How to get +12v and -12v

[Austin73]

Hi everyone, just been reading another thread about the sub commander guitar synth- looks pretty dam awsome.

Was thinking of getting a board for this but just noticed it takes 12v both + and - , so was just wondering how to go about this. I'm in the UK as well so anything with 240v please lolo

Cheers

Aus

[StickMan]

You'll need a 24V DC source.  Then use a typical voltage divider circuit and connect the middle to ground. 

[petemoore]

  IIUC when I suggested that...
  I'm not at all sure the resistive divider method will provide a 'stiff' enough ground for your purposes.
  When one side 'pulls' harder than the other side, the ground voltage may stray.
  I think a power transformer [with about the right AC voltage output], diode bridge/filter/regulators arrangements on each...+ and the - bridge output.
  See 'Power supplies for effects', GEO.

[StickMan]

What about using a 386 chip with no input?  Would that be stiff enough?

[Papa_lazerous]

I'm in the UK as well so anything with 240v please lolo

Well I am in the Uk and last time I metered a plug socket there was 230Volts there, has been 230 for donkeys years....

Anyway moving on whats to stop you using a cheap transformer a recitfier then slap a couple of caps in there then 7812 and a 7912 regulator and another few caps for stability of the regs and you got a GND thats in the centre and a +12 and -12 regulated supply.  Ok I missed details but you get the idea...... there are plenty of builds about

[mdh]

Search for "power supply basics" on geofex.com.  There are two ways demonstrated there to generate a bipolar supply from wall power.  The most common way is to start with a center-tapped transformer, and regulate with 7812 (positive) and 7912 (negative) regulators. The details that Papa_lazerous referred to are in the article on GEO.

As always, if you haven't worked with mains power before, read up on safety considerations and exercise abundant caution.

[demonstar]

I emailed ray Wilson regarding this and +/-9V from two PP3's should work according to him. (Each battery would draw around 30ma).

I'm just in the middle of doing the layouts. I'm using stripboard so it's a big job. I'm going to use +/-9v like ray proposed.

I can't guarantee it will work as I haven't tried it but Ray said it should. If you do try the +/-9v before i do, please can you let me know how it goes?

[Papa_lazerous]

the 2 batterys will work sure, but not for long before run them flat 

[demonstar]

I worked out 18 hours max battery life. I'll get some rechargeable ones. The bit that concerned me a bit was the slightly lower than recommended voltage. like I say Ray thinks it'll work.

[GibsonGM]

+1 on Papa Lazerous' idea, using the 2 regulators.  That will stabilize the voltage of a 30V wall wart (you'd need a tad more than 24v, I'm afraid, for the regulators to operate).  A simple voltage divider won't regulate very effectively.   Don't forget your heat sink!  A slight amount of work (2 IC's, 4 caps or so), but worth the effort to not have to dicker with batteries, IMO....

[Austin73]

Thanks for all the input so far chaps, great as usual. Just a thought what about using a pc power supply module?
I'm sure you could get 12v + /- from it. I suppose its a bit over kill but just a thought as i always seem to be offered them.

Aus

And would there also be a way to get some 9v off them too to power some other fx

The plan is to rack mount this lot anyway as I have no more floor space

LOL

[Gus]

You can get + and - from a 12vac no CT transfomer.

http://www.paia.com/prodimages/siabsch.pdf   
Look at the Power supply part

[Austin73]

hey gus cheers for the link, does look remarkably simple to do maybe to simple but wil check later when I get chance. Otherwise I did find a 12v dual output which I suppose I can use flip one output with a 7912 but need to order the pcb first before I embark on the power supply.

Looking at the other posts maybe if I am really struggling I could use a MAX1044 to have +/- 9v to run it

Cheers

Aus

[miqbal]

Look for the datasheet of LM7812 and LM7912, read them carefully, and (usually) at the last part it should mention on how to use them as a dual supply (+12 and -12V) power supply. You can try googling for LM78xx application...

[Barcode80]

you could also use the two regulators above with two max1044 chips. each one would put out around 17.5 to 18 volts, run one neg and one positive, then regulate them each to 12.

[miqbal]

You can use ICL7660S for MAX1044 substitute, it have boost feature also, just like MAX...

[Electric_Death]

You can use ICL7660S for MAX1044 substitute, it have boost feature also, just like MAX...

I built the circuit from geofx using the 7660's as substitutes - no good, you get unbearable wine. I found several ways to reduce it but no way to eliminate it. I did however come across a version for the 7660 that I've yet to build but shouldn't introduce noise.

[miqbal]

I built the circuit from geofx using the 7660's as substitutes - no good, you get unbearable wine. I found several ways to reduce it but no way to eliminate it. I did however come across a version for the 7660 that I've yet to build but shouldn't introduce noise.

RG Keen says on his Chargepump 9v to 18v article:

All by itself, the 1044 runs at about 7-10kHz, so there will be ripple of that amount on the C2 output and on the +9V output from the battery as well. Audio equipment that uses this voltage could have a "whine" audible if you're not careful. However, the 1044 has a frequency boost feature. If you connect pin 1 to the power supply (shown by the little open switch) then the oscillator frequency goes up by about 6:1. The oscillator then works well above the audio region. Any whine is then going to be inaudible.

The MAX1044 is about $2.68 in unit quantities at Digikey.

You can do the same thing with the cheaper  TLC7660CPA($1.58),  LMC7660 ($1.19),  NJU7660D ($0.46!) chips from Digikey and/or Mouser.

These chips all work in exactly the same circuit, except that pin 1 should not connect to +9v, and even if you connect it, it will not change the oscillator frequency, so you will have to wire carefully to keep whine out of your audio circuits. This can be done, it's just easier if you don't have to think about it.


Well, probably the 7660 version that you use does not have  the "BOOST" feature like I mention before (usually on pin 1 of the chip).
You have to use the S-version of 7660 (ICL7660S; with S at the end of the code), it has frequency boost feature on pin 1; ICL7660/7660A doesn't have it. For such case, You can use several methods to eliminate the whine; i.e, increasing the oscillator frequency up to the range that inaudible to human. you can overdriving the oscilator from external clock, or the easier way, using additional slow-down capacitor.

For -9V (minus voltage), this is RG's wiring:


Here is the data sheet for ICL7660S:
http://www.intersil.com/data/fn/FN3179.pdf

And this is for ICL7660:
http://www.spelektroniikka.fi/kuvat/icl7660.pdf

Actually, I have use it (ICL7660S)  in charge pump circuitry from RG (geofex) on my PT-80 delay pedal with good results, nice 18Volts at the output, and no whine off course. There are several more chips with the same functions, but only a few that implement the boost feature.

Hope it may help..
MIQ

[MikeH]

Tonepad has a bipolar power supply project that uses a max1044 IC, couldn't you use the same design, but with a 12V wall wart, as long as the IC can run at 12 volts?

edit:  eh, looks like it tops out at 10V: http://www.datasheetcatalog.com/datasheets_pdf/M/A/X/1/MAX1044.shtml 
anyone know how to find a pin-for-pin replacement that will go to 12V?

[caress]

it's possible to boost the +9v using the charge pump convertor feature in the max1044...


is there a way to then invert the 33v to get a + and - voltage which could be further regulated down to +/-12v?