pc power supply to symetric output (need help)

[El-even]

Hi guys, i'm in big trouble (cause i must find a solution very soon....arf)
I attempted to run my dual preamp (need +15/-15v) with the tagboard bipolar voltage CONverter but it seems that he given't enough amperes.

so  i'm thinking take a laptop power supply (19v/ -(+ /3.5A) and passing it through lm7815 and 7915 to give +15/-15v.
i don't know how to properly divide my 19v source (i'm thinking simply chain it like with a 9v daisy chain), how to manage the ground source (don't know the rule telling where to taking it) and where placing the inverter if it needed???
i post a draw to explain my idea and wish someone could correct/detail/approve it
thanks

[ξεναγος νεκροπολης]

hi mate
this is what you (and i...) have to build...

http://www.jameco.com/Jameco/Products/ProdDS/20626%20Manual%20Revision%203.pdf


i'm trying to find the smallest transformer that could do the job, cause i would like to put this thing with the rustbucket effect, in a box...

[Ciaran Haslett]

Savvas is right.  The problem is your PC PSU is already giving you DC.  So you're only options are to use an inverter circuit (which you already have and its no good) or a voltage divider which will half the supply (so no good either)

You need a centre tapped AC transformer with 18-0-18 secondary that you can then regulate with the 7815 and 7915.

[El-even]

oops, i've say voltage inverter but would mean voltage CONVERTER (this http://tagboardeffects.blogspot.fr/2014/01/bipolar-voltage-converter.html)

this is what i've used and the result is 9v to +15/-15 BUT with only 100ma (if i read correctly the datasheet http://cds.linear.com/docs/en/datasheet/1054lfh.pdf). at least i've not enough amps for my build due to this chip limitation.

ciaran; so the idea to INVERT one output from the pc psu could work....  ?
i redraw my paintwork

...something like this

the problem with the 7660 is the input voltage limitation @12v, is there an equivalent for 19v?

savvas, i've found this on the net for a rack version (but like you, i NEED a miniature power supply to fit a box...) http://www.nutsvolts.com/uploads/magazine_downloads/11/January%201998%20Thomas%20Henry%20-%20Power%20Supplies%20for%20Electronic%20Music.pdf

thanks guys


i've just found the SE555 ic with 200mA output
could this invert a +18v source to -18v?

[Ciaran Haslett]

I don't think so to be honest.  It's the current you need that will always be the problem.  The 78xx 79xx can handle up to 1 amp draw....but any miniature charge pump will only handle 10-20 milliamps at best.

This is why you tend to see transformers being used for this purpose...they can handle a much bigger current draw.

That first schematic you linked to is probably the bare minimum required to get you what you need.

Mains transformer > Rectifier > Regulators > Out

[El-even]

so the other and only "in between" alternative i see is to daisy chain TWO "1054 voltage converter" with one standard 9v psu and concider each channel like separate circuitboard (it seems a single channel can be powered sufficiantly by the 1054 converter circuit)
so
channel A supplied by one 1054
channel B   //  too

is one 9v simple adapter (i think standard give 500mA) can powering two 1054 + 3 leds and don't create interferences?

there is another issue with the circuit; when i say "a single channel can be powered sufficiantly by one 1054 converter circuit", by "almost" sufficianly i mean instead of 15v at pins, i have ~12v (due to amps or other pcb tracing... i don't know)
so,
if i use the "original" bipolar volt converter layout (with 5817 instead of my 4001) to have ~+17/-17 output, can i reasonably thinking have ~+15/-15v in the end?

[Ciaran Haslett]

So you are thinking...

9V > 1054 > 7815 >  +Out
    > 1054 > 7915 >  -Out

When you double voltage, you half the max current limit.  The 1054 will operate at 100mA at 9V, 50mA at 18V.  This set up may work as you are essentially using charge pumps in parallel effectively doubling the max current...i.e. 50mA + 50mA = 100mA.

Definitely worth a shot.

Your 9v adapter should have no problem running all this.

Please post results whatever route you go.

Cheers

[El-even]

not quite, i'm thinking

    >1054 (v+/v-) to channel A
9v                        
    >1054 (v+/v-) to channel B

plus, i noticed (even on a single converter/single channel combo) a voltage drop on the v+/v- pcb traces ending with a +/-12v (instead of the +/-15v with the 4001 combo in the bipolar converter circuit outs) at ICs pins so, i was thinking to maybe plug +/-18v (with the 5817 diodes in the converter) in the boards hoping ending with +/-~15v at pins (the values the preamps schematic need)
and this is why, i think utilise this voltage drop instead of the regulators 7815/7915
sorry guys for this f*****ing overcomplicated thread

[Ciaran Haslett]

Ah....my bad

That will work too giving 50mA a channel.

Regulators need +3 volts at their input to regulate down to their stated output so they'd need a minimum of 18V.  You will lose volts using diodes (as you've found out).  The 5817s will get you closer but maybe not close enough.  Depends on your preamps.

If all else fails, use a 12V DC PSU and those 2 1054s.

[El-even]

finally, i missed the essential question.... WHY a cascade of rc4558 need V+ and V-? is it forced to use bipolar PSU? and the final killing joke.... can i simply supplying all of them with +15v and ONLY +15v?

[Ciaran Haslett]

What preamps are you trying to power?  

[El-even]

beta lead/bass
i'm trying to post a schem




there is the correct sound version with two regulators at right and need a simple 18vac psu

[Ciaran Haslett]

The whole point of having a bipolar supply is to give more headroom to an IC.

Think of it this way....+15v and -15v is a total of 30V swing.  That allows an opamp a larger input voltage before clipping compared to a 9V power source (9V swing with rail to rail IC),  You'll see this a lot with synths where distortion is not desired.

So...
+-15 bipolar = 30V single
+-9v bipolar = 18V single

With your preamp the same thing is happening.  Trying to get as much headroom as possible.  The 4558 has a max swing of 36v to they designed it around a 30V swing for safety.

I would definitely try using a single supply...maybe 15V or 18V.  

You'd have to add a Vref (V/2).  Them match up the following... +15v = +15v, GND = Vref, -15V = 0V

That'll give you less headroom than a bipolar supply but I don't think it'll matter much in a circuit designed to distort

[El-even]

that's a f***g awesome gooooood news
but i don't clearly understand how to redraw the schem (noob), i must to run 18v anywhere the schem need +15 but for the -15 and grnd i defintivly don't understand

[Ciaran Haslett]

Those are pretty hefty filter caps.  18vAC?  Then rectification is taking place on board.  This is how they're getting the larger current supply.  A lot of the digital pedals do the same...Digitech Whammy etc.

[El-even]

so they use the original circuit and do the symetric power supply onboard...am i right?

[Ciaran Haslett]

Like this.  Wire up your PSU like on the left BUT wire the schematic like the right

[Ciaran Haslett]

...and yes.  They create a bipolar supply on the board

[El-even]

what is Vref and where i found it from the psu?

I don't understand how they have +15/-15 from 18Vac; i was thinking the circuit need double voltage transformer (36vac for +18/-18)

[Ciaran Haslett]

Vref = half supply.  That was just a label sorry.  Ignore it.  Just wire your 18V DC to the top and its Ground to the bottom.  Then wire the circuit as you see it on the right