Author Topic: How to Convert single supply voltage circuit to Dual +/- voltage supply???  (Read 155 times)

bluelagoon

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Hello Fellow Board Members,  :)
                                             I am in a bit of a quandry, trying to properly figure just how to correctly convert the Boss FA-1 circuit from single 9 Volt supply to a Dual rail +/- 9 volt supply with a centre 0v ground. I realize I shall need an appropriate charge pump to get the dual supply, but really need help to identify just which of the original grounds become -9volt and which stay as 0 volt ground, I understand that the op amp half supply voltage goes to 0 volt just mainly curious on the section circled in orange trying to get my head around, particularly where the 3M3 resistor is supposed to end up either 0V ground or -9volt? also the 1M pull down resistor does it go to -9volt or 0 ground? I see that also the voltage dividing network in there can probably be scrapped. Just need some sound advice on the matter. the rest of the circuit seems a bit more straight forward, but please chime in with every detail needs correcting for dual +/-v supply. Any and all advice is greatly appreciated

Please see attached FA-1 Schematic.


Thanks for your support.

Best Regards,

TTay

Matmosphere

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Re: How to Convert single supply voltage circuit to Dual +/- voltage supply???
« Reply #1 on: November 19, 2020, 06:35:13 AM »
No expert, but I think this will do it for you.

http://tagboardeffects.blogspot.com/2012/05/negative-voltage-inverter.html

A word of advice though, if you don't already have a 7660 laying around I'd recommend ordering a 7662 instead. Basically the same chip but rated for a higher voltage. The 7660 is rated for 10v, and I have had issues with them and things like the one-spot power supply because they tend to measure a little over 9v. However the 7662 is rated 20v. believe me, it's worth the extra few cents.

bluelagoon

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Re: How to Convert single supply voltage circuit to Dual +/- voltage supply???
« Reply #2 on: November 19, 2020, 06:55:59 AM »
Hey thanks for your reply Matmosphere.  Thanks for the tip on the 7662 chip.
I aready have the hows and whys of getting the dual supply voltage for the circuit, just need some advice on which parts of the existing single voltage supply circuit needs reconfiguring to adapt to a dual voltage +/- 0 volt ground circuit. like which parts such as involved in the voltage dividing network need scrapping and where the existing grounds go to in a dual supply ? to 0 volt ground or to  - 9 volt and already know the half supply connections from the dividing network go to the new 0 volt ground, just need to understand the rest of the story for this particular circuit.

Cheers.
« Last Edit: November 19, 2020, 06:58:34 AM by bluelagoon »

Scruffie

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Re: How to Convert single supply voltage circuit to Dual +/- voltage supply???
« Reply #3 on: November 19, 2020, 06:56:32 AM »
I assume you want a split supply for more headroom?

The J-FET is biased off centre through that divider to get more signal swing @9V, but if you're feeding it a split supply, it's probably unnecessary and the 3M3 can indeed just go to ground.
Works at Lectric-FX

bluelagoon

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Re: How to Convert single supply voltage circuit to Dual +/- voltage supply???
« Reply #4 on: November 19, 2020, 07:05:02 AM »
Yeah more headroom is the idea, the HA 1457 chips can take something like up to 25 volts each rail, apart from that I were looking to incorporate in same box as an existing circuit already on dual supply, So really want to just make everything compatable. So you would reccomend the 3M3 goes to the 0 Volt ground, okay ? Would it be correct then that the only real place the - 9 volt would need placing then would be on the op amps pin 4? Thanks for your reply and assistance.

Cheers, TTay

Scruffie

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Re: How to Convert single supply voltage circuit to Dual +/- voltage supply???
« Reply #5 on: November 19, 2020, 07:06:34 AM »
Pin 4 & R3.
Works at Lectric-FX

bluelagoon

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Re: How to Convert single supply voltage circuit to Dual +/- voltage supply???
« Reply #6 on: November 19, 2020, 07:10:34 AM »
okay thanks Scruffie, needed that help. running in the dark a bit otherwise. Much appreciated,  :)