Okay guys, I breadboarded the mixer and I'm sad to say the difference between the .1uF and 1uF is pretty significant. It sounded much warmer and deeper with the 1uF, so I guess I'll have to resolder the caps... Though it might be a bit easier than I thought, so that's positive at least. I also changed the gain by replacing the feedback resistors, 68k instead of 39k, and 10k instead of 5.1k. The level sounds fine now. Thanks for all the help, it seems I can finally put this part of the project to rest
You know about the masking threshold, yes? ( https://en.wikipedia.org/wiki/Masking_threshold )
So a noise 94 dB below the signal level is completely inaudible.
This is exactly my point. Whatever tiny imperfections exist in ceramic caps are so small that they are completely inconsequential - humans can't hear them.
Honestly, I would be more worried about the audible "distortion energy" (rustling) of the fallen leaves blowing down the sidewalk two blocks away - the sound of those is surely stronger than 94 dB below the signal.
-Gnobuddy
I thought I replied to this post earlier, but I can't find any trace of my post. 
Guess I'll have to do it one more time.
Any chance you can add the new 1uF caps in parallel with the existing 0.1 uF caps? That means you won't have to remove the 0.1 uF caps. That will make the job easier.
Keep in mind, if there's room, you may be able to solder the new caps on the underside of the PCB.
-Gnobuddy
Guess I'll have to do it one more time.Pain in the rear, I know, but at least you found the source of the problem!
Any chance you can add the new 1uF caps in parallel with the existing 0.1 uF caps? That means you won't have to remove the 0.1 uF caps. That will make the job easier.
Keep in mind, if there's room, you may be able to solder the new caps on the underside of the PCB.
-Gnobuddy
I tried out 2.2uF caps as well, could not really hear any difference there, so I'll go with the 1uF's. Especially since resoldering the resistors as well would be really boring.
Yes, i know! First I was frustrated about having to redo work, considering I've already changed the circuit one time and had to redo a lot of work. But then I'm glad the problem is solved and the sound gets cleaner!
There's not really any space to add the caps, have to desolder the old one and replace. But that's ok, I thought I had to disassemble the pots again to do it, but I'll be able to do it without taking the whole thing apart.
Yes, i know! First I was frustrated about having to redo work, considering I've already changed the circuit one time and had to redo a lot of work. But then I'm glad the problem is solved and the sound gets cleaner!
There's not really any space to add the caps, have to desolder the old one and replace. But that's ok, I thought I had to disassemble the pots again to do it, but I'll be able to do it without taking the whole thing apart.
There, took about an hour. Reminds me of the game "operation", trying to squeeze in the iron and wiggle those caps with tweezers at the same time
Family's asleep now, so I couldn't test it out too loud. But the gain is much better now, hardly had to turn the knobs now, compared to before when I had to turn them almost all the way.
Family's asleep now, so I couldn't test it out too loud. But the gain is much better now, hardly had to turn the knobs now, compared to before when I had to turn them almost all the way.
Excellent, the best possible outcome for any DIY audio project!
Congratulations!
-Gnobuddy
Only thing is there's a small static noise when I lean in close to the speaker, which is also present when nothing is connected. So it should come from the PSU (SMPS), but I'll try to connect only the PSU directly to the amp and rule out grounding issues. If it sounds the same, I'll try some LC filtering. I'd really like to have an oscilloscope for this But that's probably for another thread.
But that's probably for another thread.- Status
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