Filtering AC hum on guitar pedal power supply

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ccaudle

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You could try the 'tricks' like putting a resistor (eg 100 Ohm) in the screen connection.

That will increase the voltage drop of any screen current flowing, causing a larger interference signal at the receiver (i.e. more hum at the pedal). You would probably have better results decreasing the impedance between pedals to keep the voltage induced by noise currents as low as possible, e.g. use cable with heavy braid shield, and/or add additional copper braid straps between pedals.
 

Whoops

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Hello,
I recently put together a BigMuff style guitar pedal, and it appears that my cheap 9V power supply does a bad job filtering AC hum, at least I think so.

A good 9V pedal PSU is cheap enough, why don't you buy a good PSU?

Remember, like other people mentioned, that an hum free guitar pedal PSU is not only "Filtered" but also "Regulated".
You want a transformer, then Full bridge rectifier, then filtering, then regulator (can be a 7809), then filtering again.
 
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Newmarket

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That will increase the voltage drop of any screen current flowing, causing a larger interference signal at the receiver (i.e. more hum at the pedal). You would probably have better results decreasing the impedance between pedals to keep the voltage induced by noise currents as low as possible, e.g. use cable with heavy braid shield, and/or add additional copper braid straps between pedals.

Yes. True but at the same time increased impedance reduces the current itself. The actual figures depend on the other impedances involved. 100R is a reasonable starting point. But it's a 'trick' rather than an optimised solution.
In "Electric Guitar World" noise levels are inherently on the high side and a moderate improvement - say 10dB - can be a worthwhile improvement even if it still leaves the noise at, say -50dB.
At the end of the day unbalanced audio where one conductor is functioning as both signal conductor and screen is always going to pose problems esp when impedances involved can be on the high side.
Ideally either current or voltage is zero so that IxV=0. But I'm thinking about something that might be of practical benefit to the OP.
Agree given the choice I'd go for low 'Ground' Impedance - heavy braid + parallel ground / PEC connections.
Quite a bit of interesting work on this (albeit wrt pro audio balanced installations) and something I advocate in my non-audio work wrt noise / EMC etc. But the OP may not be in a position to benefit from it. Although if the pedals are mounted on a metal pedalboard then it could be interesting.
Similarly I'm thinking it's not practicable for the OP to modify that Input/Output schemes of the pedals to be Balanced/Ground Cancelling/Ground Sensing or whatever.
Of course, if not already tried then properly regulated and isolated power is the first thing to implement imo.
 
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