where should I filter my power supply?

[Hal]

OK - so here's how it goes so far - 9VAC/1A wall wart to bridge to 100uf cap to ground, to 7809 regulator, 1000uf cap to ground, and output to 10 plug daisy chain.  

Thats the idea.  What other filtering should I put in?  I want this thing to be _quiet,_ but I dont have the cash for 10 transformers for isolated supplies for each.

[niftydog]

it's already fiiltered. But if you want more filtering, increase the size of the caps. There's nothing to stop you having a 1000µF cap on the input side of the regulator as well.

You could also utilise an RC combination on the output if you wanted to. But I think you'll find that with large enough caps you'll be fine. I have a similar set up with two 2200µF caps.

[Hal]

cool beans.  I gotta wire it up soon :-D

[David]

Hal:

Having built one of these recently, I've already gone through something similar to what you are right now.  I note the following:

Your tranny looks like it's rated for 9VAC 1A.  OK, you know that's the rating under load, right?  Now, since your tranny puts out AC and you need DC, you will need some kind of rectifier.  This is usually a diode bridge.  Problem number 1.  This is going to cost you about a volt of output from your transformer, but at least you have DC coming it off it.

Next thing is your regulator;  if I remember R.G.'s article correctly, this is going to cost you about 2 volts.

OK, bottom line is that you need to measure *CAREFULLY* the output of your tranny when it's not under load and make sure it's putting out at least 12 VAC.

One other thing:  you should add a switch and a fuse to the transformer primary input, and a LED across the rectifier output and ground.

For what it's worth, mine is quiet as a church and I use it in church.  It's only feeding 4 pedals right now, but I expect that it could feed at least 8 more.

[Hal]

yea, I know, but 9VAC rectified becomes 12.7v DC.  This should be plenty.

The transformer is going to stay in the wall wart case, so no fuse.  Wouldn't an LED across the rect. out to ground kill the LED?  I planned on haveing some sort of power indicator, but that would be at the output...I think im missing something.

[niftydog]

put a high-ish value resistor in series with the LED. Maybe 15-20k ohms

[toneman]

put the 1000ufd on the input of the reg.
put the 100ufd on the output of the reg.
better 2 filter B$ going into reg.
Will give a higher input V.....
add .1 bypass caps at in & out)noise decoupling)
78xx regs need at least 2V more that output VoltageValue.
In your case 9 + 2 = 11V...12V?input(under load) should B OK.
4 an LED....put it on the reg's output.
use a 680ohm, 1/4 W resistor in series.
This way Reg has it's own load/lite...  
staypowered
tone

[Hal]

put the 1000ufd on the input of the reg.
put the 100ufd on the output of the reg.
better 2 filter B$ going into reg.
Will give a higher input V.....
add .1 bypass caps at in & out)noise decoupling)
78xx regs need at least 2V more that output VoltageValue.
In your case 9 + 2 = 11V...12V?input(under load) should B OK.
4 an LED....put it on the reg's output.
use a 680ohm, 1/4 W resistor in series.
This way Reg has it's own load/lite...  
staypowered
tone

ahhh conflicting stuff

I _have_ 2 1000uf caps (and some bigger ones)...I _could_ filter both.  No?  Yea, looking at schematics, i also see the .1uf caps across the lines as well.  Thanks...

[niftydog]

my resistor calc was for a fairly dull glow. The idea is not to load the power supply too much, but still give you a visual indication. Either resistor will work, but I wouldn't go much lower than 680 ohms.

With the filter caps, again, you could go either way. At the low power levels we're usually dealing with, putting large caps in both before and after doesn't hurt.

Toneman has a good point about the larger cap on the input to the regulator. This will help it do it's job without freaking out too much.

You can't really go wrong either way. Just suck it and see. If there's still too much ripple, bump up the caps - still too much, add an RC filter...

[toneman]

look at the datasheet for the 78xx series.
most of the manufactures recommend a smaller cap
on the output to allow faster compensation.
100mfd is really all U need.
If U want to add more filtering,
add it to the input as this will raise the average DC input V.
Just remember,  excess voltage is dissapated as heat.
The LED draws about 20milliamps(ma).
shouldn't even phase the reg. Also drains off caps at pwrdown.
ALA your circuit pulls less than 500ma, U shouldn't need
anything else.  If U want to pull the full 1A from the reg,
Bsure your input V doesn't drop 2 low.  This will make
the reg drop out.  BTW, if the reg gets too hot, it will
shut down on its own.  After it cools off, it will work again.
Isn't technology amazing??
stayregulated
tone

[Kleber AG]

Nice info here    Thanks

So, how to measure "riple" with just the DMM?
Only setting it to AC voltages and measuring the outputs of the adaptor?
How much AC would be low enough?

BTW: Don't forget to heat sink the regulator, mine stoped working before I did that, now it's heat sinked to the enclosure  Its solved but the enclosure if powered for enough time can burn my fingers :shock:

Thanks
Kleber AG

[David]

BTW: Don't forget to heat sink the regulator, mine stoped working before I did that, now it's heat sinked to the enclosure  Its solved but the enclosure if powered for enough time can burn my fingers :shock:

Thanks for bringing that up, Kleber.

Hal:

I forgot to mention the dropping resistor for the LED.  It was getting late.  I guess I blindly assumed that would be SOP.  My practice is to use 5mm green LEDs and I use a 1K dropping resistor with them.

Also, regarding heat sinking, I got nervous about putting line voltage in a metal enclosure given the current level of my skills.  What I wound up doing was buying one of those plastic outdoor electrical boxes from either Home Depot or Lowe's.  I also bought a metal cover for it.  I mounted the switch and LED to the cover, and also mounted the regulator to it so that the cover would act as a heat sink.  So far, I've had no problems with it, but I'd be surprised if the 4 pedals I have hooked to it pull much over 150 mA.  

Don't forget to insulate your connection points!

[Kleber AG]

I have 12 pedals pluged at this (1amp 9 and 18Vdc) adaptor, and I've already giged a lot with this setup, and it's ever working perfect (well it's hot, isn't it a good signal )!

Thanks to the guys here, who helped me before! Thanks Niftydog and everyone!

Kleber AG

[Hal]

BTW: Don't forget to heat sink the regulator, mine stoped working before I did that, now it's heat sinked to the enclosure  Its solved but the enclosure if powered for enough time can burn my fingers :shock:

Thanks for bringing that up, Kleber.

Hal:

I forgot to mention the dropping resistor for the LED.  It was getting late.  I guess I blindly assumed that would be SOP.  My practice is to use 5mm green LEDs and I use a 1K dropping resistor with them.

Also, regarding heat sinking, I got nervous about putting line voltage in a metal enclosure given the current level of my skills.  What I wound up doing was buying one of those plastic outdoor electrical boxes from either Home Depot or Lowe's.  I also bought a metal cover for it.  I mounted the switch and LED to the cover, and also mounted the regulator to it so that the cover would act as a heat sink.  So far, I've had no problems with it, but I'd be surprised if the 4 pedals I have hooked to it pull much over 150 mA.  

Don't forget to insulate your connection points!

I'm also scared of lines, so i bought the transformer as a wall wart...it was $2.  Can't beat that.  

I think the origional question, though wordered poorly, was wether to put the large filter cap before or after the regulator, and I think this was answered.  I'll go for before, and small cap after.  It it hums, then I'll worry about RC filters.  I think the LED is going after the regulator, with a 470 ohm resistor.  I also like the idea of giving it a load.  I also like the idea to use green, I was gunna use red :-D

Thanks everyone :-D

[toneman]

4 an LED, 470ohm with 9VDC is tooooo small :shock:
Use *at least* 680ohm.
Start with 1K and C if it's brite enough 4 U.
Tone

[Hal]

with a voltage drop of 2v, 470 ohms will give me around 15ma of current.  Its not a matter of it being bright, i wanted to put some load on it.