12v AC to DC question

[GeToChKn]

I took apart an old practice amp that I had for parts that I've been salvaging from it, pots, etc.  The transformer in the unit puts out 12VAC.  How could I convert this to DC to use to power my valvecaster-soon-to-be-twincaster.

[tempus]

You need to build a rectifier circuit like this:

http://en.wikipedia.org/wiki/Rectifier
http://www.play-hookey.com/ac_theory/ps_rectifiers.html

If you google Power Supply schematics you should get some stuff too.

[cortey]

Well its fairly simple

To clarify the parts:
IC1 = LM7812
C1-2 = 470uF /35V rated
D1-4 = 1N4001 (you can actually use any rectifier diodes in that series, if your unsure check the datasheets)

(*you may even want to replace the individual diodes with a bridge rectifier, its your preference)

[GeToChKn]

Ok, I think there was 4 of those diodes that I desoldered off the board too, probably why they were there.  I have a 7812 already from another circuit, and I'm sure I can find the caps around.  Thanks for the circuit, that helped so much.

[R.G.]

Even better, go read the "power supplies basics" article at geofex.com.

[cortey]

Ok, I think there was 4 of those diodes that I desoldered off the board too, probably why they were there.  I have a 7812 already from another circuit, and I'm sure I can find the caps around.  Thanks for the circuit, that helped so much.

the 2 caps are used as filters of voltage ripple so the larger the value the less ripple you have. but caution to not use too high of a capacitance value. anything from 100uF to 2200uF cap's should be ok. but it really depends on what your powering.. C2 can be smaller than C1 since the 7812 removes a huge part of the ac ripple.

[GeToChKn]

There was two nice 2200uf 35v or 50v caps that I pulled off the practice amp too.  Guess I know what they were for now.  lol.  I plan on making a little pre box.  a Twincaster powered from 12v, maybe a JFET or transistor boost in front of it, some sort of fuzz effect, a bunch of weird little things and effects all in one box just for fun.  I guess I need a 7809 regulator as well to bring the 12v down to 9v for most of the boost circuits and such.

[cortey]

yah sounds like a great concept and if you have anymore questions
about building power supplies i suggest geofex.com

Even better, go read the "power supplies basics" article at geofex.com.

[GeToChKn]

Ok, I'm willing to read the geofex.com site and have looked all over but I can't find the power supply basics sections.  lol.  The circuit does work anyways with the 4 salvaged diodes and caps from the board.  I split the power from the diode output and bring it to a 7812 and a 7809 so I can 12v and 9v power.  I'm still interested in reading more, so if someone can give me a link to the power supply section on geofex it would be appreciated because right now I can't find it for anything.

[mills]

I'm gonna jump in here fore a quick related question...

If I'm plugging a 15Vac wall wart into a pedal, I don't need a transformer since the voltage has already been stepped down?  I just deal with the 15V DC to get my +/- and ground?  THis sounds right to me, but I thought I'd see if there was any insight on here?

And thanks for the tip on the geofex reading!

[aziltz]

I'm gonna jump in here fore a quick related question...

If I'm plugging a 15Vac wall wart into a pedal, I don't need a transformer since the voltage has already been stepped down?  I just deal with the 15V DC to get my +/- and ground?  THis sounds right to me, but I thought I'd see if there was any insight on here?

And thanks for the tip on the geofex reading!

if it says 15Vac, its outputting AC and not 15VDC so you will need to rectify it.

[mills]

Yeah, I'd figured that part, but the transformer portion should be taken care of by the wall wart? 

[aziltz]

oh yes, you are correct there.

[mills]

Thanks!

[R.G.]

Ok, I'm willing to read the geofex.com site and have looked all over but I can't find the power supply basics sections.  lol.  ... if someone can give me a link to the power supply section on geofex it would be appreciated because right now I can't find it for anything.

Well, it's on the index/home page down at 11/15/01 as "Power Supplies Basics", and the link is http://geofex.com/Article_Folders/Power-supplies/powersup.htm; typing "geofex.com power supplies basics" into google returns this as the first result.

[GeToChKn]

Thanks.  As I said, taking one of the white and black lines from the power transformer, running it through the diodes and caps and the 7812 and 7809, I get a nice stable 12v and 9v.  How can I figure out the mA that the transformer is putting out?  I want the 12v to power a twincaster type circuit, so I'd like to make sure there is around 500 mA or so for that side of it.  The 9v is to only power a booster or so circuit, so that shouldn't take up much.

Also, the transformer has 3 leads coming out.  2 white and 1 black.  I used 1 white and 1 black to go into the diode circuit.  Each white one puts out around 14v or so AC.  Should I use 1 white wire into the diodes and to say the 7812 and the other one into another set of diodes for the 7809 for the 9v?  Will each white line have a certain amount of mA current coming from it or does it matter if use only 1 over both?  Sorry for the questions, but working with power is a new avenue for me.  I know I could have used a wallwart and make it easier but I like reusing parts I have laying around.

[petemoore]

  Unplug the unit, get familiar with what goes on inside before it gets very familiar with you, opening the case and getting zapped is not a fun way to start a project.
  Thanks.  As I said, taking one of the white and black lines from the power transformer, running it through the diodes and caps and the 7812 and 7809, I get a nice stable 12v and 9v.  How can I figure out the mA that the transformer is putting out?  I want the 12v to power a twincaster type circuit, so I'd like to make sure there is around 500 mA or so for that side of it.  The 9v is to only power a booster or so circuit, so that shouldn't take up much.
  Also, the transformer has 3 leads coming out.
  By clipping these with some insulation left on the old board, super-close inspections may not be needed to determine which one went where, which pretty much can say what'll go where next time [or mark them].
  2 white and 1 black.  I used 1 white and 1 black to go into the diode circuit.  Each white one puts out around 14v or so AC.
  Sounds like you've found a coil-tap [this tap probably has 2 ends like all the taps do, though center tap coils exist].
   Should I use 1 white wire into the diodes and to say the 7812 and the other one into another set of diodes for the 7809 for the 9v?
  Ac has no polarity, if you've found 14 volt of it [not a bad number to start with] and put that through a diode bridge, filter capacitence, 7809, more filtering, you should get a very nice DC9v.
  IIRC I started with ~11.4 and, DC'd, the regulators ran cool, depends on the current load.
  Will each white line have a certain amount of mA current coming from it or does it matter if use only 1 over both?  Sorry for the questions, but working with power is a new avenue for me.  I know I could have used a wallwart and make it easier but I like reusing parts I have
  Can't follow the last part here, but it took me a buncha times looking at the diode bridge before relating that to capacitor polarity, before I got the idea of controlling the 120vac signal direction.
  JD has some layouts/diagrams that may help the first one follow the rules:
  http://www.generalguitargadgets.com/index.php?option=com_content&task=category&sectionid=6&id=24&Itemid=99999999