Reducing noise and hum on Bela Mini

JulioGurb

Hello!

I am not having big problems with noise but, as I use distortion pedals to process the output of my Bela mini synth, the little noise floor that my Bela Mini generates is sometimes annoying.

I am wondering if I could reduce that noise floor for example by changing the power supply. Now I am using a phone charger and the usb micro port to power it. But perhaps using an AC adaptor could be less noisy? I’ve read in several post on the forum of people having noise issues with AC adaptors (but if they chose that first it was probably for some reason… ). Maybe are there phone chargers that are less noisy than others?

I am not considering batteries.

And I already set the software to make the hotter possible signal before clipping.

Any ideas about reducing noise floor in general?

Thank you for your attention.

All the best,
Julio

giuliomoro

It all depends on the type of noise you are experiencing. If it's about high-frequency noise being aliased by the distortion stage, try applying an analog low-pass filter on the output of BelaMini, that would reduce the high frequencies components that may be affecting your distortion pedals. I'd start with a passive RC low-pass filter:

belaoutput-----R1----+-----pedal input
                     |
                     C1       
                     |
                    GND

start off with R1=2.2k ohm and C1=10nF. This should give you a cutoff of 7.2kHz. If you experience considerable improvement this way, you can tweak the values to adjust the cutoff, which is given as:

1/(2π * R1 * C1)

(make the resistor smaller to increase cutoff).

If it's more of a hum, then possibly using a LiPo battery could help. At the very least, it would help diagnose whether there's a significant improvement to be had by using it.

JulioGurb

giuliomoro

Oh It could be that! maybe that high-frequency noise is not noticeable without distortion but once I put the distortion it becomes louder and lower in the frequency spectrum because of the aliasing you say (although isn't aliasing a digital thing?).

I will try the filter and the batteries and see what happen.

Thanks again, my namesake!
Julio

giuliomoro

I think the terms can apply to this case too: the output of the converter will have frequencies above the audio range going up in the MHz range. If somehow those frequencies can be heard in the audio range, they have been "aliased" into it.