12v to 9v power

[dubiousss]

ok so i got this 12v 500mA wall wart and a 78l09 and im getting 9v out with a 10u cap to ground, but it just gives major buzz, ive tried putting all kind of caps on it
its for 5 circuits in 1 box. perhaps i should find out how to measure current draw...

[MarcoMike]

which circuits? if they're not digital I guess even 100mA would be enough... can u measure the voltage before the 7809 when operating? It could go lower than what the 7809 likes...

[Ripthorn]

Yeah, my guess is the current load there.  Also, what do you mean by all kinds of caps?  In one of my power supplies I put in something like 3300 uF worth of filtering.

[.Mike]

ok so i got this 12v 500mA wall wart and a 78l09 and im getting 9v out with a 10u cap to ground, but it just gives major buzz, ive tried putting all kind of caps on it
its for 5 circuits in 1 box. perhaps i should find out how to measure current draw...

I don't know if current draw is the problem, but the 78L09 is only rated up to 100mA. The LM7809 is rated up to 1A.

To measure current draw, disconnect one of the power leads from your multi-effect. I don't think it matters which one, but I do it using the + side. Using your multimeter set to measure DC current, make the connection you just disconnected with your multimeter so that power flows through your meter to your circuit. It will tell you how much current is passing through the multimeter, hence the current your effect is using.



Mike

[dubiousss]

so it all works well with a battery, if only for an hour
while measureing amps im so confused, at settign 10 it reads .15
at 200m it reads 1.5
and at 20m it reads .15
from the one example i found googleing this means im only drawing 1.5mA ?
that doesnt seem right, more like 1.5 amps or 150mA?

and i am useing lm7809
also when i connected a 2000u 35v cap it made the voltage go to 13v!?

the circuits are 3 x rebotes 1 x tremulus 1 x easyvibe and 1 x small clone and 3x tl072 modulators 11 x led's

1. if multimeter is at 200m and i read 1.5 whats the amp draw?
2. if its above 1A do i need to use 2 lm7809's somehow?, i guess i could just split the circuits up to 2 lm7898's
3. whats up with the cap raising the voltage?

[dubiousss]

well i found another power supply that works fine now the 'davred pu 25'
but would still like to know how to read the meter

[Ripthorn]

My guess is that current draw was a problem, since you had those juice-sucking effects and LED's.  Telling you how to read your meter is a  little tough, but I usually trust the higher setting since there is less risk of overloading the meter. My guess is that it was actually drawing 150mA, which will create problems with a 78l09.  Glad you got a working supply though.