AC power supply

[morthek]

hey guys! i bought a AC-DC Adaptor (those with 7 outputs and various voltages) because i hate to spend all my money with batteries :cry:  . so i plugged it in my DynaComp( hand made) and there is a lot of noise :oops: . does anyone know how i could eliminate all that noise? thanks

[niftydog]

i bought a AC-DC Adaptor

linear or switch mode?  ie; heavy & big or light & small?

What sort of noise?  Hash?  Hum?  Dogs barking?  Goats bleeting?

[morthek]

switch mode, light and small. ... weel the sound( i dont what those that you said mean so...) is a constant "tuuuuuuuuuuuuuuuuuuuuuuuu" that never ends

[brett]

If it's a low hum, it's a lack of regulation.  A large cap (1000uF) across the supply will quieten it a fair bit.  For very quiet, you'll need to regulate the supply (with a 7809 or similar).

There was a recent post on a similar topic, too.

cheers

[niftydog]

is a constant "tuuuuuuuuuuuuuuuuuuuuuuuu" that never ends

hmm, I'd say that's a hum.  Is it high pitched or low pitched?

you should try what brett said.  Basically, your DC voltage has some AC voltage on it.  A good size cap should take care of most of it...

But it's not lack of regulation, it's lack of filtering.  Switch modes are by definition regulated supplies.

Adding a 7809 may improve the ripple rejection though.  It's worth a try if adding the cap doesn't help.  But, a 7809 needs at least 11 volts input to work correctly.  If this is a regulated 9V supply, a 7809 will just drop 2 volts and nothing will have improved.

[morthek]

would you recomend the "Ultra Clean PS" found in www.generalguitargadgets.com ??

[niftydog]

Ultra-clean looks fine to me... even a little OTT!  I use something similar, except that I use a fixed voltage regulator which means no messing with voltage references and all that.  (actually, I have eleven circuits like this connected to a multi-tap transformer)

The only difference is that I used bigger filter caps!  Bigger caps, less ripple.

Just bear in mind that this is pretty much what you get in a decent 9V regulated wall wart supply.

[morthek]

i can power more than one 9v stompboxes with only one 9v transformer taht have may outputs?

[javacody]

I had a similar problem and someone (brett I think) recommended using a 100ohm resistor in series with the power . It worked like a charm.

[niftydog]

power more than one 9v stompboxes with only one 9v transformer

Yes... to a degree.  It depends on how much current the supply can output, and how well regulated it is, and how much current your pedals draw.

You can run into other problems though, such as hum.  And the pedals may require different polarity wiring.

[Xlrator]

Try the 4 output power supply from GeneralGuitarGadgets.com. I made one with 1 18v regulator, 2 9v regulators and a spare winding for whatever I need later on. That way I can power my PT-80 and a BUNCH of other stuff. This is an excellent power supply with no noise and easy to find low part count.

[morthek]

hey, i was think, i have a 220 to 12v transformer here, but it is not very clean either, so i could build a cleaner , a box wich the input was the 12v and the output 3x9v . inside this box there would be a large cap , some diodes and one( or three i dont know) 78L09. I think this box woyuld be perfect to me, but there is a problem , i dont know how to put together. Can anyone help me with the schem?? thanks  

[niftydog]

You probably won't acheive much with three separate regulators.  Infact, you'll just end up wasting power accross the 7809 and you may limit the current available.  Just build one stonking supply and "daisy chain" the output.

There'll be heaps of schematics for simple 9V regulated supplies.  In fact, there's usually typical examples at the bottom of the data sheets.  Google "7809" and "7809.pdf" and "7809 schematic" etc... there's probably even one on this site somewhere!