Summing Amplifier - Revisited

Thread Starter

cl10Greg

Joined Jan 28, 2010
66
Hello Everyone again,

I have a continuation from my previous problem from my adjustments and testing that I was hoping to get help on. I am doing a multi channel mixer that pipes audio signals to different channels to go to different speakers. My previous post have pointed me to fixing the dual supply issues and saturation and all that seems fine. My latest test has a saturation that I am not sure about.

I have attached a basic schematic below. The top signal after filtering and everything is 1.44V amplitude centered around ground (no dc bias). The bottom signal after filtering is 2.12V with no DC bias.

The top signal is going to the top channel and also the bottom channel. The bottom signal is going to just the bottom channel. The top channel is just a unity gain inverting amplifier since its not really mixing anything. The output looks like exactly what I would expect. The bottom channel not so much.

The bottom channel is clipped on the top and the bottom. I have tried the following
  1. Leave the top channel on while turning off the bottom (signal generator)
  2. Leave the top channel on while turning the bottom channel to 0V
  3. Turn off the top channel and leave the bottom one on
  4. Turn the top channel to 0V and leave the bottom one on
  5. Change the frequency of either channel
  6. Change the amplitude of either channel

All of them have the same resulting signal. My limited instinct is telling me there is a feedback issue here and maybe that is the case. The last post I thought I figured out that by putting the signals into each channel with their own resistor would isolate them enough to run multiple channels like this. Is that assumption wrong and do I need some isolation to mix? My other feeling is that the resistors are creating a divider on the summing voltage based on the first channel and is causing something. But wouldn't that cause the signal to be lower rather then boosted and clipping?


Any feedback would be very helpful!

1634306063752.png
 

Thread Starter

cl10Greg

Joined Jan 28, 2010
66
I actually just tried to remove the top source from the bottom channel and its still clipping. So the feedback between channels doesn't seem like the issue as this point
 
Top