Audio out acting up after cold start

I am experiencing strange behavior of the audio output jack. When I start Shruthi (with SMR4 mkII) after a longer period of not being connected to power (in this case ca. 7 hours) and the audio plug is still connected to it, it has happened twice to me now that it doesn’t output sound even though I see it receiving MIDI notes. I have to unplug and plug the audio plug back in before I get sound from it. (The plug was definitely sitting tight in the first place, since I used it like that for hours the last time) Then it works for half a minute or so before the sound turns into a kind of low amplitude digital hum that is still vaguely related to the gate of the notes I’m playing (init patch). Only plugging it out and in a second time fixes the issue completely. It doesn’t happen again when I warm-start shruthi, e.g. when after some use I pull power and then plug it back in.

I’m not entirely sure if it’s a hard- or firmware problem. The jacks are firmly attached to the plexi case so very little pressure should be put on the actual solder joints, also I made extra sure the solder joints for all plugs were good during build because I knew they’d probably get the most stress. Also when I wiggle the plug after everything settles down, I don’t have any more sounds cut out, so I am tempted to rule out a wonky solder job, at least for the jacks themselves. The jacks are switched though, so could this be the problem of another component?

I would try replacing the cable before I poke around with the soldering iron.

OK I’ll try that and observe the behavior the next times I cold-start it

I highly doubt it’s a firmware problem…

Next time it happens, try probing the “osc>” pin to see if there is sound here, and work through the signal chain to see where the sound is interrupted.

what device are you plugging in?
I’ve experienced this kind of issue (not with shruthis though) from time to time. I remember having the problem quite recurrently with one of my very first diy, home-cooked designs (some kind of a booster/preamp) when it was plugged into a tube amplifier (peavey classic 30).
I think that it may be related to decoupling caps in series without any grounding resistor, this kind of stuff. It might be that your cable is not in perfect shape as well.

The cable is between Shruthi Out and Griffin iMic 2 In (a USB sound card). I’ll report back as soon as I get another cable to try it with.
For completeness’ sake I should mention that I could also not hear the test note you get by holding S1 for a few seconds nor did a patch change help. I do agree that it seems unlikely it is a firmware problem.

Yesterday something similar happened with a different audio cable: In some patches with sharp transients or attacks for cutoff or VCA instead of getting snappy sounds the attack sounded very fuzzy, the rest of the tone was fine and as expected. Plugging audio back in solved it yet again.

I think I may have found the culprit though. Yesterday evening when rearranging my music desk I put a bit of stress on the universal PSU’s cable and something in it must’ve broken because after that it was dead. I bought a dedicated PSU rated at 9V 1A today that will stay with Shruthi now.

Can an effect like I’ve described throughout the thread come from an unreliable/wonky power connection?

I’ll keep an eye on how it goes with the new PSU. By the way, can I leave Shruthi permanently connected to power without causing any damage or is it advised to turn it off when not in use?