Distortion after module has been playing for a long period

[TomWhitwell]

Celestial Tomes writes: "I'm having an issue with the audio quality slowly becoming distorted over time. When I turn on my system the module sounds fine. Over the course of maybe 20-30 minutes the sound quality decreases."

I also had this issue - but over a much longer timeframe - leaving the modular on overnight.

I think the problem is that there is no path to ground for the op amp input (IC4D)
Last night I added adding a 330K resistor in parallel to C4.

Based on one night's testing (!) this solved the problem completely.

I'm going to continue experimenting with this to see if this can also cure #50 - my first test with 330k seemed to improve it slightly, will try with a lower value resistor.

[TomWhitwell]

Update:
A 100k resistor works fine in that slot.
It does not fix #50 but seems to improve it

[00mb000]

tried a 200 K resistor. the volume level was cut down quite a bit. will try a 100k tomorrow

[TomWhitwell]

Are you sure you have it in the right spot? I didn't notice any output level drop - if there was a drop, I'd expect 100k would be worse than 200k.

[00mb000]

yah def wasn't 200K. I got a 100K on there now and it sounds great. Now onto the ground hum issue.

[RichardDevine]

Hello Tom, I am having the same issue with my two units. Did you replace with a 100k-ohm 1/4 watt or 1/2 watt carbon film resistor?

[TomWhitwell]

@RichardDevine 1/4watt will be fine.

[RichardDevine]

@TomWhitwell thanks going to get them today, :-)

[TomWhitwell]

@RichardDevine Cool - mail me tom.whitwell@gmail.com if you need any help

[oblivionratula]

Should this fix still be required on a kit fresh from Thonk? Guessing so since PCB says Rev 2. Just built mine tonight and getting the degradation. If needed, I wish this was in the build docs so I could have taken care of it while the iron was hot (e.g. https://github.com/TomWhitwell/RadioMusic/wiki/Building-the-Radio-Music-module ). Anyway, cool module, thanks.