Question about Amperage

[acehobojoe]

I'm trying to build a power supply using a transformer, some rectifiers and regulators.
The regulators suggested are 100mA. Does that mean that they won't power something that requires 300mA?
I'm using this transformer : http://www.tedweber.com/wpdlxfmr-1

The Spyder power supply :
http://guiguijones.free.fr/Electronique%20&%20Bouine/electronique/Schema%20Amplis%20Effets%20etc/Alim%20Cablages%20Di%20etc/Schema%20Alim/Alim%20spyder.htm

and I'm going to use 78L09 regulators.
I may need to look for 300mA regulators.

[R.G.]

Looks like I'm going to have to ask the owner of that web site to take down that content.

First - did you go and read the stuff at the original site - geofex.com? Including the warnings that are there in the latest version of that article? The warnings were not put there on a whim. They're real.

And now down to your questions. The regulators were originally specified as 78L09 because the original transformer windings could not support much more than 100ma. They served a useful purpose in limiting the DC output so that the modified transformer did not get overloaded. And yes, those regulators will current limit at 100ma and that means they will not power something that needs 300ma.

Then there are the issues with the transformer. Have you read "power supplies basics" at (the real) geofex.com?  It turns out that the quirks of full wave bridge rectification make the heating current pulled from the transformer bigger than the DC pulled out of the filter caps, by a factor of 1.6 to 1.8. If each winding of the Weber trans can do 300ma, then they're only good for 300/1.8 = 167ma DC out of the filter cap, and that's starting to look like a 100ma regulator.   

Actually, if you use the LM317L regulators, they will do about 150ma, so that's about perfect.

[acehobojoe]

ok, thanks! I actually wasn't able to access it on your site for some reason. The page here : http://www.geofex.com/article_folders/spyder/spyder.htm
didn't have any of the content below it 

But thanks! I'll use the LM317L regulator and probably try to add a switch to double the current from both in case I need 300mA.
or I could use one of these : http://www.sweetwater.com/store/detail/PPAP

I was already going to add a voltage doubler switch. The voltage doubler would be a switch that takes the 9v and ground from one output and ties it to the opposite polarity of another 9v jack. This would make it 18v.

I'll read your power supplies basics now, and i'll be careful with the AC power supply!

[Transmogrifox]

ok, thanks! I actually wasn't able to access it on your site for some reason. The page here : http://www.geofex.com/article_folders/spyder/spyder.htm
didn't have any of the content below it 

Yes, read the warnings.  RG removed the content on purpose.  The companies who commercially sell these things spend thousands of dollars on safety testing. 

For example, overloading a transformer is dangerous because if the heat exceeds the insulation system rating you can end up with a short between primary and secondary side. This connects you to the wall outlet as if there was nothing between you and the hot wire.  Now your guitar cable "ground" is the hot lead from the wall outlet.  That's the kind of thing RG is warning about.

The lesson I took from RG's disclaimer on that page is the spyder is simple enough that if you really know what you're doing (safety wise) then you know enough to design your own spyder without having to download a schematic from geofex.  The converse is true -- if you don't know enough to design it yourself then it is a scary thing to enable you to build it.  It is apparent from the retracted information that RG didn't want to become a part of somebody's misadventure with line level power.

If you really want to DIY spyder, then start with something like a 36V, 1A AC wall wart with a UL listing and then step that down to several 9V channels using transformers with the same turns ratio:
36/120 = 0.3
120*.3*.3 = 9 VAC

9 VAC RMS ==> 9/.707 = 12.7V peak, so getting a 12VDC output that you can cleanly regulate to 9V from this is possible.

In either case, if you start with a safety rated converter you can plug that into your spyder box with a normal barrel jack and you will be protected from the list of things that can go wrong on that end, resulting in potentially fatal electric shock and/or fire.  That way you leave the safety isolation part up to a company who has a lot of liability, money and backing of UL approval. 

This is another warning not to buy cheap knock-off stuff.  These outfits don't design/test to any safety standards, but they print safety ratings on their equipment with a major testing lab approval (UL) but it is an illegal use of those markings -- and probably does not pass tests to any reasonable safety standard.  They get away with it because they are based in a country that does not enforce these generally accepted international laws.

[acehobojoe]

Thank you! I am in no rush whatsoever. I'm taking my time to learn all of the procedures. I want to make it safely and not kill anyone!

Is there anything majorly important not mentioned in GEO safety?

I want to show you what I'm trying to design here later. I want to build a pedal board with a supply in it.

[Brisance]

Also, pleas use the term "current", "amperage" makes Tesla roll around in his grave

[antonis]

I'll use the LM317L regulator and probably try to add a switch to double the current from both in case I need 300mA.

I'm not sure about what you mean (but I'm not scary as long as this concerns to the secondary part..)

Maybe you'll have to add a small resistor (a couple of Ohms or so - depending on the tolerable voltage drop) in series with each regulator out for "balancing" the load..

[GibsonGM]

When getting started, I found that making a traditional stand-alone power supply, and powering up my pedals with it, to be a great first step in this area, for learning safety etc, and also for keeping things reliable/fixable on the fly.  I've never encountered the kind of hum that seems to drive many people crazy...could it be attention to shielding, using shielded wire and good layout practices?   Can't say, other than I personally wouldn't want to build that level of clean power for a pedal board unless it was purely for studio use.

Live, there are so many other sources of *hiss* that MY rig is inconsequential (thinking of how much noise the PA alone generates).  As long as my rig has about the same noise floor with my stuff plugged in or not, I'm happy, YMMV...keeping it simple always worked for me....

[acehobojoe]

Thanks guys, all I mean by a current doubler, is that i'll take what this little adapter does:
http://www.sweetwater.com/store/detail/PPAP
and use a dpdt to combine the two outputs in parallel, making one output from 2. I could also apply the same principle to create double the voltage.

So there would be 8 9v outputs, which can be combined to make 4 double current or double voltage outputs.

I would need 4 dp3t (I guess)  switches for that..

YMMV...keeping it simple always worked for me....

I'll start with something simple. I'm probably going to try to put it in a bigger hammond rack enclosure. I should be able to ground that chasis to the ground of the 3 prong plug right? That would help a little with shielding.

[Jdansti]

The "current doubler" cable may work with the Voodoo Labs PS because of the design of the PS. I  believe I read that you have to change a DIP switch setting to use this cable. Be careful, though, about combining the outputs of two DIY PSs. I'm sure that R.G. and others can shed more light on this.

[acehobojoe]

I didn't know that. I'll be testing it to see.

[karbomusic]

I didn't know that. I'll be testing it to see.

Pick up one of these first...

[acehobojoe]

I didn't know that. I'll be testing it to see.

Pick up one of these first...

I have 2 of them, want to borrow one?

[acehobojoe]

Also, the regulator mentioned above is an adjustable regulator, but it doesn't offer 150mA, it is only at 100mA.
What would happen if I used this regulator that has .5A output? http://www.diystompboxes.com/smfforum/index.php?topic=111553.msg1027068#msg1027068
Would the current just go to its max, or would it cause some sort of problem?

EDIT: Actually, it should do just fine. it is rated for a MAX of 500mA, so with the transformer's rectified output, it should be producing the 150 or so mA as stated above. But should the current be regulated too?

[R.G.]

Is there anything majorly important not mentioned in GEO safety?

There's an enormous amount of majorly important things not mentioned in GEO safety.  That's one reason I took the original article down. I kept getting notes and postings indicating that people who don't know much about power supplies in general and AC mains power in specific would wade into a the very deep pool waiting there.

There are too many majorly important things about power safety to explain on the internet. It requires some in-person training from someone who really knows what they're talking about, is not rushed, and has all the necessary time and materials to oversee the student's first attempts and correct potentially fatal mistakes.

Don't go doing primary/mains power wiring until you've had similar training. Please.

[acehobojoe]

I'll make sure to ask someone to help me who has experience before I attempt it. 

[Joe]

I agree with R.G. AC is super dangerous, and when working with it you have to ensure you are protected at all times.

When I was younger I worked for an amplifier manufacturer. One of my best friends got electrocuted by the trash compactor after a bad repair, and to this day I'm thankful he's alive. I saw another person electrocuted by a @#$%ing bass amp that had the AC wires pinched between the lid/chassis. He was okay, only because someone noticed and could shut the power off.

Sometimes schematics are wrong also. I learned this lesson when I burned up a Variac after following a schematic in a power supply book. I also didn't know about isolation transformers, which wasn't shown on the schematic.

You can't be too careful...
/rant

[acehobojoe]

The hard part is finding someone around who is pretty experienced with it. I took an amp class with Bruce Egnater, that blew my mind, but around where I live there aren't that many electronic designers.
There is one guy who I know builds amps somewhere around here, I'll ask him.

[GibsonGM]

Please do, and the 'have him checked out', too!  You need to know HE knows what's going on, etc etc.   Way too many ways to get killed, which would ruin our day!!

D@mn compactors...I unplugged a jammed one when I was 17...fished around in the guts, pulling out trash....woke up across the room - had touched a charged cap (a BIG one).   Didn't remember the actual flash...still don't.

My belief is that "first power supplies" or "first time with mains" should REALLY be done using a very simple circuit.  Cord/plug, wire nuts, fuse, trafo (120v : 12V, perhaps), bridge, cap and bleeder.  Jumpers to a meter.   That is all.   Something from a Radio Shack book, which walks you thru it....seriously.   One side of that sucker is nasty.  You only get one chance to do it right, often times.

[acehobojoe]

Does having a fuse help at all with the actual safety of it? Wouldn't it blow before allowing a HUGE current to come across?