Power Supply Project questions.

[crawler486]

i got 12 v 500ma transformer.
can i use a 1 ampere 250 volts bridge rectifier?

the transformer i got has 12v - 0 -  12v secondary taps.
can i get 2 isolated outputs out of these?

this is what i'm building
http://www.generalguitargadgets.com/index.php?option=content&task=view&id=78&Itemid=107

Many Thanks.

[SnooP_Wiggles]

the bridge rectifier should be fine. i'm not an expert but you should be able to get two isolated outputs from both taps.

[crawler486]

Thanks snoop.


I'd like to hear other opinion on my second question from others.
Anyone?

[Paul Perry (Frostwave)]

I don't know what you mean by "two isolated supplies".
If you mean a + and a - supply with a common ground,   yes, you can do that.
If you mean two + supplies with a common earth, yes.
If you mean "two supplies with nothing in common", then no.
What are you wanting to do wiht the supply?

[crawler486]

I don't know what you mean by "two isolated supplies".
If you mean a + and a - supply with a common ground,   yes, you can do that.
If you mean two + supplies with a common earth, yes.
If you mean "two supplies with nothing in common", then no.
What are you wanting to do wiht the supply?

I'm wanting to build a ps which will power 8 effects.
I'm thinking if I can get 2 outputs from a single transformer, then I only need to buy 4 of them to make 8.
From what I read in past posts, you need to cancel out noise
by giving each fx its own power source to avoid ground loop.
As what you said, since the two 12v would be sharing a common ground (0 center tap), then it would not yield an "isolated" output.

[Torchy]

crp

[RDV]

If you build a regulated supply from that transformer, then it will power a pile of pedals. I only used a 12vct 300ma tranny and I get no sag at all powering up to 6 pedals. You'll only need the two outside wires of the tranny(ignoring the center tap, that is unless you want a 6volt supply). I may not be understanding which transformer you have exactly though.

RDV

[crawler486]

From what I read in past posts, you need to cancel out noise by giving each fx its own power source to avoid ground loop.

In *most* fx pedals, signal ground is also ps ground. Even if you have isolated ps units, as soon as you plug them in to more than one fx the ps grounds are linked together thru the signal shielding. In my psu only the first output has pos and gnd, the rest only have pos. The gnd returns are via the signal gnd to the first ps output.

Do a search - Ricky (RDV) went through a lot of this recently  :wink:

hmmm.. now I'm confused whether I'd go in the direction of 8 isolated ps output or just using a single ps and just try your suggestion of lifting
out all other ps ground connections except in the first fx.

I'd love to hear a word from RDV about this... i hope he's reading.
I'd like to know the dis/advantages.

Thanks, Torchy. You brought up a good point.

[RDV]

With good filtering, you won't need to isolate. With a 12v tranny you'll only get one 9volt output anyway. If you want 8 isolated 9v outputs then you'll need to build the "Spyder" from GEOFEX.
http://www.geofex.com/Article_Folders/Spyder/spyder.htm

RDV

[RDV]

Another great source of info.
http://www.geofex.com/Article_Folders/Power-supplies/powersup.htm

RDV

[RDV]

Check these threads:
http://www.diystompboxes.com/sboxforum/viewtopic.php?t=24506&highlight=power+supply+rdv

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=25899&highlight=power+supply+rdv

RDV

[Torchy]

crp

[David]

With good filtering, you won't need to isolate. With a 12v tranny you'll only get one 9volt output anyway. If you want 8 isolated 9v outputs then you'll need to build the "Spyder" from GEOFEX.
http://www.geofex.com/Article_Folders/Spyder/spyder.htm

RDV

I'll second this.  I built a 9V 1A power supply in September.  It has four outputs now, but I plan to make it expandable.  I've got it set up so the outputs are paralleled.  I'm having no noise problems whatsoever.

[toneman]

very cute 723reg, Torchy!
Tone

[crawler486]

With good filtering, you won't need to isolate. With a 12v tranny you'll only get one 9volt output anyway. If you want 8 isolated 9v outputs then you'll need to build the "Spyder" from GEOFEX.
http://www.geofex.com/Article_Folders/Spyder/spyder.htm

RDV

I'll second this.  I built a 9V 1A power supply in September.  It has four outputs now, but I plan to make it expandable.  I've got it set up so the outputs are paralleled.  I'm having no noise problems whatsoever.

If this is the case then what good can one achieve with multiple isolated outputs like the Spyder?

[niftydog]

you get an absolute guarantee that your power supply won't be involved in any ground loop hum situations.

With a non-isolated supply, there is a chance that a ground loop from one effect to another, via the power supply ground will cause a hum.

With an isolated supply, the power supply ground for each effect is totally separate from each of the others. Therefore, the ground loops can ONLY be present in other devices.

[crawler486]

which leads me back to this post from torchy....

In *most* fx pedals, signal ground is also ps ground. Even if you have isolated ps units, as soon as you plug them in to more than one fx the ps grounds are linked together thru the signal shielding. In my psu only the first output has pos and gnd, the rest only have pos. The gnd returns are via the signal gnd to the first ps output.

[Torchy]

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[niftydog]

but the whole idea of an isolated power supply is NOT to connect the grounds together in the power supply!

in your diagram, remove the horizontal line connecting all the power supplys together and you have a truely isolated supply. Each tap of the transfomer is referenced to ground only via the effects input/output jacks.

In my custom power supply, all the taps are completely floating until you plug one of the taps into an effect. Even then, the effects only ground path is via the amplifier that it's plugged into. My guitar and every other effect is in the same boat, it's only reference is the amplifier.

one ground reference point = no ground loops.

[Torchy]

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