Reversing 9V DC supply

Frequently asked questions regarding powering your pedal.

Reversing 9V DC supply

Postby Suede » 05 Mar 2013, 01:30

Hi, I looked quite a bit around the forum to see if this been discussed before but couldn't find any very relevant topics.If I'm mistaken please refer me to the older thread an delete this one :) .

I built a Ge Fuzzface for a friend and he likes it a lot but asked me to make it run with the standard +9V dc supply, if possible.
Of course the circuit is with PNP transistors and positive ground,so I was wondering if there is a standard layout for reversing the polarity from +9V to -9V and add it to the circuit so that it works fine as is.I suppose there should be an op-amp to do such a thing along with some filtering and regulation.

Thank you for your help!
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Re: Reversing 9V DC supply

Postby davent » 05 Mar 2013, 01:44

You can use a charge pump chip such as the MAX1044 to create a -9v supply and that will allow your positive ground Fuzz to share a power supply with all your other negative ground pedals.

http://www.geofex.com/circuits/+9_to_-9.htm

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Re: Reversing 9V DC supply

Postby R.G. » 05 Mar 2013, 04:08

Only use the LT1054 instead of the MAX1044. It's a more robust chip. The MAX1044 can be a little delicate.
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Re: Reversing 9V DC supply

Postby Suede » 05 Mar 2013, 10:54

Thanks for your suggestions this is exactly what I had in mind! :D

R.G. wrote:Only use the LT1054 instead of the MAX1044. It's a more robust chip. The MAX1044 can be a little delicate.


How could I compensate the voltage drop (1.1V for the LT1054).The fface has been carefully biased and a change like that would completely change the collector voltages correct? :hmmm:
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Re: Reversing 9V DC supply

Postby Firedragn07 » 15 Apr 2013, 14:38

On the same lines as this topic - why not just reverse the electrolytics and use NPN? In all positive ground circuits...what difference does it make? I've thought about building a charge pump but am not sure which way is better/worse and why or why not.
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