolar supply is somehow set up so the bipolar "ground" is not truly isolated from the 9V supply ground, and when you connect the two, you're probably trying to force the wires to make two different DC voltages be the same, with bad results.

Post what you're trying to do and we can probably tell a bit more about how to advise you.

[Yazoo]

I've attached a simplified diagram of the two circuits I would like to power. I experimented on the breadboard again and I found that by attaching the unipolar 6V + to the bipolar ground and the unipolar ground to the bipolar 6V-, both circuits coexisted happily.



This did make sense when I though about it since the bipolar ground actually sits 6 volts above the bipolar negative. Have I got this right?