So I was doing some audio tests with pepper, and noticed I could hear some switching noise on the audio.
(Including some of the pepper demo patches, on both my peppers)

I think the reason is as the audio out is only 1.8vpp, I’m running it through a module to gain it quite significantly - which is why I think it becomes audible.

One thing I want to play with is ensuring the signal from the patch is ‘normalized’ , to ensure I get a high SNR - as I suspect that will help quite a bit.

But I’m wondering if there are other suggestions?

I had this when using the belamini with ae modular and solved it with a large inductor on the power line , but I’m not sure that’s necessary here as I’ve only heard the noise thru the pepper out not (fortunately) interesting with other modules.

I half remember something about turning bbb leds off, but noise down not seem to sync to those, so seems unlikely to help.

Thoughts ? Anyone else noticed this?

Note:
I’m running off 12v with regulator.
Salt in the same rack has no noise.

6 days later

so I tried with a different regulator (R785.0-05). This is slightly better:

alt text
vs
alt text

(this is plugged into a Focusrite Scarlett 8i6, preamp input, gain (almost?) all the way up).
I tried a ferrite bead on the 5V rail, but that did not make it any better.

I think that the reason why Salt is much quieter is because it uses the balanced output from the Bela codec and drives it through a differential amplifier.

although I seem to remember that the rev1 Salt proto was not using the balanced out and was not plagued by these issues.

Same here, lots of noise when powered from rack. Also when connected to ethernet it seem to take too much from the supply. Now I run from external power supply and run into ground loops.

I am doing some more investigations with various grounding options. It seems that powering from USB is by far the quietest option so far (~90dB SNR when plugged into a (almost full on) mic preamp). Will get back with more details.

8 months later

Has there been any developments with this? I'm having terrible noise issues using the pepper in a rack.

Hi, my investigations didn't yield any promising result, unfortunately. We designed a rev2 board which is being manufactured right now where the output circuit from Salt is used for the audio outs, which gives much better performance (-5V to 5V outs, much less noise).

    5 days later

    Ah, that's frustrating. The noise at the moment makes it pretty unusable. I've been having some luck taking out the noise with an external EQ. Would it be possible to program an EQ into the running patch or does the noise come outputs themselves, after the patch?

    giuliomoro do you think we could some how 'hack' the rev 1 board to do something similar?
    perhaps cutting traces, and putting on extra circuit on a small 'daughter' pcb?

    Id be happy to get a rev 2 board, and I could theoretically pull off the main components which make up most of the cost (jacks, pots, display, button) . but its quite a lot of desoldering and subsequent cleaning.. and tricky to remount on new board (as legs are obviously cut/shorter).

    ... I'd have 2 peppers to do ... thats said, the one in my 'dev' case could probably stay 'as is'

      That's a neat idea, and probably not totally undoable, but there are all of these components to fit in there...

      alt text

      6 days later

      On Thursday, we placed the order for the PCB breakout. Once verified, we will ship it out to any Rev1 Pepper users who ask for it, free of charge.

        giuliomoro wow that’s awesome !
        Thanks to all for making this happen.

        Perhaps you can drop a couple of them ( 2 peppers 🙂 ) in with my Trills 🙂

        No rush, and I guess the trills will be going out soonish ?! ( excited for those to arrive !)

            thetechnobear No rush, and I guess the trills will be going out soonish ?! ( excited for those to arrive !)

            Soon hopefully, they should ship from the supplier next week, but these days you never know.

            thetechnobear Perhaps you can drop a couple of them ( 2 peppers 🙂 ) in with my Trills 🙂

            We'll keep that in mind, let's see if the timing works out.

                  I will write here the instructions needed when we find the best way to do it. It's going to take a couple of weeks before we receive the PCBs

                  a month later

                  Hey there, Have there been any developments with this?

                  Hi Neil,
                  parts came in a couple of weeks ago, assembled and tested 10 days ago, then last week just disappeared because of shipping Trill. We are just picking up loose threads now. See announcement below

                  EVERYONE who has bought a rev1 Pepper and wishes for a radical improvements of the poor signal-to-noise ratio of the audio outs, we now have a remedy:
                  a dedicated PCB breakout for the circuit above which can be installed between the Bela cape and Pepper.

                  We are happy to ship out free of charge. Just email robert [at] bela . io for further details.

                  @thetechnobear , yours are in the post with your Trills already.