My core module lives :) So now I am forced to work on a power solution for my MBFM. I discovered that I have a wall wart supply that has both a 12V 500ma line and a 12.5V 200ma line. I would like to use the 12V line to power the core, and the 12.5V line to power the OPL board. Is this possible? is it a bad idea? If it is doable.. Where should I start? My other option will be to make the whole transformer power supply as shown on here, but I don’t understand the mods I would need to do to get 5v to j1 on the core. My core module is a Rev 2 from smash TV.
Bobby
- too hot…, but must answer…
no no; for the OPL3 board you need a 12 V bipolar power supply.
Bipolar PSU’s provide both positive and negative voltages (compared to a shared ground of 0V) which gives you 3 pins/poles/voltages; in this case; -12V, 0V, +12V
You can make this by using a transformer which makes 2x12V (or a bit higher) out of 220V (110V out of europ).
check this schematic;
http://www.ucapps.de/mbhp/mbhp_opl3_psu.pdf
TK uses another smaller (unipolar) transformer to also get the +5V for the core.
in short i fink your psu won’t work.
cheers, marcel
check this schematic;
http://www.ucapps.de/mbhp/mbhp_opl3_psu.pdf
If you use this schematic, don’t forget to place a fuse (100mA is more than enough here) and a two-pole switch on the primary side of the transformer!
What I was wondering was if I could replace the transformer with a 12.5 V supply and run it throught the circuitry to get both +12 and -12 out of it. I have actually decided to try the other power supply Duggle suggested in this thread http://69.56.171.55/~midibox/forum/index.php?topic=3970.0 but I am terrible at making my own pcb’s and my last attempt with stripboard worked briefly and then I released the magic smoke out of one of the capacitors :( I am much better when I have a ready made PCB, but aren’t we all. Going to try making my own traces with solder on a piece of perfboard this weekend once I get some more caps, and a new Voltage reg.
Bobby
hi bobby
What I was wondering was if I could replace the transformer with a 12.5 V supply and run it throught the circuitry to get both +12 and -12 out of it.
no, because the thing about the transformer is that it actually has two transformers (2 supplies) that both have 12V; you can connect 2the 2 together (in different ways), or use em separate.
what’s done here is to connect them in series so you get a 24V Voltage between the negative side of one and the positive side of the other.
when you consider the point where you connected them ground; you get +12V on the pos.pole and -12V on the negative pole.
you can do this with the right transformers and with batteries (9V for example) but not with a line of a power supply like a wall wart (but thats more bad experience then theory)
good luck, marcel
Hi,
You can use schematic suggested by Duggle, if you have an AC wall wart. It uses half-wave rectifying and should be ok, because OPAMPs don’t need much power.
Stable bipolar voltages are important, but voltage levels don’t matter that much ie. in a private conversation TK suggested that OPAMPs might even be powered from as low as +/-5 volts.
Bye, Moebius
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Re: Power supply question (again sorry)
« Reply #2 on: 2005-06-23 at 15:32 »
Quote
check this schematic;
http://www.ucapps.de/mbhp/mbhp_opl3_psu.pdf
If you use this schematic, don’t forget to place a fuse (100mA is more than enough here) and a two-pole switch on the primary side of the transformer!
??? :-[
Do I put the fuse on the primary 12V before the rectifier??
Christoffer
Do I put the fuse on the primary 12V before the rectifier??
No, on the primary (line voltage/220VAC) side of the transformer. (and do be careful!) 
You want the switch here also, so transformer does not stay powered when not in use…
Best
Smash