Any chance modding cheap 9V wall wart to be less noisy? What's necessary?

[pahaahv]

I assume I need some sort of filter circuit. I also have 12V wall wart, a 19V laptop charger and a PC PSU on hand.

I'd like a power supply for testing some pedals but I don't want to order a proper psu right now.

Do I have any options filtering one of the psu-s mentioned above?

Which circuit would work best?

It can be imperfect but it would be nice if the end result was a little less squeaky and noisy.

[r080]

Something simple like an RC filter might work for your 9V supply. Better might be a linear regulator with your 12V wall wart.

Random internet links similar to suggestions above:

https://www.instructables.com/Noise-filter-for-the-power-supply-effects-pedals/
https://circuits-diy.com/amp/9v-power-supply-using-lm7809-voltage-regulator-ic/

[Mark Hammer]

Something simple like an RC filter might work for your 9V supply. Better might be a linear regulator with your 12V wall wart.

Random internet links similar to suggestions above:

https://www.instructables.com/Noise-filter-for-the-power-supply-effects-pedals/
https://circuits-diy.com/amp/9v-power-supply-using-lm7809-voltage-regulator-ic/

This is likely to meet your needs.

[iainpunk]

i suggest a really large reservoir capacitor and a small value resistor before the LM7809 (recommended above). these cap and resistors will work like a low pass filter letting through the DC (0Hz) and really low frequency's but your power supply won't be generating frequency's so low, so there won't be anything but DC on the output.

cheers

[ElectricDruid]

Another +1 for using the LM7809 to build a decent 9V supply from the 12V wall wart you've got.

The only thing I'd add is that a 100n ceramic in parallel with the input cap is a good idea, especially if the 12V wall wart is a switch mode supply. Big electrolytics aren't great filters for high frequency noise.

[Mark Hammer]

i suggest a really large reservoir capacitor and a small value resistor before the LM7809 (recommended above). these cap and resistors will work like a low pass filter letting through the DC (0Hz) and really low frequency's but your power supply won't be generating frequency's so low, so there won't be anything but DC on the output.

cheers

I concur, but will add that, since we don't know how many pedals the OP intends to power at once, or what their current draw will be, make that small-value resistor a 1/2W unit, just to make sure it doesn't overheat and behave like a fuse.

[merlinb]

A common-mode choke betwen the wall wart and the regulator is a useful addition, if you have one. You can usually get them for free by scavanging them out of scrap appliances.

[Radical CJ]

I have previously built a little box implementing all the above suggestions (although the choke was just a ferrite bead), which I use with a few particularly power supply sensitive pedals (mostly 60s/early 70s style fuzzes).

Overall, it works really well, but it doesn't remove all noise from a few particularly bad/cheap power supplies I've tried it with. In these cases hum is removed but a lower frequency pulsing sound emerges.

Definitely worth building and having on hand though, even if you intend to buy a good quality supply in the future.

[antonis]

In these cases hum is removed but a lower frequency pulsing sound emerges.

A 2nd order HPF (turntable rumble style..) should be the remedy..
(tried and tested..)

[iainpunk]

In these cases hum is removed but a lower frequency pulsing sound emerges.

A 2nd order HPF (turntable rumble style..) should be the remedy..
(tried and tested..)

yes, high-pass filter work so well for DC applications, i just love getting only the turn on transient to power pedals, totally not a bad idea. 

cheers, Iain

[antonis]

 


(bad day today..)

[Rob Strand]

The best place to start for switchmode noise on pedals is to add a dummy load across the PSU.
Start with a 220 ohm 1/W resistor.    Many switchmode wall-warts are noisy with light loads.
They work but they are noisy for audio.    You might even need a lower resistor.  The key
point that the noise is caused by insufficient loads is the noise will change when you add the
220 ohm resistor.   If you still hear noise with the 220 ohm try a 100 ohm 1W.

Here's more threads on PSU noise and filters,

https://www.diystompboxes.com/smfforum/index.php?topic=125667.msg1197915#msg1197915

https://www.diystompboxes.com/smfforum/index.php?topic=125422.msg1194134#msg1194134

There are many other example threads on the forum.

Hum problems are different to noise and whine problems and need different solutions.
Hum usually comes from the older heavier wall warts which contain  transformers.
Noise and whine comes from the more modern and lightler switch-mode designs.