The voltage regulator blues

[Lobsang]

Hi evryone!
I apologize for being so anal about this, since all my last posts seem to raise this same topic, but...
Im experimenting with a multiple output power supply, intended to drive many stompboxes. On my first tests the output voltage was a tad too big, so big I fried a pedal indeed. Ive been told to use a regulator like the LM317 to hold the power down. So I did my duty and searched all I could about it. I found at GEO that the 317 puts out 1A max "if properly heatsinked", that is. The problem is my transformer puts out 5A! I can see the 317 going in a puff of smoke. The voltage I get after the rectifier section is 17v. The high amperage is intended to allow many pedals, and this works fine already. BTW, even though the pedals draw a few mA, driving two boxes with a 9v/500mA proved impossible to me, I hooked them in parallel from the wall wart and it didnt work. What gives? Supposedly I could feed 5 units or so if I follow the numbers...
So the question is, what can I use to tame the voltage with such a big amperage? (a series resistor!?) Or should I build one 317 regulator for each pedal output? Any help will be much appreciated, thanx in advance.

[Joep]

Hi Lobsang,

Your transformer doesn't put out 5A, is can deliver 5A if you need it!!

Keep in mind that a transformer puts out a certain AC voltage for example 12v this is fixed (sort off..) the amount of current (Amperes) it delivers depends on the load (resistance) you put on the transformer. This is Ohm's law:

current (amperes) = voltage / resistance (ohm)

If you rectify the AC voltage from the transformer you will get 12Vac x 1,4 = 16,8V DC. The voltage drop in the bridge rectifier will lower the voltage by 1,4V (2 x 0,7V drop)

You will definately need the LM317. If you understand Ohm's law you know why... The LM317 is able to deliver 1A maximum, this will feed at least 20 pedals.

I can't think of any pedal that draws more than 100mA (except for the big Line6 pedals maybe....)

Good luck,

Joep