GEO power supply question.

[BDuguay]

Many years ago I built the power supply with the LM317 voltage regulator from R.G.'s website and have used it to power my pedalboard ever since. Recently, I decided to change it for another application. I changed the wiring on the primary side of the transformer from parallel to series so that I can use one of the secondaries for 9VAC and the other for 9VDC. On the secondary that I'm using for DC puposes, after the bridge rectifier, I'm getting close to 10.75 VDC (before, when I wired the primary side in parallel, I was getting over 20VDC here) and it looks as though this might not be enough to allow the LM317 to function as it should. I'm still able to get 9.5 VDC after filtering and regulation but I notiiced as soon as I hooked it up to, for example, a Boss pedal, the voltage dropped to 7.5VDC when I measured it. In comparison, I tried using a battery that read 8.6VDC to power up the same pedal and it still read 8.6VDC when it was connected.
Can someone explain this to me?
Thanks,
B.

[R.G.]

Si.

The LM317 needs about 2V across it to function properly, so a drop from 9.5V in to 7.5V out sounds entirely reasonable.

Look at the LM2931 for an adjustable regulator that will regulate with a in/out differential as low as 0.2V. There are other "low drop out" regulators, that's just the first one I found.
http://www.national.com/ds/LM/LM2931.pdf

[BDuguay]

I figured that's what the problem was. What if I used a 7809 regulator?
Thanks a ton R.G.
Keep working on your Spanish, it's really coming along.
Bon chance!

[niftydog]

What if I used a 7809 regulator?

The voltage drop required will be much the same as for the 317. Have a hunt around (as R.G. suggested) for a low-drop-out regulator.

[BDuguay]

I went online to check and I think my local shop has the regulators R.G. mentioned. I'll lick this thing yet and, at the very least, learn a whole bunch while I'm doing it!
Thanks again you two.
B.