Tapping power from another unit...hum?

[jimosity]

I have a pedal that is running on 12vdc and it works just fine, but I need to power another circuit along with it and tap power off of the one that's working fine.   The problem that I'm running into is that there is a hum on the secondary circuit that is power related.
I tried a 78L05 (that's all I had on hand) and the secondary unit powers up and works without hum, but 5 volts isn't enough.
If I get a 78L09 or a LM7809, that tells me that it'll all be good - right?

Is there anything else I can use to reduce the hum aside from a second power supply?

[David]

Yup.  Did you hook two big capacitors (like 1000uF) before and after the 7809, following the datasheet?  That's the first thing.  The second thing you can do is put a 100 ohm resistor right after positive voltage enters your secondary unit.  Then, strap the + lead of a big (at least 100 uF) electrolytic capacitor and the other lead to ground.  Connect the + of your secondary effect to this point.  The resistor-capacitor combo is a filter for 60Hz hum and other crap.  I can tell you from personal experience that it works.

[jimosity]

I haven't gotten the LM7809 or 78L09 yet to test it out, but I did have a 78L05 and that eliminated the hum, but didn't provide enough voltage.
I was trying to see if there were another way around it besides the 7809 since I didn't have those in stock, but it looks like I found some locally, so I'll test it out tonight.

[merlinb]

The standard alternative is a zener-follower stabilizer, which requires only a resistor, zener and transistor. (Maybe a couple of caps too).
e.g.:

Don't add large capacitors after a 78xx regulator IC; they are not necessary, and only retard transient regulation. 10uF after the regulator IC is fine.