bipolar power supply from standard 9v dc PSU

[BlueFuzz]

Hi,

Has anyone built a bipolar power supply convertor into a pedal to run from a standard boss type centre negative power supply?

I've been looking at the circuit on geofex which uses a max1044 charge pump convertor to do this, but am concerned about ground loops. To explain, if running several pedals from the same power source, i'm not sure how the different pedals would reference ground. Is there a convention? Do pedals ever turn the positive side of the supply into ground and run on a negative voltage? This made me wonder if turning the centre (negative) terminal into ground for the bipolar pedal would ever cause a problem. If not, and i'm just showing my ignorance, then great!

Thanks,
Jon

[compuwade]

It seems to me that circuit you're looking at is designed for exactly what you want to use it for. There shouldn't be a problem with ground loops.

[Skruffyhound]

There is a problem which R.G. explains, adding the transistor, the second graphic, avoids this. I found it difficult to get my head around at first glance but further investigation revealed a nice diagram at Tonepad which shows the circuit in the context of a whole pedal.

I don't think there is anything problematic with this. The difficulties arise with circuits that use a "false" ground at 4.5 volts in order to achieve some of the bipolar benefits. If a circuit like this is connected to one with a "true" ground at 0 volts then something is not going to work quite as it should. I have only limited knowledge, but I assume that in prof. pedals the false ground section of the effect is isolated in some way so that they don't interact badly with "normal" effects.

Reading your post again, you have noticed that there is +9,0 and -9 right? If you use 0 as ground it's not going to be a problem. There are some Fuzz pedals that have a positive ground, but there are sneaky ways to get around this. Read Jack Orman/Muzique on this.

I'm just a hack, so wait a while and see if you get some more prof. explanations. Good Luck

[BlueFuzz]

Thanks guys. I guess, thinking about it, if using a decent multi-way supply then the individual power supply connectors may be isolated anyway, which would hopefully avoid any problems.

[BlueFuzz]

So, a related question...

The specs for the effect circuit in question state that two batteries are required because of the high current consumption of the circuit. The problem is, I want to be able to run the effect either off battery or a power adaptor, and DC in sockets only have one break contact (that I can find), whereas I would need two to be able to interrupt a two-battery bipolar supply. So, I figured that I could hook up the batteries in parallel (reducing the current drawn from each) upstream of the charge pump convertor, and then I would still get +/- 9V when run off batteries, thanks to the charge pump circuit, but would not dramatically reduce the time between battery changes. Equally, I should then be able to use the single break contact from a DC socket to cut out the batteries.

Does that sound plausible or am I missing an easier way???

Jon

[Skruffyhound]

Using the stereo jack switching shown on Geo, you can do this. Check out the Tonepad layout for a full circuit. Using batteries in parallel, right. Just takes space, and not knowing your application, I can't guess why you would use batteries at all, isn't it going to be expensive?
If you need to do it this seems a logical way to go about it.
Good Luck

[BlueFuzz]

I might just drop to one battery and see if it works - what's the worst that can happen...?