Wall wart noise reduction...will this work?

[daz]

Tried several wall warts to power 2 behringer effect pedals and all hum badly. Tried lifting the ground to one of the pedals with no joy. Thru process of elimination i got it down to ONE of the pedals off my board and one boss PSU thats 300mA. Way less but still slight hum, and if i left it on the board and powered one of the effects with battery and one with the WW, about 1/2 that much improvement .
Googling the issue i found this schematic ( https://www.instructables.com/Noise-...ffects-pedals/ ) with a 100R in series with the + and 2 caps across the + and - after the 100R, a polarized 100uf then a .047 non polarized. Is this worth trying or is it not likely to remove most of the hum?

[nosaj]

First see if you have a noisy wall wart. Oscillscope probe and a loop should tell you if its spitting hash.
What king of wall wart AC or DC?

nosaj

[daz]

9v DC 300Ma. No scope.

[nosaj]

Any ac ripple?
nosaj

[daz]

don't have a scope.

[nosaj]

do you have a DVM? that would tell you how much ripple .set it to ac and test it.
nosaj

[daz]

Don't know what to look for but i tried it and it gradually went down to .002v and stayed there.

[Chuck H]

The circuit does reduce ripple. You can omit the LED circuit for ease of build and testing. You can even leave all the component leads at full length so you can disassemble it and reuse the parts if it doesn't work. Cheap enough to try it.

[daz]

I wouldn't bother buying parts and paying probably 20 or 30 bucks for what amounts to a few cents worth with shipping for something that is probably more likely not to work. But i asked because i can find them on old boards/parts boxes my parts boxes but it will be a PITA to find them and a PITA to assemble it due to no female power jack. I could put them in permanent as i plan to w/o a female jack but that will be a huge PITA if it doesn't work

[Helmholtz]

The filter circuit will reduce power supply ripple and noise. If not sufficient, you can always increase the C1 capacitance.
The 100R series resistor will lower output voltage by 1V per 10mA load current.

I would wire R1 before D1 to protect D1 and the power supply against wrong polarity. But then the power rating of R1 should be increased to 1W minimum.

[daz]

The filter circuit will reduce power supply ripple and noise. If not sufficient, you can always increase the C1 capacitance.
The 100R series resistor will lower output voltage by 1V per 10mA load current.

I would wire R1 before D1 to protect D1 and the power supply against wrong polarity. But then the power rating of R1 should be increased to 1W minimum.

Thanks, thats exactly what i was about to ask because i found the parts and wired it up, tho with a different supply thats equally noisy but bare wires (because couldn't find a female power jack) so i could more or less breadboard it w/o a breadboard. And the result was pretty good but still a little hum, maybe 10-15 % as much. So I was about to ask about using different values. I'll try increasing C1 to 220uf. I left the diodes out, as not worried about reverse polarity being careful to double check everything.

[Chuck H]

So the question then would be, is .002VAC on the power supply sufficient to cause the hum in these pedals? I don't know because I've never tested for it. I would have thought that there would be some sort of filtering on the pedal jack circuit from any pedal maker, no?

[Chuck H]

I'm wondering about that 47n cap. Is it necessary? I think with the 100 ohm series resistance it would only be good for lowering ESR at frequencies over 100kHz. Maybe 470n would be better. I'm sure Helmholtz will correct me if I'm wrong.

[daz]

Well, whatever the theory it will go whoosh on me. But i tried a 220uf then added the 100uf to it and at 220uf it doesn't get any quieter adding more. But with the 220 the hum is so small i have to listen close. I have the board rigged with 2 battery holders and a switch that takes those out and at the same time switches to a power jack. So with the 220uf switching back and fourth from battery to wall wart it was hardly noticable. And no extra noise when switching the effects on. So success ! Thanks all.

[daz]

The 100R series resistor will lower output voltage by 1V per 10mA load current.

The 2 effects are 40 mA total. Are you saying i am getting 5 v? Because i didn't check the voltage but i don't think the tube screamer will work on 5 v and the chorus certainly not, or at least not well. yet both worked fine. Why? I'd just check the voltage but i have already disassembled the parts and am in the process or installing them on the board. Maybe a smaller resistor is in order? Then again, if needed why do they sound fine?