Well, no wonder it just made the signal quieter! Here is the frequency response as a function of the Pot value of 1, 100, 1000, and 10K using 100nF capacitors.
Red is 1Ω, Blue is 100Ω, Green is 1000Ω, and Teal is 10K.
If this goes in the line input to the audio speaker amp, then you shouldn't have to amplify it.
This is just a low-pass filter, so it it will cut the treble, leave the bass, much more than a tone-control would do. It will make the sound tubby. What were you expecting it to do?
I don't have any preexisting criteria for what it should sound like. I'm just trying to create some effects that I could add onto a cheap toy keyboard. I am trying to learn about electronics and that seemed like a good way to maintain my interest while also giving me some clear cut examples where I could see (or rather hear) the results.
I'm not too sure what tubby will sound like but I'm stoked to hear it.
I really appreciate your help. This is great.
Any other suggestion you want to add, please feel free!