regulated power supply voltage drop?

[foxfire]

should my regulated power supply be dropping roughly 1v when under load? from what i've read something like a drop of 0.1v is acceptable. i'm using a random 12vdc wall wart in to a filtered regulator much like the one found at GEO and GGG. unloaded i get a reading of 9.42v. i tested it with 2 pedals and got a reading down in the upper 8v's. so i tried another lm317 and it was a bit better but, it still showed a drop. with it being such a simple circuit i don't know what i could have done wrong?
Rylan   

[earthtonesaudio]

I think the 317 has a 1.2V dropout, but I'm not completely sure...
Also worst case scenario it needs to see a minimum load of 5mA, so if your load is less than that, it might not work right.

Check the unloaded output of the wall wart.  If it's less than 12V, then that sounds about right.

[foxfire]

unloaded, the wall wart is putting out 24v.

[R.G.]

should my regulated power supply be dropping roughly 1v when under load? from what i've read something like a drop of 0.1v is acceptable. i'm using a random 12vdc wall wart in to a filtered regulator much like the one found at GEO and GGG. unloaded i get a reading of 9.42v. i tested it with 2 pedals and got a reading down in the upper 8v's. so i tried another lm317 and it was a bit better but, it still showed a drop. with it being such a simple circuit i don't know what i could have done wrong?
should my regulated power supply be dropping roughly 1v when under load? from what i've read something like a drop of 0.1v is acceptable. i'm using a random 12vdc wall wart in to a filtered regulator much like the one found at GEO and GGG. unloaded i get a reading of 9.42v. i tested it with 2 pedals and got a reading down in the upper 8v's. so i tried another lm317 and it was a bit better but, it still showed a drop. with it being such a simple circuit i don't know what i could have done wrong?

Your wall wart is probably sagging a lot. As earthtones said, the 317 simply cannot produce an input/output voltage difference less than about 1.2V. The 317L (TO-92 version) can't do better than about 2V.

So if you are trying to produce 9.42V out (in your circuit) then the absolute minimum you can do this with is 10.6V with the TO-220 package 317, and 11.42V for the 317L. The trick to finding out what is happening is to measure the DC voltage at the regulator INPUT as well as output as you add load. I'm guessing that it does 9.42 with no pedals connected, maybe 9.4 with one pedal connected, then sags to the 8's when the second pedal is connected. I think you'll find the DC input is sagging down to the middle 10V range when both pedals are connected.

Wall warts always say both voltage and current. If this one is 24V unloaded and is supposed to do 12V at some specified current, that makes me think it's a very high-sag unit and may simply not have enough current rating to supply your pedals.

[foxfire]

it is rated at 12vdc, 1A. it was from an old answering machine i got at a yard sale not that it really matters. i'll do what you suggested R.G. and look for another supply.

[foxfire]

so i checked the voltage going into the regulator under load and i got  reading of 22.6v and after the regulator i got 8.4v. So it isn't the wall wart but, it was the 100Ω resistor i had in series after the regulator. i was wondering why no one else put them in their power supplies.
rylan