Wall wart big noise !

[demym]

Hi to all,

i've built some pedals recently (CarvinLegacyJFET, BSIAB2, Dr. Boogey, Krank Distortus Maximus, Tillman JFET preamp). They all work fine, but till now i've only powered them using a 9V battery.

Today, tired of having all my 9V batteries dead :-),  i bought a wall wart (from 9V to 24V, it says that it's regulated and stabilized)... But when i power those pedals with the wall wart i get a very noticeable hum/noise... The sound of the pedals is the same, only when i'm not playing i get this unbelievable noise.... Have no noise at all using the battery...

Can't figure what's happening... i'm sure the polarity of the wall wart is correct, tested it with multimeter...

I've never used a wall wart with my DIY pedals, and so i am in a very unknown territory.

Can someone please help ?

Thanks in advance, have a nice time

Demy

[Processaurus]

Sometimes having the wall wart physically close to your effects gadgets or guitar cables can hum, in that case it is Electro Magnetic Interference, EMI, from the magnetic field  of the transformer (invisibly magnetically pulsing at 60hZ) affecting stuff in your pedal.  Moving it away a couple feet usually does the trick.  Switching power supplies don't do this interestingly, just things with power transformers.

The other possibility is of a ground loop with all of the pedals connected together with a daisy chain, in that case, add one pedal at a time until the hum starts.

Or it might just not be a quiet power supply, especially if it is one of the adjustable types.  You could set it for 12v and use a LM7809 9 volt regulator and caps in a little box to regulate it (quiet it), or, use a pedal specific power supply.  I like the 1 spot, quiet and robust ($25); or the Danelectro, quiet and cheap ($10).

[demym]

Thanks very much.

The transformer is distant from pedals, so i think it's not the case.

It's a switchable type (9V to 24V), so i think i will follow the 7809 route. You are talking about capacitors; is there a schematic of such a 9V regulated voltage, using 7809 ?

Anyway, thanks once again

[Paul Marossy]

Generic wall warts are often very poorly filtered, which results in a lot of hum/buzzing. That's why I built into my pedal board an LM317 adjustable power supply, so I can whatever kind of wall wart into it and not have the noise and get a nice clean 9VDC. 

[Processaurus]

Thanks very much.

The transformer is distant from pedals, so i think it's not the case.

It's a switchable type (9V to 24V), so i think i will follow the 7809 route. You are talking about capacitors; is there a schematic of such a 9V regulated voltage, using 7809 ?

Anyway, thanks once again

Everything you need is in the datasheet:
http://www.fairchildsemi.com/ds/LM/LM7809.pdf

Specifically, look at figure 7 on page 22.  A good move is to put a reverse biased power diode (1n4001 is good) across the output back to the input (cathode to input, anode to output, so in normal operation it doesn't turn on), as some regulators will break if the output gets higher than the input.  You can also add a big electrolytic cap (say, 220uF) across the output and ground, in parallel with the little .1 cap.  You definitely need the two small caps decoupling the input and output, to avoid oscillations in the part.

LM317

Sure!  To the original poster it's the same idea, except the LM317 is an adjustable regulator, by using a couple more parts.