Excess noise when using wallwart

[alotawatts]

  I have built a number of projects from PAIA, Craig Anderton schematics, BYOC, GGG etc.
I just finished a GGG Orange Squeezer Compressor pedal. This one has me baffled as it works fine but when I use wallwart power supply I get excessive noise.
Hum and hiss is the best description. Using a 9V battery is much quieter.
My wallwarts are a Boss PS and a no-name regulated 9V supply.
 Anyone thoughts ...anyone ?
thx  

[Quackzed]

bad power supply filtering.. lots of wall warts are fine untill you use them for audio, then you hear hum and 60 cycle buzz...
you can find a wallwart that is better/quieter or you can add 100uf and a 1uf in parallel from +9v to ground on your circuit to filter the power from the wallwart...
pretty common issue.

[glesconz]

yeah! I got this with an OS, too! I found the 9V quieter and used a 100 ohm resistor between the wallwart 9v+ and FX and also added a 220uF cap to ground also, to no avail. Increasing the res value to 220 ohm helped marginally but not much. I take it you mean electrlytic caps?

And to clarify, is this what you mean.....?


----->wall 9+V----->100uF in series----------->FX 9V+
                                                        [
                                                        [
                                                     1uF
                                                        [
                                                        [
                                                    GROUND


Thanks,
Glenn

[glesconz]

Oh, and how does the polarity go on the 100uF cap? I assume the 1uF has its -ve going to  ground

Thanks,
Glenn

[Quackzed]

hmm...
what i mean is...

+9v------------------------(optional 100 ohm resistor)----->fx9v
     +   l         +   l
       100uf        1uf
      -   l         -    l   
          g             g
yes electrolytic caps... oriented - side to ground

this is a way to filter power and reduce power supply noise... generally it will help to eliminate 'dirty' unfiltered power from a wallwart.
there are other sources of noise, but if a battery is quiet and a wallwart is noisy this will in most cases resolve the issue...
both caps - side to ground

[glesconz]

Thanks heaps!

Cheers
Glenn

[.Mike]

hmm...
what i mean is...

+9v------------------------(optional 100 ohm resistor)----->fx9v
     +   l         +   l
       100uf        1uf
      -   l         -    l   
          g             g

If you're using a 100-ohm series resistor, wouldn't it be best to put it before the parallel capacitors to ground, so it plays a role in the low-pass filter? Like this...

+9v--(optional 100 ohm resistor)------------------------>fx9v
                                                     +   l         +   l
                                                       100uf        1uf
                                                      -   l         -    l   
                                                          g             g

Otherwise, I believe you are relying solely on the internal resistance of the power supply (and the small resistance of the wire leading to the capacitors) to create the filter. That would remove the 100-ohm resistor from the equation, and raise the corner frequency of the filter significantly.

Mike

[aquataur]

May I suggest that you use a .1µF (100nF) ceramic instead of the 1µF. It does not make sense to parallel a 100µF and a 1µF electrolytic.

Every type of capacitor has its own frequency characteristic. Electrolytics are good for filtering low frequencies, ceramics for high frequencies.
Both complement well in power supply filtering and that´s what they usually recommend, an electrolytic in parallel with a small ceramic.

have fun,

-helmut

[Quackzed]

yeah, ok. both good points.

[davent]

Beavisaudio has the project nicely documented for you. http://www.beavisaudio.com/projects/Huminator/index.htm

dave

[merlinb]

Filtering can be improved further by using two resistors +cap, instead of one. Putting one resistor in the negative connection as well as one in the positive will go some way to blocking out ground noise emanating from the wallwart rectifier.