I have spent the past few days fully analyzing the noise levels and signals coming from the speech game module, Coleco and Adam. Here is the technical details of that analysis. Unfortunately some people could not appreciate that it would take a little time to analyze things and demanded immediate action..
The colecovision and adam were designed and built in the 80's. The pcb's do not have ground planes and they are inherently noisy. If you turn up the volume on your TV with nothing plugged in you will hear the noise. They used 2 metal plates on the top and bottom to effectively make a ground plane. If those are removed the noise is worse. I suspect that is the case with some of you with more noise issues. The noise you are hearing is called buss noise. What this is .... is just what you'd think it is. It's the sound of the data and address lines changing from 1 to 0. If you listen close you can hear different frequencies and not noise actually. That's the sound of the CPU doing it's thing.
The AY-3-8912 has a low impedance output with a level of 1 VPP. When this signal is fed directly into the coleco or adam it is relatively noise free because there is no amplification and the buss noise gets drowned out. The speech chip on the other hand has a very high impedance and low output voltage. This device must be amplified. The op amp amplifies the speech chips output by a factor of 10. When this happens the buss noise is also amplified. This is not a defect in design nor a ground plain issue with the speech game module. This is inherently a problem with 80's technology. The fact is most of you probably don''t remember the 80s or maybe you were not there, but this was how the hardware ran.. Now I understand it's the 2010's and everyone expects crystal clear fiber optics quality sound..
There are 2 ways I see this buss noise can be reduced. one is to make sure all your ground plane metal plates are installed and your capacitors are all good on your Coleco and Adam. The second is if you are only going to use the AY sound and not the speech you can disable the op amp mixer.
If anyone has any questions, needs help or wants more information you can PM me. I'll do my best to help and explain.
I hope this clears up some concerns.