+9 and -9 from +18?

[chunks717]

firstly, this is my first post....i get answers from you all, ALL the time, but usually someone else asked the question...thanks for giving me a wonderfuly all consuming hobby

- i cannot imagine that this is difficult, but i cannot seem to wrap my head around dual power supply-
A-totaly relative yes? 0v,+9v(as ground),+18v=-9v,0v,+9v NO?
B- if yes, what to isolate...in/out probably and........( )
C-LED ground?
D-why not a voltage divider? (just like VR for op amp)(150ma(ish)tops)

i am aware of the max1044, and in fact, thats where the +18 is comming from(well, +17.35+ish)- built into my PSU, i could use another in my box to get the dual from +9, but CANNOT IMAGINE splitting 18 should be hard.......could also center tap trans, but stereo power jack?!?!

also, the guy at the electronic shop says you can use a neg. volt reg on a pos. power supply to get neg voltage....this is certainly not true...right?

all i am really asking for is a way (within the box) to convert +18 to dual 9s, and what grounds to what within that....or else i will just use ic to convert +9............thank you all.....

EDIT:regarding D- above:apparently more like 20-40ma-ish

[sean k]

I think I'm right in saying you'll never get -9V from a ground referenced +18V supply as theres nowheres to get it from.As the AC comes off a transformer you can get - and + because you rectify the - and + halves of the waveform at 50/60Hz if you have a centre tap on the winding to reference to earth.So I think what your asking is how can I change half of my positively changed potential to negatively charged potential and I'm not sure if that can be done or at least what amazing new technology is out there in a tiny cheap package that can do it.I'm sorry if I'm completely wrong and theres a chance that I could be...a big chance actually.

[jaguarcat311]

just go buy two 9 volt batteries

[chunks717]

thanks for the input... aware of battery solution, kind of wanted a one-time-cost solution. batteries are not sustainable enugh for me
...........it may be that there is no simple way...better buy stock in maxim.
i am willing to build a circuit...if that helps i.e.- does not have to be a one pkg deal..................thanks again

[niftydog]

you can do this, but it involves putting your ground reference at some potential relative to every other ground reference in your system.

This means that you can never connect it to another piece of gear without shorting one ground to another and stopping it from working.

You need a centre tapped transformer to begin with.

[zachary vex]

A-totaly relative yes? 0v,+9v(as ground),+18v=-9v,0v,+9v NO?
B- if yes, what to isolate...in/out probably and........( )
C-LED ground?
D-why not a voltage divider? (just like VR for op amp)(150ma(ish)tops)

A- basically, yes.  if you put the ground lead from the meter on the lowest voltage, you'll see 0, +9, +18.  if it's on the middle voltage, you'll see -9, 0, and +9.  if it's on the highest voltage, you'll see -18, -9, 0.

B- isolate?  if you are using the middle voltage as your ground reference and it's tied to the chassis, you'll need to isolate the +18V input with a plastic jack and not use that supply for anything else in your signal chain.

C- dunno exactly what you mean.  depends on what's going on.

D- voltage dividers are helpful for low-current applications.  if you use a resistance voltage divider for a higher-current app like this, you'll see that mid point getting dragged all over the place as the currents move around.

i use a TI rail splitter to provide mid-point grounds.  it's a 3-lead device that can provide the kinds of currents you need, i believe.  there are several models.  the one i use is in a TO-93 package like a transistor, and it's foolproof!  you connect +18 and 0 to two of the leads, and it will provide the exact midpoint voltage (+9) on the third lead.  no filtering on the output is necessary!  it's pretty darned amazing.  the thing draws no standby current to speak of... it only draws current when the circuit is active and pulling on that middle rail, which you can easily make into ground.  i use it to provide power for my two OP-275 preamp chips (rails are 40 volts apart!) in my iMP AMP and it works like a champ!  in that unit, the midpoint voltage provided by the rail splitter is chassis ground.

[chunks717]

sir <curtsy>........exactly what i wanted to hear, and a TI rail splitter to boot! -I thank you- still, i Reeeeeally want to use the same power supply.....
possibly a small 1:1 iso xformer between the rest of the supply, and the box in question? seems solid. -perhaps i ask the impossible.......

also, ive never played with your seek/stepped effects, but the concept alone throws sparks! and they say its all been done...........thanks again,
-mario

[Andi]

Could you not (though it may, like most of my suggestions, be a bit of a fudge) use a 9v regulator, then into a MAX1044? You're wasting the power supply rather, but you could get a genuine -9v, 0v, +9v set of rails.

[chunks717]

the supply im using has plenty of reg. 9v outs, i just figured that it should be easier to get the dual 9s from the 18v outs that i added.  if i were going to use a 1044(again.....) i would just use a 9v.................